:Issued: 2011 Feb 07 1220 UTC
:Product: documentation at http://www.sidc.be/products/bul
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# SIDC Weekly bulletin on Solar and Geomagnetic activity #
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WEEK 527 from 2011 Jan 31
SOLAR ACTIVITY
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There was a very low solar activity over the entire week. The X-ray background
stayed at A level, with only a few B sub-flares, mainly on Feb.4 when several
small active regions emerged simultaneously.
A large recurrent coronal hole started to influence the Earth magnetosphere
late on Jan.31. It reached its maximum speed on Feb.1 at 530km/s, and then
declined. There was only one large halo CME on Feb.1 at 23:48UT. LASCO and
STEREO coronagraphs indicate that this was a backside event.
Barring the emergence of a new large active region, solar activity is expected
to remain low over the comings days.
GEOMAGNETIC ACTIVITY
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The week started with quiet to unsettled geomagnetic conditions on Jan.31 and
Feb.1 due to the coronal hole influence. Then, conditions were mostly quiet
on Feb. 2 and 3.
On Feb.4 at 1:30 UT, a weak CME shock was recorded in the solar wind by the ACE
spacecraft. There was only a small speed increase to 400km/s, without any
significant geomagnetic effect. Then around 19:00, the wind speed rose again
steeply to 650km/s, marking the arrival of the associated magnetic cloud. This
triggered a major geomagnetic storm (Kp=6) that lasted for a few hours, until
Feb.5, 1:00UT. The origin of this very effective CME is unclear: the only
possible association is a filament eruption and streamer blowout that occured
on Jan.30, but had however a very low initial speed of 230 km/s and was not
detected in LASCO coronagraph images.
The solar wind speed reached a maximum of about 650km/s on Feb.5 around
3:OOUT. It then slowly declined down to 500km/s by the end of Feb.6. The
Earth magnetosphere remained unsettled over the last two days of the week,
due to the high wind speed, with a last brief active episode on Feb.6.
Quieter geomagnetic conditions are expected for the first days of the new
week.
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DAILY INDICES
DATE RC EISN 10CM Ak BKG M X
2011 Jan 31 023 012 81 006 A5.8 0 0
2011 Feb 01 /// 015 80 009 A4.9 0 0
2011 Feb 02 /// 014 79 008 A4.3 0 0
2011 Feb 03 /// 019 80 002 A3.9 0 0
2011 Feb 04 051 024 82 027 A4.6 0 0
2011 Feb 05 /// 010 81 019 A4.4 0 0
2011 Feb 06 /// 008 80 016 A4.4 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)
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NOTICEABLE EVENTS
DAY BEGIN MAX END LOC XRAY OP TENCM TYPE Cat NOAA NOTE
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# 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 #
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