CORE ION FLUX BURSTS WITHIN SOLITARY KINETIC ALFVEN WAVES

The Freja cold plasma analyzer (CPA) makes high time resolution measur ements of the angle-and energy-integrated core ion velocity distributi on (< 20 eV) with spatial resolutions of similar to 10 m. In a prelimi nary study, Knudsen et al. [1994] reported that in the most intense co re ion heating regions, integral ion flux becomes bursty on timescales of tens of milliseconds, implying spatial scales of hundreds of meter s. The present study demonstrates that these flux bursts are associate d with solitary kinetic Alfven waves (SKAW), and we show examples of a one-to-one correspondence between SKAW and ion flux bursts. In princi ple, the measured flux bursts can result from variations in ion temper ature, drift, density, composition, or changes in the functional form of the velocity distribution (e.g., Maxwellian versus conical), or som e combination thereof. By modeling the dependence of integral flux on various combinations of these parameters, we calculate the amount of v ariation needed to explain ion flux bursts, which can have amplitudes in excess of 10(9) cm(-2) s(-1). This value is comparable in magnitude to the ram flux of cold ions in a 10(3) cm(-3) plasma and is also com parable to the peak ion flux in ion outflow regions measured on previo us spacecraft missions. In most cases, flux bursts can be explained ei ther by localized heating to several eV or by bulk drifts of the order of 1-2 km/s; however, it is not possible to distinguish between these two possibilities from the CPA data alone. Plasma wave data show that SKAW are associated with broadband ELF waves extending from de up to and beyond the proton cyclotron frequency f(H+). Wave power above f(H) and below the oxygen cyclotron frequency f(O+) is localized within S KAW and could in principle lead to localized ion heating. The region o f the spectrum between f(H+) and f(O+) appears less localized and coul d produce a more uniform background of heated ions, depending on the r elative contributions to total heating of the different spectral regim es.