Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems often to be related to a northward turning of the interplanetary magnetic field.
Further evidence is presented that structured soft‐electron precipitation is an important source of large‐scale (λ ≳ 10 km ) F region ionization irregularities in the high‐latitude ionosphere. We show that large amplitude, 20‐km to 80‐km structured plasma exists in both the dayside and nightside auroral oval. In the latter case, the structured F layer plasma has been observed to convect into and through the field of view of the Chatanika radar. Here, and in a companion paper, we hypothesize that this soft electron precipitation is the primary source of high‐latitude structure and that convection acts to distribute the irregular plasma throughout the polar ionosphere. Indeed, at the observed production scale (20–80 km), irregularities can easily convect throughout the high‐latitude region with negligible decay from classical or anomalous diffusion, including the effects of a conducting E region. Our convection/decay model also explains the following observed features of published high‐latitude irregularity data: (1) The steep gradient in irregularity intensity at the equatorward edge of the nighttime magnetospheric convection zone. (2) The existence of irregularities throughout the polar cap. (3) The reduction of irregularity intensity in the central polar cap. (4) The dawn‐dusk asymmetry in the equatorward boundary of the high‐latitude irregularity zone. On the other hand, if classical theory is applied to a 100‐m scale structure, diffusion should rapidly limit the irregularities to an area within a few degrees of the production zone, a prediction not upheld by experimental data. Thus, plasma instabilities must operate on the large‐scale structures to produce the observed intermediate scale (100 m < λ < 10 km) power law irregularity spectra. Calculations of the instability growth rate in its generalized form, which includes field‐aligned currents (the current convective instability), shows that growth should occur. The universal drift instability should then operate on these intermediate scale features. We suggest that this latter instability maintains the shorter scale plasma structure at the expense of a more rapid decay of the intermediate scale irregularities in a cascade‐like process. Enhanced, turbulent diffusion can reduce significantly the lifetime of the intermediate scale irregularities but not of the larger structures, which can therefore still transit the polar cap.
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...
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.
The first satellite observations of the total field‐aligned component of the quasi‐dc Poynting flux are presented for two passes over the polar region, one in the noon sector and one in the afternoon. The energy input due to electron precipitation is also presented. In the noon pass the downward Poynting flux in the auroral oval was comparable to the kinetic energy input rate. The peak electromagnetic energy input rate of 6 ergs/(cm² s) equaled the peak particle input while the integrated electromagnetic value along the trajectory was 60% that of the particles. In the afternoon pass the peak electromagnetic energy input was also about 6 ergs/(cm² s), but the peak particle energy was 6 times this value. The average electromagnetic input was 10% of the particle input for the pass. In this study we can measure the Poynting flux only over a limited range of scale sizes; thus the contribution to the total energy budget in the polar cap cannot be determined. Both passes show small regions characterized by upward Poynting flux suggesting a neutral wind dynamo. There is also evidence during part of the noontime pass that the external generator acted in opposition to an existing wind field since the Poynting flux was greater than the estimate of Joule heating from the electric field measurement alone (i.e., from ΣpE²). In the course of deriving Poynting's theorem for the geophysical case we also present a proof that ground magnetometer systems respond primarily to the Hall current which does not depend upon geometric cancellation between the field generated by Pedersen and field‐aligned currents.
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