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Electrostatic probe measurements of electron concentration Ne from the TIROS 7 satellite are the basis for a study of the global response of the topside ionosphere (640 km) to magnetic disturbances at solar minimum. The quiet‐time behavior of Ne shows many of the features previously evident in Explorer 22 measurements at 1000 km. These are the daytime equatorial maximum, the nighttime midlatitude maximums, and the main trough at the boundary of the polar region. The storm‐time response of the ionosphere at 640 km takes the form of strong Ne enhancements at middle and high latitudes on the dayside and smaller enhancements on the nightside. This enhancement is in contrast to present thinking, which is based on bottomside sounding and total content measurements. At the equator, the storms produce depressions of Ne on the dayside and enhancements on the nightside. Measurements of Ne and electron temperature Te from Explorer 22 show similar but smaller Ne enhancements during storms, accompanied by slight decreases in Te, except in the polar regions where both Ne and Te are increased. It is concluded that the storm‐time enhancements of Ne may be explained in terms of the observed thermal expansion of the neutral atmosphere that lifts the entire ionosphere, thereby increasing Ne at the fixed altitude of the observations. The different behavior of the equatorial Ne is consistent with electrodynamic drift theory. The storm‐time increase of Te in the polar region may result from additional heating, while the decrease of Te at all other latitudes is caused by both increased collisional cooling to the expanded neutral atmosphere and by a decrease in the escape flux of photoelectrons which heat the upper F region.

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Intercomparison measurements of the major ionospheric parameters of ion and electron density and temperature and ionic species made by direct measurement probes on the Explorer XXXl satellite are presented. Plasma density results are compared with simultaneous data from the Alouette II satellite. Probe results are from the following experiments: planar ion trap, planar electron trap, cylindrical electrostatic probes, high resolution magnetic ion mass spectrometer, planar Langmuir plate, and spherical ion probe.The plasma densities measured by the various probes generally agree with simultaneous Alouette II sounder values to within 20 percent. Electron temperatures measured by three different types of probes generalty agree within 10 percent. Ion composition measurements by the planar ion trap and spherical probe show good agreement with the high resolution magnetic mass spectrometer. Ion temperature measurements from the ion trap are consistently higher than spherical ion probe results.

Satellite electron temperature and density data are used to calculate the structure of several stable auroral red arcs (SAR arcs) according to the thermal conduction model of the arc. The calculated λ6300 emission rates are compared with ground‐based photometric observations taken at the same time and in the vicinity of the satellite crossings of the arcs. The SAR arcs analyzed include a range of λ6300 intensities, geographical locations, and times during the associated geomagnetic storm. In addition, satellite data were obtained at different altitudes over and within the SAR‐arc region. Enhanced electron temperatures within or on the equatorward edge of an electron‐density depression are common features of all the SAR arcs examined. There is general agreement between the calculated and observed X6300 emission features for SAR arcs observed during the geomagnetic storm periods of October 29 to November 2, 1968, May 14–15, 1969, and March 8–9, 1970. For these SAR arcs, thermal conduction from the magnetosphere alone is sufficient to excite the λ6300 emission to its observed intensity.