A new perspective on magnetotail disturbances in terms of inherent diamagnetic processes

Abstract

Using the vector magnetic field data and the low-energy particle data acquired with the Geotail satellite, we have investigated the characteristics of disturbances that occurred in the magnetotail region at a geocentric distance of ∼9 to 30 RE. We focused the investigation on the changes in three kinds of energy density, considering their primary importance, their relationship, and their flux transport. We divided the disturbances into Pi2 oscillatory variation (with a period of 40-150 s) and background disturbances. Characteristics of disturbances determined here include the following: (1) Plasma thermal pressure and magnetic pressure vary exactly in out-of-phase. The intensity of energy flux is greater parallel to the magnetic field than transverse to it. The plasma fluid clearly exhibits the diamagnetic properties; (2) Characteristics are seen on almost all time scales relevant to disturbances (both Pi2s and background disturbances) and in almost all the 139 examples. The substance of magnetotail Pi2 is the slow MHD waves, and the nature of background disturbances indicates slow MHD disturbances. We argue that the magnetotail plasma sheet is comprised of two types of flux-tube plasma exhibiting compound behaviors. One is composed of the plasma that basically shrinks parallel to the magnetic field and simultaneously stretches perpendicular to it. The other is composed of the plasma that basically stretches parallel to the magnetic field and simultaneously shrinks perpendicular to it. Copyright 2003 by the American Geophysical Union.