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Unusual wave phenomena near interplanetary shocks at high latitudes
Author(s) -
Thejappa G.,
Wentzel Donat G.,
MacDowall R. J.,
Stone R. G.
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl03368
Subject(s) - physics , shock wave , whistler , geophysics , mach number , electromagnetic radiation , upstream (networking) , wave propagation , mach wave , mechanics , computational physics , atmospheric sciences , plasma , optics , nuclear physics , computer network , computer science
We report on several interplanetary shocks that are unusual because waves at about 10 Hz are highly electrostatic in the upstream region yet highly electromagnetic in the downstream region. These shocks, detected by the Unified Radio and Plasma Wave Experiment (URAP) on Ulysses are supercritical reverse shocks, which occurred predominantly at high heliographic latitudes. The level of wave activity is observed to be independent of the angle between the magnetic field and the shock normal, the Mach number, and the change in the ratio of ion thermal pressure to magnetic pressure from upstream to downstream regions. Since the energy in the upstream electrostatic waves is small compared to the downstream electromagnetic waves, mode conversion from electrostatic to electromagnetic at the shock is not a viable mechanism. The upstream and downstream waves are likely to be generated by separate mechanisms, with lower hybrid waves being the most probable candidates for the upstream waves and electromagnetic lower hybrid or whistlers for the downstream waves.