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.

Electron auroral energy flux is characterized by electron hemispheric power (Hpe) estimated since 1978 from National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite Program (DMSP) satellites after the estimates were corrected for instrumental problems and adjusted to a common baseline. Similarly, intersatellite adjusted ion hemispheric power (Hpi) estimates come from one MetOp and four NOAA satellites beginning in 1998. The hemispheric power (Hp) estimates are very crude, coming from single satellite passes referenced to 10 global activity levels, where the Hpi estimates are the difference between the total and the electron Hp (Hpi = Hpt‐Hpe). However, hourly averaged NOAA/DMSP Hpe and Hpi estimates correlate well with hourly Polar Ultraviolet Imager (UVI) Hpt and Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) far ultraviolet (FUV) Hpe and Hpi estimates. Hpe winter values were larger than summer values ∼65% of the time (when geomagnetic activity was moderate or higher), and Hpe were larger in the summer ∼35% of the time (typically for low geomagnetic activity). Hpe was ∼40% larger at winter solstice than summer solstice for the largest Hp from mostly nightside increases, and Hpe was ∼35% larger in summer than winter for the smallest Hp owing to dayside auroral enhancements. Ion precipitation differed from electron precipitation because it was almost always larger in summer than winter. Hpe and Hpi increased with Kp, solar wind speed (Vsw), and negative Interplanetary Magnetic Field (IMF) Bz, similar to previous studies. Hpi also increased strongly with positive Bz. For quiet conditions, Hpe increased with increasing 10.7‐cm solar flux (Sa), while Hpi increased with Sa up to Sa ∼115 for all conditions.

[1] We have integrated more than 600 million energetic electron spectra measured by the Special Sensor for Precipitating Particles, version 4 (SSJ4) sensor on nine Defense Meteorological Satellite Program (DMSP) spacecraft to obtain total number fluxes (J tot [#/cm 2 s sr]) and energy fluxes (JE tot [keV/cm 2 s sr]). These quantities were first separated into bins of 1°in magnetic latitude (MLat), 1 h in magnetic local time (MLT) and unit steps of Kp and then into 26 Â 26 logarithmically-spaced matrices covering the ranges 10 4 to 10 10.25 for JE tot and J tot and 10 À3 to 10 3.25 for average energy E AVE . Joint probability densities were then calculated as ratios of the number of samples within a matrix element to the total samples in each MLat-MLT-Kp bin. Our analysis shows that (1) in all bins probabilities for detecting any of the three parameters were lognormally distributed, and (2) in most bins distributions were multimodal. Measured multimodal probability distributions are well represented as superpositions of contributions from as many as four lognormal populations. These distributions have inherent positive skews with significant separations between their mean and most probable values. Average values of JE tot and E AVE now widely used to model distributions of auroral conductance at different levels of Kp are verified in the large DMSP data set. However, the lognormal and multimodal characters of their realizations in nature indicate that probabilities of detecting them at a given time in a MLat-MLT-Kp bin never exceed 10%.

D TL C IPL-TR-93-2055 9. SPONSORING.i MONITORING AGENCY .4AN 8 D 10 .SPONSOR!,NG MONITORING AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES *Boston College, Chestnut Hill, MA Reprinted from XVth International Symposium on Discharges and Electrical Insulation in Vacuum-Darmstadt-1992 12a, DISTRIUTION AVAILABILITY STATEMENT j1 2 b. DISTRIBUT'IN CODE Approved for public release; Distribution unlimited 13. ABSTRACT (Maximum2 10 wcrds) Sixteen samples of standard insulating materials with electrodes were eposed to the full variety of the Earth's space radiation beus tor 14 months. Spontaneous discharges were recorded for each sample and are compared to the radiation levels which were simultaneously monitored. Samples with the most exposed insulator surface pulsed most frequently. Pulsing correlated with electron flux, but not at all with proton flux. The pulse rate per unit electron flux was initially small, rose continuously for 7 mutahs, and then fell slightly during the last seven months. A computer model predicts the charging of the inmulators by the high energy electron flux; It took I to 6 months for the electric fields to approach steady state levels. Most of the pulses were less than 50 volts on 50 ohms. The pulsing rate decays when the satellite leaves the electron belts; the decay became more rapid after 7 months. Pulsing during the first six months had different characteristics than later pulsing. 14. SUBJECT TERMS 15. NUMBER OF PAGES Electrical Discharging Radiation Insulating 5 16. PRICE CODE 17. SECURITY CLASSIFICATION 118. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ASSTRAC0. L ON OF ASTRA UNCLASSIFIED UNCLASSIFIED I UNCLASSIFIED SAR !NSN 7540-01,280-1500 Szarda'd '-orr'9 298 (Rev 2-89) IC

Approximately 2500 equatorward boundaries of auroral electron precipitation were determined for times when hourly averages of the interplanetary magnetic field and solar wind velocity V were available. The equatorward boundaries were determined from data returned by the SSJ/3 electron detector on board the DMSP/F2 satellite in magnetic local sectors between 0400 and 1100 hours on the morningside of the oval and between 1500 and 2300 hours on the eveningside of the oval. The boundary data were separated into 1‐hour zones in magnetic local time. Within each zone the boundary locations were studied as functions of Bz and Bz², VBz and VBz². Significant results were obtained when the boundaries were correlated with hourly average of Bz and VBz for the hour preceding the one in which the boundary was measured and when the linear regression was performed separately for data points where Bz ≤ 1 nT and Bz > 1 nT. For points where Bz ≤ 1 nT, the correlation with Bz and VBz gave slopes generally between 0.8° and 1.2°/nT and between 1.5° and 2.5°/mV/m, respectively, with correlation coefficients of ∼0.7. The latitudes of the intercepts tend to decrease with increasing local time in the evening sector and with decreasing local time in the morning sector. In the range above 1 nT, the slope of the best fit line for correlation with Bz, and VBz changes sign. Slopes fall in the range −0.1° to −0.4°/nT and 0.21° to 1°/mV/m. Correlation coefficients are typically worse than −0.4. Correlations of the boundary with Bz² and VBz² for both ranges of Bz are uniformly worse than those for Bz and VBz. The trend in slopes and intercepts with magnetic local time for Bz ≤ 1 nT is found to be similar to that previously found for the correlation of the boundaries with Kp (Gussenhoven et al., 1981). In this range of Bz, Kp and VBz are found to be related by the equation Kp=2.01–0.91 VBz (mV/m). From the work of Ejiri et al. (1978) an equation relating the magnetospheric electric potential to VBz is derived. The results are in agreement with the general features of the half‐wave rectifier model of the magnetosphere and measurements of polar cap potential.