Characteristics of nighttime VLF/ELF emissions with frequency drift and estimation of the large-scale electric field from the frequency drift observed at a low latitude Indian ground station, Jammu |
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Authors: | M Altaf K K Singh S A Sheikh A K Singh and Lalmai |
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Abstract: | Characteristics of nighttime VLF/ELF emissions are examined on the basis of the data obtained at our low latitude ground station
Jammu (geomagnetic latitude, 22°26′ N; L = 1.17), India during our VLF/ELF campaign. From the detailed analysis of a huge
amount of acquired VLF/ELF data at Jammu we have found three remarkable events which clearly exhibit a rise in their frequency
in pre and past midnight sectors during magnetically quiet and substorm periods. Our analysis shows that the frequency drift
in VLF/ELF emissions seems to be a rare phenomenon at low latitudes during magnetically quiet and substorm periods in pre
and post midnight sectors. This property of temporal frequency drift (regular frequency increases with time) in VLF/ELF emissions
observed at our station Jammu are interpreted in terms of a quasi-linear electron cyclotron instability model for wave excitation.
The initial frequency increase is believed to be due to a combind effect of L-shell drift of energetic electrons. Further,
the frequency drifts in VLF/ELF emissions observed at Jammu have been used to estimate the large scale electric field during
quiet and substorm periods in pre and post midnight sectors. This investigation would be most useful for the study of the
wave-particle interaction processes, magnetospheric plasma structure and particle dynamics, especially during quiet periods
in premidnight sector at low latitudes. |
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