Core ion flux bursts within solitary kinetic Alfven waves

The Freja cold plasma analyzer (CPA) makes high time resolution measurements of the angle-and energy-integrated core ion velocity distribution (< 20 eV) with spatial resolutions of similar to 10 m. In a preliminary study, Knudsen et al. [1994] reported that in the most intense core ion heating regions, integral ion flux becomes bursty on timescales of tens of milliseconds, implying spatial scales of hundreds of meters. The present study demonstrates that these flux bursts are associated with solitary kinetic Alfven waves (SKAW), and we show examples of a one-to-one correspondence between SKAW and ion flux bursts. In principle, the measured flux bursts can result from variations in ion temperature, drift, density, composition, or changes in the functional form of the velocity distribution (e.g., Maxwellian versus conical), or some combination thereof. By modeling the dependence of integral flux on various combinations of these parameters, we calculate the amount of variation 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 comparable to the peak ion flux in ion outflow regions measured on previous spacecraft missions. In most cases, flux bursts can be explained either 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 SKAW and could in principle lead to localized ion heating. The region of the spectrum between f(H+) and f(O+) appears less localized and could produce a more uniform background of heated ions, depending on the relative contributions to total heating of the different spectral regimes.