Detection of Rain/Cloud Pixels by Ka-band AltiKa Altimeter over the Tropical Region: Development of a Rain/Cloud Flag Algorithm and its Validation     

Partha Roy  Rakesh Mohan Gairola 《Marine Geodesy》2015,38(3):86-106

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Effect of ion kinematic viscosity on large amplitude dust ion acoustic solitary waves     

Kaushik Roy  Taraknath Saha  Prasanta Chatterjee 《Astrophysics and Space Science》2014,349(2):745-751

Nonlinear dust ion acoustic solitary waves (DIASW) in dusty plasma are studied incorporating kinematic viscosity, using Sagdeev’s pseudopotential approach. The effects of kinematic viscosity and the nonextensive parameter q on the features of DIASW are investigated in some detail.  相似文献   

RETRACTED ARTICLE: Observing the result of external magnetic field with nonextensivity on DA waves for two temperature electrons in a dusty plasmas     

M. S. Zobaer  N. Roy  A. A. Mamun 《Astrophysics and Space Science》2014,350(1):231-236

This theoretical investigation has been made on dust-acoustic (DA) waves containing nonextensivity of electrons being two different temperatures, negatively charged dust grains, and Maxwellian ions. The Zakharov-Kuznetsov (Z-K) equation has been derived and numerically solved to analysis the basis features. It is observed that the characteristics of the DA solitary waves (DASWs) are significantly modified by the external magnetic field with the different temperatures for electrons followed by the nonextensive distribution. The results obtained from this analysis can be employed in understanding the nature of plasma waves both in laboratory and space plasma system.  相似文献   

Shock waves in a dusty plasma having q-nonextensive electron velocity distribution     

Kaushik Roy  Prasanta Chatterjee  S. S. Kausik  C. S. Wong 《Astrophysics and Space Science》2014,350(2):599-605

The dust-acoustic shock waves have been theoretically investigated using reductive perturbation technique. An unmagnetized four-component dusty plasma system consisting of nonextensive q-distributed electrons, Boltzmann distributed ions, and negatively as well as positively charged dust particles has been considered. The solution of Burgers equation in planar geometry is numerically analyzed. It has been observed that the nonextensive q-distribution of electrons has a significant role in the formation of shock waves. The relevance of our results to astrophysics as well as laboratory plasmas are briefly discussed.  相似文献   

Snowpack and runoff response to climate change in Owens Valley and Mono Lake watersheds     

Mariza Costa-Cabral  Sujoy B. Roy  Edwin P. Maurer  William B. Mills  Limin Chen 《Climatic change》2013,116(1):97-109

Precipitation from the Eastern Sierra Nevada watersheds of Owens Lake and Mono Lake is one of the main water sources for Los Angeles’ over 4 million people, and plays a major role in the ecology of Mono Lake and of these watersheds. We use the Variable Infiltration Capacity (VIC) hydrologic model at daily time scale, forced by climate projections from 16 global climate models under greenhouse gas emissions scenarios B1 and A2, to evaluate likely hydrologic responses in these watersheds for 1950–2099. Comparing climate in the latter half of the 20th Century to projections for 2070–2099, we find that all projections indicate continued temperature increases, by 2–5 °C, but differ on precipitation changes, ranging from ?24 % to +56 %. As a result, the fraction of precipitation falling as rain is projected to increase, from a historical 0.19 to a range of 0.26–0.52 (depending on the GCM and emission scenario), leading to earlier timing of the annual hydrograph’s center, by a range of 9–37 days. Snowpack accumulation depends on temperature and even more strongly on precipitation due to the high elevation of these watersheds (reaching 4,000 m), and projected changes for April 1 snow water equivalent range from ?67 % to +9 %. We characterize the watershed’s hydrologic response using variables integrated in space over the entire simulated area and aggregated in time over 30-year periods. We show that from the complex dynamics acting at fine time scales (seasonal and sub-seasonal) simple dynamics emerge at this multi-year time scale. Of particular interest are the dynamic effects of temperature. Warming anticipates hydrograph timing, by raising the fraction of precipitation falling as rain, reducing the volume of snowmelt, and initiating snowmelt earlier. This timing shift results in the depletion of soil moisture in summer, when potential evapotranspiration is highest. Summer evapotranspiration losses are limited by soil moisture availability, and as a result the watershed’s water balance at the annual and longer scales is insensitive to warming. Mean annual runoff changes at base-of-mountain stations are thus strongly determined by precipitation changes.  相似文献   

A megacity in a changing climate: the case of Kolkata     

Susmita Dasgupta  Asvani K. Gosain  Sandhya Rao  Subhendu Roy  Maria Sarraf 《Climatic change》2013,116(3-4):747-766

Projections by the Intergovernmental Panel on Climate Change suggest that there will be an increase in the frequency and intensity of climate extremes in the 21st century. Kolkata, a megacity in India, has been singled out as one of the urban centers vulnerable to climate risks. Modest flooding during monsoons at high tide in the Hooghly River is a recurring hazard in Kolkata. More intense rainfall, riverine flooding, sea level rise, and coastal storm surges in a changing climate can lead to widespread and severe flooding and bring the city to a standstill for several days. Using rainfall data, high and low emissions scenarios, and sea level rise of 27 cm by 2050, this paper assesses the vulnerability of Kolkata to increasingly intense precipitation events for return periods of 30, 50, and 100 years. It makes location-specific inundation depth and duration projections using hydrological, hydraulic, and urban storm models with geographic overlays. High resolution spatial analysis provides a roadmap for designing adaptation schemes to minimize the impacts of climate change. The modeling results show that de-silting of the main sewers would reduce vulnerable population estimates by at least 5 %.  相似文献   

The rapid growth and decay of severe cyclone JAL (2010) over the Bay of Bengal     

S. D. Kotal  S. K. Bhattacharya  S. K. Roy Bhowmik  P. K. Kundu 《Meteorology and Atmospheric Physics》2013,121(3-4):161-179

This study investigates the life cycle of Bay of Bengal cyclone JAL, characterized by a rapid fluctuation in its intensity during 60-h interval. The cyclone JAL underwent a period of rapid intensification during 24-h from 0000 UTC 05 November to 0000 UTC 06 November 2010. It was quasi-static during subsequent 24 h followed by a 12-h period of unusually rapid decay. During the rapid cyclogenesis phase, the system intensified (by 25 kt) from deep depression (DD) to severe cyclonic storm (SCS) and weakened (by 30 kt) from SCS to DD during the 12-h period of rapid cyclolysis. European Centre for Medium Range Weather Forecasts (ECMWF) model analysis field is used to analyze the Q vectors, K index and potential vorticity (PV) to diagnose the life cycle of this unusual cyclone. The analysis reveals that the 500–700 hPa column-averaged Q-vector convergence above the surface cyclone had strengthened and very high values of the K index produced a burst of heavy precipitation during the development stage of the cyclone. The associated latent heat release produced a substantial diabatic positive PV anomaly in the lower and middle troposphere that caused rapid cyclogenesis. The rapid cyclolysis is coincident with the weakening of the upper and lower PV anomalies and the westward shearing of the upper PV from the cyclone centre. Thus, the very latent heat release that assisted the rapid development of the cyclone also played an important role in its subsequent rapid decay. ECMWF model forecast for track and intensity is also verified.  相似文献   

Spatial patterns of diurnal variations in summer-season lightning activity across the tropical and subtropical regions of the Northern Hemispheric Americas     

Shouraseni Sen Roy  Robert C. Balling Jr. 《Meteorology and Atmospheric Physics》2013,121(3-4):199-206

Hourly lightning data were obtained from the Tropical Rainfall Measuring Mission dataset collected through the Lightning Imaging Sensor instrument from 1998 to 2011 to analyze the diurnal pattern of lightning activity in the tropical and subtropical northern hemispheric Americas. The majority of the lightning strikes occurred over land, with relatively lower strike rates over the oceanic areas. The results of our studies showed substantial spatial variations in the time of maximum and strength of the diurnal cycle in the study area. A clockwise progression in the time of maximum was observed across most of the study area, particularly over North America where an east–west orientation was observed. The findings of our study were mainly a result of the interaction between local topography such as the Andes and Rocky mountains, and surface level atmospheric circulations. The strength of the observed diurnal cycle was greatest in the Gulf of Mexico region.  相似文献   

Geochemical characteristics of Holocene sediments from Chuadanga district,Bangladesh: Implications for weathering,climate, redox conditions,provenance and tectonic setting     

Ismail Hossain  Krisna Kanta Roy  Pradip Kumar Biswas  Mahbubul Alam  Md. Moniruzzaman  Farah Deeba 《中国地球化学学报》2014,33(4):336-350

The present research deals with the geochemical characteristics of the Holocene sediments from Alamdanga area, Chuadanga district, Bangladesh. Main goals of the study are to delineate source rock characteristics, degree of chemical weathering and sorting processes and behavior of redox conditions during deposition of the sediments. Geochemical characteristics of the sediments show comparatively a wide variation in accordance with stratigraphy in their major element contents （e.g. SiO2 69.46-82.13, A1203 2.28-8.88 in wt%）, reflecting the distinctive provenance and in part an unstable period in terms of tectonic activity. Geochemical classification of the sediments shows mostly sub-arkose with few sub-litharenites. Some major and trace elements display comprehensible correlation with A1203 confirming their possible hydraulic fraetionation. The chemical index of alteration （CIA＊）, W＊ index, index of compositional variability （ICV）, plagioclase index of alteration （PIA＊） values and the ratio of SIO2/Al2O3, suggest low degrees of chemical weathering in the source areas as well as immature to moderately mature the sediments. The sediments suggest semi-arid climatic trends within oxic deltaic depositional conditions during the Holocene, at 3-12 ka. Whole rock geochemistry and discrimination diagrams demonstrate the continental signature derivatives, which might have been derived from the felsic to intermediate igneous rocks （granitic plutonic rocks） as well as from quartzose sedimentary/metamorphic provenance. These typical sources are present in a vast region of the Himalayan belt and catchment areas of Ganges. The tectonic setting of the sediments demarcates typically passive margin with slightly continental arc system.  相似文献   

The subsurface megascopic characteristics of basalt and basement rocks from Koyna-Warna area of Maharashtra,India     

D. K. Sinha  Anjan Som  Sukanta Roy 《Journal of the Geological Society of India》2017,90(6):761-768

Vertical deep boreholes of depth up to 1522.50m have been drilled in Koyna-Warna area of Maharashtra State within the Deccan Volcanic Province to study the most outstanding example of Reservoir Triggered Seismicity (RTS). The drilling of 9 bore-holes in the area has provided a window to earth scientists to peep into geological details available below Deccan Trap.The 932.50m thick pile of Deccan basalt, consisting of 30 flows at Rasati, near Koyna, which has been physically seen through cores, present a marvellous geological repository for observations. The megascopic characteristics of various flows and variation in composition have been presented in this paper. The microscopic and geochemical characteristics have been kept out of this communication, as the relevant studies are not completed to draw any conclusion. This study records the presence of granite wash (≈1m thick) over basement and below basalt representing Late Archaean to Cretaceous period hiatus. The basement rocks, presumably of Late Archaean age have been described mega-scopically. A fair picture of sub-surface pre-Deccan topography is shown with the help of borehole data, which confirm the nearly flat topography of pre-Deccan surface especially in this part of the area occupied by 30 flows of Deccan basalt. Correlation of 30 flows with the established stratigraphy has also been attempted for subsurface existence of Ambenali (Upper) and Poladpur Formations of Wai Subgroup in Koyna-Warna area.  相似文献