A statistical model of auroral electron precipitation

Abstract

A statistical study has been completed using data from the Defense Meteorological Satellite Program F2 and F4 and the Satellite Test Program P78‐1 satellites to determine the average characteristics of auroral electron precipitation as a function of magnetic local time, magnetic latitude, and geomagnetic activity as measured by Kp. The characteristics were determined for each whole number value of Kp from 0 to 5 and for Kp ≥ 6‐. At each level of Kp, the high‐latitude region was gridded, and the average electron spectrum in the energy range from 50 eV to 20 keV was determined in each grid element. The results show that the high‐latitude precipitation region separates into two parts based on the electron average energy. There is a region of relatively hot electrons (EAVE ≥ 600 eV). In this region, the electron average energies are highest on the morningside of the oval. There are two average energy maxima at each Kp level: one postmidnight and the other prenoon. The hot electron region is generally not continuous in MLT but shows a gap between 1200 and 1800 MLT. The hotter electrons carry most of the energy flux into the oval. The energy flux on the nightside increases with Kp, while the level at noon increases with Kp when Kp is small but decreases at higher Kp. The average energy of the hot electrons increases from Kp = 0 to Kp = 3 but is approximately constant for higher Kp. In the second region, average energies are low (EAVE < 600 eV). This region extends from the poleward edge of the hot electron region to the pole. The precipitating electrons in this region carry the majority of the number flux at high latitudes. The largest number fluxes are found on the dayside. The highest fluxes are confined to a crescent‐shaped region centered slightly prenoon and extending in MLT over most of dayside and, in some cases, into the nightside. There is a prenoon maximum in the number flux that shows little variability in MLT or in intensity with Kp. The average energy shows a minimum typically between 1100 and 1200 MLT and located toward the poleward edge of the crescent‐shaped region of highest integral number flux. We identify the cusp as the region near the average energy minimum and the cleft as the crescent‐shaped region.

Thermospheric atomic oxygen density estimates using the EISCAT Svalbard Radar

“…By restricting our analysis to quiet geomagnetic conditions only, i.e., Kp ≤ 2, Joule heating [Kosch and Nielsen, 1995] and heat flux of ions and electrons due to particle precipitation also become negligible [cf. Hardy et al, 1985Hardy et al, , 1989, allowing us to assume equal ion and neutral temperatures. Quiet geomagnetic conditions permit us to assume a steady state ion motion, so that the time derivative of the ion velocity is also ignored.…”

Model interpretation of the ionospheric F-region electron density structures observed by ground-based satellite tomography at sub-auroral and auroral latitudes in Russia in January–May 1999

“…The precipitating cold (average energy <1 keV) and hot (>1 keV) electrons were defined following Hardy's model requirements (Hardy et al, 1985). The maximum flux intensity of the precipitating cold electrons (with the average electron energy of E 0 =0.27 keV) in the region of the daytime cusp was I m = 1.9 · 10 9 cm −2 s −1 .…”

Ionospheric simulation compared with Dynamics Explorer observations for November 22, 1981

“…These five orbits represent the variability found during this 24-hour period, including one pass during the substonn. Figure 2 shows the selected passes, approximated as straight lines, in the polar magnetic coordinates with a Hardy et al [1985] auroral oval shown as the shaded region. Each DE 2 passage is labeled with the approximate time at which the orbit crossed the dawnside northern high-latitude region.…”

“…At the present time, no globalscale theoretical model of the magnetosphere exists. Hence, statistical (empirical) models of the magnetospheric electric field [Volland, 1978;Heelis et al, 1982;Sojka el al., 1986;Heppner and Maynard, 1987] and auroral precipitation [Spiro et aI., 1982;Hardy et al, 1985;Evans , 1987] are used as inputs to ionospheric and thennospheric models. Such studies are handicapped because statistical inputs cannot readily be adapted to simulate the spatial variations and temporal dynamics of geomagnetic storms and substorms.…”