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Title: Salient Features of Amplitude Scintillations & Faraday Polarization Fluctuations at VHF Observed at Delhi
Authors: Vijayakumar, P N
Tyagi, T R
Gupta, J K
Issue Date: Apr-1988
Publisher: NISCAIR-CSIR, India
Abstract: Nighttime ionospheric scintillation phenomena of transionospheric VHF satellite signals observed at Delhi during the ascending phase of solar activity reveal certain interesting features. There is a marked difference between the scintillations observed in the premidnight period and those observed in the postmidnight period. The former is associated with explosive growth (SI > 60%) with fading rates of 10 to 15 fades/min and often, found to cause saturation of amplitude fluctuations accompanied by strong Faraday polarization fluctuations (FPFs). In contrast, the latter is of a weak nature (SI < 50%) with fading rates of 3 to 5 fades/min and often continues up to presunrise period. These may be classified as class I and class II types, respectively, similar to their counterparts observed at magnetic equator bearing distinct relationship with postsunset bottomside spread-F. Under the influence of ascending solar activity, clear seasonal trends are present in the occurrence of FPFs, with peaks in the equinoctial months, increasing with solar activity. In contrast, the occurrence of class II type scintillation shows negative correlation with solar activity in summer and equinoctial months and is independent of solar activity in the winter months. Also, it is found that the occurrence of FPFs at Delhi is conditional to their prior occurrence at a low latitude station like Hyderabad, while they die out first at Delhi and later at Hyderabad. It is concluded that class I type of scintillation and FPFs are important manifestations of a strong magnetic equator coupling in the postsunset period in the Indian sector especially during high solar activity. The scale of irregularities which cause FPFs are distinct from those that cause general class I type scintillations. Finally, the class II type observed at Delhi may be of a different origin.
Page(s): 58-62
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.17(2) [April 1988]

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