Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm21a1981l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM21A-1981
Physics
[2114] Interplanetary Physics / Energetic Particles, [2154] Interplanetary Physics / Planetary Bow Shocks, [2164] Interplanetary Physics / Solar Wind Plasma, [2723] Magnetospheric Physics / Magnetic Reconnection
Scientific paper
Omnipresent suprathermal populations in collisionless space plasmas testify to the routine importance of kurtosis in their description. The kurtosis moment is the first mention that non-thermal physics is involved in the plasma being described. Kurtosis is often ignored in closure approximations adopted to truncate the infinite hierarchy of coupled fluid equations. These closures usually assume polytropic equations of state or phenomenological heat flux expressions that are more restatements of convenience than rigor. Without kurtosis, these moment level descriptions may be incomplete in an essential way. In this paper, we point out several types of kurtosis that may be computed with space plasma data that have different uses. Among these is an "intrinsic kurtosis" that reflects most nearly the non-thermal nature of f(v). We develop a procedure for estimating this intrinsic kurtosis from data, and show with Polar plasma data how this information can be significantly different than that contained in the standard definition of kurtosis from statistics. As an example, pressure anisotropy influences kurtosis, but not intrinsic kurtosis. The variation and interpretation of these quantities for plasma data acquired in the interplanetary medium, across the fore- and bow shocks, magnetosheath and reconnection layers will be presented. Attention will be focused on whether variations in kurtosis can be used as a marker for site(s) of suprathermal particle acceleration.
Holdaway Richard
Lopez J. Y.
Scudder Jack D.
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