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: 2017 Sep 19 0920 UTC
:Product: documentation at
# SIDC Weekly bulletin on Solar and Geomagnetic activity             #
WEEK 872 from 2017 Sep 11
During this week solar flaring activity was very low with only two low
C-class flares reported. The source region, for both flares, was the
Catania sunspot group 55 (NOAA AR 2680) which had alpha configuration of
its photospheric magnetic field during the whole week.

Three partial and one full halo CMEs were observed this week. All wide CMEs
had a source region on the back side of the Sun (the Catania sunspot group
46, i.e. NOAA AR 2673) as seen from the Earth, and were therefore not Earth
Partial halo CME on September 15 was first time observed in the SOHO/LASCO
C2 field of view at 19:48 UT. The CME was very faint and slow, not even
detected by CACTUS software. 
Second partial halo CME observed this week was first time seen in the
SOHO/LASCO C2 field of view at 12:24 UT on September 16. The CME was rather
faint and had a projected speed of about 400 km/s (as reported by CACTUS
Third CME was a full halo CME, first time observed in the SOHO/LASCO C2
field of view at 12:24 UT on September 17 (straight after the data gap).
The CME was associated with the global EIT wave and coronal dimming, and
had projected speed of about 1300 km/s (as estimated by CACTUS software). 
The fourth wide CME observed this week was a partial halo CME first seen in
the SOHO/LASCO C2 field of view at 14:24 UT on September 17. This CME was
also associated with the EIT wave and dimming, and was propagating with the
projected speed of about 750 km/s (as reported by CACTUS software).
Particle event, associated with the M8.2 flare & full halo CME from
September 10, started abruptly at about 16:30 UT on September 10 and lasted
for a several days. The steep increase of the proton fluxes, with >10 MeV,
> 50 MeV as well as > 100 MeV, was followed by very slow decay. The proton
fluxes with > 10 MeV went bellow the event threshold at about 18:00 UT on
September 14.

We did not observe any large coronal holes this week.
At about 19:20 UT on September 12, the sudden jump of the solar wind speed
(up to about 540 km/s) and simultaneous increase of the density and
interplanetary magnetic field magnitude (up to 13 nT) was observed. All
these indicated arrival of the shock wave, probably associated with the
partial halo CME first time seen in the SOHO/LASCO C2 field of view at
about 23:36 UT on September 09 (straight after the data gap). The arrival
of the shock-like structure induced minor storm geomagnetic conditions
around midnight of September 12 (local station at Dourbes reported K = 5 
and NOAA reported Kp = 6).

A fast forward shock was detected in the solar wind by DSCOVR around 00:20
UT on September 14, with clear jumps of the solar wind speed, density,
temperature, and the interplanetary magnetic field magnitude.
The solar wind speed in the post-shock sheath region was around 390 km/s,
so the departure of the shock wave from the Sun on September 10, in
association with the X8.2 flare and limb full halo CME, is probable.

The in situ observations indicated arrival of the fast solar wind,
associated with the low-latitude extension of the northern polar coronal
hole which reached central meridian at the mid-day of September 10, in the
afternoon of  September 14. The Earth was inside the fast solar wind during
the rest of the week, and at the end of the week the solar wind speed was
about 650 km/s.
Arrival of the interaction region between the slow wind and the fast solar
wind stream (which was followed by the fast stream), led to the moderate
geomagnetic storm conditions (NOAA reported Kp = 6 and local station at
Dourbes reported K = 5) in the afternoon and evening of September 14. Due
to the influence of the fast solar wind (with the speed up to 770 km/s) and
longer intervals of the southward Bz component of the interplanetary
magnetic field, intervals of active to minor storm geomagnetic conditions
were reported during the rest of the week. At the end of the week
geomagnetic conditions were active to unsettled.
DATE           RC   EISN  10CM   Ak   BKG    M   X
2017 Sep 11   034    030   080   014   B2.6   0   0   
2017 Sep 12   012    012   076   019   A8.3   0   0   
2017 Sep 13   012    015   075   014   A1.6   0   0   
2017 Sep 14   012    013   074   029   A1.4   0   0   
2017 Sep 15   012    012   073   034   A1.4   0   0   
2017 Sep 16   ///    014   072   025   ////   0   0   
2017 Sep 17   ///    015   072   016   ////   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                                       #
# Fax : 32 (0) 2 373 0 224                                           #
# Tel.: 32 (0) 2 373 0 491                                           #
#                                                                    #
# For more information, see  Please do not reply #
# directly to this message, but send comments and suggestions to     #
# ''. If you are unable to use that address, use      #
# '' instead.                                   #
# To unsubscribe, visit        #
#                                                                    #
# 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.