Observations of a Unique Cusp Signature at Low and Mid Altitudes

Abstract

Abstract.Observations of a unique cusp feature at low and mid altitudes are reported. This feature has a consistent structure at the equatorward edge of high-latitude particle precipitation and is predominantly present for high IMF By conditions. The observations are consistent with the Crooker antiparallel merging model, which predicts a narrow wedge-shaped cusp whose geometry depends greatly on the dawn/dusk component of the IMF. Various observations are presented at low altitudes (DE-2, Astrid-2, Munin, UARS, DMSP) and at mid altitudes (DE-1, Cluster) that suggest a highly coherent cusp feature that is consistent with the narrow, wedgeshaped cusp of Crooker and contains persistent wave signatures that are compatible with previously reported high-altitude measurements. A statistical survey of Astrid-2 and DMSP satellite data is also presented that shows this feature to be persistent and dependent on the IMF angle at the magnetopause, as expected. Thus, the cusp signatures observed at a wide range of altitudes present a coherent picture that may be interpreted in terms of a footprint of the magnetopause current layer.

The Polar Cusp Seen by Cluster

“…Early in the mission, Keith et al. (2005) presented Cluster observations of fully developed turbulence in the external cusp while the energy cascading from the low to high frequencies via wave modes interacting non‐linearly via three‐wave processes have been discussed by Blecki et al. (2005).…”

“…Numerous Cluster studies have shown that the low-frequency wave power correlates with the fluxes of the magnetosheath-like ions and electrons seen in the cusp (e.g., Duan et al, 2006;Grison et al, 2005;Jacobsen & Moen, 2010;Keith et al, 2005). Jacobsen and Moen (2010) pointed out that there is a greater degree of correlation between BBELF wave power and total fluxes in comparison with only field-aligned ion fluxes, suggesting that BBELF wave generation is independent of ion beam direction and therefore must be local.…”

“…Thus, the Cluster multi-point measurements have a clear advantage in comparison with single spacecraft measurements in studying turbulence. Early in the mission, Keith et al (2005) presented Cluster observations of fully developed turbulence in the external cusp while the energy cascading from the low to high frequencies via wave modes interacting non-linearly via three-wave processes have been discussed by Blecki et al (2005).…”

Multipoint observations of plasma phenomena made in space by Cluster

“…We have focused on a few basic plasma phenomena, but, for example, have not dealt with most of the vast body of work describing dynamical phenomena in Earth's magnetosphere, including the dynamics of current sheets in Earth's magnetotail and the morphology of the dayside high latitude cusp. Several review articles and special publications are available that describe aspects of that research in detail and interested readers are referred to them (see for example, Escoubet et al 2005 Multiscale Coupling of Sun-Earth Processes, p. 459, Keith et al 2005Sur. Geophys.…”