Two types of magnetospheric ELF chorus and their substorm dependences

Journal Article · Tue Nov 01 04:00:00 EST 1977 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA082i032p05112· OSTI ID:5400973

Tsurutani, B T; Smith, E J

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), Journal Name: J. Geophys. Res.; (United States) Vol. 82:32; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CHARGED-PARTICLE PRECIPITATION
CYCLOTRON RESONANCE
DIFFUSION
ELECTROMAGNETIC RADIATION
ELECTRON PRECIPITATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
GEOGRAPHICAL VARIATIONS
LATITUDE EFFECT
LEPTONS
LONG WAVE RADIATION
MAGNETIC BAYS
OGO SATELLITES
RADIATIONS
RADIOWAVE RADIATION
RESONANCE
SATELLITES
TRAPPED ELECTRONS
VARIATIONS