Two types of magnetospheric ELF chorus and their substorm dependences
Extremely low frequency (10--1500 Hz) magnetospheric chorus has been analyzed to investigate a possible dependence on substorms. Care was taken to separate effects from temporal effects by analyzing an entire year of data acquired by the Ogo 5 search coil magnetometer. A major finding of the study of spatial dependences is that chorus occurs principally in two magnetic latitude regions. Equatorial chorus is detected near the equator, and high-latitude chorus is found at magnetic latitudes above 15/sup 0/. When chorus in these two regions is analyzed separately, substorm dependences become apparent. Comparisons with AE indicate that equatorial chorus occurs primarily during substorms. High-latitude chorus is not strongly dependent on AE and often occurs during intervals of prolonged quiet with AE<100..gamma.. for the previous 12 hours or more. The dependence of equatorial chorus on local time, magnetic latitude, and L is consistent with generation by a cyclotron resonance between the whistler mode chorus and 10- to 100-keV trapped substorm electrons. Equatorial chorus has an abrupt onset in the postmidnight sector and a second enhancement from dawn to noon, a pattern which is similar to that of energetic electron precipitation. The occurrence frequency of equatorial chorus peaks at the equator, vertical-barmagnetic latitudevertical-bar<5/sup 0/, a region where cyclotron resonance is most efficient. The L value of maximum chorus occurrence increases from 5--8 postmidnight to 7--11 postdawn, a dependence which is consistent with generation by electrons which have undergone drift shell splitting. Delay times between substorms and the onset of equatorial chorus are consistent with a gradient drift of approx.25-keV electrons. Equatorial postmidnight chorus and postdawn chorus have similar occurrence rates and wave intensities. The maximum chorus ocurrence rates are 54% postmidnight and 56% postdawn.
- Research Organization:
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91103
- OSTI ID:
- 5400973
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 82:32
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MAGNETIC BAYS
LONG WAVE RADIATION
CYCLOTRON RESONANCE
DIFFUSION
ELECTRON PRECIPITATION
LATITUDE EFFECT
OGO SATELLITES
TRAPPED ELECTRONS
CHARGED-PARTICLE PRECIPITATION
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
GEOGRAPHICAL VARIATIONS
LEPTONS
RADIATIONS
RADIOWAVE RADIATION
RESONANCE
SATELLITES
VARIATIONS
640203* - Atmospheric Physics- Magnetospheric Phenomena- (-1987)