High‐latitude Earth's magnetopause outside the cusp: Cluster observations

Abstract

[1] We investigated the ambient plasma and magnetic field conditions at high latitudes, as well as the macroparameters of the magnetopause. For this purpose we used Cluster spacecraft plasma and magnetic field data when all the interspacecraft distances were less than 300 km. We analyzed 154 magnetosheath-magnetosphere transitions which allow to distinguish different boundaries between the magnetosphere and the magnetosheath. First, we found transitions similar to the low-latitude boundary layer, the plasma mantle, and cusp-associated transitions. Second, we estimated the length of these transitions. Third, we found with high statistical evidence sub-Alfvénic magnetosheath plasma flows just above the plasma mantle. These flows are supposed to stabilize magnetopause reconnection. Fourth, we carried out an analysis of the magnetopause pressure balance. We found a group of 24 transitions during which both the thermal and the magnetic magnetosheath pressure exceeded the magnetospheric pressure, providing conditions for unusual magnetopause formation. Fifth, for 52 magnetopause crossings we obtained the orientation as well as distributions of velocity, thickness, and current density of the magnetopause. It was found that the magnetopause with an attached plasma mantle moves slower, is thinner, and reaches higher current densities than the one with an adjacent low-latitude-like boundary layer. A comparison with the magnetopause at low latitudes revealed that the high-latitude magnetopause is about two times thicker.

Statistical survey of day-side magnetospheric current flow using Cluster observations: magnetopause

“…Average current densities between 30 and 85 nA m −2 regularly appear especially for C and PM cases during stronger IMF. A similar result was reported by Panov et al (2008), who evaluated the peak current density values for 52 magnetopause crossings, showing that PM current peak magnitudes were about 2 times larger than those at the LL region.…”

“…The changes in plasma density and temperature are similar to those of low-latitude-like transitions. In addition, the entry layer can be characterized by bursts of accelerated sheath plasma that exceeds the flow velocity of the magnetosheath (Panov et al, 2008). During these plasma bursts, the magnetic field often undergoes rapid fluctuations as well as drops in magnitude.…”

“…Panov et al, 2008). Particle energy spectrograms show isotropic and broadened energy distributions during cusp transitions (e.g.…”

“…Dunlop et al, 2001Dunlop et al, , 2002Dunlop and Balogh, 2005;Panov et al, 2006). Panov et al (2008) performed a statistical study of different properties of 154 magnetopause crossings including the current density magnitude calculated via the curlometer technique, but they did not analyse the calculated current directions. Using magnetic field data from about 4000 Cluster magnetopause crossing events, Anekallu et al (2013) were able to perform a larger statistical study based on single-spacecraft measurements without making use of the curlometer technique.…”

Properties of standing Kruskal-Schwarzschild-modes at the magnetopause

“…Its radial velocity and the thickness of its current and boundary layers could first be reliably determined with data from the two neighboring spacecraft ISEE 1 and 2 using timing techniques (Berchem and Russell, 1982;Le and Russell, 1994). These techniques became most useful when applied to measurements of the four spacecraft mission CLUSTER Panov et al, 2008), which also opened the door to more sophisticated analysis methods and inter-method comparisons (Haaland et al, 2004). However, the reconstruction of the (radial) magnetopause motion over extended periods of time remained subject to the integration of the boundary normal plasma velocity Published by Copernicus Publications on behalf of the European Geosciences Union.…”