This MHD analysis of resonant Alfven wave heating endeavors to use a one dimensional model of the earth's magnetotail to determine the plasma sheet boundary layer (PSBL) heating for various flow field, magnetic field, and density profiles. It is shown that for a variety of ambient field conditions, the PSBL heating is maximized at some plasma sheet temperature and decreases monotonically away from this temperature. The spectra of magnetic fluctuations in the frequency range 1.7 to 12 mHz observed by ISEE 1 and 2 during the growth phase of a substorm (onset at 1522 UT, April 24, 1979) have been related to this magnetotail model. It is shown that these spectra are consistent with (1) fluctuations being due to waves in the plasma sheet, (2) a magnetosheath source for the waves, (3) acoustic propagation in the lobe and (4) a nearby local Alfven wave resonance, where the wave phase velocity along the field matches the local Alfven speed. Resonant Alfven wave heating of the plasma sheet boundary layer is estimated from the model to be of the order of 1 mu W/m^2 . The absorption of this energy flux can account for a significant fraction of the observed increase in the plasma sheet temperature during the substorm. The resonant Alfven wave heating effect is modified by the presence of a component of the ambient magnetic field along the density gradient. While the total magnitude of the heating is only marginally affected, it is shown that the heating is distributed over a larger portion of the PSBL. Furthermore, based on a simple geometrical effect, this configuration allows the plasma to absorb energy from the parallel component of the Poynting flux. This component will typically be much larger than the other components.
- Pub Date:
- January 1990
- Physics: Fluid and Plasma, Physics: Astronomy and Astrophysics