Meaning of ionospheric Joule heating

Abstract. Maxwell's equations allow the magnetic field B to be calculated if the electric current density J is assumed to be completely known as a function of space and time. The charged particles that constitute the current, however, are subject to Newton's laws as well, and J can be changed by forces acting on charged particles. Particularly in plasmas, where the concentration of charged particles is high, the effect of the electromagnetic field calculated from a given J on J itself cannot be ignored. Whereas in ordinary laboratory physics one is accustomed to take J as primary and B as derived from J , it is often asserted that in plasmas B should be viewed as primary and J as derived from B simply as (c/4π)∇×B. Here I investigate the relation between ∇×B and J in the same terms and by the same method as previously applied to the MHD relation between the electric field and the plasma bulk flow (Vasyliūnas, 2001): assume that one but not the other is present initially, and calculate what happens. The result is that, for configurations with spatial scales much larger than the electron inertial length λ e , a given ∇×B produces the corresponding J , while a given J does not produce any ∇×B but disappears instead. The reason for this can be understood by noting that ∇×B =(4π/c)J implies a time-varying electric field (displacement current) which acts to change both terms (in order to bring them toward equality); the changes in the two terms, however, proceed on different time scales, light travel time for B and electron plasma period for J , and clearly the term changing much more slowly is the one that survives. (By definition, the two time scales are equal at λ e .) On larger scales, the evolution of B (and hence also of ∇×B) is governed by ∇×E, with E determined by plasma dynamics via the generalized Ohm's law; as illustrative simple examples, I discuss the formation of magnetic drift currents in the magnetosphere and of Pedersen and Hall currents in the ionosphere.

Section: Pedersen and Hall Currentsmentioning

confidence: 99%

mentioning

confidence: 99%

Relation between magnetic fields and electric currents in plasmas

Vasyliūnas

2005

“…The first is heating, both by direct heat flux from the magnetosphere (in the form of chargedparticle precipitation) and by dissipation resulting from electrodynamic processes. The latter is commonly referred to as "ionospheric Joule heating" but Vasyliūnas and Song (2005) have shown that it is, for the most part, collisional frictional heating from the relative motion of plasma and neutrals; the conventionally used expression J · E+V (n) ×B/c does, however, represent the total dissipation rate, about half of which goes into the neutral medium. The second process is acceleration of neutral flow by ion drag (e.g.…”

Section: Magnetospheric Perturbations Of the Neutral Atmospherementioning

confidence: 99%

Ionospheric and boundary contributions to the Dessler-Parker-Sckopke formula for <i>Dst</i>

Vasyliūnas

2006

Abstract. The Dessler-Parker-Sckopke formula for the disturbance magnetic field averaged over the Earth's surface, universally used to interpret the geomagnetic Dst index, can be generalized, by using the well known method of deriving it from the virial theorem, to include the effects of ionospheric currents. There is an added term proportional to the global integral of the vertical mechanical force that balances the vertical component of the Lorentz force J ×B/c in the ionosphere; a downward mechanical force reduces, and an upward increases, the depression of the magnetic field. If the vertical component of the ionospheric Ohm's law holds exactly, the relevant force on the plasma is the collisional friction between the neutral atmosphere and the vertically flowing plasma. An equal and opposite force is exerted on the neutral atmosphere and thus appears in its virial theorem. The ionospheric effect on Dst can then be related to the changes of kinetic and gravitational energy contents of the neutral atmosphere; since these changes are brought about by energy input from the magnetosphere, there is an implied upper limit to the effect on Dst which in general is relatively small in comparison to the contribution of the plasma energy content in the magnetosphere. Hence the DesslerParker-Sckopke formula can be applied without major modification, even in the case of strong partial ring currents; the ionospheric closure currents implied by the local time asymmetry have only a relatively small effect on the globally averaged disturbance field, comparable to other sources of uncertainty. When derived from the virial theorem applied to a bounded volume (e.g. the magnetosphere bounded by the magnetopause and a cross-section of the magnetotail), the Dessler-Parker-Sckopke formula contains also several boundary surface terms which can be identified as contributions of the magnetopause (Chapman-Ferraro) and of the magnetotail currents.

“…At the same time, the relative motion between neutrals and ionized particles will cause frictional (or Joule) heating Vasyliunas and Song, 2005), which complement thermal drivers caused by solar EUV heating and energetic particle precipitation. The coupled M-I-T system will adjust the various driving processes to result in the plasma convection and thermospheric wind pattern, which we observe.…”

Section: Introductionmentioning

confidence: 99%

Thermospheric vorticity at high geomagnetic latitudes from CHAMP data and its IMF dependence

Förster

Haaland

Doornbos³

2011

Abstract. Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both polar regions are used to deduce statistical neutral wind vorticity distributions and were analyzed in their dependence on the Interplanetary Magnetic Field (IMF). The average pattern confirms the large duskside anticyclonic vortex seen in the average wind pattern and reveals a cyclonic vorticity on the dawnside, which is almost equal in magnitude to the duskside minimum. The outer shape of the vorticity pattern agrees approximately with the outer boundary of region-1 currents in the well-known average current distributions of Iijima and Potemra (1976). The IMF dependence of the vorticity pattern resembles the characteristic FAC and ionospheric plasma drift pattern known from various statistical studies obtained under the same sorting conditions.