Different atmospheric moisture divergence responses to extreme and moderate El Niños     

Guangzhi Xu  Timothy J. Osborn  Adrian J. Matthews  Manoj M. Joshi 《Climate Dynamics》2016,47(1-2):393-410

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Palaeochannel controlled Cretaceous sandstone-type uranium deposit of Lostoin area,Mahadek basin,Meghalaya     

Pramod Kumar  B. Panigrahi  G. B. Joshi 《Journal of the Geological Society of India》2016,87(4):424-428

Sandstone–type uranium deposit hosted by reduced feldspathic sandstone sequence of lower part of Cretaceous Mahadek Formation occurs at Lostoin area of Mahadek basin and is confined within a prominent palaeochannel of NNE-SSW trend with flow towards SSW. The channel-fill comprises of about 10 m to 55 m grey to dark grey coloured, reduced, coarse to medium grained feldspathic sandstone along with abundant carbonaceous matter (5 to 15% by visual estimation) and is overlain by 5 m to 80 m of oxidized sub-feldspathic sandstone. Correlatable medium grade (～ 0.1% U₃O₈) uranium mineralization is intercepted in the boreholes aligned along the palaeochannel. Uraniferous solutions generated from the fertile provenance of south Khasi batholith flow through the channel and precipitated uranium at suitable reduction traps. Gentle slope of 2° to 3° of the basement channel facilitated prolonged interaction of uraniferous solution with reductants causing ore grade concentration. It has been envisaged that the control of palaeochannel and palaeobasement topography of the ore body would continue towards the SSW beyond Wahblei river.  相似文献   

Subsurface profiling of granite pluton using microtremor method: southern Aravalli,Gujarat, India     

Joshi  Aditya U.  Sant  Dhananjay A.  Parvez  Imtiyaz A.  Rangarajan  Govindan  Limaye  Manoj A.  Mukherjee  Soumyajit  Charola  Mitesh J.  Bhatt  Meghnath N.  Mistry  Sagar P. 《International Journal of Earth Sciences》2018,107(1):191-201

International Journal of Earth Sciences - We report, using the microtremor method, a subsurface granitic pluton underneath the Narukot Dome and in its western extension along a WNW profile, in...  相似文献   

Effect of Forest Fire on Snow Reflectance in Uttarakhand Region: An Analysis Using AWiFS and INSAT-3D Data     

Purvee P. Joshi  S. K. Singh  B. P. Rathore  I. M. Bahuguna  Raj Kumar 《Journal of the Indian Society of Remote Sensing》2018,46(12):2107-2111

In the summer of 2016, fire broke out in the forests of Uttarakhand state. The effect of forest fire was thought to have severe impact on nearby glaciated region in terms of faster melting. It is understood that contamination and heat enhance the snowmelt, which reduces the reflectance in different part of EM spectrum. In order to assess the effect, AWiFS and IMAGER data from Resourcesat-1 and INSAT-3D, respectively, for the months of April and May of the years 2012, 2013, 2014 and 2016 were used to compare the reflectance of snow. It was observed that pre- and post-fire data of 2016 show drop in reflectance in comparison with earlier years. The change in reflectance for locations near to forest fire was significantly high in comparison with previous year images, whereas far-away locations did not show much change. This drastic drop may be attributed to deposition of black carbon on nearby locations in snow-covered area. AWS data of nearby Joshimath observatory were also analysed to avoid any anomalous change in temperature for the same duration.  相似文献   

Growth and decay of the Arabian Sea mini warm pool during May 2000: Observations and simulations     

P.V. Hareesh Kumar  Madhu Joshi  K.V. Sanilkumar  A.D. Rao  P. Anand  K. Anil Kumar  C.V.K. Prasada Rao 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(4):528-540

Oceanographic surveys were carried out in the southeastern Arabian Sea in two phases during 14–17 May and 23–27 May 2000 to study the evolution of the Arabian Sea mini warm pool. The hydrographic data collected during these experiments, satellite imagery of sea surface temperature for the corresponding period and ship drift data were utilized for this purpose. Both satellite and in situ observations indicated the presence of a mini warm pool up to 14 May and its dissipation thereafter. The Arabian Sea mini warm pool region was characterized by low-salinity Bay of Bengal water (<22 sigma-t). This watermass was advected into the southeastern Arabian Sea by the East India Coastal Current mainly during November–January and recirculated in this region in an anticyclonic eddy. Immediately after the dissipation of the mini warm pool, this watermass could not be traced in this region. Simulation of mini warm pool characteristics using the Princeton Ocean Model (POM) agreed well with in situ and satellite observations. Moreover, the model showed strengthening of southerly currents in the warm pool region during its dissipation period, which caused the disappearance of the Bay of Bengal watermass. Specific experiments with the POM revealed the significance of heat flux components, low wind speed and salinity stratification in the formation and sustenance of the mini warm pool.  相似文献   

New class of regular and well behaved exact solutions in general relativity     

Neeraj Pant  R. N. Mehta  Mamta Joshi Pant 《Astrophysics and Space Science》2010,330(2):353-359

We present a new class of spherically symmetric regular and well behaved solutions of the general relativistic field equations in isotropic coordinates. These solutions describe perfect fluid balls with positively finite central pressure and positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The solutions of this class, the outmarch of pressure, density pressure-density ratio and the ratio of sound speed to light is monotonically decreasing. Keeping in view of well behaved nature in terms of central red shift and surface red shift and by assuming the surface density ρ _b =2×10¹⁴ g/cm³, we constructed a Neutral star model for k=2, resulting into maximum mass ≈6.36M _Θ, linear dimension ≈48.08 km, surface red shift ≈1.132 and central red shift ≈17.1314.  相似文献   

Pre-processing of TerraSAR-X Data for Speckle Removal: An Approach for Performance Evaluation     

Rakesh Joshi  R. D. Garg 《Journal of the Indian Society of Remote Sensing》2012,40(3):371-377

Measures to select despeckling filter to remove speckles from TerraSAR-X image have been evaluated for an area having varied land cover classes. Gamma, Lee, Sigma, Mean, Median and Frost filters were applied in different window sizes. These images are visually compared and four parameters viz. Noise Mean Value (NMV), Noise Variance (NV), Mean Square Difference (MSD) and Equivalent Numbers of Looks (ENL) are calculated. These parameters were well implemented to compare results of various despeckling filters on TerraSAR-X image recorded in high resolution spot mode and checked for the constraints. Median 7x7 filter was found most suitable among other filters to despeckle the images.  相似文献   

Relationship between interplanetary field/plasma parameters with geomagnetic indices and their behavior during intense geomagnetic storms     

Navin Chandra Joshi  Neeraj Singh Bankoti  Seema Pande  Bimal Pande  Kavita Pandey 《New Astronomy》2011,16(6):366-385

This paper presents a correlative study between the peak values of geomagnetic activity indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (Bt, Bz, E and σ_B) and plasma (T, D, V, P and β) parameters along with their various products (BV, BzV and B²V) during intense geomagnetic storms (GMSs) for rising, maximum and decay phases as well as for complete solar cycle 23. The study leads to the conclusion that the peak values of different geomagnetic activity indices are in good correlation with Bt, Bz, σ_B, V, E, BV, BzV and B²V, therefore these parameters are most useful for predicting GMSs and substorms. These parameters are also reliable indicators of the strength of GMSs. We have also presented the lag/lead time analysis between the maximum of Dst and peak values of geomagnetic activity indices, various interplanetary field/plasma parameters for all GMSs. We have found that the average of peak values of geomagnetic activity indices and various field/plasma parameters are larger in decay phase compare to rising and maximum phases of cycle 23. Our analyses show that average values of lag/lead time lie in the ≈?4.00 h interval for Kp, ap and AE indices as well as for Bt, Bz, σ_B, E, D and P. For a more meaningful analysis we have also presented the above study for two different groups G1 (CME-driven GMSs) and G2 (CIR-driven GMSs) separately. Correlation coefficients between various interplanetary field/plasma parameters, their various products and geomagnetic activity indices for G1 and G2 groups show different nature. Three GMSs and associated solar sources observed during three different phases of this solar cycle have also been studied and it is found that GMSs are associated with large flares, halo CMEs and their active regions are close to the solar equator.  相似文献   

On the relationship between Arabian Sea warm pool and formation of onset vortex over east-central Arabian Sea     

R. Deepa  C. Gnanaseelan  P. Seetaramayya  S. G. Nagar 《Meteorology and Atmospheric Physics》2010,108(3-4):113-125

The interannual variability in the formation of mini warm pool (MWP, SST ≥ 30.5°C) and its impact on the formation of onset vortex (OV) over the east-central Arabian Sea (ECAS) are addressed by analyzing the NCEP OIV 2-weekly SST data and NCEP–NCAR reanalysis 850 hPa wind fields from May to June (prior to the onset of monsoon) over the north Indian Ocean for a period of 12 years from 1992 to 2003. Strong interannual variability in the formation and intensification of MWP was observed. Further, the 850 hPa wind fields showed that OV developed into an intense system only during 1994, 1998 and 2001. It formed in the region north of the MWP and on the northern flank of the low-level jet axis, which approached the southern tip of India just prior to the onset of monsoon, similar to the vortex of MONEX-79. The area-averaged zonal kinetic energy (ZKE) over the ECAS (8–15°N, 65–75°E) as well as over the western Arabian Sea (WAS, 5°S–20°N, 50–70°E) showed a minimum value of 5–15 m² s^?2 prior to monsoon onset over Kerala (MOK), whereas a maximum value of 280 m² s^?2 (40–70 m² s^?2) was observed over the ECAS (WAS) during and after MOK. The study further examined the plausible reasons for the occurrence of MWP and OV.  相似文献   

Spectropolarimetery of umbral fine structures from Hinode: evidence for magnetoconvection     

Lokesh Bharti †  Chandan Joshi  S. N. A. Jaaffrey  Rajmal Jain 《Monthly notices of the Royal Astronomical Society》2009,393(1):65-70

We present spectropolarimetric analysis of umbral dots and a light bridge fragment that show dark lanes in G -band images. Umbral dots show upflow as well as associated positive Stokes V area asymmetry in their central parts. Larger umbral dots show downflow patches in their surrounding parts that are associated with negative Stokes V area asymmetry. Umbral dots show weaker magnetic field in central part and higher magnetic field in peripheral area. Umbral fine structures are much better visible in total circularly polarized light than in continuum intensity. Umbral dots show a temperature deficit above dark lanes. The magnetic field inclination shows a cusp structure above umbral dots and a light bridge fragment. We compare our observational findings with 3D magnetohydrodynamic simulations.  相似文献