Solar Influences Data Center (SIDC) / RWC Belgium Royal Observatory of Belgium E-mail: Pierre.Cugnon@oma.be http://sidc.oma.be SIDC WEEKLY BULLETIN -------------------- WEEK 107 from 2003 Jan 13 SOLAR ACTIVITY -------------- The solar activity was low over the whole period, and became very low after January 17, with a very low X-ray background and only a few minor B sub-flares. None of the active regions reached large sizes or magnetic complexity. The only event worth mentioning was the flareless filament eruption near central meridian on Jan 17, 02:46UT, which triggered a semi-halo CME. This week saw also the return of a major coronal hole in the Southern hemisphere. Already present during the previous solar rotations, this coronal hole has grown further. Its influence at Earth started on Jan 18, around 19:00UT, when the solar wind speed started to increase while the density started to decrease. Before that, the solar wind conditions had been rather stable with low speeds between 300 and 400km/s. The solar activity should remain low, as only a few minor active regions have appeared lately. GEOMAGNETIC ACTIVITY -------------------- The geomagnetic field was mostly quiet to unsettled over the first 5 days, with a brief active episode on Jan 18. Although the interplanetary magnetic field fluctuated between a Northward and Southward orientation, the solar wind dynamic pressure remained low (low speed and density), which prevented any significant geomagnetic disturbance. Starting on Jan. 19, when the solar wind picked up speed (now around 650km/s), geomagnetic conditions became active, with even a minor storm onset today, just past 00:00UT on Jan 20. Next week will be dominated by the influence of the large South-hemisphere coronal hole. The geomagnetic field will often be active, and other occasional minor storms will be possible. On Jan 20, a small CME disturbance associated with the Jan 17 filament eruption might also hit the Earth magnetosphere, adding to the activity. --------------------------------------------------------------------------- DAILY INDICES DATE RC 10CM Ak BKG M X 2003 Jan 13 /// 172 008 B7.1 0 0 2003 Jan 14 155 164 012 B6.2 0 0 2003 Jan 15 139 150 007 B4.6 0 0 2003 Jan 16 129 145 006 B4.1 0 0 2003 Jan 17 /// 142 006 B3.6 0 0 2003 Jan 18 /// 137 015 B3.5 0 0 2003 Jan 19 123 130 021 B3.5 0 0 # RC : Sunspot index from Catania Observatory (Italy) # 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 10CM TYPE Cat NOAA NOTE