Low-latitude HF Doppler short-period oscillations associated with storm sudden commencements

HF Doppler measurements of F-region vertical plasma drifts (Vz) at a low-latitude station, Visakhapatnam (dip–17°N) in association with two storm sudden commencements (SC*/SC) on 21 February 1994 (during daytime 0902 h UT) and 28 May 1994 (during night time 1357 h UT) are analysed. Measurements of V...

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Bibliographic Details
Published in:Current science (Bangalore) 2007-02, Vol.92 (4), p.502-506
Main Authors: Anjaneyulu, P., Das, N. Lakshmana, Rao, B. M., Ramakrishna, Ch
Format: Article
Language:English
Subjects:
Coincidence
Electric fields
Ionospheres
Latitude
Magnetic fields
Magnetic signatures
Magnetohydrodynamic waves
Observatories
Plasma drift
RESEARCH COMMUNICATIONS
Tropical regions
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Summary:HF Doppler measurements of F-region vertical plasma drifts (Vz) at a low-latitude station, Visakhapatnam (dip–17°N) in association with two storm sudden commencements (SC*/SC) on 21 February 1994 (during daytime 0902 h UT) and 28 May 1994 (during night time 1357 h UT) are analysed. Measurements of Vz at SCs are compared with the H-field variations of high latitudes down to dip equatorial latitudes. It is found that there is an abrupt enhancement in Vz (or in Doppler velocity VD) in coincidence with the main impulse of SC*/SC in both the events. In the case of the first event, upward enhancement in Vz is unusual and is nearly 2 to 3 times that of the usual velocities. Also, in the same event there is a downward trend in Vz prior to this enhancement, after which short-period oscillations (60–90 s) in Vz which are coherent with the magnetic fluctuations at several high latitudes down to equatorial latitudes are observed. The observed changes in Vz (VD) at SCs are discussed in the light of the effects of magentosphere-generated electric fields promptly penetrated to these low latitudes by means of transmission of electromagnetic waves through earth–ionosphere waveguide and direct transmission of compressional hydromagnetic waves.
ISSN:0011-3891