|A salvo of shots hitting Earth|
|Sunspot group 61 (NOAA 0696) fired a series of halo CMEs. The geomagnetic field was seriously messed up when they arrived at Earth. On November 7, the group produced a X2.0 flare accompanied with another CME. The shock arrived at this very moment (Nov 9, 09:45UT)! A severe geomagnetic storm is expected.|
|Nederlandstalige versie /Version française||posted: November 9, 2004|
On November 2, a small sunspot group started to grow suddenly in a fast and explosive manner. From that moment onwards, the group completely determined the solar landscape and output in the form of flares and CMEs. From November 3 onwards, several 'halo-cme-alerts' were broadcast by the SIDC as CACTus, an automatic CME detection software spotted the CMEs hurling towards Earth. The picture on the left gives a visual overview of the CMEs. Horizontal cuts of the picture represents the contour of the occulting disk of C2, a coronograph onboard of SOHO. The circle is cut at the south-east and stretched open. You can click on it to enlarge. On November 7, they arrived and smashed on the geomagnetic field. Celias/SOHO detected up till now 4 shocks in the solar wind data. It is not clear which CME is responsible for which shock as the plasma clouds can catch up with each other. This violent phenomenon is called 'CME cannibalism'.
Anyway, the plasma cloud that arrived late November 7 carried a strong imbedded magnetic field with a southward oriented B_z component of values up to -50nT (!). This resulted in a severe magnetic storm offering an excellent opportunity for aurora-watchers. Another interesting point is the fact that the proton levels started to increase several times caused by the subsequent flares and CMEs. The proton flux measured by GOES, an earth-orbiting satellite, stays at an elevated level as long as the CME-shockfront accelerates the protons. Once the shock passed the satellite, the proton levels decrease. In the case of a flare pushing up the proton flux, the decreasing tendency starts earlier. CMEs take in general 3 days to reach earth, a flare, 8 minutes.
On November 7, the group exploded once again and sent of an X2.0 flare. EIT onboard of SOHO captured the flare in a nice picture shown on the right. The LASCO movie shows us very clear that a nice halo CME accompanied the flare. 4 halo CMEs are visible in the movie, the one ejected late on Nov 4 which is almost out of view, the Nov 6 CME related with the M9.3 flare, the Nov 7 CME related with the X-flare and a faint halo CME leaving the occulting disk on Nov 8, around 05:42UT. On Nov 9, 09:45UT, at this very moment, a shock possibly associated with the X-flare and accompanying CME, arrived at earth. A bad time for aurora-watchers as it is in the middle of the day. GPS-users depending on exact measurements, also cross your fingers! In the near future, we expect more geomagnetic excitation as other CMEs arrive.