Lecturer: Kanako Seki (Nagoya)
Date: 2012-09-20 13:30
Place: Aniara

On roles of the K-H instability and double lobe reconnection in the CDPS formation in Earth’s magnetosphere: PSD observations and PIC simulation

Dr. Kanako Seki
Nagoya Univ.

In the nightside region of near-Earth space, a large-scale region called the plasma sheet is formed through interaction between the intrinsic terrestrial magnetic field and the solar wind. The plasma sheet becomes much cooler and denser than usual under prolonged northward interplanetary magnetic field (IMF) conditions. However, the mechanism responsible for the formation of CDPS has been under debate. The Kelvin-Helmholtz (K-H) instability driven by the velocity shear at the magnetopause has been proposed as a possible mechanism of magnetosheath plasma entry through the LLBL (low latitude boundary layer). On one hand, ''Double lobe reconnection'', i.e., reconnection of a magnetosheath flux tube with lobe field at the high-latitude magnetopause in both hemispheres, thereby becoming closed, is also an important candidate process for the dense, thick LLBL formation during northward IMF periods. Is has been also suggested that the nonlinear kinetic Alfven waves can provide a significant transport of plasma and momentum across the magnetopause.

In this study, observations of electron and ion phase space densities (PSDs) from the dayside to the nightside magnetosphere are compared with results from full-particle simulation of the K-H instability in the magnetized plasma with a density gradient so as to examine roles of the K-H instability in effective plasma transport seen in the Earth's magnetotail. The results indicate that the ''double lobe reconnection'' is responsible for formation of the outermost part of LLBL in the dusk flank, but does not directly form the plasma mixing region consisting of the main part of LLBL at the tail flank. Comparison of LLBL and CDPS observations with the simulation result, on one hand, suggests that a wavy structure observed in the LLBL is consistent with the non-linear phase of the K-H instability and that the K-H instability plays an important role in the plasma mixing in the LLBL and in formation of the CDPS. Inner boundary of CDPS observed by GEOTAIL is roughly inferred about ~3-7 Re inside from the magnetopause. Our simulation results with large simulation domain indicate that the observed spatial extent of the entry layer is explicable with formation of a broad entry layer of magnetosheath plasma by forward and inverse energy cascades of the K-H instability.

Created 2012-08-31 09:32:37 by Mats Holmström
Last changed 2012-09-13 10:13:55 by Mats Holmström