Magnetic coupling of the ring current and the radiation belt

Abstract

The magnetic influence of the storm time ring current on high‐energy particles is demonstrated by using a simulation of the ring current incorporating self‐consistent magnetic and electric fields. Observations by the Polar satellite show that the magnetic field is occasionally depressed by 50% or more near the equatorial plane at <6 RE. We call them equatorially magnetic depression events (EMDEs) and focus on the most intense EMDE observed during an intense storm on 22 October 1999. The simulation predicts that under a strong convection electric field, the magnetic field strength is highly depressed around L = 5 by newly injected ions of energy 80 keV or less. The depressed magnetic field causes a significant adiabatic decrease in the high‐energy ion flux at pitch angles near 90° to conserve the first adiabatic invariant. A more tail‐like (shortened) magnetic field line causes an enhancement of the flux at pitch angles near 0° and 180° to conserve the second adiabatic invariant. Consequently, a butterfly‐like pitch angle distribution (PAD) is formed, which agrees with the Polar observation. We propose that the adiabatic process could have acted not only on the high‐energy component of the protons but also on relativistic electrons in the outer radiation belt. This notion is supported by simultaneous Polar observation of relativistic electron fluxes that show a decrease at pitch angles near 90° and a slight increase at pitch angles near 0° and 180°. PADs of protons and electrons can be used to distinguish nonadiabatic processes acting selectively on electrons from adiabatic ones.