Core ion flux bursts within solitary kinetic Alfvén waves

Details Core ion flux bursts within solitary kinetic Alfvén waves Core ion flux bursts within solitary kinetic Alfvén waves

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...103.4157k&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A3, p. 4157-4170

Physics

35

Ionosphere: Auroral Ionosphere, Ionosphere: Particle Acceleration, Ionosphere: Plasma Waves And Instabilities, Magnetospheric Physics: Plasma Waves And Instabilities

Scientific paper

The Freja cold plasma analyzer (CPA) makes high time resolution measurements of the angle- and energy-integrated core ion velocity distribution (<20eV) with spatial resolutions of ~10m. 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 Alfvén 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 109cm-2s-1. This value is comparable in magnitude to the ram flux of cold ions in a 103cm-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 dc up to and beyond the proton cyclotron frequency fH+. Wave power above fH+ and below the oxygen cyclotron frequency fO+ is localized within SKAW and could in principle lead to localized ion heating. The region of the spectrum between fH+ and fO+ 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.

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