SUB-KILOMETER THERMAL PLASMA STRUCTURE NEAR 1750-KM ALTITUDE IN THE POLAR CUSP CLEFT

We present Freja Cold Plasma Analyzer (CPA) measurements from an encou nter with the low altitude (approximately 1750 km) polar cusp during w hich the CPA measured 2-D images of the thermal (0-16 eV) particle dis tributions at 1.2 s time resolution, and simultaneously made rapid est imates (600/s) of integrated thermal particle flux into the instrument . The high resolution data show bursty ion flux enhancements of the or der of tens of percent on time scales of tens of ms, or alternatively, hundreds of m spatial scales. The flux of electrons from 0-16 eV also varied by tens of percent and on temporal/spatial scales comparable t o those in the ion cases. There is some evidence that the thermal part icle flux variations are associated with intense low-frequency electro magnetic fluctuations with temporal/spatial scales identical to those seen by the CPA (tens of ms, hundreds of m).