Auroral zone conductances can be estimated from the energy flux and average energy of precipitating electrons. These estimates are based on the assumption that the conductances produced by the electrons are very similar to those produced by electrons with Maxwellian energy distributions having the same energy flux and average energy. There has been some confusion in the application of this method because for a Maxwellian the average energy is twice the characteristic energy or temperature. We present revised expressions that relate height‐integrated Hall and Pedersen conductance to the flux and average energy of a Maxwellian. We show that the accuracy of this method depends on the minimum and maximum energy within which the distribution is integrated to get the energy flux and average energy. We also confirm that the conductances produced by some of the more common auroral spectral distributions are similar to those produced by a Maxwellian with the same average energy and energy flux. The application of these results is demonstrated using precipitating electron measurements made by the Hilat satellite during a pass over Greenland.

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.

The Hardy et al. (1985) global patterns of the integral energy flux and average energy of precipitating auroral electrons are used to determine the global pattern of the electron-produced, height-integrated Hall and Pedersen conductivities. The conductivities were determined in spatial bins in magnetic local time (MLT)-corrected geomagnetic latitude (CGL) coordinates for all MLTs and for CGLs greater than 50 ø and for seven levels of activity as measured by Kp. The conductivities vary smoothly with latitude and MLT typically having a single peak in latitude within the auroral oval at any MLT. On the nightside the two conductivities increase with increasing Kp. The largest conductivities are found near midnight, where the peak value of the Pedersen (Hall) conductivity varies from 3.09 (4.05) mhos to 12.5 (25.9) mhos as Kp varies from 0 to _>6--. The peak conductivity decreases with MLT away from midnight with the lowest peak values found postnoon. At noon and on much of the morning side of the oval the Pedersen and Hall conductivities increase for Kp up to 2 and then decrease for higher Kp. The highest ratios of the Hall to Pedersen conductivity are on the morning side of the oval and at noon. The peak conductivities on the dayside are significant compared to the conductivities produced by solar radiation at all seasons of the year. The global maps of the integral energy flux, integral number flux, and height-integrated Hall and Pedersen conductivities at each level of Kp were fit using both spherical harmonic and Epstein functions. The Epstein functions were found to reproduce better the original maps. At Kp = 2 the distribution of differences between the Epstein function fit and the original data is roughly symmetric about zero with a full width at half maximum of 16 (20)% for the Pedersen (Hall) conductivity and 32 (40)% for the integral energy (number) flux. The distribution of differences broadens with increasing and decreasing activity. This paper is not subject to U.S. copyright. Published in 1987 by the American Geophysical Union. Paper number 6A8888. nates with separations made according to the level of geomagnetic activity as measured by Kp or AE. 12,275 12,276 HARDY ET AL.' AURORAL CONDUCTIVITY AND PRECIPITATION PATTERNS terns of Hardy et al. [1985] to derive the global Hall and Pedersen conductivities following the same procedures as Spiro et al. [1982]. These patterns, along with those of the integral number flux and integral energy flux of the electrons, are then fit to simple functional forms. The chief advantage of the present analysis over that in earlier work is that a larger data set was available to determine the precipitating electron distribution which allowed a finer binning in magnetic local time and activity and a more accurate determination of the necessary mean values. This paper is divided into five sections.In section 2 we discuss the methods for calculating the conductivities. In section 3 we present the global conductivity maps. Section 4 describes the fitting technique and the resul...

The average global characteristics of precipitating auroral ions were determined using the data from the SSJ/4 detectors on the F6 and F7 satellites of the Defense Meteorological Satellite Program (DMSP). For this study the high‐latitude region was divided into spatial elements in magnetic local time (MLT) and corrected geomagnetic latitude (CGL). One such spatial matrix was created for each of seven levels of magnetic activity as defined by Kp. Approximately 26.5 million, individual, 1‐s spectra were used to determine the average ion spectrum over the energy range from 30 eV to 30 keV in each spatial zone and at each level of activity. Where appropriate, the spectra were extrapolated to 100 keV to provide a more complete estimate of the total integral energy flux, number flux, and average energy. The global patterns of the integral energy flux, integral number flux, and average energy derived from the average spectra vary smoothly with latitude, MLT, and activity. For a given Kp value the higher levels of integral energy flux occur in C‐shaped regions symmetric about a meridian running prenoon to premidnight. The maximum integral energy flux is found premidnight; the minimum peak integral energy flux in latitude is found prenoon. Except in the prenoon region, the overall level of integral energy flux increases with Kp with the premidnight maximum increasing by a factor of 6.1 from Kp = 0 to Kp ≥ 6−. The maximum integral number flux is centered at noon and is taken to be the center of the cusp. The maximum value does not vary significantly with activity, although its location moves to lower latitude with increasing Kp. A minimum in the average energy also occurs in the noon meridian, several degrees poleward of the integral number flux maximum. The separation in latitude between the integral flux maximum and the average energy minimum of the cusp increases with Kp. The maximum average energy occurs on the eveningside of the oval near the equatorward boundary of the ion precipitation and shifts toward noon with increasing activity. The average integral number flux for the precipitating auroral ions is 1‐2 orders of magnitude less than that for the precipitating auroral electrons at all latitudes, MLTs, and activities. The integral energy flux of the ions, on the eveningside of the oval, can equal or exceed that for the electrons near the equatorward edge of the auroral region. Integrated globally, the ratio of the ion to electron number flux varies from 0.024 to 0.015 over the range of activity from Kp = 0 to Kp ≥ 6−. The ratio for the integral energy flux ranges from 0.11 to 0.17 with no trend in activity.

The geosynchronous ATS 6 environmental measurements experiment was operated during 15 evening passes when the SCATHA spacecraft was within 1-2 RE and both spacecraft were very near the geomagnetic equator. Numerous, well-defined substorm injections were recorded at both spacecraft with varying local time and radial separations. Accurate delay timing was possible since these events exhibit abrupt and essentially dispersionless (to within 10 s) plasma flux changes which replace cool preexisting plasma with hot quasi-Maxwellian distributions. The hot plasma propagates earthward in close association with an equally abrupt magnetic field increase at velocities in the range of 10-100 km/s. On this basis we identify the agent of injection as the induced electric field of the earthward propagating compression wave observed by Russell and McPherron (1973), and we refer to the propagating particle structure as the injection front. These dramatic synchronous orbit electron injection signatures are produced mainly by a boundary motion rather than by local acceleration of plasma. However, we find some evidence that the plasma sheet electrons are weakly 'heated' by the passage of each compression wave, the energy appearing mainly in the high-energy tail of the distribution. The spectral change we observe argues convincingly that the boundary in question is a precipitation-flow boundary layer (Kennel, 1969) and that the near-earth plasma sheet is significantly degraded in average energy by the addition of ionospheric plasma, especially secondary electrons emitted by the ionosphere due to precipitating energetic electrons. The presence of significant •B/•t requires that a change of mapping occur between the equatorial plane and the ionosphere, the sense being such as to map the inward moving injection front to a relatively fixed latitude in the ionosphere. Such an earthward plasma injection would not therefore require equatorward auroral motion. tionary orbit can be reproduced equally well by an injection boundary model, or a model with varying convection electric field, or a hybrid model with spatially limited time-varying electric and magnetic fields [Kivelson et al., 1980, and refer-Copyright ¸ 1981 by the American Geophysical Union. Paper number IA0733. 0148-0227/81/00 IA-0733501.00 • ences therein]. This situation illustrates the nonuniqueness of conclusions drawn from a single-satellite data set and the need for multiple-satellite observations to constrain the modeling process. This paper is an attempt to learn from the comparison of plasma data sets from ATS 6 and SCATHA relating to several substorm events. An example of the success of the first point of view appears in the paper by Barfield et al. [1977], in which an impulsive injection of plasma is observed at ATS 5 and then 11 rain later at Explorer 45, 1.2 RE earthward and at approximately the same local time. Assuming that an energetic plasma was created and released beyond a sharp, azimuthally extended boundary outside synchronous orbit, the authors were able to bui...