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251.
Suryachandra A. Rao Ashish R. Dhakate Subodh K. Saha Somnath Mahapatra Hemantkumar S. Chaudhari Samir Pokhrel Sobhan K. Sahu 《Climatic change》2012,110(3-4):709-719
Observations have shown that the Indian Ocean is consistently warming and its warm pool is expanding, particularly in the recent decades. This paper attempts to investigate the reason behind these observations. Under global warming scenario, it is expected that the greenhouse gas induced changes in air–sea fluxes will enhance the warming. Surprisingly, it is found that the net surface heat fluxes over Indian Ocean warm pool (IOWP) region alone cannot explain the consistent warming. The warm pool area anomaly of IOWP is strongly correlated with the sea surface height anomaly, suggesting an important role played by the ocean advection processes in warming and expansion of IOWP. The structure of lead/lag correlations further suggests that Oceanic Rossby waves might be involved in the warming. Using heat budget analysis of several Ocean data assimilation products, it is shown that the net surface heat flux (advection) alone tends to cool (warm) the Ocean. Based on above observations, we propose an ocean-atmosphere coupled positive feedback mechanism for explaining the consistent warming and expansion of IOWP. Warming over IOWP induces an enhancement of convection in central equatorial Indian ocean, which causes anomalous easterlies along the equator. Anomalous easterlies in turn excite frequent Indian ocean Dipole events and cause anti-cyclonic wind stress curl in south-east and north-east equatorial Indian ocean. The anomalous wind stress curl triggers anomalous downwelling oceanic Rossby waves, thereby deepening the thermocline and resulting in advection of warm waters towards western Indian ocean. This acts as a positive feedback and results in more warming and westward expansion of IOWP. 相似文献
252.
Bottom sediments of a river and of two sites of well showed significant changes in relation to different water factors. Comparatively, organic carbon, organic matter and free CaCO3 concentration were higher in the Sutapatti well than at other sites which may affect the quality of potable water considerably. 相似文献
253.
Dilip Saha 《Journal of Earth System Science》1995,104(3):419-431
In low temperature deformation of polymineralic rocks the constituent minerals often show contrasting deformation mechanisms.
In naturally deformed arkoses, feldspathic quartzites and grits under greenschist to almandine-amphibolite fades condition,
feldspar deforms by microboudinage (rigid-brittle behaviour), while quartz flows by a combination of dislocation creep, pressure
solution and solution transfer. Boudin segments develop and separate in a phased sequential manner while quartz matrix flows
in a ductile manner, indicating a brittle-ductile toggle during progressive deformation.
Both the pressure solution and dislocation creep flows are volume-conservative. Therefore, a net volume increase during the
above deformations is a necessity, unless compensated by a solution-transfer process. Hydrofracturing probably played a role
in microboudinage formation as the ambient level of differential stress is estimated to be low around 45–75 MPa.
To develop a synthetic flow law for the above type of deformation in arkoses, one needs to consider the significance of different
rate-controlling mechanisms. As feldspar pull-aparts are syntectonically filled with quartz or metamorphic minerals crystallizing
during progressive deformation, successive microboudin segmentation will depend on how fast/slow the matrix quartz moves to
the open crack or the sealing takes place by transfer of appropriate solute components by pressure solution or solution transfer,
the real rate-controlling process. 相似文献
254.
Kshudiram Saha 《Journal of Earth System Science》1993,102(1):241-247
Using the theory of plate tectonics and a concept of climate analogs, the paper speculates that a monsoon type of climate
with warm and wet summer and cold and dry winter might have first appeared over the northern part of India when during its
northward drift across the Tethys Ocean (now the Indian Ocean) it was located over the subtropical belt of the southern hemisphere
some 60 million years before present (BP). The monsoon climate gradually evolved and extended to other parts of India as the
Indian plate after crossing the equator about SO million years BP moved further northward and collided against the north Asian
plate giving rise to the Himalayas along the northern boundary of India some 40 million years BP. Recent studies suggest that
despite short and long period fluctuations, no major secular change or trend has taken place in the monsoon climate of India
since then. 相似文献
255.
Dipankar Saha Sreehari S. Sarangam Shailendra N. Dwivedi Kuldeep G. Bhartariya 《Environmental Earth Sciences》2010,61(4):799-811
The study region covers 1,650 km2 of the Mid-Ganga Basin in Bihar, experiencing intensive groundwater draft. The area forms a part of the Gangetic alluvial
plain where high incidence of arsenic groundwater contamination (>50 μg/l) has recently been detected. Seventy-seven groundwater
samples have been collected and analysed for major ions, iron and arsenic. Arsenic contamination (max 620 μg/l) is confined
in hand pump zones (15–35 m) within the newer alluvium deposited during Middle Holocene to Recent age. The older alluvial
aquifers are arsenic-safe and recorded maximum concentration as 9 μg/l. Out of 12 hydrochemical facies identified, four have
been found arsenic-affected: Ca–HCO3, Mg–HCO3, Ca–Mg–HCO3 and Mg–Ca–HCO3. The geochemical evolution of groundwater, as investigated by graphical interpretation and statistical techniques (correlation,
principal component analysis) revealed that dissolution of detrital calcite, dolomite and infiltration of rainwater are the
major processes shaping the groundwater chemistry in the newer alluvium. Arsenic and iron showed strong positive correlation.
Rainfall infiltration, carrying organic matter from recently accumulated biomass from this flood-prone belt, plays a critical
role in releasing arsenic and iron present in the sediments. Geochemical evolution of groundwater in older alluvium follows
a different path, where cation-exchange has been identified as a significant process. 相似文献