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A statistical study on the effects of IMF B z and solar wind speed on auroral ion and electron precipitation

1991; American Geophysical Union; Volume: 96; Issue: A4 Linguagem: Inglês

10.1029/91ja00157

2156-2202

D. H. Brautigam, M. S. Gussenhoven, D. A. Hardy,

Atmospheric Ozone and Climate

The variation in the average particle number and energy flux in the high‐latitude region is determined as a function of the solar wind velocity, V sw , and the z component of the interplanetary magnetic field, B z . The study is made using the data from the SSJ/4 detectors on the satellites of the Defense Meteorological Satellite Program. In the study the high‐latitude region is divided into spatial elements in magnetic local time and corrected geomagnetic latitude. One such matrix of spatial divisions is constructed for each of 30 paired ranges of values in V sw and B z . There are six divisions in B z covering the range from −10 to +10 nT and five divisions in velocity covering the range from 200 to 800 km/s. Using approximately 34 million SSJ/4 spectra, the average electron and ion spectra are determined in each spatial element for each of the 30 paired values of V sw and B z . From the average spectra, the average integral energy and number fluxes for electrons and ions are calculated in each spatial bin. These values are then spatially integrated to give the average hemispheric inputs of the integral particle energy and number flux. Both quantities are found to vary in a simple and consistent manner with both V sw and B z . For both electrons and ions the variation with B z tends to a minimum value for weak to moderately strong B z positive. For decreasing values of B z from the minimum, both quantities increase at a rate greater than linear. For increasing values of B z from the minimum, both quantities tend to increase, least for the hemispheric electron energy flux and most for the hemispheric ion number flux. The variation in both quantities with V sw for both electrons and ions is generally linear with the steepest slopes for the electron hemispheric energy flux. The variation with B z and V sw for all four quantities can be well fit by a simple quadratic equation either of the form ƒ( B z , V sw ) = a ( B z − b )² + cV sw + d or ƒ( B z , V sw ) = [ a ( B z − b)² + 1][ cV sw + d ]. Either form indicates that the variation is no greater than quadratic in B z and no more than linear in V sw and that the variation is approximately symmetric for values above and below the minimum value of B z , namely, b . This result is significantly different than either the half‐wave rectifier or epsilon function for describing the solar‐wind magnetospheric interaction.