Open AccessEstimating local plasma sheet PV 5/3 from single‐spacecraft measurements
Author(s) -
Wolf R. A.,
Kumar V.,
Toffoletto F. R.,
Erickson G. M.,
Savoie A. M.,
Chen C. X.,
Lemon C. L.
Publication year - 2006
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2006ja012010
Subject(s) - physics , flux tube , plasma sheet , magnetosphere , plasma , spacecraft , mechanics , magnetic flux , magnetohydrodynamics , flux (metallurgy) , computational physics , solar wind , magnetic field , classical mechanics , materials science , quantum mechanics , astronomy , metallurgy
The theory of plasma transport in Earth's plasma sheet depends critically on the entropy parameter PV 5/3 , where P is particle pressure and V is the volume of a closed flux tube containing one unit of magnetic flux. Theory suggests that earthward moving flow bursts that inject plasma into the inner magnetosphere consist of flux tubes that have PV 5/3 values that are lower than those of neighboring slow‐moving flux tubes. However, there is no way to measure flux tube volume from one spacecraft or a small number of spacecraft. We propose a formula for estimating local PV 5/3 from a single spacecraft in the plasma sheet based on a simple two‐dimensional analytic model of plasma in force equilibrium, with some parameters set from local measurements at a spacecraft and other parameters set to fit a series of equilibrated Tsyganenko models. To gain an idea of the expected error, the resulting formula is then tested against various relaxed Tsyganenko models, an equilibrium magnetic field/plasma model with a depleted channel and also a thin‐filament MHD calculation. The formula is used to estimate the entropy parameter of flux tubes injected in two substorms, using spacecraft measurements near X = −10 R E in the central plasma sheet.