Physics – Plasma Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsm44a..03j&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SM44A-03
Physics
Plasma Physics
7800 Space Plasma Physics, 7827 Kinetic And Mhd Theory, 7859 Transport Processes, 7871 Waves And Instabilities, 2752 Mhd Waves And Instabilities
Scientific paper
Closure in the low frequency MHD regime is an old problem. Polytropic one and two fluid closures have been assumed in collisionless MHD codes and low frequency dispersion analysis; double adiabatic closures have also been explored in spite of the presence of parallel electric fields and heat flow. The collisionally motivated adiabatic value for γ ≃ 5/3 is often inserted. Two years of Polar data collected in the high density regions of the magnetosheath/ entry layers have been analyzed in 15min segments to determine (i) if polytropic relations characterize the electrons and/or ions and (ii) what values of γ e,i are implied. Of the possible 7900 intervals attempted, successful fits were obtained for ions in 239 intervals, while 1552 electrons intervals had successful fits. Frequently there was insufficient dynamic range in the density to determine the polytropic index. However, only 122 intervals had good simultaneous polytropic characterizations of ions and electrons. Of those intervals with common fits there is a general trend for higher electron γ e to accompany increases in γ i. Most surprising are the distribution of values for γ j ; the good electrons fits are especially bimodal, with a strong peak near 0 and another in the vicinity of 5/3, but a deep void in between. With poorer statistics the ions also show this behavior. The incidence of γ i = 5/3 is rare, representing less than 5% of the good ion fits that were possible. Examples of representative observations in the newly defined regime γ e < 1; γ i < 1 that have no classical analogue will be presented. A simple model of circumstances that permit these observations will be presented.
Jaeger Theodore
Scudder Jack D.
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