Latitudinal distribution of nighttime auroral precipitation during magnetic calm and near the time of substorm onset

The unresolved problems of the physics of auroral substorms include the issue of localization and the mechanism of the start of the substorm expansion phase. The new information needed to solve this problem can be obtained by comparing the results of observations from low-altitude spacecraft with observations in the equatorial plane of the magnetosphere. For this purpose, the morphological projection method was used, which does not require knowledge about the configuration of the magnetic field. This paper considers the latitudinal profiles of the auroral precipitation characteristics at ionospheric altitudes obtained from DMSP F7 spacecraft observations and the radial distribution of ion pressure in the equatorial plane according to the THEMIS mission during periods of magnetic calm and at time intervals close to the auroral breakup. Special attention was paid to the position of the maximum energy flux of the precipitation of ions with energy larger than 3 keV and ion pressure profiles. The average ion pressure latitudinal profiles at low altitudes were determined and compared with the average pressure distributions in the equatorial plane of the magnetosphere under similar to averaged values of solar wind and geomagnetic activity parameters. It is shown that, if under geomagnetic calm the pressure maximum at low altitudes is mapped to geocentric distances of ~7−8 Re, before the substorm onset it is mapped to a distance of ~5−6 Re. The averaged values of the pressure maxima during the magnetic calm, as well as before and after substorm onset were obtained. The brightness of the auroral luminosity in the 557.7 nm emission was estimated from DMSP F7 observations of the average energy and energy flux of the precipitated electrons.