SIDC Weekly Bulletin

Review of past solar and geomagnetic activity.
Source SIDC (RWC-Belgium)
Frequency Weekly
Format Plain text
Mail header SIDC Weekly Bulletin
SIDC code bul


Latest issue

:Issued: 2021 Jul 27 0058 UTC
:Product: documentation at
# SIDC Weekly bulletin on Solar and Geomagnetic activity             #
WEEK 1073 from 2021 Jul 19
Over the past week the solar activity varied between very low and low
levels. The week started with two C-class flares from behind the east limb
on July 19th, a C1.3 flare with peak time 19:07 UTC and C1.2 with peak time
20:52 UTC, respectively. There were in total seven active regions on the
visible solar disk (NOAA 2842 and NOAA 2844-2849), which produced five
C-class flares. The most active sunspot group was NOAA 2849 which is
responsible for three of the C-class flares, namely C1.0 on July 20th (peak
time 23:27 UTC), C1.2 on July 21st (peak time 16:04 UTC) and C4.3 on July
23rd (peak time 00:33 UTC). NOAA 2845 produced a single C1.3 class flare
with peak time at 20:05 UTC on July 21st. The most complex active region
was NOAA 2842, which developed into magnetic type beta-gamma soon before
its rotation over the west limb and produced a single C1.5 class flare
(peak time 02:06 UTC) on July 24th. The rest of the active regions
exhibited very low levels of activity over the entire week.

Throughout the week there were several on disk flare-driven Coronal Mass
Ejections (CMEs) with prominent coronal dimming and coronal waves, but none
of them were estimated to have Earth-directed component. No other
Earth-directed CMEs were detected in the available chronograph imagery and
none ICMEs were observed in the available solar wind data. 

The greater than 10 MeV proton flux remained at background levels over the
entire week. The greater than 2 MeV electron flux remained under the 1000
pfu threshold and the electron fluence was at nominal levels for the entire
The solar wind parameters (based on DSCOVR and ACE data) throughout the
week reflected minor enhancements due the arrival of high speed stream
(HSS) from a rather small positive-polarity equatorial coronal hole (CH),
which crossed the central meridian on July 17th. The main effect of the HSS
associated with this CH was registered in the period of July 19th to July
23rd and have subsided after. The solar wind conditions were most elevated
on July 20th and July 21st registering moderate solar wind speeds above
500km/s. The total magnetic field was rather weak throughout the entire
week, in the range of 0.9 nT to 7.7 nT. The minimum recorded Bz component
was -7.4 nT.

The geomagnetic conditions throughout the week were mostly quiet to
unsettled under the mild influence of the HSS. Two isolated global active
periods were recorded right before noon on July 22nd and only a single
geomagnetically active interval was registered locally in Dourbes at 09:00
DATE           RC   EISN  10CM   Ak   BKG    M   X
2021 Jul 19   062    044   083   012   B1.6   0   0   
2021 Jul 20   ///    042   087   016   B2.0   0   0   
2021 Jul 21   077    065   094   010   B2.2   0   0   
2021 Jul 22   083    072   089   009   B2.0   0   0   
2021 Jul 23   070    053   087   006   B1.5   0   0   
2021 Jul 24   ///    028   084   004   B1.7   0   0   
2021 Jul 25   ///    031   082   003   B1.0   0   0   
# RC   : Sunspot index (Wolf Number) from Catania Observatory (Italy)
# EISN : Estimated International Sunspot Number
# 10cm : 10.7 cm  radioflux (DRAO, Canada)
# Ak   : Ak Index Wingst (Germany)
# BKG  : Background GOES X-ray level (NOAA, USA)
# M,X  : Number of X-ray flares in M and X class, see below (NOAA, USA)

# Solar Influences Data analysis Center - RWC Belgium                #
# Royal Observatory of Belgium                                       #
#                                                                    #
# Website                                #
# E-mail                                #
# To unsubscribe          #
#                                                                    #
# Legal notices:                                                     #
# - Intellectual Property Rights:                                    #
#    #
# - Liability Disclaimer:                                            #
#     #
# - Use and processing of your personal information:                 #
# #


This report is sent once a week, typically on a monday.
The weekly bulletin gives an overview of solar and geomagnetic activity of the past week and includes a noticeable solar events list.
Check the ISES code book for information on ISES codes.