The role of Shabansky orbits in compression‐related electromagnetic ion cyclotron wave growth

Abstract

[1] Electromagnetic ion cyclotron waves at high L values near local noon are often found to be related to magnetospheric compression events. These waves arise from temperature anisotropies in trapped warm plasma populations. There are several possible mechanisms that can generate these temperature anisotropies, including both energizing and nonenergizing processes. In this work we investigate a nonenergizing process arising from dayside bifurcated magnetic field minima. There are two kinds of behavior particles undergo in the presence of bifurcated minima: particles with high initial equatorial pitch angles (EPAs) are forced to execute so-called Shabansky orbits and mirror at high latitudes without passing through the equator, while those with lower initial EPAs will pass through the equator with higher EPAs than before; as a result, perpendicular energies near the equator increase at the cost of parallel energies. By using a 3-D particle tracing code in a tunable analytic compressed-dipole field, we explore the effects of Shabansky orbits on the anisotropy of the warm plasma and contrast with the anisotropy resulting from drift shell splitting. We show that Shabansky orbits are an independent source of temperature anisotropy for warm dayside ions.

THEMIS observations of electromagnetic ion cyclotron wave occurrence: Dependence on AE, SYMH, and solar wind dynamic pressure

“…Particles with 90° pitch angles drift through the equator but particles with lower pitch angles can mirror at high latitudes without passing through the equator, executing so‐called Shabansky orbits. As a result, the ion perpendicular temperature near the equator increases relative to the parallel temperature, the resultant anisotropy giving rise to EMIC waves [see, e.g., McCollough et al , 2012]. Both drift shell splitting and Shabansky mechanisms provide a continuous source of dayside anisotropy, lasting for several hours while the magnetosphere remains compressed.…”

Radiation belt 2D and 3D simulations for CIR-driven storms during Carrington Rotation 2068

“…This type of discontinuity in the second invariant occurs when an electron drifts into a region where the minimum B value along a field line bifurcates above and below the equatorial plane, called a Shabansky orbit (Shabansky, 1971;Ozturk and Wolf, 2007;McCollough et al, 2011). Conserving both first invariant and total energy requires that an electron increasing its second invariant must move outward to weaker B and vice versa (McCollough et al, 2011). In order to distinguish between temporal and spatial changes in the electron drift we have to run the same initial trajectory through a frozen magnetic field Fig.…”

Some characteristics of the magnetospheric source of dayside subaroural proton precipitations during magnetospheric compression

“…That is, appar ently, related to the fact that in this region an increased anisotropy of the pitch angle distribution of energetic protons [17] caused by drift shell splitting [18] and particle motion along the "Shabansky orbits" [19,20] is permanently observed. Both these mechanisms pro vide larger proton anisotropy for larger "day-night" asymmetry in the magnetospheric magnetic field.…”