Cluster survey of the high-altitude cusp properties: a three-year statistical study

Abstract

Abstract. The global characteristics of the high-altitude cusp and its surrounding regions are investigated using a threeyear statistical survey based on data obtained by the Cluster spacecraft. The analysis involves an elaborate orbit-sampling methodology that uses a model field and takes into account the actual solar wind conditions and level of geomagnetic activity. The spatial distribution of the magnetic field and various plasma parameters in the vicinity of the low magnetic field exterior cusp are determined and it is found that: 1) The magnetic field distribution shows the presence of an intermediate region between the magnetosheath and the magnetosphere: the exterior cusp, 2) This region is characterized by the presence of dense plasma of magnetosheath origin; a comparison with the Tsyganenko (1996) magnetic field model shows that it is diamagnetic in nature, 3) The spatial distributions show that three distinct boundaries with the lobes, the dayside plasma sheet and the magnetosheath surround the exterior cusp, 4) The external boundary with the magnetosheath has a sharp bulk velocity gradient, as well as a density decrease and temperature increase as one goes from the magnetosheath to the exterior cusp, 5) While the two inner boundaries form a funnel, the external boundary shows no clear indentation, 6) The plasma and magnetic pressure distributions suggest that the exterior cusp is in equilibrium with its surroundings in a statistical sense, and 7) A preliminary analysis of the bulk flow distributions suggests that the exterior cusp is stagnant under northward IMF conditions but convective under southward IMF conditions.

Interplanetary magnetic field rotations followed from L1 to the ground: the response of the Earth's magnetosphere as seen by multi-spacecraft and ground-based observations

“…Lately, some studies have been done on the open-closed field line boundary and the cusp and the dependence on the IMF (Pitout et al, 2006;Hu et al, 2007;Cai et al, 2009), where it was found that the reconnection line moves equatorward/poleward of the cusp when the IMF changes sign, and compatible with the pictures obtained from statistical studies (Lavraud et al, 2004(Lavraud et al, , 2005. The cusp was observed to react rather fast to local (i.e.…”

Distribution of Field‐Aligned Electron Events in the High‐Altitude Polar Region: Cluster Observations

“…This suggests an alternative path of entering the low-altitude polar region. Some authors considered that solar wind or magnetosheath electrons could be the main source for downward electrons in the cusp region (Lavraud et al, 2004;Shi et al, 2014;Smith & Lockwood, 1996), and the magnetotail electrons should be the main source for the downward electrons or precipitation in the nightside auroral oval (Barth et al, 2004;Berko & Hoffman, 1974;Crooker, 1992;Teste et al, 2007).…”

3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

“…The exterior cusp has been shown to have three boundaries (Lavraud et al, 2004a;Paschmann et al, 1976;Haerendel et al, 1978;Onsager et al, 2001): the day-side plasma sheet on the sunward side, the tail-lobe or mantle on the night-side, and the magnetosheath in the exterior. Though it has been suggested that the outer boundary may represent an intermediate or slow transition (Lavraud et al, 2002) Published by Copernicus Publications on behalf of the European Geosciences Union.…”