Modeling of local ionospheric time varying characteristics based on singular value decomposition over low-latitude GPS stations     

Raghavendra Neeli  J R K Kumar Dabbakuti  V. Rajesh Chowdhary  Nitin K. Tripathi  Venkata Ratnam Devanaboyina 《Astrophysics and Space Science》2018,363(9):182

Singular Value Decomposition (SVD) model is implemented to recognize the Total Electron Content (TEC) time series of daily, temporal as well as seasonal characteristics throughout the 24th solar cycle period of the year 2015 in the study. The Vertical (vTEC) analysis has been carried out with Global Positioning System (GPS) data sets collected from five stations from India namely GNT, Guntur (16.44^° N, 80.62^° E), and IISC, Bangalore (12.97^° N, 77.59^° E), LCK2, Lucknow (26.76^° N, 80.88^° E), one station from Thailand namely AITB, Bangkok (14.07^° N, 100.61^° E), and one station from South Andaman Island namely PBR, Port Blair (11.43^° N, 92.43^° E), located in low latitude region. The first five singular value modes constitute about 98% of the total variance, which are linearly transformed from the observed TEC data sets. So it is viable to decrease the number of modeling parameters. The Fourier Series Analysis (FSA) is carried out to characterize the solar-cycle, annual and semi-annual dependences through modulating the first three singular values by the solar (F10.7) and geomagnetic (Ap) indices. The positive correlation coefficient (0.75) of daily averaged GPS–TEC with daily averaged F10.7 strongly supports the temporal variations of the ionospheric features depends on the solar activity. Further, the significance and reliability of the SVD model is evaluated by comparing it with GPS–TEC data and the standard global model (Standard Plasma-Spherical Ionospheric Model, SPIM and International Reference Ionosphere, IRI 2016).  相似文献   

Analysis on the effect of salinity in underwater wireless optical communication     

Sanjay Kumar  Jinka Venkata Aravind  Santosh Kumar G 《Marine Georesources & Geotechnology》2020,38(3):291-301

Abstract

This article deals with the effect of salinity variation on underwater wireless optical communication (UWOC). Effect of different concentration of salt on underwater optical communication has been carried out experimentally in terms of received power at different link lengths. Based on the analysis of experimental data, a mathematical model has been proposed to describe the saline water channel. A simulation study is performed for different data rates and link lengths. It is seen that with increased salinity the attenuation is higher and the UWOC system performance degrades with higher data rate and increased link length.  相似文献   

Heavy metal monitoring of beach sands through environmental magnetism technique: a case study from Vengurla and Aravali beaches of Sindhudurg district,Maharashtra, India     

Venkata Lakshmi Bandaru  Praveen B. Gawali  Pramod T. Hanamgond  Deenadayalan Kannan 《Environmental Earth Sciences》2016,75(8):678

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Vegetation damage assessment due to Hudhud cyclone based on NDVI using Landsat-8 satellite imagery     

Venkata Giri Raj Kumar Konda  Venkatesh Reddy Chejarla  Venkata Ravibabu Mandla  Vani Voleti  Nagaveni Chokkavarapu 《Arabian Journal of Geosciences》2018,11(2):35

Developing nations are abandoned against tropical cyclones because of climatic changeability; the atmosphere is probably going to expand the recurrence and extent of some outrageous climate and calamity occasions. Urban areas and towns arranged along the coastline front belt in Visakhapatnam region experienced serious harm because of Hudhud cyclone, which happened on October 12, 2014. The fundamental motivation behind this exploration was to distinguish the vegetation damage in Visakhapatnam and neighbouring towns. In this analysis, Landsat-8 satellite datasets procured prior and then afterward the cyclone have been utilized; image processing techniques have been completed to evaluate the progressions of pre- and post-disaster condition. Vegetation index strategy was utilized to assess the damage to vegetation. Arrangement results and land utilize land cover change investigation demonstrate that 13.25% of agriculture Kharif and 31.1% of vegetation was damaged. Normalized difference vegetation index (NDVI) maps were produced for the previously, then after the cyclone circumstance, and vegetation biomass damage was evaluated in Visakhapatnam and Bhimunipatanam. General loss of vegetation in both the spots was 30.67 and 43.37 km². The result of this review can be utilized by decision makers for the post-disaster support for rebuilding of influenced regions.  相似文献   

Relationship in metastasis of coal fire and land use/cover using thermal imagery and support vector machine classifier     

Amartanshu Srivastava  Suresh Pandian Elumalai  Elluru Venkata Ramana Raju 《Arabian Journal of Geosciences》2018,11(6):120

The objective of the present study was to delineate temporal and spatial changes in the coal fire and land use/cover within Bastacolla area of Jharia coal field. Studying this variation helped to decipher interconnection among the dynamics of the coal fire and concomitant changes in land use/cover. The detection of coal fires during a span of 14 years along with transitioning land use/cover was cost-effective and enabled planning for management of coal resources and environment. Landsat series of satellite data of 2002, 2009, 2013, and 2016 were processed for generating land surface temperature profiles vis-a-vis classified land use/cover of the study area. A single cut-off temperature was derived for mapping of coal fires using land surface temperature profile from 2002 to 2016. The satellite images were classified using support vector machines, and for depicting land use/cover change, post-classification change detection was done. Classification accuracy obtained was excellent with kappa coefficient ranging from 0.897 for classified image of 2002 to 0.799 for classified image of 2016. Results revealed that coal fires had shifted to the central west part of the area. Furthermore, pockets of coal fire from northern and eastern part of the study area have diminished. OB dumps and coal quarry/coal dump may be attributed towards the spatial change in coal fire while; OB dumps showed connotation with the highest temperature zones. Ground verifications for temperature profiles and coal fires were carried out using thermal camera which enunciated good agreement with results.  相似文献   

Experimental Seasonal Forecast of Monsoon 2005 Using T170L42 AGCM on PARAM Padma     

J. Venkata Ratnam  D. R. Sikka  Akshara Kaginalkar  Amit Kesarkar  N. Jyothi  Sudipta Banerjee 《Pure and Applied Geophysics》2007,164(8-9):1641-1665

As a part of the Experimental Extended Range Monsoon Prediction Experiment, ensemble mode seasonal runs for the monsoon season of 2005 were made using the National Centre for Environmental Prediction (NCEP), T170L42 AGCM. The seasonal runs were made using six initial atmospheric conditions based on the NCEP operational analysis and with forecast monthly sea-surface temperature (SST) of the NCEP Coupled forecast system (CFS). These simulations were carried out on the PARAM Padma supercomputer of Centre for Development of Advanced Computing (C-DAC), India. The model climatology was prepared by integrating the model for ten years using climatological SST as the lower boundary. The climatology of the model compares well with the observed, in terms of the spatial distribution of rainfall over the Indian land mass. The model-simulated rainfall compares well with the Tropical Rainfall Measuring Mission (TRMM) estimates for the 2005 monsoon season. Compared to the model climatology (7.81 mm/day), the model had simulated a normal rainfall (7.75 mm/day) for the year 2005 which is in agreement with the observations (99% of long-term mean). However, the model could not capture the observed increase in September rainfall from that of a low value in August 2005. The circulation patterns simulated by the model are also comparable to the observed patterns. The ensemble mean onset is found to be nearer to the observed onset date within one pentad.  相似文献   

Simulation of monsoon depressions using MM5: sensitivity to cumulus parameterization schemes     

J. Venkata Ratnam  E. A. Cox 《Meteorology and Atmospheric Physics》2006,93(1-2):53-78

Summary The sensitivity of the simulation of the monsoon depressions to the cumulus parameterization schemes used in a numerical model is studied using the Pennsylvania State University – National Center for Atmospheric Research (PSU-NCAR) model MM5 version 3.6.2. Three different cases of monsoon depressions were studied with a two way interacting domains of 45 km and 15 km resolutions. Two different cumulus parameterization schemes namely Grell (GR) and Kain-Fritsch (KF) were used for the sensitivity study. The model was integrated for 48 hours with the initial and boundary conditions of European Center for Medium Range Weather Forecasting Reanalysis (ERA-40) data. The results show that both the schemes are able to simulate the large scale features of the monsoon depressions realistically. However, both the schemes failed to simulate the exact location of the depression after 24- and 48-hour simulation. The rainfall simulations of both the schemes were very different. The model with the GR scheme tends to over predict the rainfall. The KF scheme could simulate the distribution of the rainfall comparable to the observations. The KF scheme could simulate the maximum observed rainfall but due to locational errors of the simulated depression, the location of the maximum rainfall was not exact. It is also seen that the resolution of the model has a positive impact on the rainfall simulation. The GR and KF schemes were able to realistically simulate the apparent heat sources, but the apparent moisture profile simulated with KF scheme was more comparable to the verifying analysis. The root mean square errors of mean sea-level pressure, temperature, zonal wind and meridional wind were smaller for KF simulation compared to the GR simulation. Permanent affiliation: Center for Development of Advanced Computing, Pune University Campus, Ganeshkhind, Pune-411 007, India.  相似文献   

Weak discontinuities in relativisitic MHD     

A. V. Gopalakrishna  M. S. Ganagi 《Astrophysics and Space Science》1986,120(1):139-149

By using singular surface theory and ray theory the speeds of propagation of fast and slow waves, propagating into a medium in arbitrary motion, have been obtained in relativistic magnetohydrodynamics. The differential equation governing the growth of these waves along the rays has been derived and the solution has been presented in integral form.  相似文献   

Interannual variability of Kelvin wave propagation in the wave guides of the equatorial Indian Ocean,the coastal Bay of Bengal and the southeastern Arabian Sea during 1993–2006     

R.R. Rao  M.S. Girish Kumar  M. Ravichandran  A.R. Rao  V.V. Gopalakrishna  P. Thadathil 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):1-13

The observed variability of the Kelvin waves and their propagation in the equatorial wave guide of the Indian Ocean and in the coastal wave guides of the Bay of Bengal (BoB) and the southeastern Arabian Sea (AS) on seasonal to interannual time scales during years 1993–2006 is examined utilizing all the available satellite and in-situ measurements. The Kelvin wave regime inferred from the satellite-derived sea surface height anomalies (SSHA) shows a distinct annual cycle composed of two pairs of alternate upwelling (first one occurring during January–March and the second one occurring during August–September) and downwelling (first one occurring during April–June and the second one occurring during October–December) Kelvin waves that propagate eastward along the equator and hit the Sumatra coast and bifurcate. The northern branches propagate counterclockwise over varied distances along the coastal wave guide of the BoB. The potential mechanisms that contribute to the mid-way termination of the first upwelling and the first downwelling Kelvin waves in the wave guide of the BoB are hypothesized. The second downwelling Kelvin wave alone reaches the southeastern AS, and it shows large interannual variability caused primarily by similar variability in the equatorial westerly winds during boreal fall. The westward propagating downwelling Rossby waves triggered by the second downwelling Kelvin wave off the eastern rim of the BoB also shows large interannual variability in the near surface thermal structure derived from SODA analysis. The strength of the equatorial westerlies driven by the east–west gradient of the heat sources in the troposphere appears to be a critical factor in determining the observed interannual variability of the second downwelling Kelvin wave in the wave guides of the equatorial Indian Ocean, the coastal BoB, and the southeastern AS.  相似文献   

Observed intra-seasonal to interannual variability of the upper ocean thermal structure in the southeastern Arabian Sea during 2002–2008     

V.V. Gopalakrishna  F. Durand  K. Nisha  M. Lengaigne  T.P. Boyer  J. Costa  R.R. Rao  M. Ravichandran  S. Amrithash  L. John  K. Girish  C. Ravichandran  V. Suneel 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(6):739-754

The southeastern Arabian Sea (SEAS), located in the Indian Ocean warm pool, is a key-region of the regional climate system. It is suspected to play an important role in the dynamics of the Asian summer monsoon system. The present study reports the salient features derived from a newly harvested observational dataset consisting of repeated fortnightly XBT transects in the SEAS over the period 2002–2008. The fortnightly resolution of such a multi-year record duration is unprecedented in this part of the world ocean and provides a unique opportunity to examine the observed variability of the near-surface thermal structure over a wide spectrum, from intra-seasonal to interannual timescales. We find that most of the variability is trapped in the thermocline, taking the form of upwelling and downwelling motions of the thermal stratification. The seasonal variations are consistent with past studies and confirm the role of the monsoonal wind forcing through linear baroclinic waves (coastally-trapped Kelvin and planetary Rossby waves). Sub-seasonal variability takes the form of anomalous events lasting a few weeks to a few months and occurs at two preferred timescales: in the 30–110 day band, within the frequency domain of the Madden–Julian oscillation and in the 120–180 day band. While this sub-seasonal variability appears fairly barotropic in the offshore region, the sign of the anomaly in the upper thermocline is opposite to that in its lower part on many occasions along the coast. Our dataset also reveals relatively large interannual temperature variations of about 1 °C from 50 to 200 m depth that reflect a considerable year-to-year variability of the magnitude of both upwelling and downwelling events. This study clearly demonstrates the necessity for sustained long-term temperature measurements in the SEAS.  相似文献