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 Apr 19 1457 UTC
:Product: documentation at
# SIDC Weekly bulletin on Solar and Geomagnetic activity             #
WEEK 1059 from 2021 Apr 12
The solar activity was at very low levels over the entire week. There were
in total 3 active regions on the solar disk, namely NOAA AR 2814 (Catania
87), AR 2815 and AR 2816. All of them exhibited bipolar magnetic field and
were classifies as magnetic type Beta. The flaring activity remained below
C-class flare level throughout the entire week. The highest activity
registered was a B9.7 class flare originating from behind the east limb
(S21E88) on April 17th with a peak time 17:17 UTC. This flare was
associated with a back-sided CME and a type II radio emission.

No Earth-directed Coronal Mass Ejections (CMEs) were detected in the
available chronograph imagery for the entire week. 

The greater than 10 MeV proton flux remained at background levels over the
entire week. The greater than 2 MeV electron flux crosses the 1000 pfu
threshold on April 17th and registered prolonged period with values above
10000 on April 18th. The electron fluence was at nominal levels until April
18th when moderate levels were reached.
The solar wind parameters (based on DSCOVR and ACE data) reflected a slow
solar wind regime until April 15th, when a drop of the temperature,
increase in the magnetic field and density, and some increase in the solar
wind speed suggested the arrival of an ICME at Earth. The source for the
ICME was identified as a coronal mass ejection setting off the west solar
limb in the UTC morning of April 10th. On April 16th enhancements in the
solar wind speed, temperature and magnetic field values were registered
with the mixed arrival of two high speed streams (HSSs) emanating from a
small equatorial negative-polarity coronal hole and from a high-latitude
extension of the souther polar coronal hole (with negative polarity as
well). Enhanced solar wind speed and temperature prevailed throughout the
rest of the week with registered high solar wind velocity of up to 668

The geomagnetic conditions were mostly quiet until April 15th, when the
ICME arrival caused an isolated period of minor geomagnetic storm based on
the global NOAA Kp index between 21:00 UTC on April 14th and 00:00 UTC on
April 15th. Locally in Dourbes only active conditions were detected on that
day. From 18:00 UTC on April 16th throughout 09:00 UTC on April 17th the
arrival of the HSSs resulted in multiple periods with minor geomagnetic
storm levels, as registered by NOAA Kp and K Dourbes indices. Mostly active
to unsettled conditions prevailed throughout the rest of the week.
DATE           RC   EISN  10CM   Ak   BKG    M   X
2021 Apr 12   ///    016   083   006   A2.7   0   0   
2021 Apr 13   024    019   073   006   A2.5   0   0   
2021 Apr 14   021    020   074   008   A3.7   0   0   
2021 Apr 15   ///    025   072   014   A4.7   0   0   
2021 Apr 16   ///    037   077   020   A4.8   0   0   
2021 Apr 17   ///    018   075   031   A4.4   0   0   
2021 Apr 18   ///    017   078   020   A7.4   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                                       #
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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.