Field‐aligned distribution of the plasmaspheric electron density: An empirical model derived from the IMAGE RPI measurements

Abstract

[1] We present a newly developed empirical model of the plasma density in the plasmasphere. It is based on more than 700 density profiles along field lines derived from active sounding measurements made by the radio plasma imager on IMAGE between June 2000 and July 2005. The measurements cover all magnetic local times and vary from L = 1.6 to L = 4 spatially, with every case manually confirmed to be within the plasmasphere by studying the corresponding dynamic spectrogram. The resulting model depends not only on L-shell but also on magnetic latitude and can be applied to specify the electron densities in the plasmasphere between 2000 km altitude and the plasmapause (the plasmapause location itself is not included in this model). It consists of two parts: the equatorial density, which falls off exponentially as a function of L-shell; and the field-aligned dependence on magnetic latitude and L-shell (in the form of invariant magnetic latitude). The fluctuations of density appear to be greater than what could be explained by a possible dependence on magnetic local time or season, and the dependence on geomagnetic activity is weak and cannot be discerned. The solar cycle effect is not included because the database covers only a fraction of a solar cycle. The performance of the model is evaluated by comparison to four previously developed plasmaspheric models and is further tested against the in situ passive IMAGE RPI measurements of the upper hybrid resonance frequency. While the equatorial densities of different models are mostly within the statistical uncertainties (especially at distances greater than L = 3), the clear latitudinal dependence of the RPI model presents an improvement over previous models. The model shows that the field-aligned density distribution can be treated neither as constant nor as a simple diffusive equilibrium distribution profile. This electron density model combined with an assumed model of the ion composition can be used to estimate the time for an Alfven wave to propagate from one hemisphere to the other, to determine the plasma frequencies along a field line, and to calculate the raypaths for high frequency waves propagating in the plasmasphere.Citation: Ozhogin, P., J. Tu, P. Song, and B. W. Reinisch (2012), Field-aligned distribution of the plasmaspheric electron density: An empirical model derived from the IMAGE RPI measurements,

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

“…This latitudinal range being narrow and the latitudinal variation of the integrand in the bounce integral remaining weak (see Appendix D and A from Mourenas et al, 2012b,a), the diffusion rate integrated over λ can be further approximated by this integrand taken at λ and ω = ω m , multiplied by λ and by B 2 sp ω /B 2 sp (ω m ) (Mourenas et al, 2012b). Finally, it is assumed that the plasma density does not vary strongly with latitude for latitudes smaller than about 40 • , in agreement with observations between L ∼ 2 and 7 (Denton et al, 2006;Ozhogin et al, 2012).…”

“…In this domain, the discrepancy between analytical estimates and the numerical lifetimes remains smaller than a factor of 2. This is much smaller than the uncertainties associated with outer-belt density models (Sheeley et al, 2001;Denton et al, 2006;Ozhogin et al, 2012) and chorus intensity models (Meredith et al, 2001;Shprits et al, 2007;Li et al, 2011;Artemyev et al, 2012b and τ s+l ∝ pe at high density, as predicted in Eqs. (14)-(15).…”

Effect of plasma density on diffusion rates due to wave particle interactions with chorus and plasmaspheric hiss: extreme event analysis

“…There are several models of the electron plasma density in the magnetosphere including the Global Plasma Core Model (GCPM) (Gallagher et al, 2000), IZMIRAN (Chasovitin et al, 1998;Gulyaeva et al, 2002), the Carpenter model (Carpenter and Anderson, 1992) and also empirical models based on CRRES data (Sheeley et al, 2001), POLAR data (Denton et al, 2004) or IMAGE Auroral Electrojet (RPI) measurements (Ozhogin et al, 2012). The electron plasma density resulting from these models can be different from one model to another and in each model the plasmapause location, the transition between the high density region within the plasmasphere and the low density region outside the plasmasphere, is different.…”

Deduction of the rates of radial diffusion of protons from the structure of the Earth's radiation belts

“…As a result, I found L dependences of the rates of ionization losses for the protons with different values of µ (from 0.2 to 7 keV nT −1 ). For these calculations, I used the modern empirical models of the plasmasphere (Østgaard et al, 2003;Zoennchen et al, 2013) and exosphere (Moldwin et al, 2002;Ozhogin et al, 2012). The methodology of these calculations is described in detail in Kovtyukh (2016).…”