Using Van Allen Probes and Arase Observations to Develop an Empirical Plasma Density Model in the Inner Zone

• Published in: Journal of geophysical research. Space physics Vol. 128; no. 3
• Main Authors: Hartley, D. P., Cunningham, G. S., Ripoll, J.‐F., Malaspina, D. M., Kasahara, Y., Miyoshi, Y., Matsuda, S., Nakamura, S., Tsuchiya, F., Kitahara, M., Kumamoto, A., Shinohara, I., Matsuoka, A.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-03-2023
• Subjects: Arase; Diffusion coefficient; Diurnal variations; Empirical analysis; Empirical models; Hiss; Inner radiation belt; Ionosphere; Latitude; Mathematical models; Modelling; Plasma; Plasma density; plasmasphere; Probes; Radiation; Radiation belts; Statistical analysis; Van Allen Probes
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2022JA031012

A new empirical density model is developed for the inner zone between 1 < L < 3 using plasma densities inferred from the upper hybrid resonance on Arase, and hiss‐inferred density values from Van Allen Probes. The Van Allen Probes hiss‐inferred densities are first recalibrated and validated against Arase observations, using both a conjunction event and statistical analyses. The newly developed density model includes dependencies on L, magnetic latitude, and magnetic local time (MLT). Between 1.5 < L < 3.0, the equatorial density variation with L is shown to be equivalent to that of the Ozhogin et al. (2012, https://doi.org/10.1029/2011JA017330) model. However, for L < 1.5, this dependence changes as the plasma density increases at a faster rate with decreasing L. The latitudinal dependence of the plasma density is shown to present a flatter profile than previous models, meaning lower densities extend to higher latitudes. This dependence is well‐modeled by updated fitting coefficients. A clear MLT dependence of the plasma density is identified, which was not found or included in some previous models. This variation is consistent with the diurnal variation of the ionosphere, peaking near MLT = 14 and becoming larger in amplitude with decreasing L. A function describing this MLT dependence is presented. Overall, the new L, latitude, and MLT‐dependent empirical model can provide density values in areas outside the validity region of many previous models, making it a useful resource for accurately determining diffusion coefficients and predicting electron dynamics and their lifetimes in the inner radiation belt.
Key Points
Radiation Belt Storm Probes and Arase data are used to build a new empirical plasma density model for the inner zone, including L, latitude, and magnetic local time (MLT) dependencies
MLT dependence consistent with diurnal variation of ionosphere. Variation is largest in amplitude at low L, but persists out to L = 3
New model provides density in areas outside previous model bounds, making it a useful resource for modeling inner radiation belt dynamics