Simulation Simulation of Radiation Belt Simulation of Radiation Belt

INTRODUCTION

The interaction of a CME-driven magnetic cloud with the earth's magnetosphere on January 10-11, 1997, produced an increase in outer zone relativistic electron fluxes by several orders of magnitude, depending on energy and radial location [Li et al., 1998; Reeves et al., 1998a; Selesnick and Blake, 1998]. The expanding magnetic cloud, imbedded in nominal solar wind flow speed $\sim$400 km/s, produced an interplanetary shock which crossed the WIND spacecraft $\sim$01:00 UT on January 10. The shock impacted the magnetosphere 20 minutes later, followed by a period of average southward IMF beginning $\sim$04:40 UT, which lasted until 17:30 UT on January 10 [Burlaga et al., 1998]. There was substantial buildup of the ring current to Dst $\sim$ -85 nT prior to northward turning of the IMF, with substorm activity indicated by a maximum three hour average K_p = 6, using preliminary index data from the ISTP web site (www-spof.gsfc.nasa.gov/istp/cloud_jan97/).

Here we will focus on simulations of the rise in relativistic electron flux occurring first around L = 4.5 [Li et al., 1998; Reeves et al., 1998a], as seen by GPS satellites in circular (L = 4.2, 55 deg inclination) orbit, which map flux at L > 4.2 extrapolated from measurements off-equator, and provide a relatively continuous determination of the rise in flux vs. L within geosynchronous orbit at 0.2  - 0.4, 0.4 - 0.8, 0.8 - 1.6 and 1.6 - 3.2 MeV. In addition, POLAR provides cuts in L every 17.5 hours which show a jump in flux of >1.6 MeV electrons between outer zone crossings at 04:00 - 07:00 UT on January 10, and 20:00 - 01:00 UT on January 10 - 11, by a factor of 10³ - 10⁴, peaking around L = 4.3 [Selesnick and Blake, 1998]. Geosynchronous data, on the other hand, show a rise in > 1.6 - 2 MeV electron fluxes somewhat later, with peak values and rise times sensitive to local time [Reeves et al., 1998b].

Simulation Simulation of Radiation Belt Simulation of Radiation Belt