排序方式： 共有26条查询结果，搜索用时 140 毫秒
1.
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
2.
A Mary Selvam A S Ramachandra Murty R Vijayakumar S K Paul G K Manohar R S Reddy B K Mukherjee Bh. V. Ramana Murty 《Journal of Earth System Science》1980,89(2):215-230
The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively. The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment. The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value. The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above. The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand. The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm?3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona. 相似文献
3.
IUE has made very successful long term and intense short time-scale monitoring spectroscopic study of NGC 4151, a Seyfert 1 galaxy for over nearly 18 years from its launch in 1978 to 1996. The long-term observations have been useful in understanding the complex relation between UV continuum and emission line variability Seyfert galaxies. In this paper, we present the results of our studies on the short-timescale intense monitoring campaign of NGC 4151 undertaken during December 1–15, 1993. A most intense monitoring observation of NGC 4151 was carried out by IUE in 1993, when the source was at its historical high flux state with a shortest interval of 70 min between two successive observations. We present our results on emission line and continuum variability amplitudes characterized by \(F_{\mathrm{var}}\) method. We found highest variability of nearly 8.3% at 1325 \(\AA \) continuum with a smallest amplitude of 4% at 2725 \(\AA \). The relative variability amplitudes (\(R_\mathrm{max}\)) have been found to be 1.372, 1.319, 1.302 and 1.182 at 1325, 1475, 1655 and 2725 \(\AA \) continuum respectively. The continuum and emission line variability characteristics obtained in the present analysis are in very good agreement with the results obtained by Edelson et al. (1996) and Crenshaw et al. (1996) from the analysis of the same observational spectral data. The large amplitude rapid variability characteristics obtained in our study have been attributed to the continuum reprocessing of X-rays absorbed by the material in the accretion disk as proposed by Shakura and Sunyaev (1973). The continuum and emission light curves have shown four distinct high amplitude events of flux maxima during the intense monitoring campaign of 15 days, providing a good limit on the amplitude of UV variability and the BLR size in low luminosity Seyfert galaxies and are useful for constraining the continuum emission models. The decreasing \(F_{\mathrm{var}}\) amplitude of UV continuum with respect to increasing wavelength obtained in the present study and consistent with similar observations by Edelson et al. (1996) and Crenshaw et al. (1996) is a significant result of the intense monitoring observations. 相似文献
4.
K. Prabhu B. Ravindra Manjunath Hegde Vijayakumar H. Doddamani 《Astrophysics and Space Science》2018,363(5):108
Coronal holes (CHs) play a significant role in making the Earth geo-magnetically active during the declining and minimum phases of the solar cycle. In this study, we analysed the evolutionary characteristics of the Recurring CHs from the year 1992 to 2016. The extended minimum of Solar Cycle 23 shows unusual characteristics in the number of persistent coronal holes in the mid- and low-latitude regions of the Sun. Carrington rotation maps of He 10830 Å and EUV 195 Å observations are used to identify the Coronal holes. The latitude distribution of the RCHs shows that most of them are appeared between \(\pm 20^{\circ }\) latitudes. In this period, more number of recurring coronal holes appeared in and around \(100^{\circ }\) and \(200^{\circ }\) Carrington longitudes. The large sized coronal holes lived for shorter period and they appeared close to the equator. From the area distribution over the latitude considered, it shows that more number of recurring coronal holes with area \(<10^{21}~\mbox{cm}^{2}\) appeared in the southern latitude close to the equator. The rotation rates calculated from the RCHs appeared between \(\pm 60^{\circ }\) latitude shows rigid body characteristics. The derived rotational profiles of the coronal holes show that they have anchored to a depth well below the tachocline of the interior, and compares well with the helioseismology results. 相似文献
5.
6.
S. Suresh Babu V. Sreekanth Vijayakumar S Nair S.K. Satheesh K. Krishna Moorthy 《Journal of Atmospheric and Solar》2010,72(11-12):876-882
Altitude profile of aerosol Single Scattering Albedo (SSA), derived from simultaneous in-situ airborne measurements of the coefficients of aerosol absorption and scattering off the west coast of India over the Arabian Sea (AS), during January 2009 is presented. While both the absorption and scattering coefficients decreased with altitude, their vertical structure differed significantly. Consequently, the derived SSA, with a surface value of 0.94, decreased with altitude, illustrating increasing relative dominance of aerosol absorption at higher altitudes. Altitude profile of SSA, when examined in conjunction with that of hemispheric backscatter fraction, revealed that the continental influence on the aerosol properties was higher at higher altitude, rather than the effect of marine environment. During an east–west transect across the peninsular India at an altitude of ～2500 m (free troposphere), it was found that the aerosol scattering coefficients remained nearly the same over both east and west coasts. 相似文献
7.
Real-time storm detection and weather forecast activation through data mining and events processing 总被引：1，自引：0，他引：1
Xiang Li Beth Plale Nithya Vijayakumar Rahul Ramachandran Sara Graves Helen Conover 《Earth Science Informatics》2008,1(2):49-57
Each year across the USA, destructive weather events disrupt transportation and commerce, resulting in both loss of lives
and property. Mitigating the impacts of such severe events requires innovative new software tools and cyberinfrastructure
through which scientists can monitor data for specific severe weather events such as thunderstorms and launch focused modeling
computations for prediction and forecasts of these evolving weather events. Bringing about a paradigm shift in meteorology
research and education through advances in cyberinfrastructure is one of the key research objectives of the Linked Environments
for Atmospheric Discovery (LEAD) project, a large-scale, interdisciplinary NSF funded project spanning ten institutions. In
this paper we address the challenges of making cyberinfrastructure frameworks responsive to real-time conditions in the physical
environment driven by the use cases in mesoscale meteorology. The contribution of the research is two-fold: on the cyberinfrastructure
side, we propose a model for bridging between the physical environment and e-Science1 workflow systems, specifically through events processing systems, and provide a proof of concept implementation of that model
in the context of the LEAD cyberinfrastructure. On the algorithmic side, we propose efficient stream mining algorithms that
can be carried out on a continuous basis in real time over large volumes of observational data.
1 e-Science is used to describe computationally intensive science that is typically carried out in highly distributed network 相似文献
8.
Modala Naga Raghuveer Ale Srinivasulu Goldberg Daniel W. Olivares Miriam Munster Clyde L. Rajan Nithya Feagin Rusty A. 《Theoretical and Applied Climatology》2017,129(1-2):263-280
Potential changes in future climate in the Texas Plains region were investigated in the context of agriculture by analyzing three climate model projections under the A2 climate scenario (medium–high emission scenario). Spatially downscaled historic (1971–2000) and future (2041–2070) climate datasets (rainfall and temperature) were downloaded from the North American Regional Climate Change Assessment Program (NARCCAP). Climate variables predicted by three regional climate models (RCMs) namely the Regional Climate Model Version3–Geophysical Fluid Dynamics Laboratory (RCM3-GFDL), Regional Climate Model Version3–Third Generation Coupled Global Climate Model (RCM3-CGCM3), and Canadian Regional Climate Model–Community Climate System Model (CRCM-CCSM) were evaluated in this study. Gaussian and Gamma distribution mapping techniques were employed to remove the bias in temperature and rainfall data, respectively. Both the minimum and maximum temperatures across the study region in the future showed an upward trend, with the temperatures increasing in the range of 1.9 to 2.9 °C and 2.0 to 3.2 °C, respectively. All three climate models predicted a decline in rainfall within a range of 30 to 127 mm in majority of counties across the study region. In addition, they predicted an increase in the intensity of extreme rainfall events in the future. The frost-free season as predicted by the three models showed an increase by 2.6–3.4 weeks across the region, and the number of frost days declined by 17.9 to 30 %. Overall, these projections indicate considerable changes to the climate in the Texas Plains region in the future, and these changes could potentially impact agriculture in this region.
相似文献9.
Knowledge of wake characteristics in the stern region is important for ensuring good propeller design and performance. This work examines the utility of CFD in the analysis of flow in the case of full aft beam vessels having characteristic cut stern shape to facilitate propeller aperture. The underwater stern shape may be more complex due to the occurrence of stern appendages such as bossings, strut supports and local shape variations. To this extent, CFD offers an effective tool for both qualitative as well as quantitative assessment of the local geometry. Wake estimate is required for choice of the most favorable propeller geometry. In the present method, the analysis quantifies the effects of small changes in stern rake angles and offers an inverse design approach towards finalising the stern shape. The method consists of solving the standard k-ε turbulent model of RANS equations in cell centered finite volume multi zone grid in the flow domain. This approach has been used in estimating the velocity at the propeller plane. The results have been compared with experimentally obtained values of nominal wake. The approach suggests that CFD can provide a cost effective and quick assessment of flow. It is also an attractive means of pre-empting heterogeneous flow related problems such as vibration and noise due to unfavorable wake in the stern region. 相似文献
10.
Vijayakumar Manghnani Sethu Raman Devdutta S. Niyogi Vinayaka Parameswara John M. Morrison S. V. Ramana J. V. S. S. Raju 《Boundary-Layer Meteorology》2000,97(3):411-430
The variability in boundary-layerstructure over the Indian Ocean during a north-eastmonsoon and the factors influencing it areinvestigated. This study was made possible as acomponent of the Indian Ocean Experiment (INDOEX),conducted from February 19 to March 30, 1998. The dataused are, surface-layer mean and turbulencemeasurements of temperature, humidity and wind, andvertical soundings of temperature and humidity.Significant spatio-temporal variability was observedin the boundary-layer structure throughout the cruise.The ITCZ was characterized as the region withstrongest winds and maximum surface turbulent fluxesof momentum and heat. One of the important findingsfrom this study was a strong influence of continentalair masses on the boundary-layer structure in theNorthern Hemisphere, even at a distance of 600 km offthe Indian coast. This was generally evident in theform of an elevated plume of dry continental airbetween altitudes of 1500 m and 2700 m. Advection ofcontinental aerosols in this layer presents potentialfor significant entrainment into shallow clouds inthis region, which eventually feed deeper clouds atthe ITCZ. This finding provides an explanation foranomalous higher aerosol concentrations found duringprevious studies. The structure of the marineboundary layer was influenced by various factors suchas proximity to land, an anomalous warm pool in theocean and the ITCZ. In the southern hemisphere, theboundary-layer height was primarily governed bysurface-layer sensible heat flux and was found to behighest in the vicinity of the ITCZ. North of theequator it was strongly influenced by land-air-seainteractions. In addition to this synoptic modulation,there was also a significant diurnal variability inthe boundary-layer height. 相似文献