Florian Nichitiu a,* , James R. Drummond a , Jiansheng Zou a , Robert Deschambault b

1. Solar Particle Events seen by the MOPITT instrument Florian Nichitiu a,*, James R. Drummond a, Jiansheng Zou a, Robert Deschambault b a) Department of Physics, University of Toronto, Canada,60 St. George Street, Toronto, Ontario, CANADA, M5S 1A7; b) COM DEV, Cambridge, Ontario, Canada Introduction Since its launch on Dec. 18, 1999 the MOPITT(Measurements Of Pollution In The Troposphere) instrument has collected atmospheric data while flying aboard the Terra spacecraft. Terra is in a sun-synchronous polar orbit, has an orbital period of 98.88 minutes, and an altitude of 705 km.   For more than two years the MOPITT piezoelectric accelerometers have recorded satellite outliers by showing short, high intensity signals well correlated with the high-energy radiation environment. 29 Oct 2003 Solar Proton Event Max Proton Flux (pfu) > 10 MeV > 100 MeV 29/10 : 29500 186 30/10 : 3300 110 MOPITT DSE Total # # /Day 29/10 : 9 2.15 30/10 : 7 2.15 Day – Night Asymmetry SAA: Day/Night = 0.72 Poles & Bg: Day/Night = 1.04 SAA events = 54 % Background = 20.4% Poles ( +/- 65 ) = 25.6 %; North/South (poles) asymmetry=0.43 MOPITT instrument is an infrared gas correlation radiometer. Multi-component force measurements Kistler: K-Shear accelerometer. Sensing element: quartz crystal This SPE induced a high daily rate for MOPITT DSE on two consecutive days when, as in previous cases, the high energy component (>100 MeV) reaches a large value. These MOPITT DSEs are also located on the polar regions. The South Atlantic Anomaly South Polar region Solar Proton Events (SPEs) Detected by MOPITT accelerometer Max p Flux pfu @ >10 MeV >100 MeV Y1 Jul 14/15: 2000 24000410 Y2Nov 09: 2000 14800 347 N1 Sept 25: 2001 12900 31 Y3 Nov 06: 2001 31700253 N2 Nov 24: 2001 18900 4 Correlation with Solar Activity Monthly smoothed Solar Spot Number (SSN)(dashed) and F10.7 (continous) for Solar Cycle (SC) # 22 and SC #23 During normal operation, there are short fluctuations (spikes, lasting for only one telemetry sample), which apparently increase the normal level of vibration by more than 4 sigma. There is an overall increase ( ~ 2x) of MOPITT DSE daily rate during the time period Nov 2001 – Feb 2002 (second Solar sub-maximum) Time series of DSE daily rate and correlation with SPEs. Y# (large SPEs which affect the DSE daily rate) and N# (large SPEs whith no effect on the DSE daily rate) refer to SPEs identified in Table 1. The continuous white line is the daily average rate smoothed over 27 days. MOPITT Accelerometer anomalies are correlated with Solar Activity as shown by Solar centimetric Radio Flux : Ottawa index F10.7 The MOPITT Accelerometer detects SPE at 6 Nov (during the second peak of proton flux) even if the Solar Event start at 4 Nov Location of MOPITT Device Single Events During High Solar Activity period ( II sub-max) the relative contribution of trapped particles in SAA decrease from ~70% to ~40%, Background remain almost constant(~20%) and Poles contribution increase (from ~15% to ~40%). This is a consequence of direct injection of more high energy particles (via poles) during High Solar Activity. The energetic particles detected by the MOPITT (piezoelectric) accelerometer are mainly high energy protons . Summary and Conclusions Analysis of MOPITT anomalous accelerometer signals shows a direct correlation of the DSE daily rate with solar activity, a Day/Night asymmetry caused probably by interaction of trapped particles with the neutral atmosphere, and a direct correlation with high intensity solar proton events (SPEs). The high energy particles – the source of anomalous accelerometer signals- are localized mainly in SAA region, but the polar regions, particularly the southern pole, are also regions of higher risk for satellites mainly during intense SPEs. We have also found that at least during the Solar maximum, there is a correlation of the particle population responsible for DSEs in the piezoelectric accelerometer with solar activity as expressed better by the F10.7 Solar Radio Flux than the SSN. During the second sub-maximum of Solar Cycle SC23, the fraction of events over the poles relative to the SAA region increase, which mean that, probable there are more high-energy particles of non-trapped origin in this time interval, and a good proxy of Solar activity for this purpose is the F10.7 index. Acknowledgments The MOPITT project is funded by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Meteorological Service of Canada and the Canadian Space Agency (CSA). The US team and the Terra spacecraft are funded by NASA. ---------- *) nichitiu@atmosp.physics.utoronto.ca Correlation between number of DSE during SPEs and the SPE proton fluence for E> 15 MeV ( in units of 1010 particles/cm2). Y# and N# refer to SPRs identified in above Table . MOPITT DSE location during intense Solar Proton Events (SPE). Open circles are daytime, stars are nighttime. There is only one DSE in SAA region. Daily rate=1.06 ev/day Total Nr events over SAA = 54% SAA rate= 0.57 ev/day South Atlantic Anomaly (SAA) MOPITT spend only 6.25% of time over SAA  SAA rate=9.14 ev/day