The Plasmasphere Boundary Layer

Abstract

Abstract.As an inner magnetospheric phenomenon the plasmapause region is of interest for a number of reasons, one being the occurrence there of geophysically important interactions between the plasmas of the hot plasma sheet and of the cool plasmasphere. There is a need for a conceptual framework within which to examine and discuss these interactions and their consequences, and we therefore suggest that the plasmapause region be called the Plasmasphere Boundary Layer, or PBL. Such a term has been slow to emerge because of the complexity and variability of the plasma populations that can exist near the plasmapause and because of the variety of criteria used to identify the plasmapause in experimental data. Furthermore, and quite importantly in our view, a substantial obstacle to the consideration of the plasmapause region as a boundary layer has been the longstanding tendency of textbooks on space physics to limit introductory material on the plasmapause phenomenon to zeroth order descriptions in terms of ideal MHD theory, thus implying that the plasmasphere is relatively well understood. A textbook may introduce the concept of shielding of the inner magnetosphere from perturbing convection electric fields, but attention is not usually paid to the variety of physical processes reported to occur in the PBL, such as heating, instabilities, and fast longitudinal flows, processes which must play roles in plasmasphere dynamics in concert with the flow regimes associated with the major dynamo sources of electric fields. We believe that through the use of the PBL concept in future textbook discussions of the plasmasphere and in scientific communications, much progress can be made on longstanding questions about the physics involved in the formation of the plasmapause and in the cycles of erosion and recovery of the plasmasphere.

Multi-spacecraft observations of small-scale fluctuations in density and fields in plasmaspheric plumes

“…Density irregularities exist inside the plasmasphere measured by Cluster (Darrouzet et al, 2004). The small-scale density structures inside PBL (plasmasphere boundary layer) are one of the research topics discussed by Carpenter and Lemaire (2004). Goldstein et al (2004) reported density fluctuations detected by LANL (Los Alamos National Laboratory) geosynchronous satellites.…”

The relationship between plasmapause, solar wind and geomagnetic activity between 2007 and 2011

“…The outer boundary of the plasmasphere, called the plasmapause, represents the cutoff in the plasma density, the location of which depends on the level of the geomagnetic disturbances. In the equatorial plane the plasmapause is typically found near 5-7 R E (e.g., Chappell et al, 1970a;Carpenter and Lemaire, 2004;Pedatella and Larson, 2010).…”

Whistlers observed outside the plasmasphere: Correlation to plasmaspheric/plasmapause features

“…1.1.3. Asymmetric Whistler Observation Across Plasmasphere Boundary Layer Both ground-based [Carpenter et al, 1968;Carpenter and Šulić, 1988] and space-based [Platino et al, 2005, and references therein] observations of lightning-generated, ducted whistlers have clearly demonstrated an asymmetry in the observations across the plasmasphere boundary layer [Carpenter and Lemaire, 2004]. While observation of whistlers inside of the plasmasphere is a common occurrence, the same does not hold true beyond the plasmapause boundary layer.…”

“…The outer boundary of the plasmasphere, often referred to as the plasmapause [e.g., Lemaire and Gringauz, 1988] or the plasmaspheric boundary layer [Carpenter and Lemaire, 2004], is typically characterized by an abrupt 1 to 2 orders of magnitude decrease in plasma density as a function of geocentric distance. The exception to this typical picture of the plasmapause occurs during extended periods of geomagnetic quiescence.…”