Observational evidence indicates that high‐latitude magnetic activity can be causally related to fluctuations and reversals of the equatorial electric field. Using Birkeland currents as the driving forces, we have made numerical calculations of the ionospheric electric fields and currents that distribute globally. Our calculations utilize a fairly realistic empirical ionospheric conductivity model and the field‐aligned current distribution inferred from TRIAD measurements. The results presented here demonstrate that the field‐aligned currents observed during disturbed periods can account for the equatorial fluctuations and reversals in electric field and associated magnetic disturbances noted during such times. In this way, magnetospheric dynamics has a direct and significant influence on the equatorial ionosphere through the ionospheric conductivity.

This review deals with the several energy and momentum theorems that relate to magnetospheric processes that have been developed. The region of primary consideration in this paper is the magnetospheric domain that extends between the ionosphere and the interplanetary medium, although, for studying certain phenomena, ionospheric and solar wind properties are of central importance and must be included. Both energy theorems and momentum theorems with their applications are presented. Since energy is an integral property of the system variables, analytical results can be found without knowledge of detailed dynamical processes. Thus, relations are derived between particle and magnetic system energies, and application is made to the shape of the magnetopause and various phases of a magnetic storm. Particular attention is given to symmetric and asymmetric ring currents, including energy and momentum equilibrium condi. tions; a review of nonlinear self-consistent models and a discussion of how charge exchange and energy diffusion participate in the recovery phase are presented. Comprehensive expressions for the storm time disturbance field are given in terms of both ring current and boundary current energies, and changes that occur during magnetospheric compressions are discussed. The momentum theorems center around the requirement of static force balance during geomagnetically quiet intervals. Whereas the energy theorems give expressions for the average disturbance field over the earth, the momentum theorems give the gradient in the disturbance field across the earth. The forces between earth and the boundary current, the ring current, and the tail current are derived for various models. It is noted that existing vacuum models of the geomagnetic tail are deficient in meeting the combined requirements of energetics and dynamics of the quiet time tail. Introducing the plasma sheet removes the difficulty by allowing an extra degree of freedom in adjusting the force between the earth and the tail. The role of the plasma sheet in making force adjustments is shown to be consistent with the observed thinning of the plasma sheet before substorms.

A study of the relationship between diffuse auroral and plasma sheet electron distributions in the energy range from 50 eV to 20 keV in the midnight region was conducted using data from the P78-1 and SCATHA satellites. From 1« years of data, 14 events were found where the polar-orbiting P78-1 satellite and the near-geosynchronous SCATHA satellite were approximately on the same magnetic field line simultaneously, with SCATHA in the plasma sheet and P78-1 in the diffuse auroral region. For all cases the spe.ctra from the two satellites are in good quantitative agreement. For 13 of the 14 events the pitch angle distribution measured at P78-1 was isotropic for angles mapping into the loss cone at the SCATHA orbit. For one event the P78-1 electron flux decreased with pitch angle toward the field line direction. At SCATHA the distributions outside the loss cone were most commonly butterfly or pancake, although distributions peaked toward the field line were sometimes observed at energies below 1 keV. Electron distributions, as measured where there is isotropy within the loss cone but anisotropy outside the loss cone, are inconsistent with current theories for the scattering of electrons by electrostatic waves. Using P78-1 data to specify the pitch angle distribution in the loss cone for the distribution measured at SCATHA, the electron precipitation lifetimes were calculated for the 14 events. Because the distributions are anisotropic at pitch angles away from the loss cone, the calculated lifetimes significantly exceed the lifetimes in the limit when the flux is isotropic at all pitch angles. The computed precipitation lifetimes are found to be weakly dependent on magnetic activity. The average lifetimes exceed those for the case of isotropy at all pitch angles by a factor between 2 and 3 for Kp -< 2 and approximately 1.5 for Kp > 2. 10,061 10,062 SCHUMAKER ET AL.: DIFFUSE AURORAL AND PLASMA SHEET ELECTRONS " 80000 0 SC5 DAY 180 ELECTRONS TIME 37400.-37600. ß ß ß ß ß ß ß : ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß i 2:0 40 60 80 I00 120 140 PITCH ANGLE ß ß ß _ I•0 180 0 20 L• -z 166 o • 132 o>• J 98 ,,, q 64 x -;• ..• 500 z z 300 o J 11875 ___ > z :c 8750 m 5625 SC5 DAY 180 ELECTRONS TIME 37400.-37600. ß ß ß ß ß ß ß ß ß ß ß ß ß ß , I I I ß ß ß _ ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß i-16000 o • 12000 ! --

The hydrodynamic equations which describe the radial solar wind expansion are linearized and specialized to treat corotating perturbations. Approximate solutions are found which are time stationary in the corotating reference frame. The solutions predict the behavior of corotating structures for a given boundary condition close to the sun. In particular, the structure resulting from the interaction of fast and slow streams is described. Comparison with sector structure data shows reasonable qualitative and quantitative agreement.

In this paper we present and discuss the cryogenic infrared radiance instrumentation for shuttle (CIRRIS) 15-•m CO2 and 5.3-•m NO data with respect to limb emission variability and within the context of latitudinal, diurnal, and geomagnetic variations during two days of observations onboard shuttle flight STS 39, April 29-30, 1991. About 50 limb emission profiles were examined for the two emissions. Enhancements were observed at high latitudes relative to midlatitudes and low latitudes at 140 km altitude for the 15-•m CO2 emission (factor of 2-5). The high-latitude enhancement in the 5.3-•m NO emission was larger (factor of 11-14). The high-latitude nighttime data were collected in the auroral zone during a class III aurora. Diurnal variations are examined at midlatitudes. A significant enhancement in the 15-•m emission was observed between 0500 and 0700 LT at 140 and 160 km. This effect was modeled by the SHARC atmospheric generator (SAG) which uses the mass spectrometer incoherent scatter (MSIS) model. Species concentrations from the thermosphere-ionospheremesosphere electrodynamics general circulation model (TIME-GCM) and SAG models were input to the SHARC radiance code to simulate the CIRRIS limb emission data.The TIME-GCM predicted the 15-btm CIRRIS radiances generally well for 100 km < z < 120 km but for higher altitudes the data was consistently a factor of 2 higher. For the 5.3-•m simulation the TIME-GCM predicted the data well at low latitudes and midlatitudes, but some significant discrepancies were found at higher latitudes. The altitude of the peak radiance of the 5.3-•m NO emission was found to vary between 110 to 135 km with little systematic global pattern. During high-latitude auroral events the peak of the 5.3-•m emission was consistently observed at higher altitudes than the peak of the 3914• N2 + first negative emission, in agreement with previous observations.

The latitude of the equatorward auroral boundary near local midnight has been determined for 162 Defense Meteorological Satellite Program (DMSP) images in November-December 1972. When grouped according to Kp and •IE, these observations show approximate linear decreases in the average boundary latitude with increasing values of these magnetic indices. There appears also to be a slight diurnal variation in the boundary location. Mapping of the appropriate Mcllwain injection boundaries to auroral latitudes shows good agreement with the average DMSP equatorward auroral boundary latitude. Similar analyses at 2000 and 2200 CGLT (corrected geomagnetic local time) rising a different set of DMSP images yield similar results, with somewhat poorer agreement under quiet conditions. 6½ 64 613, ß ß ß ß ß I I ß ß

Using realistic models of the ionospheric conductivity and the field‐aligned currents, we have determined how the distribution of the electric field in the polar cap ionosphere is controlled by the day‐night contrast in conductivity and by the relative strengths of the region 1 and region 2 field‐aligned currents. The sunward directed conductivity gradient acts to set up a space charge in the polar cap which crowds the equipotentials toward the dawn sector for current sources of both region 1 and region 2 polarity; this effectively shifts the polar cap convection pattern toward dawn. Our results show further that for a given conductivity distribution the orientation of the electric field in the central polar cap depends sensitively on the relative strengths of the Birkeland current pairs: for very weak region 2 currents (quiet times) the polar electric field is directed ≈ 60° east of noon, for equal region 1 and 2 currents (disturbed times) the direction is ≈ 10° east of noon, and for stronger region 2 than 1 currents (which may happen on occasion) the electric field points into the prenoon sector. These findings imply that the orientation of the polar cap electric field should serve as a measure or index of the ratio of region 1 to region 2 net current intensity and should possess correlations with geomagnetic activity similar to those of this ratio. This analysis does not include effects of possible source currents in the region of the polar cusp.

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