Polar cap plasma patch primary linear instability growth rates compared

Robert Burston,Ivan Astin,Cathryn Mitchell

doi:10.1002/2015ja021895

Robert Burston, Ivan Astin + Show 1 more

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https://doi.org/10.1002/2015ja021895

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Abstract

AbstractFour primary plasma instability processes have been proposed in the literature to explain the generation of phase scintillation associated with polar cap plasma patches. These are the gradient drift, current convective, and Kelvin‐Helmholtz instabilities and a small‐scale “turbulence” process. In this paper the range of possible values of the linear growth rates for each of these processes is explored using Dynamics Explorer 2 satellite observations. It is found that the inertial turbulence instability is the dominant process, followed by inertial gradient drift, collisional turbulence, and collisional shortwave current convective instabilities. The other processes, such as Kelvin‐Helmholtz, collisional gradient drift, and inertial shortwave current convective instabilities, very rarely (<1% of the time) give rise to a growth rate exceeding 1/60, that is deemed to be significant (in publications) to give rise to GPS scintillation.

Highlights

Large regions of enhanced electron concentration drifting according to an E × B force from the auroral dayside ionosphere into the polar-cap region of the ionosphere were theorised by Hill [1963] as an explanation for “sporadic F” observations via foF2 measurements in these areas.This theory was confirmed experimentally by Buchau et al [1983] using optical all-sky camera images and the structures (100s – 1000s km in scale) became generally known as polar-cap plasma patches
Turbulence, inertial Gradient Drift Instability (GDI) and shortwave collisional Convective Instability (CCI) would regularly give the rise-times of approximately 60s or less observed in the cusp region during patch formation [e.g. Carlson et al, 2007 and references there-in]
The relative importance of the various mechanisms could be significantly different in the non-linear regime [Gondarenko, and Guzdar, 2006; Gondarenko and Guzdar, 2004a; Gondarenko et al, 2003; Gondarenko and Guzdar, 1999; 2004b; Guzdar et al, 1998]

Summary

Introduction

Large regions of enhanced electron concentration drifting according to an E × B force from the auroral dayside ionosphere into the polar-cap region of the ionosphere were theorised by Hill [1963] as an explanation for “sporadic F” observations via foF2 measurements in these areas This theory was confirmed experimentally by Buchau et al [1983] using optical all-sky camera images and the structures (100s – 1000s km in scale) became generally known as polar-cap plasma patches. Scintillation inducing irregularities are considered to form through a cascade of energy from longer wavelengths to shorter ones in a manner analogous to that which occurs in the generation of turbulence in neutral fluids [Kintner and Seyler, 1985] This requires some initial process to create wavelike structures in the plasma where there are none to start with – a primary plasma instability [Kelley, 2009]

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