Wednesday, June 10, 2009

Log: (06-07-2009)

7 June 2009 (L+24, DOY 158)

Space weather and SREM data during Days 1-21

Herschel has launched during what has been an unprecedentedly low minimum of solar activity in modern times, with more than 150 consecutive spotless days preceding launch. It is expected that Herschel operations will cover the rise to and peak of the next solar maximum, so monitoring space weather during the mission is important, as is the level of activity at maximum; predictions have stated that the later the rise to maximum starts, the lower the maximum is likely to be.

Herschel carries the SREM (Space Radiation Environment Monitor) as a passenger (left image below), to measure constantly the radiation environment to which Herschel is exposed. Herschel Science Centre scientists analyse this data daily and are looking for possible correlations with solar activity and with predictions of future activity.

On Day 18 a sunspot group with 13 spots formed, leading to a small (B1-class) flare at 08:07UT on June 1st (OD-18), a second B1-class flare at 06:39UT on June 2nd (OD-19). These were the first two flares registered during the mission. Later, three B-class flares were seen on June 3rd (OD20-21).

SREM data (middle image below) shows that there has been no important activity registered in the SREM data since Herschel crossed the Van Allen Radiation Belts. The variations in count rate can all be attributed to noise.

The peak count rate during the Van Allen Belt crossing was about 3 orders of magnitude greater than the count rate at any other point during the transfer orbit. A closer look at the data on an expanded scale (right image below) shows no evidence of an increase in the SREM counts at the time of first two flares, which are marked with arrows.

Space Radiation Environment Monitor (SREM) mounted on Herschel SREM count rates (OD-0001 to OD-0021) SREM count rates (closer look)

[M. Kidger & M. Sánchez Portal from HSC ESAC, posted 9 June 2009]