Radiation near <formula>2fp and intensified emissions near <formula>fp in the dayside and nightside auroral region and polar cap

Details Radiation near <formula>2fp and intensified emissions near <formula>fp in the dayside and nightside auroral region and polar cap Radiation near <formula>2fp and intensified emissions near <formula>fp in the dayside and nightside auroral region and polar cap

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jgr...102.4787c&link_type=abstract

Journal of Geophysical Research, Volume 102, Issue A3, p. 4787-4798

Physics

15

Magnetospheric Physics: Plasma Waves And Instabilities, Radio Science: Magnetospheric Physics, Magnetospheric Physics: Auroral Phenomena, Magnetospheric Physics: Polar Cap Phenomena

Scientific paper

This paper reports the discovery in the DE 1 data of propagating radiation near 2fp (the H component) and relatively intense electromagnetic waves near fp with fields typically <~1mVm-1 (the PF or plasma frequency component) on both the dayside and the nightside of Earth. These emissions are observed at auroral and polar cap latitudes for radial distances ranging from 2.5 to 4.5RE. The H component is unique in that no other 2fp emissions are known to be generated where the electron gyrofrequency fg exceeds 2fp. Since existing theories for 2fp radiation assume fg/fp<1, new theories will be required to explain the H component. The PF waves near fp are electromagnetic, but with large ratios E/cB~20. On the basis of cold plasma theory, the wave frequencies and the ratios E/cB, the PF component plausibly consists of z-mode and/or whistler mode waves near fp, presumably driven by an electron instability. The H emissions have modest bandwidths of ~50% at frequencies ranging from 5 to 20 kHz. Grounds for interpreting the H component as emissions generated near 2fp are provided by the very good frequency tracking of the PF and H components and typical frequency ratios near 2.0. Strong evidence exists that part of the H component is propagating, electromagnetic radiation, based on propagation effects and spin modulation patterns. However, no magnetic signals have yet been detected for the H component, so that it could be partly electrostatic. Cold plasma theory and the observed wave characteristics favor interpreting the H component as composed of o mode and/or z mode signals. Combining the DE 1 observations with rocket observations, it is predicted that the much more intense Langmuir-like fields observed in the low altitude auroral zones should also generate observable 2fp radiation. This prediction should be testable using Polar and future rocket flights. Directions for future research are also described.

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