Plasma Waves in the Plasmapause Region: Recent Results

Details Plasma Waves in the Plasmapause Region: Recent Results Plasma Waves in the Plasmapause Region: Recent Results

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm42e..04g&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SM42E-04

Computer Science

Sound

2730 Magnetosphere: Inner, 2740 Magnetospheric Configuration And Dynamics, 2752 Mhd Waves And Instabilities, 2768 Plasmasphere, 2772 Plasma Waves And Instabilities

Scientific paper

Over the last several decades a number of space-born plasma wave instruments have observed a characteristic emission peak that has frequently been used to determine the local plasma electron density in the plasmapause region. The emission has sometimes been referred to as the upper-hybrid resonance or uhr (where fuhr**2 = fp**2 + fg**2, with fg being the electron gyrofrequency and fp the electron plasma frequency). The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite makes observations of natural emissions but also performs radio sounding, which creates both long-range and short-range echoes. The short-range echoes are from local resonances that sometimes can yield accurate information on both in situ electron density and magnetic field strength, which in turn can be used to determine the true fuhr for comparison against the commonly observed emission peak. From this technique it has been found that the peak of the emission is near but not typically at the uhr frequency. This emission peak, actually occurring in the upper hybrid wave band, has also been observed to be near the source of the low-frequency portion of the non-thermal continuum (~10 to 100 kHz). The generation of the continuum is believed to occur when fuhr = (n +1/2)fg at the plasmapause. The source region of the non-thermal continuum at higher frequencies (~100 to greater than 800 kHz), also known as the kilometric continuum (KC), was unknown until recently. The KC, observed by wave instruments on both IMAGE and Geotail, has been found to be associated with plasmaspheric bite-out structures as observed by the IMAGE Extreme Ultraviolet (EUV) instrument. In addition, the KC source appears to lie deep within the bite-out at the plasmapause near the magnetic equator and has been observed to coincide with an intensification of the emission near the fuhr, much like its lower frequency counterpart. The resulting KC emission cone, assumed to be corotating with the plasmasphere, is observed to be within 10 degrees of the magnetic equator, and has a typical magnetic longitudinal extent of ~42 degrees. The KC emission has been observed at all local times.

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