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Ann. Geophys., 23, 2457-2464, 2005
www.ann-geophys.net/23/2457/2005/
© European Geosciences Union 2005
VHF and L-band scintillation characteristics over an Indian low latitude station, Waltair (17.7° N, 83.3° E)
P. V. S. Rama Rao, S. Tulasi Ram, K. Niranjan, D. S. V. V. D Prasad, S. Gopi Krishna, and N. K. M. Lakshmi
Space Physics Laboratories, Department of Physics, Andhra University, Visakhapatnam 530 003, India
Abstract. Characteristics of simultaneous VHF (244 MHz) and L-band (1.5 GHz)
scintillations recorded at a low-latitude station, Waltair (17.7° N,
83.3° E), during the low sunspot activity year of March 2004 to March
2005, suggest that the occurrence of scintillations is mainly due to two
types, namely the Plasma Bubble Induced (PBI), which maximizes during the post
sunset hours of winter and equinoctial months, and the Bottom Side Sinusoidal
(BSS) type, which maximizes during the post-midnight hours of the summer
solstice months. A detailed study on the spectral characteristics of the
scintillations at both the frequencies show that the post-sunset
scintillations are strong with fast fading (≈40 fad/min) and are
multiple in nature in scattering, giving rise to steep spectral slopes,
whereas the post-midnight scintillations, which occur mostly on the VHF signal
with low fading rate (≈4 fad/min), are of the BSS type, often showing
typical Fresnel oscillations with reduced roll off spectral slopes, indicating
that the type of irregularity resembles a thin screen structure giving rise
to weak scattering. Using the onset times of several similar scintillation
patches across the two satellite (FLEETSAT 73° E, INMARSAT
65° E) ray paths (sub-ionospheric points are separated by 82 km), the
East ward movement of the irregularity patches is found to vary from 150 to
250 m/s during the post sunset hours and decrease slowly during the post
midnight hours. Further, the east-west extent of the PBI type of
irregularities is found to vary from 100 to 500 km, while that of the BSS
type extend up to a few thousand kilometers.
Keywords. Ionosphere (Ionospheric irregularities; Auroral
ionosphere; Electric fields and currents)
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