Estimating local plasma sheet PV^5/3 from single‐spacecraft measurements

Abstract

[1] 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 = À10 R E in the central plasma sheet.

Tearing stability of a multiscale magnetotail current sheet

“…It is also interesting that a similar result can be obtained for another equilibrium with y = −A 0 cos(pz/(2D)) exp(−ax) and the constant current sheet thickness L z ∼ D [Voigt, 1986], which does not even belong to the general class of the locally Harris sheets (2). As follows from Wolf et al [2006], for that model VB z /(2D) = 1.…”

Bursty bulk flows and dipolarization in MHD simulations of magnetotail reconnection

“…[7] Here we note that entropy in this context is typically measured by the quantity PV g , where P is the plasma pressure, V = R ds/B is the volume of a flux tube of unit magnetic flux, and g = 5/3 is the adiabatic constant [e.g., Wolf et al, 2006]. This definition is suitable for equilibrium states, when P is constant along field lines.…”

“…However, using plausible analytic field models, Wolf et al [2006] were able to provide estimates of reduced entropy in rapidly earthward moving flux tubes in association with two substorms.…”

Quasi-parallel electron beams and their possible application in inferring the auroral arc's root in the magnetosphere

“…Under such a geometry, the local B z would not differ substantially from its equatorial value. To support our argument we estimate the equatorial B eq z using the Wolf et al (2006) model (see their Eq. 9) and overplot it in Fig.…”