Portal de Periódicos da CAPES

On the relationship between dynamics of the polar thermosphere and morphology of the aurora: Global‐scale observations from Dynamics Explorers 1 and 2

1988; American Geophysical Union; Volume: 93; Issue: A4 Linguagem: Inglês

10.1029/ja093ia04p02675

2156-2202

T. L. Killeen, J. D. Craven, L. A. Frank, J. ‐J. Ponthieu, N. W. Spencer, R. A. Heelis, L. H. Brace, R. G. Roble, P. B. Hays, G. R. Carignan,

Geomagnetism and Paleomagnetism Studies

Simultaneous measurements of global‐scale auroral luminosity distributions and neutral winds over the northern (winter) polar cap have been obtained using instrumentation on the Dynamics Explorers 1 and 2 spacecraft. Several examples of these simultaneous measurements are presented to illustrate the relationship between the circulation of neutral air in the high‐latitude F region and the spatial distribution of the aurora. The auroral images are obtained using the Spin‐Scan Auroral Imager on the high‐altitude spacecraft (DE 1), and the neutral wind vectors are obtained along the orbit of the low‐altitude spacecraft (DE 2), using the Fabry‐Perot interferometer and the Wind and Temperature Spectrometer. These measurements make it possible to appreciate more fully the pattern of neutral winds when placed in the context of global auroral activity. Supplementary DE 2 measurements of neutral composition, ion densities, and the cross‐track component of the ion drift enable the ion drag force on the neutral gas to be correlated with the aurora. Our initial study of these data indicates (1) that a definite correlation exists between boundaries in the neutral wind field and the location of the auroral oval, with large‐scale features of the neutral circulation tracking the substorm‐dependent expansion and contraction of the auroral oval, (2) that the influence of ion drag from sunward convecting ions can extend to latitudes much lower than those normally associated with the auroral oval, (3) that the sunward neutral flow associated with the auroral oval in the dusk sector is, in general, more pronounced than that associated with the dawn sector and that this asymmetry is ascribed to the different effect of the Coriolis force in the two sectors, (4) that the flow patterns for neutrals and ions within the geomagnetic polar cap are generally asymmetric with respect to the noon‐midnight meridian, an effect considered to be controlled by the orientation of the interplanetary magnetic field, (5) that the region of the polar cusp and the apparent “midday gap,” or reduction in luminosities observed in the VUV wavelength auroral images near local noon, is closely associated with a large, antisunward surge in the neutral wind, and (6) that the morphology of the ion drag force in the polar regions is considerably more complex, even for very quiet geomagnetic conditions, than that computed by the National Center for Atmospheric Research thermospheric general circulation model for the “steady state.” This last result is considered to be a consequence of the short‐term variability in the characteristics of high‐latitude ion convection and, in particular, the motion of convection boundaries with respect to boundaries in the less responsive neutral circulation pattern.