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Ann. Geophys., 23, 773-779, 2005
www.ann-geophys.net/23/773/2005/
© European Geosciences Union 2005
Simultaneous VHF radar backscatter and ionosonde observations of low-latitude E region
A. K. Patra1, S. Sripathi1, P. B. Rao2, and K. S. V. Subbarao3
1National MST Radar Facility, Tirupati, India
2National Remote Sensing Agency, Hyderabad, India
3Space Physics Laboratory, VSSC, Trivandrum, India
Abstract. The first results of simultaneous observations made on the low-latitude
field-aligned irregularities (FAI) using the MST radar located at Gadanki
(13.5° N, 79.2° E, dip 12.5°) and the Es parameters
using an ionosonde at a nearby station Sriharikota (13.7° N, 80.1° E,
dip 12.6°) are presented. The observations show that while the
height of the most intense radar echoes is below the virtual height of
Es (h'Es) during daytime, it is found to be either below
or above during nighttime. The strength of the FAI is better correlated with
the top penetration frequency (ftEs) and the blanketing frequency
(fbEs) during the night (r=0.4 in both cases) as compared to the
day (r=0.35 and -0.04, respectively). Furthermore, the signal strength of FAI
is reasonably correlated with (ftEs-fbEs) during daytime
(r=0.59) while very poorly correlated during nighttime (r=0.18). While
the radar observations in general appear to have characteristics close to
that of mid-latitudes, the relationship of these with the Es parameters
are poorer than that of mid-latitudes. The observations reported here,
nevertheless, are quite consistent with the expectations based on the gradient
drift instability mechanism.
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