:Issued: 2011 Oct 04 1454 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 561 from 2011 Sep 26
SOLAR ACTIVITY
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The week started with a moderate activity due to 2 M flares from
active region NOAA1302 (Catania#82) on Sept.26. This F active region,
which featured a naked-eye sunspot, was the dominant one early in
the week. It was stable and then decayed slowly as it rotated across
the disk, producing only one weak M flare and C flares for the rest
of the week.
Starting on Sept.29, active region NOAA1305 (Catania#85), an H-type
group, started to grow and took a Beta-gamma-delta configuration. It
produced a succession of 3 M flares on Sept.30, Oct.1 and 2. The
strongest one was an M3.9 flare at 00:40UT Oct.2. Those events
occurred near disk center and were associated with rather slow
Earth-directed CMEs.
The >10MeV proton flux was above event threshold on Sept.26. This was
the tail of a proton event associated with the multiple flares of
Sept.22 and 23. The flux decayed below event threshold on Sept.27.
The main solar wind transient occurred on Sept.26 around 12:00UT. This
was a CME associated with the M7 flare of Sept.24. The solar wind speed
peaked at 650km/s (IMF strength= 33nT) on Sept.26. The wind speed then
slowly declined to 500km/s on Sept.28. A second weaker shock hit the
Earth around 00:00UT Sept.29. This CME was associated with the M
flare of Sept.26. and raised the solar wind speed to 550km/s.
The solar wind speed declined again down to 400km/s before rising
to 550km/s on Oct.1 due to the influence of a small coronal hole in
the Southern hemisphere.
GEOMAGNETIC ACTIVITY
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The week started with a major geomagnetic storm (Kp=6 to 7) during a
few hours in the second half of Sept.26. This was triggered by
the first strong CME mentioned above. The activity declined to active
to minor storm on Sept.27 and then declined further to unsettled on
Sept.28. On Sept.29, the second weaker CME triggered a short minor
storm. This was followed by a decline to quiet levels on Sept.30.
Over the last 2 days of the week, the geomagnetic activity rose
slightly again to unsettled levels under the influence of the fast
solar wind stream associated with the coronal hole.
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DAILY INDICES
DATE RC EISN 10CM Ak BKG M X
2011 Sep 26 140 072 148 035 C1.4 2 0
2011 Sep 27 /// 071 139 028 B5.2 0 0
2011 Sep 28 /// 071 133 018 B3.8 1 0
2011 Sep 29 154 082 137 020 B4.0 0 0
2011 Sep 30 131 072 138 007 B4.0 1 0
2011 Oct 01 162 080 137 019 B5.6 1 0
2011 Oct 02 /// 078 131 015 B4.9 2 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
username:DATA_SIDCadminDAY BEGIN MAX END LOC XRAY OP TENCM TYPE Cat NOAA NOTE
26 0506 0508 0513 N13E34 M4.0 1B 360 IV/1 82 1302
26 1437 1446 1502 N14E30 M2.6 2B III/2 82 1302
28 1324 1328 1330 N13E03 M1.2 1N 110 82 1302
30 1855 1906 1915 N08E06 M1.0 1F 260 III/2,II/1 85 1305 halo CME
01 0856 0959 1017 N10W06 M1.2 1N 180 IV/2,V/3,II/1 85 1305
02 0037 0050 0059 N09W12 M3.9 1N 85 1305
02 1719 1723 1726 N09W56 M1.3 SF 82 1302
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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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