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Featured researches published by S. V. B. Rao.


Journal of Geophysical Research | 2014

Quiet time short-period and day-to-day variations in E × B drift studied using 150 km radar echoes from Gadanki

P. Pavan Chaitanya; A. K. Patra; S. V. B. Rao

In this paper we present short-period and day-to-day variations in E × B drift during low solar and magnetically quiet conditions, based on radar observations of daytime 150 km echoes from Gadanki, India. Short-period (<100 min) variations in E × B drift show amplitude as large as 7 m s−1 and display large day-to-day variation. Spectral analysis reveals that drift velocity fluctuations consist of several components of short periods in the range of 4–100 min. Among these periods, the most frequently occurring periods are 6–60 min. Observations also show that amplitudes of these periods increase with increasing period. Interestingly, signal-to-noise ratio (SNR) variations also show periods of 3–19 min, which have also been observed in velocity variations. In addition, amplitudes of the periodic variations in SNR tend to increase with increasing period, which is also similar to those observed in drift velocity fluctuations. No correlation between SNR and velocity variations, however, has been found. Noticeable day-to-day variations in drift velocity are found in all seasons, and the variation is as large as ±25 m s−1. Day-to-day variations also show wave-like features with period of 2–4 days. Observed E × B drift variations of 7 m s−1 at short time scale and 25 m s−1 on a day-to-day basis indicate zonal electric field variations of 0.25 mV/m and 0.9 mV/m, respectively. We surmise that quiet time E × B drift variations with periods <100 min and 2–4 days are likely to be the manifestations of gravity wave and planetary wave wind-induced electric fields, respectively, consistent with those reported earlier.


Journal of remote sensing | 2013

On Rayleigh lidar capability enhancement for the measurement of short-period waves at upper mesospheric altitudes

V. Kamalakar; A. Taori; K. Raghunath; S. V. B. Rao; A. Jayaraman

We used a combination of simultaneous measurements made with Rayleigh lidar and O2 airglow monitoring to improve lidar investigation capability to cover a higher altitude range. We fed in instantaneous O2 airglow temperatures rather than model values at the peak altitude for a subsequent integration method of temperature retrieval using Rayleigh lidar backscattered signals. Using this method, errors in the lidar temperature estimates converge at higher altitudes indicating better altitude coverage compared with regular methods where model temperatures are used rather than real-time measurements. This improvement enables the measurement of short-term waves at upper mesospheric altitudes (∼90 km). Using two case studies, we show that above 60 km the amplitude of a few short-term waves drastically increases while some of the short-term waves show either damping or saturation. We claim that by using such combined measurements, significant and cost-effective progress can be made in the understanding of short-term wave processes that are important for coupling across different atmospheric regions.


Journal of Geophysical Research | 2009

Low‐altitude quasi‐periodic echoes studied using a large database of Gadanki radar observations

N. Venkateswara Rao; A. K. Patra; S. V. B. Rao

[1] In this paper we present studies on low-altitude quasiperiodic (LQP) echoes based on a large database of Gadanki radar observations. LQP echoes have been observed 33% of the time during daytime and 39% during nighttime. Their occurrence is found to be maximum in the summer (daytime, 58%; nighttime, 57%), followed by the September equinox (daytime, 32%; nighttime, 48%), the March equinox (daytime, 26%; nighttime, 36%), and minimum in the winter (daytime, 25%; nighttime, 26%). Height-time occurrence of LQP echoes shows two local time maxima: one in the morning (0700- 1100 LT) and another in the evening ( 1900-0000 LT). The most significant results not reported earlier are the large occurrence rate of LQP echoes and the height-time occurrence maps showing a descending pattern with close resemblance to tidal wind behavior. The Doppler velocities are upward-northward (downward-southward) for positive- (negative-) sloped LQP echoes. Also, we find the Doppler spread as high as 200 m s -1 at times underlining the presence of strong plasma turbulence in the collision-dominated lower E region. These results are discussed in the light of the current understanding of the LQP echoes.


Journal of Geophysical Research | 2016

Unusual behavior of the low-latitude ionosphere in the Indian sector during the deep solar minimum in 2009

P. Pavan Chaitanya; A. K. Patra; N. Balan; S. V. B. Rao

In this paper we carry out a comparative study of the daytime (7–18 LT) behavior of the near-equatorial ionospheric F region at the end of the long deep solar minimum (2009) with respect to that of the previous normal solar minimum (1995) in the Indian longitude sector using ionosonde observations of F layer parameters, radar observations of E × B drift, and the IRI-2012 (International Reference Ionosphere-2012) model. We investigate the F2 and F3 layer behaviors separately. The results reveal that the peak frequencies of the F layer (fpeak), F2 layer (foF2), and F3 layer (foF3) in 2009 are consistently lower than those in 1995. Maximum difference in fpeak/foF2/foF3 between 2009 and 1995 observations is found in the equinoxes followed by winter and summer. The annual mean, seasonal mean, and 10 day mean peak electron density (corresponding to fpeak) in 2009 were lower than those in 1995 by as much as 34%, 46%, and 65%, respectively. Solar rotation effect is less conspicuous in 2009 than in 1995, consistent with the solar rotation signature in F10.7. Observations also show considerable amount of equinoctial asymmetry in electron density, which is found to be closely linked with the corresponding asymmetry in the vertical E × B drift. Seasonal mean peak electron densities of the F layer (corresponding to fpeak) and the F2 layer (corresponding to foF2) observed during the deep solar minimum of 2009 were smaller than those corresponding to IRI-2012 model foF2 by as much as 45% and 50%, respectively, underlining the need to incorporate the data collected during the long deep minimum in the IRI model. The unusually weak ionosphere observed in 2009 is discussed in terms of the direct effect of the low solar EUV flux in 2009 as compared to 1995 and its indirect effects on ionospheric electric field, thermospheric composition (or O/N2 ratio), and thermospheric neutral winds.


Climate Dynamics | 2016

Precipitation climatology over India: validation with observations and reanalysis datasets and spatial trends

P. Kishore; S. Jyothi; Ghouse Basha; S. V. B. Rao; M. Rajeevan; I. Velicogna; Tyler C. Sutterley


Journal of Geophysical Research | 2008

Some new aspects of low‐latitude E‐region QP echoes revealed by Gadanki radar: Are they due to Kelvin‐Helmholtz instability or gravity waves?

N. Venkateswara Rao; A. K. Patra; S. V. B. Rao


Journal of Geophysical Research | 2009

Characteristics of the Tropical Easterly Jet: Long‐term trends and their features during active and break monsoon phases

M. Roja Raman; V. V. M. Jagannadha Rao; M. Venkat Ratnam; M. Rajeevan; S. V. B. Rao; D. Narayana Rao; N. Prabhakara Rao


Journal of Geophysical Research | 2013

First simultaneous observations of F3 layer and E×B drift in Indian sector and modeling

P. Pavan Chaitanya; A. K. Patra; N. Balan; S. V. B. Rao


Journal of Atmospheric and Solar-Terrestrial Physics | 2012

Simultaneous Rayleigh lidar and airglow measurements of middle atmospheric waves over low latitudes in India

A. Taori; V. Kamalakar; K. Raghunath; S. V. B. Rao; James M. Russell


Annales Geophysicae | 2015

Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012

P. Pavan Chaitanya; A. K. Patra; N. Balan; S. V. B. Rao

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A. K. Patra

National Atmospheric Research Laboratory

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M. Venkat Ratnam

National Atmospheric Research Laboratory

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P. Pavan Chaitanya

National Atmospheric Research Laboratory

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A. Taori

National Atmospheric Research Laboratory

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N. Venkateswara Rao

National Atmospheric Research Laboratory

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I. Velicogna

University of California

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P. Kishore

University of California

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A. Jayaraman

National Atmospheric Research Laboratory

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G.N. Madhavi

Sri Venkateswara University

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Ghouse Basha

National Atmospheric Research Laboratory

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