New approach for interpretation of scattered ground magnetic data in a part of Delhi Fold Belt-NW Indian shield     

Prabhakara Prasad P.  Satish Kumar K.  Seshunarayana T.  Rama Rao Ch. 《Arabian Journal of Geosciences》2014,7(7):2633-2639

Randomly distributed ground magnetic data sets, collected along parallel and closely spaced profiles, in small blocks, the blocks being separated/distributed widely over a large area, become, sometimes, unamenable for deriving a meaningful geological model. In such a situation, an approach of “Cumulative Total Intensity Magnetic Anomaly Field (CTIMAF)” has been devised to interpret the sparsely distributed magnetic data sets. A case history has been presented from the lead–zinc mineralized provenance of Ajabgarh Formation of Delhi Fold Belt in the northern part of Ajmer Town. Log-normalized radially averaged power spectrum was computed for the Cumulative Total Intensity Magnetic Anomaly data and depth to the basement is derived. The computed depth of 4.5 km is in good agreement with the Deep Seismic Studies.  相似文献   

Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time     

R G Rastogi  H Chandra  P Janardhan  Thai Lan Hoang  Louis Condori  T K Pant  D S V V D Prasad  B Reinisch 《Journal of Earth System Science》2014,123(6):1273-1285

The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.  相似文献   

Impact of Doppler weather radar data on thunderstorm simulation during STORM pilot phase—2009   总被引：1，自引：1，他引：0  

S. Kiran Prasad  U. C. Mohanty  A. Routray  Krishna K. Osuri  S. S. V. S. Ramakrishna  Dev Niyogi 《Natural Hazards》2014,74(3):1403-1427

This study assesses the impact of Doppler weather radar (DWR) data (reflectivity and radial wind) assimilation on the simulation of severe thunderstorms (STS) events over the Indian monsoon region. Two different events that occurred during the Severe Thunderstorms Observations and Regional Modeling (STORM) pilot phase in 2009 were simulated. Numerical experiments—3DV (assimilation of DWR observations) and CNTL (without data assimilation)—were conducted using the three-dimensional variational data assimilation technique with the Advanced Research Weather Research and Forecasting model (WRF-ARW). The results show that consistent with prior studies the 3DV experiment, initialized by assimilation of DWR observations, performed better than the CNTL experiment over the Indian region. The enhanced performance was a result of improved representation and simulation of wind and moisture fields in the boundary layer at the initial time in the model. Assimilating DWR data caused higher moisture incursion and increased instability, which led to stronger convective activity in the simulations. Overall, the dynamic and thermodynamic features of the two thunderstorms were consistently better simulated after ingesting DWR data, as compared to the CNTL simulation. In the 3DV experiment, higher instability was observed in the analyses of thermodynamic indices and equivalent potential temperature (θ _e) fields. Maximum convergence during the mature stage was also noted, consistent with maximum vertical velocities in the assimilation experiment (3DV). In addition, simulated hydrometeor (water vapor mixing ratio, cloud water mixing ratio, and rain water mixing ratio) structures improved with the 3DV experiment, compared to that of CNTL. From the higher equitable threat scores, it is evident that the assimilation of DWR data enhanced the skill in rainfall prediction associated with the STS over the Indian monsoon region. These results add to the body of evidence now which provide consistent and notable improvements in the mesoscale model results over the Indian monsoon region after assimilating DWR fields.  相似文献   

Retrieval and Validation of Chlorophyll-a Concentrations in the Coastal Waters Off Yanam and Kakinada (Godavari) Basin Along East Coast of India     

T. Preethi Latha  P. V. Nagamani  K. H. Rao  S. K. Dash  S. B. Choudhury  Aziz Rehman  V. V. S. S. Sarma  M. Naveen Babu  P. Amarendra  B. Srinivasa Rao  T. D. V. Prasad 《Journal of the Indian Society of Remote Sensing》2014,42(1):129-138

In this study chlorophyll measurements were made during March 2012 in the estuarine waters of Off Kakinada and Yanam coast, Bay of Bengal onboard a coastal vessel. In-situ water samples and optical data was collected at 21 stations (surface to 150 m depth) using Underwater radiometer (Hyperpro-II). In-vivo chlorophyll profiles were collected using wet labs fluorometer integrated with underwater Hyperspectral radiometer. Chlorophyll-a concentrations were estimated using HPLC by collecting the water samples at each sampling location. And also chlorophyll-a concentrations were retrieved from the OCM-2 data of OCEANSAT-2 satellite, processed using SeaDAS v.6.2 with the available global ocean colour algorithms namely, OC2 and OC4V4. A total of 33 samples used covering all the stations for chlorophyll-a estimation, and surface water samples of all the stations only being used for direct comparison among chlorophyll concentrations of HPLC, in-situ (fluorometrically integrated to Hyperpro-II) and retrieved from OCM-2. A good correlation found between the Fluorometer derived and HPLC measured chlorophyll-a concentration with an R² value of 0.78. The relation between Chlorophyll-a concentration measured from HPLC and retrieved from OCM-2 (OC2 and OC4V4 algorithms) using SeaDASv.6.2 for 10 samples has been compared for validation and obtained an R² value of 0.6. Also comparisons done with the in-situ measured (fluorometer) Chlorophyll-a concentration with OCM-2 chlorophyll data (OC4-V4 and OC2 algorithms) and validation with 10 concurrent in-situ surface measurements showed a significant overestimation by OCM-2 at low chlorophyll-a concentrations and underestimation at high chlorophyll-a concentrations.  相似文献   

Persian Gulf response to a wintertime shamal wind event     

Prasad G. Thoppil  Patrick J. Hogan 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(8):946-955

The results from a～1 km resolution HYbrid Coordinate Ocean Model (HYCOM), forced by 1/2° Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric data, were used in order to study the dynamic response of the Persian Gulf to wintertime shamal forcing. Shamal winds are strong northwesterly winds that occur in the Persian Gulf area behind southeast moving cold fronts. The period from 20 November to 5 December 2004 included a well defined shamal event that lasted 4–5 days. In addition to strong winds (16 m s^?1) the winter shamal also brought cold dry air (T_a=20 °C, q_a=10 g kg^?1) which led to a net heat loss in excess of 1000 W m^?2 by increasing the latent heat flux. This resulted in SST cooling of up to 10 °C most notably in the northern and shallower shelf regions. A sensitivity experiment with a constant specific humidity of q_a=15 g kg^?1 confirmed that about 38% of net heat loss was due to the air–sea humidity differences. The time integral of SST cooling closely followed the air–sea heat loss, indicating an approximate one-dimensional vertical heat balance. It was found that the shamal induced convective vertical mixing provided a direct mechanism for the erosion of stratification and deepening of the mixed layer by 30 m. The strong wind not only strengthened the circulation in the entire Persian Gulf but also established a northwestward flowing Iranian Coastal Current (ICC, 25–30 cm s^?1) from the Strait of Hormuz to about 52°E, where it veered offshore. The strongest negative sea level of 25–40 cm was generated in the northernmost portion of the Gulf while the wind setup against the coast of the United Arab Emirates established a positive sea level of 15–30 cm. The transport through the Strait of Hormuz at 56.2°E indicated an enhanced outflow of 0.25 Sv (Sv≡10⁶ m³ s^?1) during 24 November followed by an equivalent inflow on the next day.  相似文献   

Free-convection flow in the stokes problem for a vertical plate with variable surface temperature     

Basant Kumar Jha  Ravindra Prasad  Surendra Rai 《Astrophysics and Space Science》1991,175(1):157-163

The free-convection flow of an incompressible viscous fluid past an infinite, vertical plate for impulsive as well as uniformly accelerated motion of the plate is discussed when the plate temperatuve varies as the square root of time. The Laplace transform technique is used to obtain the expressions for velocity and skin-friction. The influence of the various parameters, entering into problem, on the velocity field and skin-friction is extensively discussed.  相似文献   

MHD free-convection and mass transfer flow through a porous medium with heat source     

Basant Kumar Jha  Ravindra Prasad 《Astrophysics and Space Science》1991,181(1):117-123

An analytical study is performed to examine the heat source characteristics on the free-convection and mass transfer flow past an impulsively started infinite non-conducting vertical plate of a viscous, incompressible electrically-conducting fluid under the action of a uniform magnetic field through porous medium. The effects of various parameters on the velocity field are extensively discussed.  相似文献   

Hall effects on oscillatory MHD boundary-layer flow under variable suction     

M. U. S. Reddy  N. K. Samria  R. Prasad  H. N. Gupta 《Astrophysics and Space Science》1991,183(2):273-283

The effects of Hall current on the oscillatory hydromagnetic boundary-layer flow under variable suction, past an infinite porous flat plate in the presence of a transverse magnetic field is discussed. The expressions for velocity and skin-friction are obtained and their variations for small and large frequency of oscillations are extensively discussed.  相似文献   

Partial redistribution effects on line polarization in the presence of velocity fields     

K. N. Nagendra 《Solar physics》1996,164(1-2):67-78

Velocity fields in line formation regions strongly affect the line polarization. The conventionally used observer's frame method of solving the polarized transfer equation becomes expensive and inaccurate for partial redistribution problems, when large amplitude velocity fields have to be considered in the observer's frame. An alternative method of solution is the comoving frame method. Partial redistribution problems are solved using comoving frame formalism for line polarization caused by resonance scattering.  相似文献   

Non-static conformally flat spherically symmetric perfect fluid distribution in Einstein-Cartan theory     

R. B. S. Yadav  U. Prasad 《Astrophysics and Space Science》1993,205(1):37-42

In this paper we have obtained general solution representing conformally-flat, non-static spherically-symmetric perfect fluid distribution in Einstein-Cartan theory. In particular, the solution has been also discussed in co-moving coordinates. The explicit expressions for pressure, density, expansion, rotation, shear and non-vanishing components of flow vector have also been found.  相似文献