Abstract
Abstract. The global characteristics of the high-altitude cusp and its surrounding regions are investigated using a three-year 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.
Highlights
Extensive studies of the low- and mid-altitude cusp regions of the magnetosphere have been made using data from many spacecraft (Newell and Meng, 1988; Newell et al, 1989; Escoubet et al, 1992; Lockwood and Smith, 1992; Woch and Lundin, 1992; Newell and Meng, 1994; Yamauchi et al, 1996)
We have reported on new statistical results from encounters of the Cluster spacecraft in the high-altitude cusp region during the first three years of operations
By use of an elaborate sampling method we have determined the spatial distributions of the ion and magnetic measurements from Cluster which gave an unprecedented opportunity to study the global high-altitude cusp characteristics
Summary
Extensive studies of the low- and mid-altitude cusp regions of the magnetosphere have been made using data from many spacecraft (Newell and Meng, 1988; Newell et al, 1989; Escoubet et al, 1992; Lockwood and Smith, 1992; Woch and Lundin, 1992; Newell and Meng, 1994; Yamauchi et al, 1996). The deviation between the two configurations (spacecraft data and model) led them to conclude that there is the presence of an indentation at the magnetopause in this region They did not give reasons for their inconsistency with the results of Zhou and Russell (1997). Merka et al (2002) investigated the location and spatial extent of the cusp-like plasma regions observed by the Magion-4 satellite (part of the Interball mission). For this purpose they used the mid- and highaltitude Magion-4 measurements, which they mapped to lowaltitudes using the Tsyganenko (1996) model with the actual solar-wind conditions.
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