A category S2 (Moderate) Solar Radiation Storm is in progress. This event began with high energy proton flux above event levels at 7:05 p.m. Mountain Daylight Time (MDT) on August 15, 2001. Current proton fluxes are at a level equivalent to S2 (Moderate) on the NOAA Solar Radiation Storm scale. Effects may include, but are not limited to, single-event upsets on satellites in earth orbit, and degradation of high frequency radio communications at polar latitudes, also known as Polar Cap Absorption (PCA). The NOAA S-scale is defined by the lower energy proton flux (10 MeV), but because this event also includes a significant higher energy flux component (100 MeV), other effects are also possible, including increased radiation exposure for manned space flight operations, more widespread radio communication effects, and a wider range of potential impacts on satellites, such as "snow" in imaging systems and degradation of satellite components due to radiation exposure. Major proton events generally follow energetic x-ray flares from active sunspot regions on the visible side of the sun. This event was somewhat unusual in that no notable x-ray enhancement was seen on satellite monitors prior to its occurrence, suggesting a more unusual "backside" event, from a sunspot region that has rotated beyond the side of the sun facing Earth. Subsequent imagery received from the LASCO instrument on the SOHO satellite, operated by NASA/ESA, confirm that a major coronal mass ejection (CME) emerged from a backside source starting at about 5:54 p.m. MDT on August 15th. Proton enhancements were first observed on the SOHO SIS instrument at 6:25 p.m. MDT, indicating that these particles were ejected from the sun at a velocity near 30% of the speed of light. By 7:05 p.m. MDT, the flux of energetic protons observed on the NOAA GOES-8 satellite had risen to the threshold for a major proton event (as determined by 100 MeV proton flux). A second threshold for lower energy protons (10 MeV proton flux) was reached at 7:35 p.m. MDT. An associated Polar Cap Absorption (PCA) began at 8:10 pm MDT. The last S2 (Moderate) event with flux levels similar to the one in progress occurred on 18 April 2001, and lasted for about two days. Interestingly, that event was also caused by a backside CME. Aug 15, 2001 Shift Report ------------------------- Current ACE solar proton flux levels are rising due to the full-halo CME which was observed yesterday, although it appears they may be leveling off. Now at about 390. Kp is 2.67. Since we are using HRC for the next several days we are not concerned with ACIS proton damage as a result of this event. Aug 16, 2001 Shift Report -------------------------- SCS107 ran last night at 228:0208 in response to high EPHIN E1300 rates. S/C is safe and a replan is underway for handling tomorrow's eclipse and return to science. Aug 17, 2001 Shift Report -------------------------- - Proton radiation levels peaked early this AM and have been decreasing since then - Electron levels still slowly decreasing since peak at 228:0000 - EPHIN P4GM was at about 40 last pass, E1300 was at 6.7 and has been decreasing and P41GM is at about 3 and also decreasing. - Decision to be made at 1:45 EDT telecon whether or not to resume science. EPHIN levels typically must be below 1/3 of triggers, although they are not there yet it looks possible that they will be by later on today. Notes from Radiation Telecon at 17:45GMT: - Since first science in new AUG1701B is load is HRC-S w/LETG, main concern is whether or not environment would trip SCS 107 again if re-enabled. - Predictors exist in ACE and GOES measurements for EPHIN P4GM and P41GM, and these suggest that levels would be below the RADMON trip levels. No reliable predictor for E1300, which caused this current SCS 107 action. - Decision was made that upon contact with Chandra, if EPHIN levels were "only somewhat above" the nominal one-third of trip level criteria, that we would proceed and uplink and activate the load, given the fairly steady and "quiet" downward trend of the rad levels - Upon contact, rates met the criteria, with the only one close to the limit being the E1300 channel at 3.0. This met the criteria to proceed described earlier, so the decision was made to uplink the rest of the AUG1701B load and enable. - Possible radiation telecon tonight ONLY IF there is a significant change from the generally downward trend in the radiation environmental levels. If necessary, call telecon via sot_red_alert.