SOHO Status Report - April 2005
The Fine Sun Pointing Attitude Anomaly Detector (FSPAAD) triggered on 18 February, probably due to a particle blocking the FSPAAD again. It had been clear since the last ESR on 8 December 2004. The trigger did not result in an ESR since the output to the failure detection electronics had been left disabled. The FSPAAD was still blocked as of 1 April.
Operations and Archiving
All instruments are nominal and SOHO science operations are progressing smoothly. During the March 2005 high gain antenna keyhole, VIRGO, GOLF, and MDI data were recorded continuously with the on-board recording patch. With a fall-back strategy in place to record only these instruments in case of ground problems, LASCO and CELIAS data could be recorded during most gaps. Normal recording mode (all instruments) was used occasionally thanks to good availability of 70-meter stations. Links to the SOHO archives (including mirrors) are accessible at http://soho.estec.esa.nl/data/.
Active region NOAA 10720 has turned out to be one of the most flaring regions of the last few years, with 15 M-class and 5 X-class flares between 14 and 22 January. The energetic particle event that was associated with the X7.1 on 20 January was the strongest radiation storm since October 1989, based on the flux level of the highest energy protons (> 100 MeV). This event was covered in near real-time in a special feature on the SOHO home page and attracted considerable media attention. The SWAN team has determined the direction of the interstellar neutral hydrogen flow as it enters the inner heliosphere. It is found to be deflected relative to the helium flow by about 4 degrees. The most likely explanation of this deflection is a distortion of the heliosphere under the action of an ambient interstellar magnetic field. In this case, the helium flow vector and the hydrogen flow vector constrain the direction of the magnetic field and act as an interstellar magnetic compass. The results appeared in the 4 March issue of Science magazine.