THE STUDY WILL USE MMS/HPCA DATA TO MEASURE THE PLASMA SHEET DENSITY AND COMPOSITION AND WIND/SWE DATA AND ACE/SWEPAM DATA TO MEASURE THE HE++ AND H+ DENSITIES AND THEIR RATIO IN THE SOLAR WIND. THE RESEARCH WILL USE A COMBINATION OF CASE STUDIES AND STATISTICAL STUDIES. FOR THE CASE STUDIES, TIME PERIODS WHEN THERE ARE SHARP CHANGES IN SOLAR WIND PARAMETERS AND MMS IS IN THE PLASMA SHEET WILL BE IDENTIFIED. THE TIME LAG BETWEEN THE CHANGES OBSERVED IN THE SOLAR WIND AND THE CHANGES IN THE PLASMA SHEET AT DIFFERENT LOCATIONS WILL BE USED TO ASSESS THE TIME FOR TRANSPORT. FOR THE STATISTICAL STUDY, WE WILL CREATE A DATABASE OF H+, HE++ AND O + DENSITIES IN THE PLASMA SHEET, AVERAGED OVER 5 MINUTES TO OBTAIN ADEQUATE STATISTICS TO ALLOW CORRECTIONS TO THE MINOR SPECIES DENSITIES CAUSED BY ON-BOARD COMPRESSION. CORRELATIONS BETWEEN THE HE++/H+ RATIO IN THE PLASMA SHEET AND IN THE SOLAR WIND UNDER VARIOUS SOLAR WIND AND IMF CONDITIONS USING DIFFERENT TIME LAGS WILL BE USED TO DETERMINE THE PATHWAYS AND TIME SCALES FOR SOLAR WIND ENTRY. COMPARISONS WILL BE MADE AT DIFFERENT LOCATIONS IN THE PLASMA SHEET TO IDENTIFY THE LIKELY LOCATIONS OF ENTRY, AND THE INTERPLAY BETWEEN THE SOLAR WIND AND IONOSPHERIC SOURCES.