Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm31b0771l&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM31B-0771
Physics
2118 Energetic Particles, Solar, 2740 Magnetospheric Configuration And Dynamics, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Using data from the polar-orbiting SAMPEX satellite, we have measured the location of the geomagnetic cutoff latitude for energetic particles (typically 8-15 MeV/nucleon He) 4 times every orbit, or about every 25 minutes, during large solar energetic particle events. We typically find large variations in the cutoff location, often by more than 5o in less than one day. These variations are reasonably well correlated with changes in the geomagnetic activity index Dst, but the most sudden drops in the cutoff often occur up to several hours before the corresponding change in Dst, while the cutoff latitude recovered much more quickly than Dst during the two largest storms (15 July 2000 and 31 March 2001). In this report we include measurements during the large particle events of March and April 2001, in which Dst plunged below -350 nT and the cutoff decreased by >10o. We investigate the correlation of the cutoffs with both Dst and the Kp index, and we examine the dependence of the cutoff on magnetic local time. We also study how the cutoff depends on conditions in the interplanetary medium determined by the ACE spacecraft, such as the magnitude and direction of the interplanetary magnetic field and the solar wind velocity and density. As an important implication of these measurements, we note that when the size of the polar region expands during geomagnetic cutoff suppressions, spacecraft in mid- to high-inclination orbits such as the International Space Station (ISS) experience a significant increase in potential radiation exposure. Cutoff suppresions during the large storms of July 2000 and March 2001, for example, would increase the average exposure of the ISS to >30 MeV solar energetic protons by more than five fold over that expected under geomagnetically quiet conditions. This work was supported by NASA under contract NAS5-30704 and grant NAGW-1919.
Labrador Allan Wayne
Leske Richard A.
Mewaldt Richard A.
Stone Edward C.
von Rosenvinge Tycho T.
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