Empirical Model of Precipitating Ion Oval

Abstract

In this brief technical report published maps of ion integral flux are used to constrain an empirical model of the precipitating ion oval. The ion oval is modeled as a Gaussian function of ionospheric latitude that depends on local time and the Kp geomagnetic index. The three parameters defining this function are the centroid latitude, width, and amplitude. The local time dependences of these three parameters are approximated by Fourier series expansions whose coefficients are constrained by the published ion maps. The Kp dependence of each coefficient is modeled by a linear fit. Optimization of the number of terms in the expansion is achieved via minimization of the global standard deviation between the model and the published ion map at each Kp. The empirical model is valid near the peak flux of the auroral oval; inside its centroid region the model reproduces the published ion maps with standard deviations of less than 5% of the peak integral flux. On the subglobal scale, average local errors (measured as a fraction of the point‐to‐point integral flux) are below 30% in the centroid region. Outside its centroid region the model deviates significantly from the H89 integral flux maps. The model's performance is assessed by comparing it with both local and global data from a 17 April 2002 substorm event. The model can reproduce important features of the macroscale auroral region but none of its subglobal structure, and not immediately following a substorm.

Epoch‐Based Model for Stormtime Plasmapause Location

“…However, our practical goal is to develop an analytical model that explicitly includes plumes. One straighforward approach is Fourier expansion (e.g., Allen et al, ; Goldstein, ). However, our preliminary study found that harmonic expansion was not well suited to the very aperiodic shape of the dayside plume (Goldstein, Baker, et al, ).…”

Empirical Characterization of Low‐Altitude Ion Flux Derived from TWINS

“…(a–c) The 30 keV polar ionospheric maps ( Λ × MLT). Dashed white curve: zero‐order ion oval latitude of H89 model (Goldstein, ; Hardy et al, ), i.e., A 0 from Appendix . (d, e, f) Differential ion flux versus MLT, nine energy bins, at H89 model latitude.…”

“…For comparison with these TWINS J TOT curves, we extracted integral number flux from the polar maps of the H89 statistical model (Hardy et al, ; Goldstein, ); cf. Appendix .…”