Abstract
Abstract. DMSP F7 spacecraft observations for the whole of 1986 were used to construct the empirical model of the midnight auroral precipitation during a substorm. The model includes the dynamics of different auroral precipitation boundaries and simultaneous changes in average electron precipitation energy and energy flux in different precipitation regions during all substorm phases, as well as the IMF and solar wind plasma signatures during a substorm. The analysis of the model shows a few important features of precipitation. (1) During the magnetic quietness and just before the beginning of the substorm expansive phase the latitudinal width of the auroral precipitation in the nightside sector is about 5 – 6° CGL, while that of the auroral oval is about 2 – 3° CGL during such periods. (2) For about 5 min before the substorm onset a decrease in the average precipitating electron energy in the equatorward part of auroral zone was observed simultaneously, with an increase in both the average electron energy and energy flux of electron precipitation in the poleward part of the auroral zone. (3) The isotropy boundary position in the beginning of the substorm expansive phase coincides well with the inner edge of the central plasma sheet. The analysis of interplanetary medium parameters shows that, on average, during the substorm development, the solar wind dynamic pressure was about 1.5 times that of the magnetic quietness period. Substorms occurred predominantly during the southward IMF orientation, suggesting that substorm onset often was not associated with the northern turn or decrease in the southward interplanetary Bz . The Northern Hemisphere’s substorms occurred generally during the positive interplanetary By in winter, and they were observed when the interplanetary By was negative in summer.Key words. Ionosphere (auroral ionosphere; particle precipitation) – Magnetospheric physics (storm and substorm; magnetosphere-ionosphere interaction)
Highlights
DMSP satellites database for the whole of 1986 was created to investigate different types of auroral precipitation features
Substorms occurred predominantly during the southward IMF orientation, suggesting that substorm onset often was not associated with the northern turn or decrease in the southward interplanetary Bz
Sotirelis and Newell (2000) published the boundaryoriented model of the global configuration of electrons precipitating into the polar ionosphere based on DMSP spacecraft observations
Summary
DMSP satellites database for the whole of 1986 was created to investigate different types of auroral precipitation features. Our database is based on more modest statistics (1 year of observations), but it has an advantage in that it contains, in addition to different auroral precipitation boundary co-ordinates, additional information including interplanetary medium conditions, magnetic activity indices and magnetospheric substorm phases. Each of the 1, 2 and 3 phases was divided into three equal temporary intervals, corresponding to the initial, middle and final stage of each substorm phase (subphases) Such detailed separation allows one to obtain three experimental statistical points for each phase and to investigate the precipitation boundary dynamics and auroral electron characteristics during the magnetospheric substorm development, in detail. Just before the beginning of the substorm expansive phase, the energy flux in all regions remained about constant with the exception of the b4s–b5 region, where the flux increase of about 1.5 times was registered
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