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.

No abstract

The great spatial and temporal variability of auroral ionospheric conductivity significantly influences the ionospheric closure path for high-latitude, field-aligned currents. Because these closure paths can extend to low latitudes, changes in auroral zone conductivity can influence the global electric field distribution. In this paper, synoptic Chatanika radar observations of auroral zone conductivity that cover -•62 ø to 68 ø geomagnetic latitude are presented. They are representative of quiet winter, active winter, and equinoctial conditions. During the daytime the solar contribution to the height-integrated conductivity is well represented by •p,. -• (5, 10) cosl/•(X ), where X is the solar zenith angle. The nighttime, height-integrated Pedersen and Hall conductivities (•p and •Vl) in the electron density trough are, at times, below our detection threshold of-•0.5 mho. Following magnetic substorm onset, enhanced conductivity regions move southward and intensify. As the recovery phase begins, the conductivity pattern recedes northward and diminishes. The onset and cessation of precipitation associated with these events can be as abrupt as a few minutes. In one example the behavior of •p and 5•. are examined in the vicinity of the Harang discontinuity, which was quite sharp (•< 30 min) in local time. At the Harang discontinuity on that day, the ratio of •Vl to •p decreased, indicating a softening of the precipitating energy distribution. INTRODUCTION Our understanding of the large-scale current systems of the magnetosphere and ionosphere has evolved greatly in recent years, largely as a result of the growing number of in situ and ground-based measurements of high-latitude phenomena. (Recent reviews of this subject include: Kamide [1979]; Potemra [1979]; Stern [1979]; and Swift [1979]). The general morphology (at least during magnetically quiet times) of auroral zone electrodynamics is emerging. For example, large-scale electric field measurements from satellites [Cauffman and Gurnett, 1971; Heppner, 1977], balloons [Mozer and Lucht, 1974], and radars [Rino et al., 1974; Banks and Doupnik, 1975; Tsunoda, 1975; Greenwald, 1977; Evans et al., 1980] are generally consistent with a two-celled magnetospheric convection pattern such as Axford and Hines [1961] originally proposed. Also, it is well established that field-aligned, or Birkeland, currents are a permanent feature of the high-latitude ionosphere-magnetosphere system [Zrnuda and Armstrong, 1974; Iijima and Potemra, 1976a, b]. Recent evidence indicates that the magnetospheric circuit is coupled to the ionosphere not only at high latitudes but globally as well. Observational evidence has directly linked ionospheric electric field perturbations at the equator with highlatitude disturbances [Gonzales et al., 1979; Gonzales, 1979; Kelley et al., 1979]. Attempts in modeling the global ionospheric circuit combine the statistical distribution of field-aligned currents, observed by the Triad satellite [Iijima and Potemra, 1976a, b; 1978], with a global conductivity mo...

Electron density measurements made by the Chatanika radar during times when auroral particle precipitation was absent have been used to determine the variation of E region ionization and heightintegrated ionospheric conductivity as a function of solar zenith angle and solar flux. From the Chatanika radar data taken over an entire solar cycle we habe derived the electron density as a function of aliitude between 90 and 250 km for five solar zenith angles between 45 ø and 85 ø and for four different levels of solar flux. From 16 to 40 profiles were averaged together to determine the mean values; typically, the standard deviations were less than 25% of the mean. The height-integrated conductivities computed from these profiles increase by about a factor of 2 between the lowest and highest levels of solar flux. The solar contribution to the Hall and Pedersen conductances Y'n and Y.p is well represented by Y'n = 1.5 (Sa cox ;00'5 -1.7 Zp, where Z is the solar zenith angle and Sa is the 10.7-cm solar flux. In order to determine the total conductance when other ionization sources are present the altitudedependent production rate is required. This was computed from the data by using an altitude-dependent model for the effective recombination coefficient.

Eight days of synoptic data from the Chatanika incoherent scatter radar have been analyzed in an attempt to determine the characteristic morphology of auroral zone energy deposition by Joule heating and precipitating particles. The observations cover invariant latitudes between -62 ø and 68 ø. The composite spatial morphology derived from these eight days of data shows that morning sector particle precipitation deposits energy into the thermosphere at a faster rate and at lower altitudes than evening sector precipitation. The Joule heating rate has the opposite asymmetry about midnight, i.e., more Joule heating results for a given premidnight eastward electrojet current than for the same morning sector westward electrojet current intensity. This complementary asymmetry about midnight between the Joule and particle precipitation heating rates is consistent with the changes in ionospheric conductivity implied by the local time variation of precipitating particle hardness. The Joule heating rate generally dominates particle energy deposition in the premidnight sector. However, the daily averages of the two energy sources are roughly equal.