Two temperature viscous accretion flows around rotating black holes: Description of under-fed systems to ultra-luminous X-ray sources     

S.R. Rajesh  Banibrata Mukhopadhyay 《New Astronomy》2010,15(3):283-291

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Possible solar control on primary production along the Indian west coast on decadal to centennial timescale     

Siby Kurian  Rajesh Agnihotri  D. V. Borole  S. Wajih A. Naqvi  Ana M. Ferreira  Carlos Vale 《第四纪科学杂志》2009,24(2):109-116

Using multiple geochemical proxies including specific biomarkers (dinosterol, phytol, stigmasterol and β‐sitosterol) measured in a high‐sedimentation rate core collected from the inner shelf (depth ～45 m) off Goa (India), we reconstruct surface productivity, which is mainly controlled by the monsoon upwelling in this region, during the last ca. 700 a. Surface productivity appears to have varied in tandem with the Konkan–Goa rainfall and sunspot activity during the instrumental period (last 250 a). The productivity proxies also covary with the total solar irradiance reconstructed for the period beyond the instrumental era, within the considerable uncertainty of the age model. This suggests that solar forcing may control coastal upwelling intensity and biological productivity in the eastern Arabian Sea on decadal to centennial timescales. During the late Anthropocene (last ca. 50 a), steep increases in all four biomarkers indicate greatly enhanced productivity in response to high solar irradiance as well as anthropogenic inputs of nutrients. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Propagation Characteristics and Generation Mechanism of ELF/VLF Hiss Observed at Low-latitude Ground Station (L = 1.17)     

Kalpana Singh  Rajesh Singh  A. K. Singh  R. P. Singh 《Earth, Moon, and Planets》2007,100(1-2):17-29

Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag. lat. 22°16′ N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values (L = 4–5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave–particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF/VLF hiss.  相似文献   

Four-dimensional structure and sub-seasonal regulation of the Indian summer monsoon multi-decadal mode     

Rajesh  P. V.  Goswami  B. N. 《Climate Dynamics》2020,55(9-10):2645-2666

A better understanding of the drivers and teleconnection mechanisms responsible for the multi decadal mode (MDM) of variability of the Indian summer monsoon rainfall (ISMR) with major socio-economic impacts in the region through clustering of large-scale floods or droughts is key to improving the poor simulation of ISMR MDM by most climate models. Here, using the longest instrumental record of ISMR available (1813–2006) and longest atmospheric and oceanic re-analyses, the global four dimensional (space–time) structures of atmospheric and oceanic fields of the multi-decadal mode of ISMR and sub-seasonal evolution of the teleconnection mechanism are brought out, essential for understanding underlying drivers but lacking so far. The relationships between the spatial structure of winds, Sea Surface Temperature (SST) and thermocline depth with the ISMR MDM indicate that the tropical ocean over the Indo-Pacific domain is passive responding primarily to the surface winds associated with the mode. A close association between the Atlantic Meridional Overturning Circulation (AMOC), north Atlantic (NA) SST, NA sea surface salinity (SSS) and the ISMR MDM indicate a slow oceanic pathway linking NA SST and the ISMR. In addition to strong correlation (~ 0.9) between global spatial patterns of JJAS SST associated with the MDMs of ISMR, NA SST and AMOC, strong temporal coherence (correlations ~ 0.9) between them is suggestive of regulation of the ISMR MDM (T ~ 65-years) by the NA SST associated with the Atlantic Multidecadal Oscillation (AMO) through a ‘fast’ atmospheric bridge. On a seasonal time scale, the atmospheric bridge manifests in the form of a stationary Rossby wave train generated by an anticyclonic (cyclonic) barotropic vorticity located above positive (negative) SST anomaly over NA in two phases of the AMO. That the AMO SST is the driver of the ISMR MDM is further supported when we unravel the sub-seasonal face of the teleconnection between the two. We show that phase locking of active (break) spells with annual cycle during positive (negative) phases of the ISMR MDM are forced by a similar phase locking of barotropic anticyclonic (cyclonic) vorticity over the NA SST with the annual cycle through the generation of a quasi-stationary Rossby wave train with an anticyclonic (cyclonic) vorticity at upper level over the Indian region with the NA columnar vorticity leading Indian monsoon rainfall by about a week. Our findings provide a basis for enhanced predictability of tropical climate through slow modulation by extra-tropical SST.

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Assessment of seawater mixing in a coastal aquifer by high resolution electrical resistivity tomography   总被引：1，自引：0，他引：1  

S. Sathish  L. Elango Ph.D.  R. Rajesh M.Sc.  V. S. Sarma Ph.D. 《International Journal of Environmental Science and Technology》2011,8(3):483-492

Seawater intrusion is a major problem in urbanized coastal regions of India which is due to over exploitation of groundwater for various purposes. This study was carried out with the objective of assessing the zone of mixing between seawater and groundwater in the coastal aquifer in south of Chennai, Tamil Nadu, India using high resolution electrical resistivity tomography. High resolution electrical resistivity tomography was carried out in five profiles perpendicular to the sea using IRIS make SYSCAL Pro-96 system with 2.5 m or 5 m inter-electrode separation. The maximum length of the profile was 170 m which resulted in a depth of investigation of 28.7 m. The apparent resistivity measured in this area varies from 0.3 ohm-m to 30,000 ohm-m. The apparent resistivity of saturated zone decreases towards the sea, indicating the influence of seawater. This was also confirmed by measuring the electrical conductivity of groundwater, which gradually increases from 156 μS/cm to 3430 μS/cm towards the sea. Further, the concentration profiles of electrical conductivity, sodium, chloride and chloride / bicarbonate ratio are compared with the high resolution electrical resistivity tomography profile. The distance of influence of seawater is comparatively high in northern part than in southern part of the area. The high resolution electrical resistivity tomography was effectively used to determine the effect of seawater mixing with groundwater.  相似文献   

Biological stabilization of mine dumps: shear strength and numerical simulation approach with special reference to Sisam tree     

Rajesh Rai  B. K. Shrivastva 《Environmental Earth Sciences》2011,63(1):177-188

The stability of mine waste dump is very important for an economic and safety point of view. The biological method is the most popular and eco-friendly approach to stabilize the mine waste dump in the long term. Trees outclass grasses and shrubs for long term stability as the roots of trees are stronger and penetrate deeper. Their roots bind the dump material and form a composite material having high shear strength. The mechanics of stabilization by tress have yet not been fully understood. Moreover, one always refers to biological stabilization of slope qualitatively rather than quantitatively. A numerical simulation tool has been used in the present paper to assess the increased factor of safety of a vegetated dump slope. The Sisam tree was chosen for the present study as it is commonly available in northern India, needs little care and has high economic value. The increased shear strength of the dump mass having tree roots was calculated by shear box test. The tree roots occupy large space, hence, a large size shear box (1.5 m × 1.5 m × 0.75 m) has specifically been designed and fabricated for determining the shear strength of dump root matrix. A small size shear box (0.30 m × 0.30 m × 0.15 m) has also been designed and fabricated to determine the increased shear strength due to small trees. It was observed that the Sisam tree of even moderate size binds the upper layers of mine dump and improve the factor of safety substantially. It was also observed that the stability of dump slope improves with time (i.e. size of tree).  相似文献   

Gas-hydrate stability thickness map along the Indian continental margin   总被引：2，自引：0，他引：2  

Kalachand Sain  V. Rajesh  N. Satyavani  K.V. Subbarao  C. Subrahmanyam 《Marine and Petroleum Geology》2011,28(10):1779-1786

The gas-hydrate stability thickness (GHST) map along the Indian continental margin is prepared from available bathymetry, sea-bottom temperature and geothermal gradient data. The bottom-simulating reflector (BSR) often marks the base of gas-hydrate stability zone. The prior information about the stability thickness in a particular area will help in identifying BSR on seismic data. The map is also useful to the exploration scientists to set a depth window within which proxies for gas-hydrate can be looked into. A GHST map was initially prepared in 1998 based on the-then available data. A lot of new data has been generated by various organizations under the Indian National Gas Hydrate Programs for the advancement of exploration and exploitation activities. By incorporating the new data from the published and available documents, we have modified the GHST map along the Indian margin. Besides filling the data gap, the new map shows the gas-hydrate stability zone in the Andaman offshore. In addition, we show maps of sea-bottom temperature, sediment thickness, geothermal gradient and heat flow to provide a bird’s eye view of these parameters along the continental margin of India.  相似文献   

Interplanetary turbulences causing unusual anisotropic wave trains in cosmic rays     

Rajesh K. Mishra  Rekha Agarwal Mishra 《Astroparticle Physics》2007,26(6):387-397

The various observed harmonics of the cosmic ray variation may be understood on a unified basis if the free space cosmic ray anisotropy is non-sinusoidal in form. The major objective of this paper is to study the first three harmonics of high amplitude wave trains of cosmic ray intensity over the period 1991–1994 for Deep River Neutron Monitoring Station. The main characteristic of these events is that the high amplitude wave trains shows a maximum intensity of diurnal component in a direction earlier than 1800 Hr/co-rotational direction. It is noticed that these events are not caused either by the high-speed solar wind streams or by the sources on the Sun responsible for producing these streams such as polar coronal holes. The direction of semi-diurnal anisotropy shows negative correlation with Bz. The occurrence of high amplitude events is dominant for the positive polarity of Bz component of IMF. The diurnal amplitude of these events shows a negative and the time of maximum shows a weak correlation with disturbance storm time index Dst. The direction of tri-diurnal anisotropy of these events is found to significantly correlate with geomagnetic activity index Ap.  相似文献   

Harmonics of exceptionaly low amplitude anisotropic wave train events in cosmic ray intensity     

Rajesh K. Mishra  Rekha A. Mishra 《Astrophysics》2007,50(2):254-264

The unusually low amplitude anisotropic wave train events (LAEs) in cosmic ray intensity using the ground based Deep River neutron monitor data has been studied during the period 1991–94. It has been observed that the phase of the diurnal anisotropy for the majority of the LAE events remains in the co-rotational direction. However, for some of the LAE events the phase of the diurnal anisotropy shifts towards earlier hours as compared to the annual average values. On the other hand, the amplitude of the semi-diurnal anisotropy remains statistically the same, whereas phase shift-towards later hours; a similar trend has also been found in case of tri-diurnal anisotropy. The high-speed solar wind streams do not play a significant role in causing the LAE events. The occurrence of LAE is independent of the nature of the Bz component of IMF polarity. Published in Astrofizika, Vol. 50, No. 2, pp. 313–324 (May 2007).  相似文献   

Ionic characters of lake water of Bharti promontory,Larsemann Hills,East Antarctica     

Prakash K. Shrivastava  Rajesh Asthana  M. Javed Beg  Rasik Ravindra 《Journal of the Geological Society of India》2011,78(3):217-225

The Larsemann Hills area represents a unique environmental setting between marine and glacial ecosystems. One of the promontories of this region, named Bharti, depicting similar set up was selected for the study of chemical parameters with special reference to its ionic characters. Water samples from 6 selected lakes of Bharti promontory, Larsemann Hills area were collected during the austral summer of 2004–05 and analysed for major ionic concentration and Total Dissolved Solid (TDS). This study is aimed at understanding the water chemistry of lakes of this island with emphasis on correlation between different ionic concentrations, TDS and its possible causes. The study will provide baseline data that will be useful for planning further studies. Analytical result shows that the water chemistry of these lakes is mainly governed by the lithology, precipitation, drainage and marine environment. Minor contribution of evaporation, has also been observed on the chemistry of one of the lake water. The main source of water for these lakes comes mainly from snow precipitation and its melting. The drainage line mostly goes towards eastern direction for these lakes.  相似文献