CHARACTERIZING THE STATE OF THE MAGNETOSPHERE - TESTING THE ION PRECIPITATION MAXIMA LATITUDE (B2I) AND THE ION ISOTROPY BOUNDARY

Recently, efforts to characterize and monitor the state of the magneto sphere have intensified, along with the rising interest in space weath er. The latitude of the ion energy flux precipitation maxima (''b2i'') , which almost invariably occurs near the equatorward edge of the nigh tside main auroral oval, has been suggested as one such parameterizati on. It has been suggested that b2i corresponds to the ion isotropy bou ndary (IB), which has been independently researched as a measure of th e extent to which the magnetotail is stretched. By comparing simultane ous observations by the Defense Meteorological Satellite Program (DMSP ) and NOAA spacecraft, we confirm a close association between b2i and the isotropy boundary of 30 keV protons. Using 2.5 years of simultaneo us data from DMSP and GOES spacecraft, we verified that magnetic field inclination (the extent to which the magnetotail is stretched) strong ly controls the b2i/IB latitude. Based on use of the b2i latitude, cor rected for local time variation, as an index of magnetic stretching in the tail to show a considerable dawn-dusk asymmetry, we find that the magnetic field is more depressed and stretched at dusk than at dawn, and asymmetry increases with increasing magnetotail stretching. This a symmetry is consistent with the rotation of the symmetry line of the b 2i(MLT) curve toward premidnight hours and suggests the growth of a so -called ''partial ring current'' system with increasing activity. Fina lly, the utility of the b2i/IB boundary as a characterization of the s tate of the magnetosphere is shown by demonstrating that the average p ressure in the magnetotail is better specified by b2i than by Kp.