Focusing of nonducted whistlers by the equatorial anomaly

Journal Article · Mon May 01 04:00:00 EDT 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JA02756· OSTI ID:207229

Sonwalkar, V S; Inan, U S ^[1]; Aggson, T L ^[2]

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1. Stanford Univ., CA (United States)
2. NASA Goddard Space Flight Center, Greenbelt, MD (United States); and others

Impulsive ELF/VLF electric field instrument (VEFI) on the Dynamic Explorer 2 (DE2) satellite on almost every crossing of the geomagnetic equator in the evening hours are interpreted as originating in lightning discharges. These signals that peak in intensity near the magnetic equator are observed within 5-20{degrees} latitude of the geomagnetic equator at altitudes of 300-500 km with amplitudes of the order of {approximately} mV/m in the 512- to 1024-Hz frequency band of the VEFI instrument. Whistler-mode ELF/VLF wave propagation through a horizontally stratified ionosphere predicts strong attenuation of subionospheric signals reaching the equator at low altitudes. However, ray tracing analysis shows that the presence of the equatorial density anomaly, commonly observed in the upper ionosphere during evening hours, leads to the focusing of the wave energy from lightning near the geomagnetic equator at low altitudes, thus accounting for all observed aspects of the phenomenon. The observations presented here indicate that during certain hours in the evening, almost all the energy input from lightning discharges entering the ionosphere at <30{degrees} latitude remains confined to a small region (in altitude and latitude) near the geomagnetic equator. The net wideband electric field, extrapolated from the observed electric field values in the 512- to 1024-Hz band, can be {approximately}10 mV/m or higher. These strong electric fields generated in the ionosphere by lightning at local evening times may be important for the equatorial electrodynamics of the ionosphere. 31 refs., 8 figs.

• OSTI ID: 207229
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A5 Vol. 100; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ELECTRIC FIELDS
GEOMAGNETIC EQUATOR
HZ RANGE
IONOSPHERE
KHZ RANGE 01-100
LIGHTNING
WAVE PROPAGATION
WHISTLERS