:Issued: 2010 May 31 2140 UTC :Product: documentation at http://www.sidc.be/products/bul #--------------------------------------------------------------------# # SIDC Weekly bulletin on Solar and Geomagnetic activity # #--------------------------------------------------------------------# WEEK 491 from 2010 May 24 SOLAR ACTIVITY -------------- Four sunspot groups on the solar disk were reported during the week: Catania numbers 74, 76, 77 (NOAA numbers 1072, 1073, 1075 respectively) and the NOAA AR 1076 that did not have a Catania number. They did not produce any significant flaring activity. The strongest flare was the B6.5 flare peaking at 15:55 UT on May 26 in the Catania sunspot group 74. A partial halo CME (angular width around 245 degrees) was detected by SOHO/LASCO C2 on May 24 starting at 14:06 UT. It was associated with the B1.1 flare peaking at 14:46 UT around N20W30 (in a filament channel not associated with any active region) and accompanied by coronal dimmings and post-eruption arcade observed by SOHO/EIT. The CME speed according to the LASCO data was around 350 km/s. The associated interplanetary disturbance arrived to the Earth on May 29-30 (see below). A low-latitude extension of the northern polar coronal hole reached the solar central meridian on May 28. GEOMAGNETIC ACTIVITY -------------------- On May 24-28 the Earth was situated inside the slow solar wind flow with weak to average interplanetary magnetic field (IMF) magnitude. The geomagnetic conditions were quiet. An interplanetary shock wave was detected by ACE and SOHO/CELIAS around 02:05 UT on May 28. The solar wind speed jumped from 300 to 380 km/s, and clear jumps in the solar wind density and temperature were registered as well. The discontinuity in the IMF magnitude was very weak, so the shock did not lead to increased north-south IMF component. The geomagnetic conditions remained quiet. An interplanetary magnetic cloud driving this shock arrived to the Earth in the evening of May 28. The magnetic field in the cloud quickly turned southward, and the magnitude of the north-south component reached -14 nT. However, the solar wind speed remained low (around 360 km/s), so only minor geomagnetic storm conditions resulted (K = 5 as reported by Dourbes, IZMIRAN and NOAA). The magnetic cloud was most probably associated with the full halo CME observed on the Sun on May 23. Another solar wind discontinuity (possibly a weak shock wave) was detected by ACE and CELIAS around 21:20 UT on May 29. A shocked sheath plasma followed this discontinuity, and the interplanetary magnetic field became oscillating. The discontinuity also marked the end of the magnetic cloud. Some cold ICME-like material with slightly elevated IMF magnitude arrived on May 30. The solar wind speed was still low (400 - 450 km/s), so the sheath and the possible ICME produced only active to minor geomagnetic conditions (K = 4 as reported by Dourbes and IZMIRAN and K = 5 as reported by NOAA). The possible ICME structure was compressed from behind by the fast solar wind stream from a low-latitude extension of the northern polar coronal hole (see above). The possible ICME structure was associated with the partial halo CME on May 24. --------------------------------------------------------------------------- DAILY INDICES DATE RC EISN 10CM Ak BKG M X 2010 May 24 026 012 73 003 A3.6 0 0 2010 May 25 018 012 73 006 A3.1 0 0 2010 May 26 023 008 72 006 A2.8 0 0 2010 May 27 023 007 73 003 A2.4 0 0 2010 May 28 022 008 73 014 A2.9 0 0 2010 May 29 036 017 74 025 A3.1 0 0 2010 May 30 /// 017 73 026 A2.6 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) --------------------------------------------------------------------------- NOTICEABLE EVENTS DAY BEGIN MAX END LOC XRAY OP TENCM TYPE Cat NOAA NOTE #--------------------------------------------------------------------# # 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 http://www.sidc.be. Please do not reply # # directly to this message, but send comments and suggestions to # # 'sidctech@oma.be'. If you are unable to use that address, use # # 'rvdlinden@spd.aas.org' instead. # # To unsubscribe, visit http://sidc.be/registration/unsub.php # #--------------------------------------------------------------------#