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S. Naseema Beegum K. Krishna Moorthy Vijayakumar S. Nair S. Suresh Babu S. K. Satheesh V. Vinoj R. Ramakrishna Reddy K. Rama Gopal K. V. S. Badarinath K. Niranjan Santosh Kumar Pandey M. Behera A. Jeyaram P. K. Bhuyan M. M. Gogoi Sacchidanand Singh P. Pant U. C. Dumka Yogesh Kant J. C. Kuniyal Darshan Singh 《Journal of Earth System Science》2008,117(1):303-313
Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from tshe adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (～1) over the Arabian Sea compared to Bay of Bengal (BoB) (～1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB. 相似文献
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Monthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North
Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar
patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics
of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that
the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation
off the east coast of India: wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult
at present to assess the relative importance of these three processes. 相似文献
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S. K. Satheesh K. Krishna Moorthy Y. J. Kaufman T. Takemura 《Meteorology and Atmospheric Physics》2006,91(1-4):45-62
Summary The Arabian Sea region (4° N–20° N to 50° E–78° E) has a unique weather pattern on account of the Indian monsoon and the associated
winds that reverse direction seasonally. The aerosol data, collected using ship-borne and island platforms (for 8 years from
1995 to 2002) along with MODIS (onboard TERRA satellite) data (from 2000 to 2003) have been used to evolve a comprehensive
characterisation of the spatial and temporal variation in the physical, chemical, and radiative properties of aerosols over
the Arabian Sea. The aerosol optical depth (AOD) was found to increase with latitude between the equator and 12° N. Over the
northern Arabian Sea (regions lying north of 12° N), AODs do not show significant latitudinal variations; the average aerosol
optical depth for this region was 0.29±0.12 during winter monsoon season (WMS; November to March) and 0.47±0.14 during summer
monsoon season (SMS; April/May to September). The corresponding Angstrom exponents were 0.7±0.12 and 0.3±0.08, respectively.
The low values of the exponent during SMS indicate the dominance of large aerosols (mainly dust particles >1 μm). The latitudinal
gradient in AOD in the southern Arabian Sea is larger during SMS compared to WMS.
The size distribution of aerosols shows two well-defined modes, one in the accumulation size regime and the other in the coarse
size regime. During WMS, a third mode (nucleation) also appears in the sub micron range below ∼0.1 μm. The single scattering
albedo does not show significant seasonal variations (remains within ∼0.93 to 0.98 through out the year). During WMS (SMS),
top of the atmosphere diurnally averaged aerosol forcing remains around −6.1 (−14.3)W m−2 over the northern Arabian Sea up to around 12° N and decreases southwards till it attains a value of −3.8 (−3.4)W m−2 at the equator. The surface forcing remains around −16.2(−15.2)W m−2 over the northern Arabian Sea up to 12° N and decreases southwards to a value of −5.5 (−3.5)W m−2 at the equator. Over the north Arabian Sea, instantaneous forcing (flux change) at the surface can be as high as −50 W m−2. The instantaneous forcing decreases with latitude in the southern Arabian Sea at a rate of ∼3 W m−2deg−1. 相似文献
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SK Nag 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):69-76
Remote sensing techniques using satellite imagery have proved to be an indispensible tool in morphometric analysis and groundwater studies. In the present area, morphometric analysis using temote sensing techniques have been carried out in Chaka river sub-basin of Manbazar Block, Purulia district, West-Bengal, which is one of the most drought affected area in West-Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu). Form factor (Rf), Circulatory ratio (Rc), and Drainage density. The morphometric analysis suggests that the area is covered by fractured, resistant, permeable rocks, the drainage network not so affected by tectonic disturbances. Using satellite imageries of LANDSAT and IRS, different hydrogeomorphological units have been delineated. The study shows that moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration. 相似文献
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T. Nishanth M. K. Satheesh Kumar K. T. Valsaraj 《Journal of Atmospheric Chemistry》2012,69(2):101-126
Continuous measurements of surface ozone (O3), NOx (NO + NO2) and meteorological parameters have been made in Kannur (11.9?°N, 75.4?°E, 5?m asl), India from November 2009 to October 2010. It was observed that O3 and NOx showed distinct diurnal and seasonal variabilities at this site. The annual average diurnal profile of O3 showed a peak of (30.3?±?10.4) ppbv in the late afternoon and a minimum of (3.2?±?0.7) ppbv in the early morning. The maximum value of O3 mixing ratio was observed in winter (44?±?3.1) ppbv and minimum during monsoon (18.46?±?3.5) ppbv. The rate of production of O3 was found to be higher in December (10.1?ppbv/h) and lower in July (1.8?ppbv/h) during the time interval 0800?C1000?h. A correlation coefficient of 0.52 for the relationship between O3 and [NO2]/[NO] reveals the role of NO2 photolysis that generates O3 at this site. The correlation between O3 and meteorological parameters indicate the influence of seasonal changes on O3 production. Investigations were further extended to explore the week day weekend variations in O3 mixing ratio at an urban site reveals the enhancement of O3. The variations of O3 mixing ratio with seasonal air mass flows were elucidated with the aid of backward air trajectories. This study also indicates how vapor phase organic species present in the ambient air at this location may influence the complex chemistry involving (VOCs) that enhances the production of O3 at this location. 相似文献
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Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L?1, 150 mg L?1, 300 mg L?1, 450 mg L?1 and 600 mg L?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L?1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L?1 (22% reduction) and 600 mg L?1 (31% reduction), indicating that sediment concentrations above 450 mg L?1 may negatively affect brown trout populations. 相似文献
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Neethu Chacko Muthalagu Ravichandran Rokkam R. Rao Sadananda Satheesh Chandra Shenoi 《Ocean Dynamics》2012,62(5):671-681
Sea surface temperature (SST) variability over the Bay of Bengal (BoB) has the potential to trigger deep moist convection
thereby affecting the active-break cycle of the monsoons. Normally, during the summer monsoon season, SST over the BoB is
observed to be greater than 28°C which is a pre-requisite for convection. During June 2009, satellite observations revealed
an anomalous basin-wide cooling and the month is noted for reduced rainfall over the Indian subcontinent. In this study, we
analyze the likely mechanisms of this cooling event using both satellite and moored buoy observations. Observations showed
deepened mixed layer, stronger surface currents, and enhanced heat loss at the surface in the BoB. Mixed layer heat balance
analysis is carried out to resolve the relative importance of various processes involved. We show that the cooling event is
primarily induced by the heat losses at the surface resulting from the strong wind anomalies, and advection and vertical entrainment
playing secondary roles. 相似文献
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The colonization of diatom groups on the acrylic panels submerged in Kudankulam coastal waters, east coast of India, was studied for one year from October 2004 to August 2005. Results showed temporal variability in the abundance of dominant diatom groups. Diatoms belonging to 19 genera colonized the panels. Navicula and Nitzschia were the dominant diatoms observed throughout the present study. The abundance of diatoms on test panels increased with the length of exposure. Significant variations in the abundance of Navicula and Nitzschia were observed between the sampling months. Temporal changes in biofilm diatom community composition in this study attain significance from the view point of macrofouling community recruitment on marine structures. 相似文献