mercoledì 25 gennaio 2012

SIDC Weekly Bulletin

:Issued: 2012 Jan 24 1524 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 577 from 2012 Jan 16 

SOLAR ACTIVITY
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Solar activity was dominated by Catania sunspot groups 20 and 21 (NOAA ARs 1401 and 1402 respectively), which produced numerous C-class flares and three M-class flares (two in Catania sunspot group 20 and one in Catania sunspot group 21). The first two M-class flares (on January 17 and 18) were confined, and the M3.2 flare on January 19 was associated with a full halo CME (see below).

Three halo CMEs were detected by SOHO/LASCO during the week. A full halo CME was detected on January 16, first appearing in the LASCO C2 field of view at 03:12 UT and moving at a speed around 500 km/s (according to the CACTus software). The CME was associated with the C6.5 flare peaking at 04:44 UT in Catania sunspot group 21 (NOAA AR 1402) situated at N34E86, coronal dimmings and a post-eruption loop arcade detected by SDO/AIA. Due to the position of the CME source region near the solar limb, the bulk of the CME was not directed at the Earth. Only the CME-driven shock arrived at the Earth on January 21 (see below).

A partial halo CME was detected on January 18, first appearing in the LASCO C2 field of view at 12:12 UT. The CME had angular width around 140 degrees and moved at the speed around 720 km/s. The CME was associated with the coronal dimmings and filament eruption near the solar disk center, and a post-eruption arcade in Catania sunspot group 16 (NOAA AR 1399), as observed by SDO/AIA starting around 10:13 UT. A B9.6 flare peaking at 12:30 UT associated with this eruption was detected by GOES. The bulk of the CME material was moving southward of ecliptic. This CME probably interacted with the full halo CME erupted on January 19, and the joint interplanetary disturbance arrived at the Earth on January 22 (see below).

A full halo CME was detected on January 19, first appearing in the LASCO C2 field of view at 15:24 UT and moving at the plane-of-the-sky speed around 1300 km/s. The CME was associated with coronal dimmings, filament eruption and a post-eruption arcade in and around Catania sunspot group 21 (NOAA AR 1402), as observed by SDO/AIA starting around 13:58 UT. An M3.2 flare peaking at 16:05 UT associated with this eruption was detected by GOES. The bulk of the CME material was moving northward of the ecliptic plane. This CME probably interacted with the partial halo CME erupted on January 18, and the joint interplanetary disturbance arrived at the Earth on January 22 (see below).

The flux of solar protons at energies above 10 MeV started to rise on January 19, probably in association with the propagating interplanetary shock wave driven by the full halo CME erupted on January 19. The proton flux remained significantly above the background level, although below the event threshold, until the end of the week.

GEOMAGNETIC ACTIVITY
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On January 16 the Earth passed through the interaction region between a slow and a faster sold wind flow. The faster solar wind flow originated from a narrow low-latitude coronal hole. Although the interplanetary magnetic field (IMF) magnitude reached 15 nT, the geomagnetic conditions were quiet due to relatively low solar wind speed (up to 520 km/s) and fluctuating north-south IMF component. On January 17-20 the Earth was inside a slow solar wind flow, and geomagnetic conditions remained quiet.

An interplanetary shock wave was detected by ACE at 04:00 UT on January 21. The shock was most probably associated with the full halo CME observed on the Sun on January 16 (see above). No ICME material was detected. Due to low downstream solar wind speed, no geomagnetic disturbance resulted from the shocked solar wind flow.

Another interplanetary shock wave was detected by ACE at 05:15 UT on January 22. The proton flux peaked at the shock arrival, but did not reach the event threshold. The shock was driven by the complex ICME resulting from halo CMEs observed on the Sun on January 18 and 19 (see above), which interacted on their way to the Earth. The peak solar wind speed was moderate (around 480 km/s), but the IMF magnitude reached 33 nT in the sheath region between the shock and the ICME. The north-south IMF component Bz was fluctuating in the post-shock sheath, resulting only in active geomagnetic conditions (K = 4). The ICME had only a glancing blow at the Earth, with ICME material arriving late on January 22 and on January 23. The IMF magnitude already decreased at that time, resulting only in minor geomagnetic storm conditions (K = 5) as reported by NOAA and IZMIRAN.

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DAILY INDICES
DATE          RC  EISN  10CM  Ak  BKG    M  X
2012 Jan 16  ///    098  140  010  C1.0  0  0
2012 Jan 17  ///    092  139  008  B5.2  1  0
2012 Jan 18  143    085  148  005  B5.7  1  0
2012 Jan 19  133    069  157  002  B5.9  1  0
2012 Jan 20  162    063  141  005  B6.0  0  0
2012 Jan 21  ///    068  142  008  B4.9  0  0
2012 Jan 22  ///    062  141  025  B5.5  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
17  0441  0453 0507 N18E54 M1.0 1N                                      1401
18  1904  1912 1927 N17E33 M1.7 1N                                  20  1401
19  1344  1605 1750 N32E22 M3.2 SF                                  21  1402


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# Royal Observatory of Belgium                                      #
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