[1] We have developed an auroral precipitation model which separately categorizes the discrete aurora and both the electron and ion diffuse aurora. The discrete aurora includes acceleration by two distinct physical mechanisms, namely, quasi-static electric fields, producing monoenergetic peaks, and dispersive Alfvén waves, producing broadband electron acceleration. The new model is not merely finer in magnetic latitude (MLAT) and magnetic local time (MLT) resolution than previous models but is parameterized by solar wind driving instead of Kp and is based on functional fits to the solar wind coupling function which best predicts auroral power. Each of the four auroral types in each MLAT and MLT bin is separately fitted, a departure from the traditional compilation of a handful of discrete models, each assigned to represent a Kp (or other activity index) range. The variation of any of these four types of aurora at any local time can be predicted on the basis of the specific solar wind history of an epoch. This approach permits perhaps the first comprehensive comparison of the hemispheric contribution of each type of aurora. It turns out that the diffuse aurora is surprisingly dominant, constituting 84% of the energy flux into the ionosphere during conditions of low solar wind driving (63% electrons, 21% ions). The diffuse aurora is far from quiescent, tripling in power dissipation from our low to high solar wind-driving conditions. Even under the latter condition, the diffuse aurora contains 71% of the hemispheric energy flux (57% electrons, 14% ions). The monoenergetic aurora contributes more energy flux (10% quiet, 15% active) than does broadband acceleration signatures (6% quiet, 13% active). However, the broadband aurora rises fastest with activity, increasing by a factor of 8.0 from low to high driving. Moreover, this most dynamic auroral type contributes very high number fluxes, even exceeding monoenergetic aurora under active conditions (28% of hemispheric precipitation versus 21%). Thus, dynamic ionospheric heating and ion outflow is likely heavily affected by the wave aurora. Although energy flux peaks on the nightside, number flux peaks on the dayside. The cusp, as previously reported, is much better defined by ions than electrons. Hence, the ion number flux peak is confined, corresponding to the cusp, while the region with high electron number flux is broad (a cleft, corresponding to the boundary layers, including the closed low-latitude boundary layer).

Studying magnetically conjugate phenomena at very high latitudes requires a magnetic coordinate system that is smooth and well defined at the geographic poles. In addition, it should provide for accurate comparisons at different altitudes. In this report we present a variation on the corrected geomagnetic coordinate system that is well defined and smooth over the entire globe. It provides an analytic expression relating geographic coordinates, including altitude, to the magnetic coordinates. The coordinate system is produced by tracing magnetic field lines using the IGRF85 reference magnetic field model with time derivatives updating the model to 1988. An expansion of the relationship in terms of spherical harmonics has been determined, which then provides the required well‐defined and smooth relationship over the entire globe. Independent expansions for different altitudes show a smooth functional relationship of the coefficients of the expansion with altitude, and therefore simple interpolation schemes can be used to provide an appropriate expansion at any altitude between 0 km and approximately 600 km. By reversing the process, the inverse expansions relating the magnetic coordinates to geographic coordinates have also been determined. The effects of the seasonal variation in the Sun's declination along with the variation in the Sun's apparent position due to the eccentricity of the Earth's orbit result in a variation of nearly 1 hour of magnetic local time for a fixed UT over the course of a year. In many applications this variation may be important and should be included when presenting data in terms of magnetic latitude and MLT.

[1] The only previously established seasonal auroral variation is that of intense monoenergetic aurora, corresponding to quasi-static acceleration by geomagnetic-fieldaligned electric fields. Here we investigate the separate seasonal dependence of both types of electron accelerated aurora (broadband, or wave, in addition to monoenergetic) and both ion and electron diffuse aurora. Dayside and nightside variations are separately considered, as are conditions of low and high solar wind driving. Across these many combinations, several clear patterns emerge. One is that the dayside tends to maximize precipitation in the summer and much more so for low solar wind driving. Nightside precipitation is higher in the winter and much more so for high solar wind driving. The dayside effects are strongest in number flux and stronger in diffuse aurora than accelerated aurora. The ease of ion entry through the summer cusp, along with the constraints of charge quasi-neutrality, and the rise in dayside currents in the summer hemisphere adequately explain much (perhaps all) of the dayside behavior. Nightside effects are more apparent in energy flux, with the winter/summer ratio of monoenergetic aurora being the largest: 1.70 for high solar wind driving. However, both other types of electron aurora, diffuse (1.30) and broadband (1.26), also have winter/summer energy fluxes well above unity for high solar wind driving. The nightside seasonal variation of ions is much smaller, with slightly more energy flux postmidnight in the winter but with slightly higher energy fluxes premidnight in the summer. Since the increased nightside fluxes into the winter hemisphere occur primarily under strong solar wind driving, and are much more prominent in energy flux than number flux, they likely reflect increased energization in the winter ionosphere when stronger currents are being driven into the ionosphere from the magnetosphere. Equinoctial behavior tends to lie between the summer and winter hemisphere values, but typically closer to the latter. As a result, nightside electron energy flux summed over the hemispheres is higher around equinox, simply because there is no summer hemisphere.

Abstract. A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirety, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and Fll satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, w.idens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X < --10 to -12 Roe, depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

[1] During periods of northward IMF, plasma sheet ions often have two components: hot (magnetospheric origin) and cold (magnetosheath origin). The temperatures of the cold-component ions are $30-40% higher in the dawn sector compared to the dusk sector, implying the dawnside magnetosheath ion heating of $30-40%. As a result, the magnetosheath ions are less distinguishable from the hot-component ions, which have lower temperatures on the dawnside, leading to a higher occurrence of the ions having (apparent) one-component distribution. As the duration of the hourly averaged IMF being northward (Dt) increases from 1 to 10 hours, the occurrence of two-component ions increases from 65% to 83% in the dusk flank, but in the dawn flank it remains relatively stable at around 45%. In contrast, the occurrence of ions best characterized by kappa (k) distribution increases from 25% to 35% in the dawn flank whereas in the dusk flank it remains relatively insensitive to Dt (10%). The occurrence of a one-component Maxwellian distribution appears to be most pronounced in the region of the plasma sheet close to the midnight meridian, and these ions appear to be characteristic of the nominal plasma sheet (hot component) ions. The densification of the plasma sheet, as Dt increases, mainly results from the influx of the magnetosheath ions. However, the cooling of the plasma sheet ions can be attributed not only to the influx of the cold magnetosheath ions but also to the cooling of the nominal plasma sheet ions. The dawn-dusk asymmetries observed in the cold magnetosheath ion profiles should provide constraints that can help determine the roles of various proposed magnetosheath ion entry mechanisms.Citation: Wing, S., J. R. Johnson, P. T. Newell, and C.-I. Meng (2005), Dawn-dusk asymmetries, ion spectra, and sources in the northward interplanetary magnetic field plasma sheet,