Past SIDC Seminars

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Date & TimeLocationSpeakerAffiliationTitleRemarksAbstract
2010-09-14 at 14:30:00 TV Room Leif Svalgaard Calibration of Sunspot Numbers On TUESDAY! Display the abstractWaldmeier [1971] found a very tight relationship between the F10.7 solar radio flux and the sunspot number and suggested using the flux for an objective calibration of the sunspot number. He suggested that if this relationship changed later on, the sunspot number should be re-calibrated, assuming that the calibration must have drifted with time. I repeat his analysis using data up to the present and it is, indeed, clear that the relationship has changed significantly. This could be due to a drift of the calibration or to a secular change in the visibility of sunspots, or both.
2010-09-10 at 14:00:00 Meridian Room Dipankar Banerjee Indian Institute of Astrophysics, Bangalore, India Propagating Waves in the Polar Coronal Holes Note the unusual day and time! Display the abstractWith modern imaging and spectral instruments observing in the visible, EUV, X-ray and radio wavelengths, the detection of oscillations in the solar outer atmosphere has become a routine event. These oscillations are considered to be the signatures of a wave phenomenon and are generally interpreted in terms of magnetohydrodynamic (MHD) waves. I will present some new observational report on the detection of accelerating waves in the polar regions of the Sun. These observations are taken from Hinode and SoHO. I will discuss if these waves can be important for the acceleration of the solar wind. Interpretation in terms of flows versus waves will be also discussed. Finally I will briefly discuss on the Aditya project. Recently Inidan Space Research Organisation (ISRO) have approved a coronagrapgh payload to be flown on Aditya mission.
2010-08-26 at 14:30:00 Meridian Room Yi-Ming Wang Naval Research Laboratory (USA) Semiempirical Models of the Slow and Fast Solar Wind Display the abstractCoronal holes can produce several types of solar wind with a variety of compositional properties, depending on the location and strength of the heating along their open magnetic field lines. High-speed wind is associated with (relatively) slowly diverging flux tubes rooted in the interiors of large holes with weak, uniform footpoint fields; heating is spread over a large radial distance, so that most of the energy is conducted outward and goes into accelerating the wind rather than increasing the mass flux. In the rapidly diverging open fields present at coronal hole boundaries and around active regions, the heating is concentrated at low heights and the temperature maximum is located near the coronal base, resulting in high oxygen freezing-in temperatures and low asymptotic wind speeds. Although coronal holes are its main source, slow wind is also released continually from helmet streamer loops by reconnection processes, giving rise to plasma blobs (small flux ropes) and the heliospheric plasma sheet.
2010-07-08 at 14:30:00 Meridian Room Alexander Urnov Lebedev Physical Institute, Russian Academy of Science Hot Coronal Plasma Phenomena Seen by the CORONAS Missions Display the abstractThe advent of XUV full-Sun monochromatic imaging spectroscopy in the SPIRIT experiment on CORONAS-F (2001-2005) helped to reveal highly dynamic 4-20 MK coronal plasma structures characterized by various sizes from 6 arc sec through 0.3 solar radii and lifetimes from several minutes to several days. A new phenomenon of hot spots (hot X-ray bright points, HXBP) has been disclosed in addition to the previously reported giant post-eruptive sources (spiders). The whole Sun X-ray emission (GOES) was shown to be the result of a superposition of a series of low intensity elemental bursts lasting for 10-20 min and recurring at the same locations on the solar disk. These events were classified as impulsive events (IE) and gradual ones (GE) implying different mechanisms of formation and decay. A new concept based on a quasi-static model was proposed to explain the observable features of gradual events. It was used to provide a theoretical description of the spider phenomena using generalized Chandrasekhar-Prendergast model of a spherical magnetic vortex. This model reveals remarkable properties that help to explain how the conditions sufficient for fast and efficient energy release, specific for a weak flare, may take place sporadically without disrupting the whole system. The results of observations of highly dynamical coronal structures by CORONAS-PHOTON mission (2009-2010) will be also presented.
2010-06-01 at 15:00:00 Meridian Room Igor Veselovsky Skobeltsyn Institute of Nuclear Physics, Moscow State University Аstrophysics and Plasma Physics of Solar Wind Origins Display the abstractWhy does the solar wind blow? When and how did it start to blow? What are the main energy and momentum sources of the solar wind? The spherically symmetric model of the quasi-steady flow in the stellar atmospheres (Bondi, 1952) is very simple and physically transparent for analytical considerations. Three admissible types of solutions of the governing Bernoulli equation are available in this model: (1) static v=0, (2) expanding wind type flow v>0, (3) contracting accretion type flow v<0. The selection between them depends on the imposed internal and external boundary conditions. This means that the solar wind origin problem cannot be properly addressed nor completely explained in the framework of this model alone without additional assumptions. More appropriate and complicated non-steady state and inhomogeneous models are not well developed. Nevertheless, the Bondi model is useful for the demonstration of the necessity of the time dependent approach for obtaining a physically correct answer to the long standing question: why does the solar wind blow? It is not only because of the instantaneous hot corona and rarefied interstellar medium around the Sun, as often correctly assumed (Parker, 1957), but also because of the evolutionary state of our star and its magnetic activity. Magnetic stresses dominate in coronal holes and coronal mass ejections. Solar-like stars of the same type as the Sun can exist with a hot corona and situated in a rarefied interstellar medium, but without any wind or even in the accretion state because of magnetic forces. The existence of such stars (acceptors) is not prohibited by any physical laws and could be searched in UV line Doppler shift measurements as well as of other stars similar to the Sun in this respect (donors). The role of rotation, convection, and radiation transports is also discussed.
2010-04-28 at 14:30:00 Meridian Room Nandita Srivastava Udaipur Solar Observatory, Physical Research Laboratory (India) Automated Detection of Filaments and Their Disappearance Using Full-Disc H-alpha Images Display the abstractIn this talk, I will present a newly developed algorithm that automatically detects filaments on the Sun in full-disc H-alpha images. After applying pre-processing techniques on the H-alpha images for limb darkening and foreshortening corrections, we apply suitable intensity and size thresholds to extract disc filaments, while other solar features, e.g. sunspots and plages, are removed. Filament attributes such as their position on the solar disc, total area, length, and number of fragments are also determined. In addition, every filament is also labeled with a unique number for identification. The algorithm is capable of following a particular filament through successive H-alpha images, which allows us to detect their changes and disappearance. We have analyzed several cases of activated/eruptive filament from different observatories, and the results obtained will be presented. The algorithm will eventually be integrated with an upcoming telescope at the Udaipur Solar Observatory for real-time monitoring of activated/eruptive filaments. This aspect should prove to be of particular importance in studies pertaining to space weather.
2009-11-26 at 14:30:00 TV-Room Pavel Leontiev and Anatoly Vuiets National Technical University ''KPI'', Kiev, Ukraine Some Aspects of NEMO Operational Development Full affiliation: The Educational Scientific Complex ''Institute for Applied System Analysis'' of National Technical University of Ukraine ''KPI'' Display the abstractThe fast development of space instrumentation and telemetry technology caused an urgent need of the specially tailored pattern recognition tools. An interesting and practically important task is the automatic tracking of Coronal Mass Ejections(CMEs) as introduced and developed by Berghmans (1999); Robbrecht & Berghmans (2004). The EUV Imager (EIT) of the solar corona onboard of the SOHO spacecraft has uncovered a new generation of various eruptive events often identified as on-disk CME precursors (Bisecker & Thompson 2002; Zhukov, 2004). The NEMO code (Novel EIT wave Mashine Observing) autonomously detects solar eruptions in the image sequences from EIT in real time. The NEMO technique is based on the general statistical properties and underlying physics of the eruptive on-disk events (Podladchikova & Berghmans, 2005). In this talk we present a number of NEMO algorithm updates that allow us to raise the recognition efficiency of the solar eruptions, which we identify as the eruptive dimmings linked to CMEs, namely: - DIMMING AREA COMPUTATION. The dimming Area is computed directly in the square kilometers instead of the EIT pixels, taking into account that an EIT image, is in fact, a projection of the solar sphere. - NEMO CLUSTER ANALYSIS FOR DIMMING ALLOCATION is improved. The NEMO splits the set of areas with the low intensity on the subsets of dimmings. The proximity criterion of clusterized areas on the given radius vicinity is used instead of that on longitude and latitude. - EXTRACTION TECHNIQUE OF DIMMINGS connected to CMEs is modified. We introduce the new criteria based on the dimming “volume” (the product of the dimming area and intensity) instead of that based on its area. The intensity criterion is introduced by Bewsher & Harrison, 2007. - The processing of image areas close to solar limb is improved. - The Eruptive Dimming Extraction code is simplified and highly structured.
2009-11-24 at 14:30:00 Meridian Room Rossitsa Miteva Astrophysikalisches Institut Potsdam Parameter Study on Electron Acceleration at Shock Waves with Upstream Whistler Turbulence Display the abstractWe present a model on electron acceleration at quasi-perpendicular shock waves in space plasma considering the presence of wave-activity in the upstream region of the shock. This theoretical approach combines two different models for particle acceleration: shock-drift acceleration at quasi-perpendicular shocks and stochastic acceleration due to resonant energy exchange between waves and particles. Plasma supports a broad spectrum of wave modes and different studies concentrate on different wave modes and/or their combination. We consider only the whistler mode. An electron-independent source of whistler waves with respect to the ad hoc assumptions for the wave spectrum is proposed. We present a parameter study on this acceleration model, taking into account simultaneous variations in the upstream plasma density, temperature, magnetic field strength, orientation, and shock speed. We found that a certain combination of plasma and shock parameters is necessary for producing non-thermal electron fluxes via the model of resonant whistler interaction. Finally, the model predictions are compared with several observed shock events in the solar corona and in the interplanetary space.
2009-09-07 at 14:30:00 TV-Room Josef Koller Los Alamos National Laboratory Applications of the Los Alamos Data Assimilation Framework Exceptionally on Monday! Display the abstractI will review the data assimilation effort DREAM (Dynamic Radiation Environment Assimilation Model) and present results from studying the radiation belt enhancements. The quantitative comparison of data and model output enables us to estimate where forecast and observations drift apart. In addition, our data assimilation framework can automatically estimate the location of active acceleration regions and the overall efficiency of wave-particle interactions. I'll present our recently developed residual method to quantitatively evaluate the effect of different physical processes on the forecast capability of our model. We have also developed a new method of drift shell modeling and calculating the adiabatic invariant L*. In a dynamic and realistic field, calculating L* needs sophisticated magnetic field models which, in turn, require computationally intensive numerical integration. This has turned into a computational bottleneck for many radiation belt models. Our method is based on a neural network and is 5-6 orders of magnitudes faster that the standard integration technique. This new surrogate model has applications to real-time radiation belt forecasting, analysis of data sets spanning decades of observations, and other space weather applications. Further, I will present an overview of ADAPT, the Airforce Data Assimilative Photospheric Flux Transport Model. We have incorporated the Los Alamos Data Assimilation framework with a generalized photospheric flux transport model by Worden & Harvey (2000). The model takes photospheric flux magnetograms and combines it with our ensemble Kalman filter. This will allow high quality, reliable snapshots of the photospheric field distribution and improve the NSO time-dependent solar photospheric magnetic field flux transport using rigorous data assimilation methods.
2009-09-02 at 14:30:00 Meridian Room Roman Brajša Hvar Observatory, Coratia Predictions for the 24th Solar Cycle Exceptionally on Wednesday! Display the abstractApplying and combining different methods, the strength and epochs for the next 24th solar cycle are predicted. The combined method consists of the three parts: (i) the calculation of the asymmetry of the ascending and descending solar cycle phases, (ii) the correlation of the relative sunspot numbers in and around solar activity minima with the following activity maxima, and (iii) the method of the autoregressive moving average model (ARMA) applied to the relative sunspot number data measured up to now. The used data sets include yearly, corrected yearly, monthly and smoothed monthly relative sunspot number values. With these combined procedures a lower amplitude of the next solar activity maximum, in comparison with the previous one, is estimated.
2009-07-23 at 14:30:00 TV-Room Alexander Urnov and Farid Goryaev Lebedev Physical Institute, Russian Academy of Science and ROB On the CORONAS program at the Lebedev Physical Institute of RAS / Hot plasma investigation in Active Regions with CORONAS-F/SPIRIT and Hinode/XRT data A. Urnov, F. Goryaev, S. Parenti, J.-F.Hochedez, S. Shestov, S. Kuzin, A. Ulyuanov, S. Bogachev, F. Reale Display the abstractA short survey of the observations, carried out by the CORONAS-F (2001-2005) and the CORONAS-Photon (2009-) satellites, along with the main features of both experiments, SPIRIT and TESIS respectively, will be presented. Results of the study of the temperature content in the non-flaring active region (AR) plasma by means of differential emission measure (DEM(T)), inferred from SXR (Hinode) and EUV (CORONAS) data will be given. The crucial point of this treatment is the application of the method of the DEM(T) reconstruction (firstly used for the DEM analysis) based on the regular statistic approach to the spectroscopic inverse problem and the iterative procedure using the Bayes’s theorem. This work was carried out also in order to study the abilities of the method used and its application to the measured linear EUV spectra and SXR wide-band imaging observations. One of the main purposes of the present work is to provide a reliable experimental evidence for the presence of hot plasma with T ≥ 5 MK in non-flaring ARs and its temperature content.
2009-06-11 at 14:30:00 Meridian Room Farzad Kamalabadi Department of Electrical and Computer Engineering, University of Illinois, USA Assimilative Time-Dependent 3D Models of Density and Temperature in the Solar Corona: Results from STEREO Display the abstractKnowledge of the corona's three-dimensional structure is important for modeling the solar wind and the propagation of solar disturbances out to the near-Earth space environment. White-light and extreme ultraviolet (EUV) 2D images of the corona at different solar rotation angles, as measured routinely by a variety of dedicated space-based and ground instruments, can be combined to produce quantitative 3D reconstructions of persistent, large-scale coronal density and temperature structures. In this talk, I will describe a state-space framework through which one can estimate the state of the corona as a function of time. Since the 3D, time-dependent nature of the estimation scheme demands computational methods that scale well with the problem size, I will describe a new sequential Monte Carlo technique based on recursive estimation and optimal filtering, in conjunction with new spatial localization concepts for line-integral measurement operators, that dramatically reduce computational complexity and enable global assimilative models of the solar corona. I will present quantitative reconstructions using STEREO measurements and compare the new time-dependent reconstructions of coronal density to a sequence of static reconstructions. We find that the new dynamic reconstructions are more robust at capturing transient features of the corona and are less prone to computational artifacts that result from the static assumption.
2009-06-04 at 10:30:00 Meridian Room Marilena Mierla Institute of Geodynamics ''Sabba S. Stefanescu'', Romania On the 3D Reconstruction of Coronal Mass Ejections Unusual time! Display the abstractCoronal Mass Ejections (CMEs) are enormous eruptions of magnetized plasma expelled from the Sun into the interplanetary space, over the course of minutes to hours. They can create major disturbances in the interplanetary medium and trigger severe magnetic storms when they collide with the Earth's magnetosphere. It is important to know their real speed, propagation direction and 3D configuration in order to accurately predict their arrival time to the Earth. Using data from SECCHI-COR coronagraphs onboard STEREO mission which was launched in October 2006 we can infer the propagation direction and the 3D structure of such events. First, we present a summary of different techniques which have been used to infer the 3D configuration of CMEs in COR field of view. Then, we apply these techniques on different CMEs observed by coronagraphs. A comparison of results obtained from the application of different reconstruction algorithms is presented and discussed.
2009-04-02 at 14:30:00 Meridian Room Vladimir Krasnoselskikh LPCE/CNRS-University of Orleans, France Eigenmodes of Langmuir Waves Trapped into the Density Holes Display the abstractRecently Ergun with co-authors (PRL, 2007) have published an interesting observation by WAVES experiment onboard STEREO (S/WAVES) satellite: Langmuir wave eigenmodes trapped into the density holes in the solar wind. We present the theoretical study of such eigenmodes trapped into the density holes in the framework of the first Zakharov equation, where the prescribed density profile is supposed to be moving but static. We assign different 2 and 3 dimensional density holes, in the last case we consider the profiles having cylindrical symmetry and we analyze the eigenmode type solutions. We compare electric field envelope profiles with the observations of the S/WAVES experiment. We obtain the condition that relates the density hole depth with its characteristic spatial scales for the trapped wave mode to exist. It is similar to the Zakharov’s condition that defines the threshold for nonlinearity to dominate over dispersion. The major consequence of this study consists in the conclusion that the role these wave modes can play in the process of the beam-plasma interaction is determined by the characteristics of the density fluctuations in the solar wind. They can be important if the probability of the occurrence of density fluctuations satisfying the condition for the wave trapping is large enough.
2009-03-31 at 14:30:00 ROB Meeting Room Leon Ofman NASA GSFC, USA Three-Dimensional MHD Models of Waves in Active Regions Display the abstractRecent high resolution observations by TRACE, Hinode, and STEREO spacecraft show ample evidence of waves in active regions. The waves appear in individual loops, as well as global ''EIT'' waves. The properties of the waves, such as the propagation speed, and the damping time provide information on the magnetic and density structure of the loops, and can be used for ''coronal seismology''. The global properties of active regions can also be determined from the propagation, transmission, and reflection of the global waves. Previous studies have shown that the transverse and the global waves are fast magnetosonic waves. Other possible interpretation of the waves will be discussed. The trapping of the fast magnetosonic waves in individual loops can lead to kink oscillations. Slow magnetosonic waves were also detected in active region loops, and in low-beta plasma these waves propagate along the magnetic field. The results of recent 3D MHD models motivated by observations of individual loop oscillations and of global waves in active regions excited by impulsive events will be shown. The implications of the model results on the understanding of the structure of active regions and loops will be discussed.
2009-01-29 at 14:30:00 Meridian Room Bartosz Dabrowski ROB Correlation of Decimetric Radio Emission and Hard X-rays in Solar Flares Display the abstractThe emission of decimetric flare radiation, in particular narrowband spikes and pulsations, is generally considered to originate from accelerated non-thermal particles. On the other hand, non-thermal hard X-rays (HXR) are well accepted results of such acceleration. Are radio emissions and HXR signatures of the same acceleration process? Good correlation of the light curves in the radio and HXR range may evidence it. The correlation of decimetric radio emission and HXR in solar flares was analyzed using data from the RHESSI spacecraft and the Phoenix-2 spectrometer in Bleien (Switzerland). For the first time we have the possibility of a systematic search on the radio-HXR relation in the range from 100 MHz to 4 GHz. The measured delays have a distribution with a FWHM of 4.9 s and 4.7 s for pulsations and spikes, respectively, evaluated from a Gauss fitting method. The mean delay for pulsations was found to be -1.4±0.9 seconds (minus indicates that hard X-rays emission comes first), and for narrowband spikes to -2.5±2.5 seconds. The delays do not depend on centre frequency, cross-correlation coefficient, duration of the correlating sequence and position on the disk. However, we find an increase in delay for the spikes with GOES magnitude (peak soft X-ray emission) of the flare and with peak hard X-ray flux.
2009-01-22 at 14:30:00 Meridian Room Kathy Reeves Harvard-Smithsonian Center for Astrophysics Observations of the Sun's Corona using the X-Ray Telescope on Hinode Display the abstractThe corona, the outer atmosphere of the Sun, is tenuous, hot and dynamic. In this talk, we will review observations of the corona, particularly results from the X-Ray Telescope (XRT) on the Hinode Satellite. This new telescope shows the hot plasma of the corona in spectacular detail, and it is revolutionizing our view of coronal activity. We examine observations pertinent to the coronal heating problem, the morphology and structure of active regions, and the dynamic energy release that occurs in solar flares and coronal mass ejections. Special attention will be paid to analyzing the temperature structure of the post-flare loops by utilizing a differential emission measure (DEM) method that takes advantage of the many X-ray filters available on XRT. Using this method, we see clear evidence of multiple temperatures in the post-flare loops systems. We also find that intensity changes in the XRT images are due to cooling plasma in one of the flares, and decreasing emission measure in the other flare.
2009-01-15 at 14:30:00 Meridian Room Laurent Dolla ROB Solar Off-Limb Line Widths: Alfvén Waves, Ion-Cyclotron Waves, and Preferential Heating Display the abstractAlfvén waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind (HELIOS spacecrafts) and, recently, in the upper corona (UVCS/SOHO remote-sensing results). In the lower corona, one can use the line profiles to infer the ion temperatures. But the value of the so-called ''nonthermal'' (or ''unresolved'') velocity, potentially related to the amplitude of Alfvén waves propagating in the corona, is critical in firmly identifying ion-cyclotron preferential heating. We propose a method to constrain both the Alfvén wave amplitude and the preferential heating, above a polar coronal hole observed with the SUMER/SOHO spectrometer. Taking into account the effect of instrumental stray light before analysing the line profiles, we rule out any direct evidence of damping of the Alfvén waves, and show that ions with the lowest charge-to-mass ratios are preferentially heated.
2008-12-18 at 14:30:00 TV-Room Elena Moise University of Hawai'i Detection of an Extended Near-Sun Neutral Helium Cloud from Ground-Based Infrared Coronagraph Spectropolarimetry Display the abstractSensitive spectropolarimetric observations from the Haleakala SOLARC coronagraph and infrared imaging spectropolarimeter have detected an extended diffuse surface brightness flux at the 1083nm wavelength of neutral helium (He I). This has the polarization signature of light scattered by an extended He I cloud in the vicinity of the Sun. A series of observations obtained during the last two years suggest that this signal originates from an "inner source" of neutral helium atoms in the solar corona.
2008-12-04 at 14:30:00 Meridian Room Sabri Mekaoui RMI Preliminary Measurements of the Total Solar Irradiance Using DIARAD:SOVIM onboard the International Space Station Display the abstractThe Total Solar Irradiance is the primary source of energy reaching the Earth-atmosphere system. While its variability has been successfully studied over various time scales, its absolute value remains an open issue. Since 1978 different radiometers have successively and sometimes simultaneously addressed this problem. Current measurements from DIARAD/VIRGO, PMO06/VIRGO and ACRIM3 radiometers agree well together but differ from TIM/SORCE by about 5 W/m2. This difference is higher than the sum of the claimed individual absolute accuracies of the instruments. In this context the SOLAR payload on the International Space Station embarks the SOVIM package. We give the first results of the differential absolute radiometer (DIARAD) inside SOVIM. DIARAD has been developed at the Royal Meteorological Institute of Belgium. We describe the processing of DIARAD data and discuss its associated uncertainties.
2008-11-24 at 14:30:00 RMI Meeting Room Bojan Vršnak Hvar Observatory, Faculty of Geodesy, University of Zargeb (Croatia) Large-Scale MHD Shocks in the Solar Corona and Interplanetary Space Unusual location - RMI Meeting Room! Exceptionally on Monday! Display the abstractObservational signatures of large-scale coronal and interplanetary MHD shocks are reviewed, stressing the historical background. Special attention is paid to Moreton waves, coronal and interplanetary type II radio bursts, and the in situ solar wind measurements. The relationship between shocks, coronal mass ejections (CMEs), and flares is summarized, emphasizing the implications concerning the coronal shock formation. The observational characteristics of the shocks, as well as their relationship to flares and CMEs, are explained applying basic theoretical principles that govern the formation and nonlinear evolution of large-amplitude MHD waves. Specifically, the 3-dimensional piston mechanism is employed to model the wavefront evolution, providing an estimate of the time/distance at which the shock is formed. The application of the model to case-studies is illustrated, showing the importance of combining the multi-technique observations with careful theoretical considerations in identifying the source of coronal shocks. Finally, the evolution of shocks in the high corona and interplanetary space is discussed, paying attention to the nature of the driver, the decrease of the ambient plasma density, and the radial dependence of the Alfven speed. Various evolutionary options are considered emphasizing the space weather aspect, in particular the prediction of the arrival of the shock at the Earth.
2008-11-06 at 14:30:00 Meridian Room Nandita Srivastava Udaipur Solar Observatory (India) Use of Statistical Models for Predicting Geo-effective Events Display the abstractSpace weather prediction involves forecasting of the time of onset and magnitude of geomagnetic storms. Continuous datasets of coronal mass ejections or CMEs obtained from various space observatories like Yohkoh, TRACE and SoHO and ground observatories have led to systematic characterization of a large number of geo-effective events, which can also be used for statistical-model-based prediction of space weather. In this talk, I will evaluate several such models for the prediction of the occurrence of intense to super-intense geomagnetic storms (Dst < -100 nT). These models have been implemented using a series of solar and interplanetary variables that characterized major geo-effective events recorded during 1996-2008. The success and constraints of these models will also be discussed.
2008-10-30 at 14:30:00 Meridian Room Sergey Kuzin Lebedev Physical Institute, Russian Academy of Sciences (Russia) The EUV Imaging Spectroscopic Experiment TESIS onboard the CORONAS-Photon Satellite Display the abstractCORONAS-Photon is the third Russian satellite aimed to study the solar corona from space. Lebedev Physical Institute provides new complex instrument TESIS to study solar corona in the EUV by the method of imaging spectroscopy. The tasks of the experiment, and the description of the instrument will be presented.
2008-10-23 at 14:30:00 TV Room David Berghmans ROB PROBA2 Science Center Developments, Including Ideas on Subversion Display the abstract
2008-10-16 at 14:30:00 TV-Room Eva Robbrecht NRL First STEREO Observation of a Quiet Sun CME Display the abstractStreamer-blowouts form a particular class of CMEs characterized by a slow rise and swelling of the streamer that can last for days. While they are more massive than the average CME, their slow development complicates their association with features/activity in the low corona and hampers studies on their initiation mechanism(s). This paper reports on the first observation from 2 viewpoints of a streamer blowout CME. The event was observed by the SECCHI/COR2 A instrument as a typical flux-rope type CME, while a very faint partial halo was observed in COR2-B. The CME erupts from the east limb in the COR2 A field of view. EUVI-171 A images show a bright feature above the limb, traveling from the southern hemisphere towards the equator after which it rises into the coronagraphic fields of view developing into the flux-rope structure CME. At the time of eruption the separation between the two STEREO spacecraft is sufficiently large (54 deg) to observe the source region face-on in STEREO-B. However, inspection of EUVI B data didn't reveal any particular source region, other than the quiet sun. No flaring activity could be related to the eruption. This observation shows unambiguously that a CME eruption does not necessarily have clear on-disk signature. Also it sheds light on the long-standing question of the necessity of having a flare for producing a CME. This result supplies strong constraints for CME initiation models. This type of observation could not have been achieved without the multi-viewpoint observations by STEREO.
2008-09-25 at 14:30:00 TV-Room Marilena Mierla ROB 3D Reconstruction of Coronal Mass Ejections using SECCHI-COR Data Display the abstractThe data from SECCHI-COR1 and SECCHI-COR2 coronagraphs onboard STEREO mission which was launched in October 2006 provided us with the first-ever stereoscopic images of the Sun's corona. These observations were found to be extremely useful in reconstructing the 3-D structure of coronal mass ejections (CMEs). In this talk we describe four methods for reconstructing the CMEs: 1) Local correlation (to identify the same feature in COR Ahead and COR Behind images) plus tie-point reconstruction technique; 2) Center of mass (along epipolar lines) plus tie-point reconstruction technique; 3) Polarization ratio technique (see for e.g. Moran and Davila 2004); 4) Forward modeling technique (see Thernisien et al. 2006). The four techniques are applied on three structured CMEs observed by COR1 and COR2 instruments on 15 May 2007, 31 August 2007 and 25 March 2008. The separation angles of the two spacecraft were 8 degrees, 28 degrees and 47 degrees, respectively. A discussion on which method gives the most reliable results, at different separation angles, is done. Also, the results of the four methods are analyzed and compared.
2008-09-18 at 14:30:00 TV-Room (TBC) Jack Ireland Goddard Space Flight Center (USA) Automatically Detecting Oscillating Regions in Extreme Ultraviolet Imaging Data Display the abstractThe corona is now known to support many different types of oscillation. Initial detection of these oscillations currently relied on manual labor. With the advent of much higher cadence EUV (extreme ultraviolet) data at better spatial resolution, sifting through the data manually to look for oscillatory material becomes an onerous task. Further, different observers tend to see different behavior in the data. To overcome these problems, we introduce a Bayesian probability-based automated method to detect areas in EUV images that support oscillations. The method is fast and can handle time series data with even or uneven cadences. Interestingly, the Bayesian approach allows us to generate a probability that a given frequency is present without the need for an estimate of the noise in the data. We also generate simple and intuitive ''quality measures'' for each detected oscillation. This will allow users to select the ''best'' examples in a given dataset automatically. The method is demonstrated on existing datasets (TRACE, STEREO). Its application to Solar Dynamics Observatory data is also discussed. We also discuss some of the problems in detecting oscillations in the presence of a significant background trend which can pollute the frequency spectrum.
2008-09-11 at 14:30:00 TV-Room Matthew West ROB An Assessment of Heat Conduction Models in Loop Cooling Display the abstractThe cooling of plasmas in closed coronal loops by thermal conduction is important when considering their detectability at X-ray and EUV wavelengths. A non-local formalism of thermal conduction originating in laboratory plasmas is used and it is shown that while the effect is unlikely to be important for loops that are in a steady state, it does play a significant role in loops that are impulsively heated (e.g., by nanoflares). Such loops are “under-dense”, and so hot electrons have a relatively long mean free path. An analytic model is presented, and it is shown that conduction cooling times are lengthened quite considerably.
2008-09-04 at 14:30:00 TV-Room Susanna Parenti ROB Heating and Dynamics of Coronal Loops Display the abstractLoops may be considered the building blocks of the solar corona. Understanding their heating and dynamics becomes extremely important to solve the heating problem in the full corona. The debate on weather steady or impulsive heating (such as envisioned by the nanoflare scenario) should be considered as the dominant heating process in loops, is still lively in the solar community. From the observational point of view, key elements to progress on the understanding of the corona are the correct interpretation of the observational data together with precise measurements. Limitations are often present because of the finite resolution of the instruments, their limited temperature coverage and the fact that we are dealing with optically thin plasma when observing the corona. In spite of such limitations, considerable progress has been made in the past years. Results obtained in the past decades are now strengthened by the new observations from the Hinode and STEREO missions. This talk will show and discuss new observational results that address selected aspects as key elements to understand the physics of loops. These include: the monolithic vs. multi-thread configurations (can we resolve the elemental coronal loop?); flows and dynamics (new exciting results from SOHO and Hinode); loops and active region thermal structures (do we have a complete map of them?).
2008-07-09 at 14:30:00 IRM Meeting Room Bernd Inhester Max-Planck-Institut für Sonnensystemforschung (Germany) Coronal Magnetic Field Extrapolation - Presence, Problems, Prospects Exceptionally on WEDNESDAY! Note an unusual location! Display the abstractThe coronal magnetic field is by far the largest energy reservoir in the solar corona. Unfortunately, it cannot be observed directly but it is conventionally extrapolated from field observations on the solar surface. Vector magnetographs which have recently come into operation have increased the amount of information which can be used for the extrapolations. Yet the extrapolation remains a highly ill-posed boundary value problem. At presence, extrapolation codes cannot cope with the observed spatial resolution nor do they cover the entire corona. We discuss models and schemes used at present, their problems and try to give an outlook how they might evolve in the future.
2008-05-29 at 14:30:00 Meridian Room Bidzina Shergelashvili KU Leuven MHD Waves in the Nonequilibrium Media Display the abstractWe start with the brief outline of the recent astrophysical and plasma wave problems, solved within the framework of either the nonequilibrium statistical mechanics or thermodynamics. Then we concentrate on one of those examples in more detail. Namely, the propagation of compressional MHD waves is addressed for an externally driven system. It is assumed that the combined action of the external sources and sinks of the entropy results in the harmonic oscillation of the entropy (and temperature) in the system. It is found that with the appropriate resonant conditions fast and slow waves get amplified due to the phenomenon of parametric resonance. Besides, it is shown that the considered waves are mutually coupled as a consequence of the nonequilibrium state of the background medium. The coupling is strongest when the plasma beta is around 1. The proposed formalism is sufficiently general and can be applied for many dynamical systems, both under terrestrial and astrophysical conditions. Finally, some future perspectives will be discussed.
2008-05-28 at 14:30:00 Meridian Room Christian Monstein ETH Zurich Radio Astronomical Instrumentation at ETH Zurich Exceptionally on WEDNESDAY! Display the abstractChristian Monstein works at the ETH Zurich institute where he designed and built a set of radio receivers dedicated to solar observations. In particular, he recently developed a world-wide network of radio spectrometers called CALLISTO. In the framework of the STCE, and the renewal of solar radio observations at the Humain station, he provided us with one of these receivers, which will be used to monitor the solar activity in the metric and decimetric range. He will present a summary of the radio instrumentations in Zurich and explain the concept of CALLISTO in more details.
2008-05-22 at 14:30:00 Meridian Room Joseph Lemaire BIRA Kinetic and Fluid Models in Space Plasmas Display the abstract
2008-04-17 at 14:30:00 TV-Room Dan Seaton University of New Hampshire (USA) Modeling Current Sheets During Solar Flares Display the abstractThe dynamics of reconnecting current sheets are an important but complex problem for those who want to understand the processes that drive solar flares and coronal mass ejections. In this talk, I will discuss an approach to solving this problem that makes use of a method developed by B. Somov and V. Titov in which we average the MHD equations across the current layer, reducing the MHD equations to an analytically solvable set. By integrating thermal conduction into this framework we can produce a relatively simple, one-dimensional model of a current sheet that agrees with existing numerical models and observations of solar flares. We have integrated this current sheet model into a CME/flare model by K. Reeves and T. Forbes to make some specific predictions about energy release during solar eruptions.
2008-04-03 at 14:30:00 TV-Room Stéphane Régnier University of St. Andrews (UK) Precursors of solar eruptions Display the abstractLarge-scale solar eruptions such as flares and coronal mass ejections (CMEs)are rapid releases of magnetic energy in the corona leading to the re-configuration of the magnetic field in the solar atmosphere and in the interplanetary medium. The classical models of eruption include at least four main ingredients which are precursors (or prerequisites) for eruptions: (i) transverse motions on the photosphere, (ii) magnetic topology (e.g., null points), (iii) coronal converging inflows to facilitate the occurrence of magnetic reconnection, (iv) twisted flux tubes accounting for the storage of magnetic energy in the corona. I will describe such precursors in the frame of a force-free model of the corona.
2008-02-14 at 14:30:00 TV-Room Marilena Mierla ROB Structures in the Solar Corona: Dynamics and 3D Reconstruction Display the abstractDifferent aspects of the solar corona dynamics will be discussed. First, by using LASCO-C1 spectral data, an analysis of thermal motions and nonthermal effects (such as turbulence) is performed. Then, the 3D reconstruction of CMEs and their true propagation is analyzed by using STEREO-COR1 data.
2008-01-22 at 15:00:00 Meridian Room David Berghmans ROB SWAP Towards Improved Space Weather Monitoring Note unusual day and time! Display the abstractSolar eruptions such as coronal mass ejections and flares influence the space environment of the Earth. 'Space weather monitoring' is the scientific discipline that studies these solar-terrestrial interactions from an applied perspective: how can we timely observe, understand and forecast the solar activity and provide a warning service useful to society? I will briefly overview the space weather monitoring system that has been gradually deployed at ROB since 2000 and underline in particular how advanced IT-techniques have allowed us to make this system 'better, cheaper and faster'. This same design philosophy has been applied on the most ambitious element of the SIDC space weather system yet: a space-born observing facility providing independent access to all space weather significant events on the Sun. "PROBA2" is a Belgian-built micro-satellite carrying onboard two solar instruments built in a collaboration between the Royal Observatory of Belgium and the Centre Spatial de Liège. LYRA is the "Lyman Alpha radiometer", with an additional important Swiss contribution from PMOD/WRC (Davos), and SWAP is the "Sun Watcher using APS and image processing". SWAP, the main topic of this presentation, is an EUV telescope that will image the full solar corona at a cadence of 1 min. Thanks to an innovative optical design, new detector technology and the revolutionizing onboard software algorithms, SWAP will be able to continue the CME watch program of SOHO/EIT with the minimum of onboard resources provided by a micro-satellite. Special attention will be given to the current calibration effort of SWAP, in collaboration with KULeuven/CPA, and the preparation for the launch and operational phase later this year.
2008-01-10 at 14:30:00 TV-Room Jasmina Magdalenic Faculty of Geodesy, University of Zagreb (Croatia) Some Aspects of Type II Radio Bursts - Signatures of Coronal Shock Waves Display the abstractEnergy release during the flare/CME process can be followed by the formation of large scale disturbances and shock waves that travel through the corona and the interplanetary space. Electrons that are accelerated at propagating MHD shock waves radiate at the local plasma frequency and/or its harmonics and can be observed in the dynamic spectrum as slowly drifting emission lanes - type II radio bursts. Both fundamental and harmonic emission bands of type II bursts are frequently being split in two parallel lanes. The interpretation of the band-splitting as the emission from the upstream and downstream shock regions is used in a statistical study of type II bursts. Using this interpretation, the shock amplitude, i.e. the Mach number, the Alfvén velocity and the magnetic field are estimated, covering distances from the lower corona up to 1 AU. The question of the relation between coronal shock waves, flares and CMEs is discussed. In a longstanding debate, coronal shock waves have been attributed either to solar flares or CMEs, or some combination of these two phenomena. Since CMEs and flares are usually very well synchronized, it is difficult to make a decisive conclusion. It is certain that CMEs play a very important role in the formation of coronal waves, and most of the interplanetary shocks are driven by CMEs. However, it remains unclear if coronal shocks are CME driven, or flare ignited. The multi-wavelength case study of coronal waves associated with the CME/flare event of 24 December 1996, is presented. Kinematics and evolution of shock wave signatures - type II radio bursts and the EIT-wave - are analyzed and compared with the flare evolution and the CME kinematics. Results are compared with a theoretical model of the 3D piston scenario for the formation of large scale disturbances in the solar corona.
2007-11-22 at 14:30:00 TV-Room Boris Giordanengo ROB AlGaN UV photodetectors simulations with a powerful PEDs solver Display the abstract
2007-10-11 at 14:30:00 TV-Room Ingolf Dammasch ROB Solar UV Spectroscopy with SUMER on SOHO Display the abstractThe SOHO instrument that is best known to the public is probably EIT; its colored UV images and movies could be seen in many TV science or news reports and enhanced the popularity of solar research. The telescope and spectrometer SUMER, for which I worked since 1989, may be less popular. I will give a short overview on the development of SOHO and SUMER, and demonstrate its capabilities with some examples of research that I was involved in. This includes current findings on spicules and the height of the transition region, as well as the redshift (downflow) within various kinds of loops.
2007-10-04 at 14:30:00 TV-Room Matthew West Imperial College London, Space and Atmospheric Physics Group The Detectability of Coronal Magnetic Reconnection Display the abstractIt's now well established that plasma jets are associated with the magnetic reconnection process; in the corona the twisting of flux tubes around one another leads to localised current sheets and reconnection, creating impulsive heating. Spectral line profiles associated with these heating events in the solar corona are calculated. We assess if the jets produced in magnetic reconnection are observable through line broadenings generated from their bulk motions. Previous models used to calculate expected line broadenings allowed these jets to travel for large distances uninhibited. In reality, these jets will encounter surrounding coronal magnetic fields, where they will be inhibited due to magnetic tension forces, and then dissipated through conduction along the surrounding field lines. We adopt a model where the surrounding field acts to impede the produced jets, treating the reconnection event as an explosion balanced by the surrounding magnetic tension forces. This acts to restrict the growth of the jet, and the decrease in volume increases the density and emission measure of individual jets. We look at the observability of single jets and a convolution of several jets generated with the model, and the effects of varying various coronal parameters such as the magnetic field, density, temperature and the power law from which an events' energy is drawn. We show that the broadening is too small to be observed with current spectrometers, and is on the limit of current instrument resolution.
2007-09-27 at 14:30:00 Meridian Room Dieter Nickeler Ondrejov Observatory Finite Time Singularities in MHD - a Possible Mechanism for Eruptive Flares or Excitation Mechanism for Coronal Waves? Display the abstractFinite time singularities in MHD, like discussed by Imshennik und Syrovatskii, or in the mathematical literature so called blow-up solutions, provide a collapse of a physical system: within a finite time interval different physical values diverge. Thus these collapse processes mark a breakdown of the corresponding fluid theory and may indicate quick, sudden and violent instabilities like they can be recognized in solar eruptive flares. We discuss that collapse times depend on initial conditions, maybe providing time scales for the excitation of coronal waves or eruptive flares.
2007-09-25 at 14:30:00 TV-Room Judith de Patoul ROB B2X-Flares - an Automatic EUV Flares Detector. Exceptionally on TUESDAY! Display the abstractSolar flares are large and sudden increases of the photon flux and represent some of the most powerful examples of solar activity. The SoHO/EIT and now STEREO/SECCHI provide a high resolution and very complete sampling of the solar corona in time, space and brightness, thereby allowing large statistical studies of EUV flares. Such studies will improve significantly our understanding of EUV flare phenomena with respect to better studied X-ray flaring processes. We present and discuss several ‘B2X flares’ methods able to detect automatically EUV flares belongs to class B to X in EUV images SoHO/EIT and STEREO/SECCHI (19.5 nm, 17.1 nm, 30.4 nm, 28.4 nm). Some basic event features can be determined from those methods: Time (start, peak and end of the event), localization on the solar disk, evolution of the intensity and area, etc. We finally describe a technique called Receiver Operating Characteristic (ROC) curves which allows to compare different methods and to evaluate the ability of the B2X algorithm with regard to the GOES catalog. A first comparisons of GOES catalog and B2X results show some differences between X-ray and EUV flares evolution.
2007-09-20 at 14:30:00 TV-Room Susanna Parenti ROB On the Observational Constraints to Loop Heating Models Display the abstractIn 2002 started a new series of workshops dedicated to coronal loops heating. Their aim is to solve some critical questions coming out from inconsistency in the loop observations. I will summarize the main achievements, and point out at the issues that still need to be solved.
2007-06-28 at 14:00:00 TV-Room Laurent Jacques Communications and Remote Sensing Laboratory, Université catholique de Louvain A Short Introduction to Compressed Sensing Display the abstractNowadays, a torrent of data is flooding every field of sciences and technology. Most of the time, to swim in this overwhelming quantity of information, a compression of each piece of data is realized after its initial recording (sampling). In other words, the whole discretization of a given signal (e.g. sound, image, video, ...) has to be known before to find the correct basis (e.g. wavelet, curvelet, dictionary, ...) where only a few basis elements will represent the original signal up to a controlled error. Since a couple of years, a new field of signal processing that records and compresses a signal in one step has been discovered. This approach is named "Compressed Sensing". The presentation will introduce the basic mathematical concepts of this theory and several recent extensions of it. We will conclude by giving an overview of two recent technological applications of this concept.
2007-06-08 at 14:30:00 Meridian Room Sean Bruinsma CNES, Toulouse Atmospheric Neutral Density Observed With Accelerometers Display the abstractAtmospheric neutral densities can be used to study the following, non-exhaustive, list of topics: (1) analysis of short- and long-term thermospheric variability; (2) evaluation of proxy-indicators for solar or geomagnetic activity, such as F10.7, the chromospheric Mg II index, E10.7, (sectorial) Kp; (3) thermospheric wave activity/traveling atmospheric disturbances related to geomagnetic storm events; (4) analysis and improvement of thermosphere models. An overview of results obtained over the last 6 years for these 4 topics will be given. Total atmospheric density has been derived from the CHAMP accelerometer data, and presently about 5.5 years of observations are available. Using a similar procedure, GRACE accelerometer data can also be used to derive densities approximately 100 km higher. At present, this has been done for solar storm events only. The German satellite CHAMP was launched in a circular, nearly-polar orbit at 460 km altitude in July 2000. The two main mission objectives are the mapping of the magnetic and gravity fields of the Earth. The US/German GRACE satellites were launched in March 2002, also in a circular, nearly-polar orbit, but at 500 km altitude. The mission objective is to track changes in the Earth’s gravity field. The CHAMP and GRACE satellites carry STAR accelerometers, positioned at their centers of mass, and GPS receivers and attitude sensors in order to determine accurate satellite positions as well as accurate accelerometer calibration parameters. Satellites and instruments are still healthy and the missions have been extended to 2009. In a few years, CHAMP will very probably be the first mission to provide the community with consistent and geographically well-distributed total density data, covering solar maximum through minimum.
2007-06-07 at 14:30:00 TV-Room Andrea Verdini Arcetri Astrophysical Observatory Alfvén Waves and MHD Turbulence in Coronal Heating and Solar Wind Acceleration Display the abstractIn situ solar wind measurements of MHD turbulence first showed, 30 years ago, that Alfvén waves propagating away from the sun are a dominant component, at least in high speed streams at solar minimum, with sufficient energy to explain the heating of the distant solar wind. Such waves should presumably have a solar origin, being coupiosly produced in the chromosphere and lower corona. Alfvénic fluctuations in the solar wind present a power law spectrum wich evolves with distance. The origin of such a turbulent spectrum is still unclear and its shape in the low corona, or deeper in the chromosphere, represents one of the key points for the understanding of the coronal heating and the solar wind acceleration problem. The stratification of the atmosphere and the solar wind expansion play a fundamental role in the formation and evolution of the turbulent spectrum. The waves, propagating outwards from the photosphere, are partially reflected by the density gradients. Nonlinear interactions, which occur only among counterpropagating waves, are therefore driven by reflection: we discuss the propagation and cascade using phenomenological and numerical models considering first the large and small scales properties of Alfvén waves in a specified atmosphere and then considering their backreaction on the solar wind.
2007-06-05 at 14:30:00 Meridian Room (TBC) Milan Maksimovic LESIA & CNRS - Observatoire de Paris The PHOIBOS mission: Probing Heliospheric Origins with an Inner Boundary Observing Spacecraft Display the abstractThe aim of this seminar is to present the PHOIBOS mission which has been submitted to the ESA ''Cosmic Vision'' program. This mission is designed to make comprehensive measurements in the never-observed region of the heliosphere from 0.3 AU to as close as 3 solar radii from the Sun’s surface. The primary scientific goal of PHOIBOS will be to determine the structure and dynamics of plasmas and magnetic fields in the outer solar atmosphere which give rise to the corona, the solar wind and the heliosphere. Despite the tremendous increase of our knowledge of the solar and heliospheric physics since the beginning of the space era, the fundamental mystery of how the solar corona is heated and the solar wind is generated remains unsolved. The reason for such a situation is mostly due to the large gap in our knowledge of the heliosphere inside of Mercury’s orbit. Remote-sensing strategies have probed the coronal properties by analysing the photons emitted, scattered, or absorbed by the Sun's outer atmosphere, within the first few solar radii. In this regards, there are both theoretical limitations (in the understanding of the physics of the coupling between photons and plasma) and experimental limitations (limited number of observables such as spectral lines or the hardly solvable inverse problem of the line of sight integration). On the other hand solar wind in-situ measurements have had access to the very detailed state of the local plasma properties (full particles velocity distribution functions, observations of the electromagnetic plasma fluctuations over a huge frequency range) but at locations far from the corona and the solar wind acceleration region. To understand the engine at the source of the solar wind one must probe the region from the photosphere to about 20 Rs, where internal, electric, magnetic and turbulent energy in the coronal plasma is channeled into bulk energy of the supersonic solar wind flow. Understanding the solar wind is of fundamental significance to all of astrophysics since it is the prototype for all stellar winds and related astrophysical flows. Approaching as close as three solar radii from the surface will allow direct detection of the plasma physical processes at work in coronal heating. An exploratory mission to make such observations has long been a top priority of the solar and space physics community. Yet the implementation of a Solar Corona Probe was hindered by technical problems, associated with (i) the use of a RTG, (ii) the use of gravity assistance by Jupiter, (iii) the duration of the orbital period, (iv) the need to identify materials with tolerable outgassing, for the heat-shield, and (v) the difficulty to dump data while the probe is near the Sun. We propose to implement a new mission based on a different concept which is simpler and avoids the difficulties listed above. The main characteristics of the PHOIBOS mission will be: (i) Use retractable solar panels that avoid the use of RTGs (Radioisotope Thermoelectric Generators) (ii) Reach the final operational orbit (4 Rs to 3.7 AU with an inclination up to ~70 deg.) by using electric propulsion and Earth and Venus flybys. Therefore there is no need for gravity assistance by Jupiter. (iii) With such a trajectory the orbital period is reduced to 2.33: at least three fly-by’s of the Sun, under different phase of the solar cycle are possible (iv) Use a protective shield with already identified materials that maintain the outgassing to an acceptable level (v) Use a 5 to 10 Gbit memory to store the data and transmit them after perihelion if necessary
2007-06-01 at 14:30:00 TV-Room Véronique Delouille ROB Magnetic Field Properties of Flaring versus Flare Quiet Active Regions Display the abstractAccording to the recent literature, it is relatively simple to observe changes in the physical properties of an Active Region associated with an energetic event. In this talk, I will make a critical review of some methods described in the literature to observe these changes. In particular, I will focus on the work by Leka and Barnes (ApJ 2003, 2006, and 2007). The authors propose an extensive search of photospheric magnetic field properties that can discriminate between flare-quiet and flare-productive active regions. Their general conclusion parallel other results given in the literature. However, an operational system with a low flaring prediction error rate still needs to be built. Towards this goal, the choice of parameters as well as the classification method is crucial. I will end the talk by an introduction to the Support Vector Machine classification method, which enjoys optimal properties for classification in a linear and the non-linear setup.
2007-05-24 at 14:30:00 TV-Room Emmanuel Chané CPA, K.U. Leuven 3D Numerical Simulations of Space Weather Events at the CPA E. Chané, S. Poedts, C. Jacobs, B. Van der Holst and R. Keppens Display the abstractCoronal Mass Ejections (CMEs) belong to the most violent and fascinating events in the solar system. The shocks and magnetic clouds generated by CMEs play a key role in the study of space weather. In order to understand the CMEs evolution in the interplanetary (IP) space and the impact with a planet or a satellite, numerical simulations are often used. We present an overview of the research done at the K.U. Leuven on simulations of CMEs. Three-dimensional numerical simulations of the initiation and IP evolution of CMEs are performed in the framework of ideal magnetohydrodynamics. The interactions with the magnetosphere of the Earth and of Jupiter are also simulated.
2007-03-01 at 14:30:00 Meridian Room Russell Howard Naval Research Laboratory (USA) The First Stereoscopic Solar TErrestrial RElations Observatory Display the abstractSTEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program. This two-year mission will employ two nearly identical space-based observatories - one ahead of Earth in its orbit, the other trailing behind - to provide the first-ever stereoscopic measurements to study the Sun and the nature of its coronal mass ejections, or CMEs. The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) is a suite of solar and heliospheric imagers being prepared by a consortium of institutions under the leadership of the Naval Research Laboratory. SECCHI is being built by institutions from the US, UK, Belgium, France, and Germany. More specifically, STEREO's scientific objectives are to: - Understand the causes and mechanisms of coronal mass ejection (CME) initiation. - Characterize the propagation of CMEs through the heliosphere. - Discover the mechanisms and sites of energetic particle acceleration in the low corona and the interplanetary medium. - Improve the determination of the structure of the ambient solar wind. Some of the first results of the mission will be presented.
2007-02-15 at 14:30:00 TV-Room Don Hassler South-West Research Institute, USA Exploring High Time Resolution Coronal Dynamics with the Rapid Acquisition Imaging Spectrograph (RAISE) Sounding Rocket Program D. M. Hassler, C. E. DeForest, S. McIntosh, D. Slater, T. Ayres, J.-F. Hochedez, H. Mason, H. Michaelis, U. Schuehle, R. J. Thomas Display the abstractThe Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation high resolution imaging spectrograph to study the dynamics of the solar chromosphere and corona on time scales as short as 100 ms. High speed imaging from TRACE has shown that rapid motions and reconnection are central to the physics of the transition region and corona, but cannot resolve the differences between propagating phenomena and bulk motion. SoHO/CDS and SoHO/SUMER have yielded intriguing measurements of motion and heating in the solar atmosphere, and Solar-B/EIS will capture EUV spectra of flares in progress; but no currently planned instrument can capture spectral information in the chromosphere, transition region, or cool corona on the ~1-10 Hz time scale required for few-second cadence spectral imaging or rapid wave motion studies. RAISE is uniquely suited to exploring this hard-to-reach domain. The first flight of RAISE is scheduled for late Fall, 2007 (Flight 36.219) and will focus on the study of high frequency, small-scale dynamics of active region structures and the high frequency wave structure associated with these active regions. This work is supported by NASA Grant NNG04WC01G to the Southwest Research Institute.
2006-12-15 at 11:00:00 Meridian Room Marco Velli Jet Propulsion Laboratory and Arcetri Observatory Coronal Heating, Nanoflares, and Anisotropic MHD Turbulence TBC Display the abstractCoronal heating is at the origin of the X-ray emission and mass loss from the Sun and many other stars. While different scenarios have been proposed to explain the heating of magnetically confined and open regions of the corona, they all rely on the transfer, storage and dissipation of the abundant energy present in photospheric motions. Here I focus on the field line tangling mechanism originally proposed by Parker. I will give a pedagogical introduction before presenting long-time high-resolution simulations of the dynamics of a coronal loop in cartesian geometry within the framework of reduced magnetohydrodynamics (RMHD). The magnetic field in the loop develops small scales following a turbulent cascade, though the overall kinetic energy remains much smaller than the magnetic energy. The heating rate and energy spectra depend on two parameters: the loop aspect ratio and the ratio of coronal Alfvén speed to the exciting photospheric velocity field magnitude. As these parameters vary, the turbulent spectra correspondingly span the various regimes of anisotropic MHD turbulence, from weak to strong: spectral slopes of magnetic energy are steeper for strong axial magnetic fields and short loops, while they are flatter for weak fields and long loops. As a consequence the scaling of the heating rate with axial magnetic field intensity B, which depends on the spectral index of magnetic energy for given loop parameters, varies from B^1.5 for weak fields to B^2 for strong fields at a given aspect ratio. Simulations from simpler, shell model, calculations, which allow reaching larger Reynolds numbers and longer time periods will be used to describe the statistical properties of the energy release mechanism, and the relationship of this anomalous regime of MHD turbulence to nanoflares.
2006-12-14 at 14:30:00 Meridian Room Karl-Ludwig Klein Observatoire de Paris, LESIA Solar Energetic Particles and Radio Evidence on Their Acceleration and Propagation Display the abstractSolar energetic particle events are transient enhancements of charged particle fluxes which may reach relativistic energies. Their origin is attributed to acceleration in flares or at CME-driven shock waves. We will discuss evidence on the origin of different types of particle events in the corona, based on radio observations. These observations, combining spectrography and imaging, provide evidence on the temporal relationship of particle (electron) acceleration in the corona. They also give hints to the magnetic structures that guide particles through the corona and interplanetary space.
2006-11-09 at 14:30:00 Meridiaanzaal/Salle Méridienne Frédéric Clette ROB From the Wolf Number to the International Sunspot Index: 25 Years of SIDC TBC Display the abstractBy encompassing four centuries of solar evolution, the sunspot number provides the longest available record of solar activity. Nowadays, it is still widely used as "the" reference solar index on which innumerable published studies are based, in various fields of science, beyond solar physics itself. In this review, we will retrace the history of this central solar index, from its roots at the Zurich Observatory up to the current modern statistical product established and distributed by the SIDC, as World Data Center for the International Sunspot Index founded in 1981, exactly 25 years ago. We will clarify the meaning of this visual index, describe the variable properties of the 400-year sunspot time series and also show that even now, the sunspot index stands the test of time versus more recent quantitative indices. Looking towards the future, we will also present new SIDC "extended" sunspot products. To conclude, we will outline the prospects and requirements for a possible transition from the visual index heritage towards a future image-based photospheric activity index.
2006-10-12 at 14:30:00 TV-Room Tom Van Doorsselaere CPA, KU Leuven Coronal Loop Oscillations: the Effect of Curvature and Implications for Coronal Heating Display the abstractTwo aspects of coronal loop oscillations on which I have been working on after my PhD defense will be discussed in this seminar. The first aspect will be the influence of curvature on the oscillations of coronal loops. The dispersion relation of Van Doorsselaere et al. (2004, A&A) will be corrected. Furthermore, the dispersion relation will be solved numerically, and the eigenfunctions will be sought. As a second topic, the energetics of coronal loop oscillations will be discussed. As can be observed in simulations, the energy of the oscillations is mainly deposited at the loop footpoints. A comparison between the simulated heating profile and the observed heating scale heights is performed.
2006-10-03 at 14:30:00 Salle Méridienne/Meridiaanzaa Alexander Baranovski ROB Sunspot Number and Scientific Theory: Prediction Methods and Their Performance Display the abstract
2006-09-26 at 14:30:00 TV-Room Gemma Attrill MSSL Using the Evolution of Coronal Dimming Regions to Probe the Global Magnetic Field Topology Display the abstract"Unidentical twins": a new interpretation of the May 12, 1997 event
2006-09-25 at 14:30:00 TV-Room Laurent Demanet California Institute of Technology Curvelets and Wave Atoms MONDAY! Display the abstractI will give a not-too-technical overview of curvelets and wave atoms, two new wavelet-type transforms in 2D and 3D. These transforms could be useful for representing various features that can be found in the sun's coronal loops. Why should physicists use fancy tools for data analysis? I will try to answer this question within the classical setting for statistical estimation and detection: maximum likelihood. A keyword for the answer is sparsity.
2006-06-29 at 14:30:00 TV-Room Alexander Baranovski ROB Nonlinear Solar Cycle Forecasting: Theory and Perspectives Display the abstractIn our talk we develop a modern approach in a solar cycle forecasting, based on mathematical theory of nonlinear dynamics. We start from a design of the static curve fitting model for the experimental yearly sunspot number series on the time scale of 306 years since 1700 and establish Pearson?s type III distribution as a least square optimal pulse shape of a solar cycle. An evolution of the parameters of the cycle shape identifies different patterns like e.g. Gleissberg cycle and a strong anomaly in the cycle evolution during the Dalton minimum. On the next step we extract a nonlinear mapping for the successive values of one of the key model parameters ? the rate of the exponential growth-decrease of the solar activity during nth cycle and provide its probabilistic analysis: calculation of the invariant distribution and autocorrelation function. We find analytical relationships for the sunspots maximum and minima as well their occurrence times as functions of chaotic values of the parameter. On the base of Lyapunov spectrum analysis of the embedded mapping we establish a horizon of predictability of the method, which allows us to give most probable forecasting of the upcoming solar cycle 24 with an expected peak height of 87+/-10 occuring in 2011/2012. Finally we discuss ways to modify the approach to self-learning algorithm as a key mechanism to get a most adequate nonlinear dynamical system of solar activity.
2006-06-23 at 10:30:00 TV-Room Michael Knolker High Altitude Observatory (USA) Instruments and Research Activities of the HAO Coronagraph Team Display the abstract
2006-06-08 at 14:00:00 TV-Room Jesse Andries CPA, KULeuven On the Continuous Spectrum of Leaky MHD Modes, and the Associated Quasi-modes Display the abstractWhen the MHD operator is considered on an unbounded spatial domain the self-adjointness of the operator can still be established, resulting in the fact that eigenfrequencies are necessarily either real or imaginary, and that a complete spectral representation can be constructed. Nevertheless, considering an unbounded domain removes one of the boundary conditions (at the boundary which is moved to infinity) resulting in the appearance of additional continuous spectra as infinity becomes a singular point in the equations. These additional leaky continuous spectra are the MHD analog of the free electrons in the quantum mechanical model of the hydrogen atom. As soon as the spatial domain is unbounded the continuous spectrum does not only consist of the classical Alfvén and slow continuous spectrum, but is to be extended with a fast and slow leaky continuous spectrum. The eigenmodes that are associated with the leaky MHD continuum are shown to be improper in the sense that they carry an infinite amount of energy (just like the Alfvén continuum modes, or the Case - van Kampen modes in Vlasov plasmas), and are therefore not contained in the Hilbert space of square integrable functions. The unstable leaky modes found by Wilson (1981), Spruit (1982) and Cally (1986) are quasi-modes and are found by continuation of the Green's function into the lower half of the complex frequency plane. The physical relevance of these modes in the context of the observed damping of oscillations in the solar corona is subject of a debate by Ruderman and Roberts (2005) and Cally (2006). The present discussion is intended to shed light on the debate and to clarify at least the mathematical status of the unstable leaky quasi-modes in terms of the mathematical process of continuum damping.
2006-06-01 at 14:00:00 TV-Room Elena Podladchikova ROB Statistical Lattice Models for Coronal Heating Display the abstractSolar coronal heating is a complex problem due to the variety of scales and physical phenomena involved, and intricacy of boundary conditions. Models of coronal heating generally assume energy injection at large scales by photospheric motions, while dissipation occurs at small scales, for example by the dissipation of small-scale current sheets (DC mechanisms). Small scales can appear due to inhomogeneities or turbulent cascades provided they have sufficient time to develop. Moreover, dissipation involves processes with a complex microphysics, such as reconnection or anomalous resistivity. Lattice models and self-organised criticality provide means to model phenomenologicaly some of the physics involved over a wide range of scales, and reproduce certain statistical features of solar flares, including power-laws in their occurence rate. This, however, raises the question of comparing unambiguously theories and models with observations of the solar corona. This not only requires to relate the observations in different wavelengths (EUV, H-alpha, X-ray) to physical quantities such as released (magnetic) energy, but is also complicated by the many spatial and temporal scales involved in the problem from the slow and large scale driving and build-up of unstable configurations to small-scale fast dissipations mechanisms.
2006-05-18 at 15:00:00 TV-Room Susanna Parenti ROB Looking for Signature of Coronal Heating in the Radiative Emission of a Coronal Loop Display the abstractUsing a reduced MHD model we built the energy input for a multi-stand loop hydrodynamic model. This energy has a distribution that follows a power law with index -1.6. Here we investigate if and under which conditions this specific property can be transmitted to the plasma response. Our results show that only the high temperature emission conserves a power law distribution with index close to that of the input energy.
2006-04-27 at 14:00:00 TV-Room Eugene Romashets CPA, KULeuven Plasma Flows around Magnetic Obstacles in Solar Wind E. Romashets, S. Poedts Display the abstractIt is very important to describe the plasma parameter distributions in the vicinity of magnetic clouds and other stable structures in solar wind. Assuming that the magnetic field around the object is determined or measured, the velocity fields can be calculated from the frozen-in equation. The plasma density and pressure are then given by explicit formulas expressing plasma pressure and density as functions of only B and V. Clearly, an alternative is to solve the full system of MHD equations numerically. But even in this case such analytical estimates would be also of use when formulating initial and boundary conditions. It is shown in recent numerical simulations and data analyses that the area in front of magnetic clouds is important from the point of view of the geo-efficiency of the magnetic cloud which has a very complicated magnetic and plasma structure. For a detailed analysis of generic phenomena of magnetic clouds and particular features of individual clouds, it is necessary to treat these structures in terms of analytical functions. First, the velocity and magnetic field distributions satisfying specific boundary and frozen-in conditions are determined. Next, the plasma density and pressure are calculated. In this way, three-dimensional distributions are found for the case of an inclined cylindrical cloud.
2006-04-19 at 14:00:00 TV-Room Robertus Erdelyi University of Sheffild (UK) Dynamical Coupling of the Solar Photosphere to the Corona: When the Tail Wags the Dog... Display the abstractSOHO and TRACE have clearly demonstrated that the solar atmosphere and its magnetic structures are highly inhomogeneous at almost all spatial and time scales. Would the ubiquitously magnetic solar atmosphere have any effects on solar global oscillations? Does the random nature of the solar atmospheric plasma influence the characteristics of the observed global modes? Fundamental questions like these naturally arise. In my talk I will demonstrate the mechanism of magnetic coupling of the solar interior to the atmosphere that takes place in the Sun. I will discuss how the solar global oscillations can (resonantly) interact with the overlaying magnetic carpet and the structured and stratified solar atmosphere. Solar global acoustic oscillations are also traditionally considered to be somewhat less important for the dynamics of the solar atmosphere ranging from low chromosphere to the tenuous corona. This thinking may have also been considerably changed in light of the currently available high spatial and time resolution observations and their MHD modelling allowing us to perform advanced magnetic atmospheric seismology. In the second part of my talk I will discuss the new data and how they can be used for atmospheric diagnostics, including topics such us randomly heated coronal loops or even short-lived dynamical events like spicules, their formation and impact on coronal and space plasmas.
2006-04-10 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract
2006-04-03 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract
2006-03-27 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract
2006-03-23 at 14:00:00 TV-Room Petra Vanlommel ROB The Estimated International Sunspot Number: a Brew from the Previwitches Display the abstract
2006-03-16 at 14:00:00 TV-Room Dirk Callebaut University of Antwerp Approach of a Grand Solar Minimum and Effect on the Climate Display the abstractThe latitudes of the boundaries of the large-scale unipolar magnetic field regions make a jump to lower latitudes after polar reversal and then oscillate a bit around these so-called rest-latitudes until a new cycle starts. These rest-latitudes show a steady decrease during the last 12 cycles: for the higher ones from 53° to 37.5° and for the lower ones from 29.5° to 16.5° (averaging), north and south. The lower ones are approaching the limiting 11°, corresponding to the limiting maximum Wolf number 40, below which no polar reversals happen and which may be taken as defining a grand minimum. Using an extrapolation we expect next grand minimum to occur at cycle 26 or just after it. Seven other arguments contribute to belief this hypothesis. Some counter arguments are given too. It is expected that a grand minimum may give a decrease of about 1 K on Earth, although this will partially be masked by the increasing atmospheric pollution and the corresponding global warming. This slightly reduced temperature may give the wrong impression that the present high temperatures are just a fluctuation and hence that one may further increase the pollution. That would be disastrous. Moreover, after a grand minimum (say about 5 cycles) we may expect to recover the lost 1 K with catastrophic results.
2006-03-15 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract- Eruptions solaires: - scénario d'une éruption, des précurseurs à la phase post-éruption - Structure et dynamique - Spectre d'émission (des UV aux spectre gamma nucléaire) - Mécanismes et modèles d'éruption - Ondes EIT et de Moreton.
2006-03-14 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract- Emission coronale: diagnostics tirés du spectre lumineux (DEM) - Structures de la couronne (boucles, trous coronaux) - Chauffage de la couronne - Le vent solaire - l'héliosphère (... et fin de la pose du décor "calme") - Eruptions solaires: - Intro: le Soleil par rapport aux autres étoiles.
2006-03-02 at 14:00:00 TV-Room Michel Roth BIRA On Formation of Discrete Auroral Arcs M. Roth, M. Echim, and J. De Keyser Display the abstractThe aurora has been studied intensely for several decades, but our understanding of the mechanisms behind the formation of auroras is still rather fragmented and uncertain. At altitudes below a few Earth radii there are strong field-aligned electric fields which accelerate electrons down towards the Earth. The discrete auroral arcs, the most intense type of aurora, result from the collisions of these accelerated electrons with the upper atmosphere, and are associated with magnetic field-aligned currents. It is generally believed that these field-aligned currents are carried by some type of generator in the outer magnetosphere. We first show that magnetospheric DC generators (or electromotive - EMF - sources) are appropriate to quasi-stable discrete auroral arcs, and result from potential structures across interfaces between two magnetized plasma populations. The EMF associated with the magnetospheric generator can be compared to a DC battery under load: provided the generator is a large reservoir of electrons - or if a velocity shear across magnetic field lines is sustained - the source of precipitating electrons is constantly fed and a large EMF is maintained. The magnetospheric potential differences map down into the ionosphere and drive large Pedersen currents provided the local ionospheric conductivity is large enough. This is all the more the case because the increase of the ionization by the precipitating electrons diminishes the ionospheric resistivity. The resulting reduction of the electric potential gradients in the ionosphere leads to the formation of field-aligned potentials such that the circulation of the electric field along the whole circuit is equal to zero (assuming a time-independent magnetic field distribution). The EMF and the luminosity of the arc eventually begin to fall with the smoothing of density, temperature and velocity gradients inside the magnetospheric interface. We address the plausible origin of magnetospheric DC generators as well as their internal structure deduced from a kinetic model of magnetized plasma interfaces. Finally we solve the current continuity equation for a electric circuit supplied by a DC magnetospheric generator under ionospheric load. Our solutions show auroral structures whose arc width and precipitating energy flux span a broad range of values. We also analyze the scaling of the auroral structures as a function of the plasma temperature and density at magnetospheric regions forming a plasma interface - the source of the EMF - as well as of the altitude of this source.
2006-03-01 at 10:00:00 TV-Room Frédéric Clette ROB Introduction to Solar Physics Display the abstract
2006-02-09 at 14:00:00 TV-Room Steven Dewitte IRM-KMI The DIARAD Type Radiometer and Its Contribution to a Long Term Total Solar Irradiance Record Display the abstract
2006-02-03 at 11:00:00 TV-Room Nandita Srivastava Udaipur Solar Observatory (India) On the Role of Solar and Interplanetary Parameters in Predicting Space Weather FRIDAY!! 11:00!! Display the abstractSpace weather prediction involves advance forecasting of the magnitude and the on-set time of major geomagnetic storms at the earth. In this talk, I will discuss a newly-developed statistical model for the prediction of occurrence of geomagnetic storms based on both solar and interplanetary inputs. The solar parameters used in the model have been identified on the basis of an exhaustive study of the solar origins of major geomagnetic storms that occurred during 1996-2002. The results indicate that solar parameters contribute relatively less in the prediction of geomagnetic storms, as compared to the interplanetary parameters. A key solar input is the initial speeds of the coronal mass ejections (CMEs), however the propagation speeds profiles of CMEs in the interplanetary medium are not very well understood. An attempt to investigate the nature of the propagation profiles of CMEs close to the sun in the outer corona has been made, and it is found that most of the strong events show a blast-wave type propagation. Another important parameter that decides the maximum speed of a CME ensued from the source active region is its magnetic energy. The role of these parameters in the model and in improving its predictive capability, particularly for severe storms, will also be discussed.
2006-01-26 at 14:00:00 TV-Room Judith De Patoul ROB Global wavelet spectrum analysis for detection of flares, and prediction of solar eruptions using spatio-temporal statistical models Display the abstractThis talk will be divided into two parts. In the first part, we are studying a sequence of EIT images. We use the continuous wavelet transform, and more precisely its associated wavelet spectrum to summarize the informations contained in these images. We build pertinent time series that give the evolution of the signal energy present in the corona at different scales. From this time series, we are able to propose a method for detecting eruptions and post-flaring activity in EUV image sequences. These results have been published in [1]. In the second part of the talk, I will present the research proposal that will be submitted to the Action 2 program. The aim of this project is to establish a spatio-temporal statistical model for predicting the starting time and the intensity of solar eruptions. To this end, we will first build a relevant data base, containing as much pertinent precursors as possible. [1] V. Delouille, J. de Patoul, J.-F. Hochedez, L. Jacques, and J.-P. Antoine (2005) "Wavelet spectrum analysis of EIT/SoHO images", Solar Physics, 228(1), pages 303-323.
2006-01-19 at 14:00:00 TV-Room Christophe Marqué ROB Forward Modeling of the Electron Density and Temperature Distribution in the Solar Corona, Using PFSS Extrapolations and Radio Metric Observations Display the abstractThe Sun is a powerful radio source which has been observed since the very beginning of Radioastronomy. In the metric radio range (lambda~0.5-2 m), the radio emission is most of the time dominated by plasma emissions due to non-Maxwellian populations of electrons accelerated during flares or CMEs. When the solar activity is low or moderate, the thermal emission of the corona (free-free mechanism) prevails. With improving imaging techniques, metric radio maps have depicted the large scale structures of the corona, like coronal holes, the base of the streamer belt or the thermal counterpart of active regions. However due to the refraction and scattering of radio waves in the corona, retrieving a quantitative parameter such as the electron density relies on models of the electron density profile, or a priori knowledge of the electron temperature. In this talk, I will present a forward modeling approach to this problem, using PFSS magnetic extrapolations to build realistic models of the electron density and temperature distribution in the corona. For each computed field line, and assuming a hydrostatic profile, the base density and temperature is set according to scaling laws involving the photospheric magnetic field strength as well as the loop length. For a given set of scaling laws, the radio emission is calculated, taking into account the refraction of radio waves, and synthetic radio images are compared with metric radio maps from the Nancay Radioheliograph. A genetic algorithm implementation, called PIKAIA, is used to determine the optimum values of the parameters of the model. I will present the results of this modeling for a set of radio observations during the last solar cycle minimum.
2005-12-15 at 15:00:00 Salle Méridienne/Meridiaanzaal Ineke D High Nautical School of Antwerp The Effects of Space Weather on Navigation on the Sea Display the abstractMost of the instruments for communication and navigation on board of vessels use the Earth's atmosphere: waves are reflected or absorbed by the ionosphere. Hence they are influenced by spaceweather. Space weather is the direct effect of the solar variability on the Earth and its surrounding. Solar variability includes sudden phenomena like (1) flares - a sudden increase in radiation most visible in the high frequency spectrum, (2) coronal mass ejections (CMEs) - clouds of plasma ejected away from the Sun with speeds higher than 400 km/s and (3) the acceleration of high energy electrons and protons travelling at ~ relativistic speeds. These phenomena can occur simultaneously. Also the more predictable high speed solar wind stream originating in the solar coronal holes can induce geomagnetic effects. The Earth is generally well-protected against these violent events. However, sometimes the Earth's magnetic "shield" is not capable to avoid the events to perturb the Earth's magnetic field and atmosphere. The exact consequences for navigation and communication are not well-known yet. Further research is necessary.
2005-12-01 at 14:00:00 TV-Room Alexander Baranovski IRM/KMI Extreme value analysis of stochastically and deterministically forced systems Display the abstractA number of geophysical phenomena are associated with the evolution of variables forced by an impulse type of signal when their values exceed some threshold. In this communication the probability density function and power spectra density of the response to this type of signal are analyzed. Connections with the theory of point processes and the classical theory of extreme values are outlined such as those induced by a chaotic mapping or a chaotic oscillator.
2005-11-10 at 14:00:00 TV-Room Inigo Arregui CPA, KU Leuven MHD coronal seismology using the period and damping of resonantly damped quasi-mode kink oscillations Display the abstractTransverse coronal loop oscillations, observed with instruments on board TRACE, have been used in the past for the determination of unknown coronal physical properties, such as the magnetic field strength, by a comparison between the observed wave properties and the characteristics of linear MHD waves in straight uniform flux tubes. Observations reveal that these oscillations are very rapidly damped and previous theoretical understanding supports the idea that damping by resonant absorption may be a significant component operating in the observed decay. In this seminar, first, the results obtained with the most recent theoretical models for quasi-mode damping by resonant absorption are summarised. Then, the possibility of using both the period and the damping rate of loop oscillations to obtain information about the physical parameters of seismic interest in coronal loops is addressed. It is shown that a restriction on the physical parameters of interest, such as the density contrast, the inhomogeneity scale-length and the internal Alfven speed, can be obtained. The described method may not only allow the determination of unknown physical parameters in the corona, but can also be used to test the assumed physical damping mechanism.
2005-10-27 at 14:00:00 TV-Room Luciano Rodriguez ROB Internal Characteristics of Magnetic Clouds Display the abstractMagnetic clouds (MCs) are a special kind of interplanetary coronal mass ejections (ICMEs) in which the magnetic field exhibits a characteristic configuration. One of the most challenging scientific problems is to gain insights into their internal structure. Using in-situ data provided by instruments onboard Ulysses, 40 magnetic clouds have been identified and analysed. The ionization level of the solar wind plasma serves as a robust tool to differentiate MCs from other types of solar wind. It represents a direct indication of the temperature in the source region of the solar wind. MCs show increased temperatures with respect to non-cloud ICMEs and surrounding solar wind. By combining these data with a magnetic field model, insights into the internal structure of MCs are provided. Zones of increased temperatures are found to be confined to the flux rope region. At higher energies, the elemental composition of the ~1 MeV/nuc energetic particle population contained in MCs has been used to identify the mechanism by which these particles are accelerated. The abundance ratios found are consistent with those for gradual solar energetic particle events (SEPs). Bidirectional proton flows have been quantified and used as a proxy for the cloud-Sun connectivity.
2005-09-29 at 14:00:00 TV-Room Ingo Baumann ROB Magnetic Flux Transport on the Sun Display the abstractThe solar magnetic field is generated by a dynamo in the Sun's interior and emerges as bipolar magnetic regions on the solar surface as a consequence of rising flux tubes. The photospheric magnetic field is redistributed by turbulent diffusion, differential rotation and a meridional flow. Numerical simulations of the evolution of the surface magnetic field are performed using a flux transport model. In this talk, I will summarize the main results of my thesis work: - A parameter study in order to investigate the influence of a variety of solar cycle parameters on the solar magnetic field with focus on the Sun's total surface field and the polar field. - The extension of the existing flux transport model by a term parametrising radial decay processes. The necessity of this extension follows from comparing numerical simulations with observations. - The use of a source surface model in order to calculate the Sun's open magnetic flux and the attempt to model the historic IMF record on the basis of the Greenwich sunspot database.
0000-00-00 at 14:30:00 TV-Room Matthieu Kretzschmar ROB Statistical Analysis of Solar Irradiance Display the abstractThe study of Solar irradiance and its variability, in particular in the UV and X/EUV spectral range, are of interests both for terrestrial weather, space weather, and because it tells us something about the Sun itself. Beside the radiometric calibration that is essential to study its impact on Earth, the spectral distribution of the irradiance temporal variation at all scales can reveal important information. Recently, an effort has been made to apply various statistical analysis to UV and X/EUV solar irradiance datasets acquired by different instruments: SEE onboard TIMED, SEM onboard SOHO, and SOSLTICE-SUSIM onboard UARS and SORCE. Techniques like multivariate analysis, source separation, and scaling analysis, allow us to explore several aspects of the irradiance time series and to foresee some applications, in particular in the context of space weather. We will present a review of these recent efforts.

If you want to give a seminar, or if you want more info, please send an e-mail to Andreï Zhukov