Statistical study of the proton isotropy boundary

• Main Authors: E. A. Lvova, V. A. Sergeev, G. R. Bagautdinova
• Format: Article
• Language: English
• Published: Copernicus Publications 2005-06-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/23/1311/2005/angeo-23-1311-2005.pdf

Based on a large data set of polar NOAA-type satellite observations we studied the latitude-MLT shape of the 80keV proton isotropy boundary (IB) as a function of the solar wind parameters and magnetic activity. Using "snapshots" of isotropy boundaries near-simultaneously crossed at four points we found that its equatorward expansion, as well as its dawn-dusk shift, depends mostly on the <i>AE</i>-index and on the corrected <i>D_st</i>*, whereas the amplitude of the IB daily variation is mostly controlled by the solar wind dynamic pressure. Applying a nonlinear, multi-parametric, least-square regression procedure, the empirical relationship describing the IB latitude as a function of MLT and <i>AE</i>, Pd, <i>D_st</i>* parameters was obtained. Comparing it with the predictions from the Tsyganenko-2001 model we found a good agreement during the quiet time but some important differences during the disturbed periods. Interpretation of these results in terms of the properties of the magnetospheric configuration is briefly discussed.