Local time variations of particle flux produced by an electrostatic field in the magnetosphere

Self Cite

An approximate expression for the variation with L of the equatorial pitch angle of a particle undergoing adiabatic convection in a dipole magnetic field is obtained. The additional assumptions of no particle loss and the other usual conservation laws then are invoked to describe the variation of such bulk parameters as pressure and density for any assumed initial distribution function. Explicit solutions are obtained for initial distributions separable in energy and pitch angle with sink α0 dependence on pitch angle and are shown to be weakly dependent on k. The expressions obtained are compared with the results predicted for the case of strong pitch angle diffusion to obtain bounds on the variation. The approximation for the L dependence of the equatorial pitch angle is also used to show how pitch angle anisotropy is modified during inward convection, and the rapid development of anisotropy for sharply falling initial spectra is noted.

Section: Adiabatic Motionmentioning

confidence: 99%

An approximate analytic description of plasma bulk parameters, and pitch angle anisotropy under adiabatic flow, in a dipolar magnetospheric field

Southwood¹,

Kivelson²

1975

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“…Smith and Hoffman [1974] pointed out that unusual 'nose' proton distributions seen near the plasmapause on the Explorer 45 spacecraft might be explained in terms of the spacecraft encountering static energy dependent boundaries produced by convection. Kivelson and Southwood [1975b] showed that Frank's [1970] observations of longitudinal asymmetry in energetic ring current proton distributions could be described by recognizing both the presence of a steady state convection boundary and the longitudinal dependence of convection acceleration. Plasma observations at synchronous orbit regularly show evidence of static convection induced boundaries which are energy dependent [DeForest and Mcllwain, 1971;Mauk and Mcllwain, 1974;Kivelson et aL, 1979].…”

Section: Introductionmentioning

confidence: 99%

Drift boundary approximations in simple magnetospheric convection models

Southwood¹,

Kaye²

1979

We analyze features of particle behavior in magnetospheric convection using simple analytic forms for the electrostatic potential which have been used in other recent works. We show that analytic approximations for the shape and position of surfaces delimiting closed and open particle orbits can be derived. These approximations are good for any pitch angle and at most energies. They break down only for the medium‐energy protons that are predicted by such models to penetrate far inside the plasmapause. The expressions we derive allow rapid tests of a variety of electric field models when analyzing particle data, and we illustrate this by intercomparing field models with several observations.

“…Outside the plasmapause the lower cutoff is not present, but the upper one remains. Kivelson and Southwood [1975] showed that this effect was evident in Frank's [1970] ring current data.…”

Section: Cutoffs In the Energy Distributionmentioning

confidence: 95%

Evolution of ion cyclotron instability in the plasma convection system of the magnetosphere

Kaye¹,

Kivelson²,

Southwood³

1979

Liouville's theorem and approximate but extremely accurate expressions which reflect the invariance of µ and J can be used to determine analytically the evolution of an adiabatically convecting energetic particle distribution. Features of the convecting distribution which are reproduced by our model include positive pitch angle anisotropy, regions in velocity space in which ∂f/∂v⊥ >0, and the energy dependence of the degree of particle injection. The energy dependence of the injection yields upper and lower cutoffs to the distribution within the plasmasphere, and only an upper cutoff outside. We have used this approach to study the evolution of ion cyclotron waves in a convecting particle distribution, and have found that the upper cutoff to the distribution restricts the growth of these waves, both on and off the geomagnetic equator, to a narrow range of frequencies which grow only inside the plasmasphere. In addition, we found that the upper cutoff limits wave growth to a few hours on either side of dusk. We have examined the results for two source distributions, a power law and a Maxwellian, and we found that for distributions with equivalent mean energies the power law is unstable over a greater range of frequencies and radial distances than the Maxwellian.