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Search Results: 1 - 10 of 197013 matches for " D. Narayana Rao "
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Estimation of temperature and humidity from MST radar observations
K. Mohan,D. Narayana Rao,T. Narayana Rao,S. Raghavan
Annales Geophysicae (ANGEO) , 2003,
Abstract: Retrieval of vertical profiles of temperature and humidity parameters using a VHF radar is described in this paper. For this, Indian MST radar located at Gadanki (13.5° N, 79.2° E) has been operated in a special mode. First, vertical velocities are collected continuously using the radar and are subjected to Fast Fourier Transform (FFT) analysis to obtain Brunt-V is l oscillations. From the measured Brunt-V is l oscillations, temperature profile is obtained from the radar observations following Revathy et al. (1996). The various terms required for the retrieval of vertical profiles of humidity are the eddy dissipation rate, ε, the volume reflectivity, η, and the potential refractive index gradient, M. The eddy dissipation rate, ε, is calculated from the spectral width after removing the effects due to non-turbulence. The volume reflectivity, η, of the turbulence scattering is calculated using the signal-to-noise ratio as a function of height. The potential refractive index gradient, M, is evaluated using the measured Brunt-V is l oscillations, the eddy dissipation rate and the volume reflectivity, η. Vertical profiles of humidity are retrieved following Tsuda (1997) using the radar derived temperature as well as the balloon measured temperature and are compared with the humidity as measured by the radiosonde. The sign of the potential refractive index gradient, M, is taken from the simultaneous measurements of balloon soundings. The retrieved vertical profiles of temperature and humidity have been compared with the radiosonde data, which are released simultaneously with the radar observations at the radar site. A fairly good comparison is seen between the two measurements on some days and there are some discrepancies on some other days. The strengths and limitations in estimating the vertical profiles of temperature and humidity from the radar observations are discussed. Key words. Atmospheric composition and structure (pressure, density and temperature; enhancements and techniques)
Mean winds observed with Indian MST radar over tropical mesosphere and comparison with various techniques
M. Venkat Ratnam,D. Narayana Rao,T. Narayana Rao,S. Thulasiraman
Annales Geophysicae (ANGEO) , 2003,
Abstract: Temporal variation of mean winds between the 65 to 85 km height region from the data collected over the course of approximately four years (1995–99), using the Indian MST radar located at Gadanki (13.5° N, 79.2° E), India is presented in this paper. Mesospheric mean winds and their seasonal variation in the horizontal and vertical components are presented in detail. Westward flows during each of the equinoxes and eastward flows during the solstices are observed in the zonal component. The features of the semi-annual oscillation (SAO) and the quasi-biennial oscillation (QBO) in the zonal component are noted. In the meridional component, contours reveal a northward motion during the winter and a southward motion during the summer. Large inter-annual variability is found in the vertical component with magnitudes of the order of ± 2 ms-1 . The MST observed winds are also compared with the winds observed by the MF radar located at Tirunelveli (8.7° N, 77.8° E), India, the High Resolution Doppler Imager (HRDI) onboard the Upper Atmospheric Research Satellite (UARS), and with the CIRA-86 model. A very good agreement is found between both the ground-based instruments (MST radar and MF radar) in the zonal component and there are few discrepancies in the meridional component. UARS/HRDI observed winds usually have larger magnitudes than the ground-based mean winds. Comparison of the MST derived winds with the CIRA-86 model in the zonal component shows that during the spring equinox and the summer, the winds agree fairly well, but there are a lot of discrepancies in the other seasons and the observed winds with the MST radar are less in magnitude, though the direction is same. The strengths and limitations in estimating reliable mesospheric mean winds using the MST radar are also discussed. Key words. Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics; waves and tides)
Thermospheric density structures over the polar regions observed with CHAMP
K. Kishore Kumar, A. R. Jain,D. Narayana Rao
Annales Geophysicae (ANGEO) , 2005,
Abstract: Several campaigns have been carried out to study the convective systems over Gadanki (13.5° N, 79.2° E), a tropical station in India, using VHF and UHF radars. The height-time sections of several convective systems are investigated in detail to study reflectivity, turbulence and vertical velocity structure. Structure and dynamics of the convective systems are the main objectives of these campaigns. The observed systems are classified into single- and multi-cell systems. It has been observed that most of the convective systems at this latitude are multi-cellular in nature. Simultaneous VHF and UHF radar observations are used to classify the observed precipitating systems as convective, intermediary and stratiform regions. Composite height profiles of vertical velocities in these regions were obtained and the same were compared with the profiles obtained at other geographical locations. These composite profiles of vertical velocity in the convective regions have shown their peaks in the mid troposphere, indicating that the maximum latent heat is being released at those heights. These profiles are very important for numerical simulations of the convective systems, which vary significantly from one geographical location to the other. Keywords. Meteorology and atmospheric dynamics (Mesoscale meteorology; Convective processes) – Radio science (Remote sensing) Full Article (PDF, 2458 KB) Citation: Kishore Kumar, K., Jain, A. R., and Narayana Rao, D.: VHF/UHF radar observations of tropical mesoscale convective systems over southern India, Ann. Geophys., 23, 1673-1683, doi:10.5194/angeo-23-1673-2005, 2005. Bibtex EndNote Reference Manager XML
Evaluation of performance metrics of leagile supply chain through fuzzy MCDM
D. Venkata Ramana,K.Narayana Rao,J. Suresh Kumar
Decision Science Letters , 2013, DOI: 10.5267/j.dsl.2013.03.003
Abstract: Leagile supply chain management has emerged as a proactive approach for improving business value of companies. The companies that face volatile and unpredictable market demand of their products must pioneer in leagile supply chain strategy for competition and various demands of customers. There are literally many approaches for performance metrics of supply chain in general, yet little investigation has identified the reliability and validity of such approaches particularly in leagile supply chains. This study examines the consistency approaches by confirmatory factor analysis that determines the adoption of performance dimensions. The prioritization of performance enablers under these dimensions of leagile supply chain in small and medium enterprises are determined through fuzzy logarithmic least square method (LLSM). The study developed a generic hierarchy model for decision-makers who can prioritize the supply chain metrics under performance dimensions of leagile supply chain.
Seasonal variation of vertical eddy diffusivity in the troposphere, lower stratosphere and mesosphere over a tropical station
D. Narayana Rao,M. V. Ratnam,T. N. Rao,S. V. B. Rao
Annales Geophysicae (ANGEO) , 2003,
Abstract: Long-term VHF radar (53 MHz with 3° beam-width) observations at Gadanki (13.5° N, 79.2° E), India, during the period from September 1995 to August 1999 are used to study monthly, seasonal and annual medians of vertical eddy diffusivity, K in the troposphere, lower stratosphere and mesosphere. First, the spectral width contribution due to non-turbulent effects has been removed for further analysis and the monthly, seasonal medians of K are calculated. The monthly median of K in the troposphere shows maximum and minimum in June-July and November-December, respectively. In general, large values of K are seen up to 10 km and then decrease with height. Larger values of K are observed during monsoon and post-monsoon than in winter and summer. In general, the maximum and minimum values of the annual median of K (in logarithmic values) in the troposphere are found to be 0.25 and - 1.3 m2 s-1 respectively. In the mesosphere, the monthly median of K shows maximum and minimum during June-July and November-December, respectively, similar to the lower atmosphere. The value of K in the mesosphere becomes larger and it increases with height up to 75 km and again decreases above that height. The maximum values are seen during the summer, followed by equinoxes and a minimum during the winter. In general, the maximum and minimum values of K (in logarithmic values) are found to be 0.7 and 0.3 m2 s-1, respectively, in the mesosphere. A comparison of Doppler spectral parameters in different beam directions shows anisotropy in both signal-to- noise ratio (SNR) and spectral widths in the mesosphere, whereas it shows isotropy in SNR and anisotropy in the spectral widths in troposphere and lower stratosphere. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; waves and tides)
Intra-Scrotal Extra-Testicular Leiomyoma, a Common Mesenchymal Tumor at a Rare Site: Emphasizing the Need for Awareness of Its Occurrence  [PDF]
Kiran Krishne Gowda, Raman Narayana Rao
Open Journal of Pathology (OJPathology) , 2015, DOI: 10.4236/ojpathology.2015.51002
Abstract: Leiomyoma is a benign tumor of smooth muscles. Leiomyoma originating from the scrotum is a rare entity. We report a case of 53-year-old African male who presented with a 3 cm lump in the right side of scrotum. Clinically, it was provisionally diagnosed as sebaceous cyst and was excised. The histopathology showed a leiomyoma. There was no cytological atypia or mitosis. The patient also had squamous papilloma over left gluteal region.
First results from the CAWSES-India Tidal Campaign
S. Gurubaran, D. Narayana Rao, G. Ramkumar, T. K. Ramkumar, G. Dutta,B. V. Krishna Murthy
Annales Geophysicae (ANGEO) , 2008,
Abstract: The first CAWSES-India Tidal Campaign was conducted by the Indian scientific community during March–April 2006. The objectives of this campaign were: (1) To determine the characteristics of tides in the troposphere and lower stratosphere (0–20 km) and mesosphere and lower thermosphere (MLT) region (80–100 km), (2) to explore and identify what lower atmospheric processes drive middle atmospheric tides in the Indian continental region and (3) to provide information on those short-term variabilities of MLT tides that are likely to have an impact on the ionospheric variabilities and contribute to the upper atmospheric weather. Data sets from experiments conducted at the three low latitude radar sites, namely, Trivandrum (8.5° N, 76.9° E), Tirunelveli (8.7° N, 77.8° E) and Gadanki (13.5° N, 79.2° E) and fortnightly rocket launches from Thumba were made use of in this study. An important observational finding reported in this work is that the radar observations at Tirunelveli/Trivandrum indicate the presence of 15–20 day modulation of diurnal tide activity at MLT heights during the February–March period. A similar variation in the OLR fields in the western Pacific (120–160° longitude region) suggests a possible link between the observed tidal variabilities and the variations in the deep tropical convection through the nonmigrating tides it generates.
Development of radio acoustic sounding system (RASS) with Gadanki MST radar – first results
T. V. Chandrasekhar Sarma, D. Narayana Rao, J. Furumoto,T. Tsuda
Annales Geophysicae (ANGEO) , 2008,
Abstract: A high-power acoustic exciter was designed and developed for the Gadanki MST Radar to facilitate observations in the Radio Acoustic Sounding System (RASS) mode. Sweep range of acoustic signal frequencies was set to 94–125 Hz so as to satisfy Bragg matching condition for temperature range of 90°–40°C between surface and the tropopause (about 17 km). Raytracing of acoustic wave propagation was used to predict the antenna beam directions along which optimum RASS echoes could be obtained. During the RASS observation period of about 18 h on 23–24 July 2006 height profiles of atmospheric virtual temperature were obtained between 1.5 km and 10 km and occasionally up to 14 km. In comparison with the three simultaneous radiosonde launches, RASS derived temperature profiles had the r.m.s. discrepancy of about 1 K, although deviation of the RASS results sometimes appeared when the radial wind velocity was not fully available for the correction of apparent sound speed. This study has successfully demonstrated capability of the RASS application with the Gadanki MST radar, which will be used for continuous monitoring of the temperature profiles in the troposphere and lower stratosphere region in the tropics.
Lidar observations of sodium layer over low latitude, Gadanki (13.5° N, 79.2° E): seasonal and nocturnal variations
P. Vishnu Prasanth, V. Sivakumar, S. Sridharan, Y. Bhavani Kumar, H. Bencherif,D. Narayana Rao
Annales Geophysicae (ANGEO) , 2009,
Abstract: In this paper, we present seasonal and nocturnal variations of mesospheric sodium (Na) layer parameters observed over Gadanki (13.5° N, 79.2° E), based on 166 nights during the period from January 2005 to December 2006, for the first time. The total Na content decreases during the evening and reaches a minimum value around midnight and maximum in the early morning. The year-to-year variations illustrate that Na layers reach the peak value close to 93.5 km for the year 2005 and ~93 km for the year 2006 and falls to near zero value around 110 km. Though, seasonal variation of sodium density illustrate maximum values in September, December and March, we require a larger data base for September months to conclude the statement. The column abundance shows maximum during autumn equinox and minimum during winter. The obtained seasonal and nocturnal variation of sodium layer parameters are compared with mid-latitude observations and further possible mechanisms are discussed.
Lidar observations of sporadic Na layers over Gadanki (13.5° N, 79.2° E)
P. Vishnu Prasanth, S. Sridharan, Y. Bhavani Kumar,D. Narayana Rao
Annales Geophysicae (ANGEO) , 2007,
Abstract: We studied the characteristics of sporadic sodium layers (SSLs) observed with the sodium (Na) resonance scattering lidar at Gadanki (13.5° N, 79.2° E). The SSLs were observed on a total of 63 occasions during 464 h of Na lidar observations from January 2005 to February 2006. The observations showed that one SSL event occurred, on average, every 7 h. The most prominent sporadic layer, which formed on 12 February 2005, exhibited a peak density of 60 722 Na atoms/cm3 around 92 km and it was nearly twice the peak density reported from elsewhere using ground-based observations. In general, the SSLs exhibited the following characteristics: (1) they developed at heights between 88 and 98 km with an average height around 94 km; (2) maximum density occurred during the early morning hours between 02:00 and 05:00 IST; (3) the ratio of the maximum peak Na density to the average density was normally around 3 to 5 and it exceeded even 10 in some cases; (4) the events lasted from a few minutes to several hours. The formation period of the SSLs was longer compared to the decay period of the SSLs. Most of the SSL events showed downward motions.
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