Electrostatic Waves in the Magnetosphere
Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves (lightning whistlers, chorus, triggered emissions, high pass noise). In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The OGO 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Near the geomagnetic equator, intense waves with f≃ (n + 1/2)f c - are detected on auroral L shells during most passes in the midnight-dawn-noon LT sector. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging. Another region of unusually intense magnetospheric wave activity occurs at the boundary of the hot cusp plasma and cold plasma-sphere.
KeywordsSearch Coil Wave Particle Interaction Electrostatic Wave Closed Field Line Polar Cusp
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