Simulation of Indian summer monsoon: experiments with SSTs     

S. K. Deb  H. C. Upadhyaya  O. P. Sharma  A. Chakraborty 《Meteorology and Atmospheric Physics》2006,94(1-4):43-64

Summary Hindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from an ensemble of numerical simulations performed with a global model by changing SST. Two sets of ensemble simulations have been produced without vegetation: (i) by prescribing the weekly observed SST from ECMWF (European Centre for Medium Range Weather Forecasting) analyses, and (ii) by adding weekly SST anomalies (SSTA) of April to the climatological SST during the simulation period from May to August. For each ensemble, 10 simulations have been realized with different initial conditions that are prepared from ECMWF data with five each from April and May analyses of both the years. The predicted June–July monsoon rainfall over the Indian region shows good agreement with the GPCP (observed) pentad rainfall distribution when 5 member ensemble is taken from May initial conditions. The All-India June–July simulated rainfall time series matches favourably with the observed time series in both the years for the five member ensemble from May initial condition but drifts away from observation with April initial conditions. This underscores the role of initial conditions in the seasonal forecasting. But the model has failed to capture the strong intra-seasonal oscillation in July 2002. Heating over equatorial Indian Ocean for June 2002 in a particular experiment using 29th May 12 GMT as initial conditions shows some intra-seasonal oscillation in July 2002 rainfall, as in observation. Further evaluation of the seasonal simulations from this model is done by calculating the empirical orthogonal functions (EOFs) of the GPCP rainfall over India. The first four EOFs explain more than 80% of the total variance of the observed rainfall. The time series of expansion coefficients (principal components), obtained by projecting on the observed EOFs, provide a better framework for inter-comparing model simulations and their evaluation with observed data. The main finding of this study is that the All-India rainfall from various experiments with prescribed SST is better predicted on seasonal scale as compares to prescribed SST anomalies. This is indicative of a possible useful seasonal forecasts from a GCM at least for the case when monsoon is going to be good. The model responses do not differ much for 2002 and 2003 since the evolution of SST during these years was very similar, hence July rainfall seems to be largely modulated by the other feedbacks on the overall circulation.  相似文献   

4D-variational assimilation over the Bay of Bengal using the Adjoint of a Variable Resolution Global Ocean Model     

S. K. Deb  H. C. Upadhyaya  O. P. Sharma 《Meteorology and Atmospheric Physics》2006,93(3-4):129-145

Summary The adjoint technique has been widely used over the last two decades in applications involving the dynamics of the Atmosphere and Ocean. This present study applies this technique in the assimilation of oceanic parameters such as temperature and net-surface heat flux, in a variable resolution Ocean General Circulation Model (OGCM). The National Center for Environmental Prediction (NCEP) 1999 July–August global data (sea-surface temperature and derived surface heat flux) and vertical temperature profiles collected from ORV Sagar Kanya and INS Sagardhwani during the Bay of Bengal Monsoon Experiment (BOBMEX 1999) are used for assimilation over the Bay of Bengal. The net-surface heat flux and temperature obtained after assimilation show good agreement with their respective seasonal patterns over the whole Indian Ocean, though there are some differences in the numerical values of heat fluxes. The vertical profiles of temperature after assimilation over the Bay of Bengal show strong resemblance with the corresponding ship observations, emphasizing the importance of the adjoint technique in ocean data assimilation.  相似文献   

Soil and soil conservation survey for watershed management in parts of North cachar hills and karbi — Anglong districts of ASSAM     

M. L. Manchanda  Jitendra Prasad  H. S. Iyer  S. K. Deb  R. Pathak 《Journal of the Indian Society of Remote Sensing》1984,12(1):7-18

Soil and Soil Conservation surveys for watershed management were conducted using aerial photos of 1:60,000 scale in parts of North Cachar and Karbi-Anglong districts of Assam. The area was divided into different river catchments and sub-watersheds. The erosion, slope, landuse and soils in relation to physiogrphy were studied in each sub-watershed. The different physiographic units identified in the area were high, medium, low and very low hills; pediplains; alluvial plain and the valleys. These units were further subdivided based on slope, landuse and erosion etc. The soils were classified according to Soil Taxonomy. For priority determination, weightage was alloted to each of the sub-watersheds considering their physiography, slope, landuse, erosion,soil texture, depth and delivery ratio and sediment yield was calculated for each subwatershed. It has been found that out of 122875 ha, an area of 1745 ha had very high priority, 30590 ha high, 37290 ha medium, 51957 ha low and 1294 ha very low priority for soil conservation purposes.  相似文献   

Sensitivity of Indian Monsoon to Entrainment and Detrainment in Mass Flux Schemes     

S. K. Deb  H. C. Upadhyaya  O. P. Sharma  J. Y. Grandpeix 《Pure and Applied Geophysics》2007,164(8-9):1667-1681

A new analytical formulation of entrainment and detrainment in the Tiedtke's mass flux cumulus parameterization is presented here in which cloud height is one of the key parameters. The proposed analytical profiles of entrainment and detrainment are tested in GCM for long-term simulation and are evaluated in the light of the results from the original Tiedtke's scheme and another mass flux scheme due to Emanuel. The variations of Indian monsoon rainfall have been examined with these schemes in a general circulation model. Evaluation of the simulated rainfall against observations is done by empirical orthogonal function (EOF) analysis for the Indian Monsoon region. It is noted that the spatial and temporal variations of the all-India monsoon rainfall are sensitive to the formulation of entrainment and detrainment in a mass flux scheme, and that the new formulation can effectively represent the increased dilution with height in deep clouds.  相似文献   

Propagation of plane relativistic shock waves     

G. Deb Ray 《Astrophysics and Space Science》1979,61(1):81-89

Similarity solutions for propagation of plane shock waves in a relativistic gas, where the nucleon number density varies linearly as distance from its edge at near vacuum is obtained. The shock front moves with constant speed and the solutions are applicable only to an isothermal medium or cold gas.  相似文献   

Solar Cycle Variations of Large-Scale Flows in the sun     

Basu  Sarbani  Antia  H.M. 《Solar physics》2000,192(1-2):469-480

Using data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO), we study the large-scale velocity fields in the outer part of the solar convection zone using the ring diagram technique. We use observations from four different times to study possible temporal variations in flow velocity. We find definite changes in both the zonal and meridional components of the flows. The amplitude of the zonal flow appears to increase with solar activity and the flow pattern also shifts towards lower latitude with time.  相似文献   

Forecasting climate change impacts and evaluation of adaptation options for maize cropping in the hilly terrain of Himalayas: Sikkim,India   总被引：1，自引：0，他引：1  

Proloy Deb  Sangam Shrestha  Mukand S Babel 《Theoretical and Applied Climatology》2015,121(3-4):649-667

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Comparison of Kalpana-1 atmospheric motion vectors with other observations     

S. K. Deb  Inderpreet Kaur  C. M. Kishtawal  P. K. Pal 《Theoretical and Applied Climatology》2014,115(3-4):693-702

The operational derivation of atmospheric motion vectors (AMVs) using infrared (10.5–12.5 μm) and water vapor (6.3–7.1 μm) channels of successive geostationary satellite images started in the 1980s. Subsequently, AMVs have become an important component for operational numerical weather prediction throughout the globe for the last decade or so. In India, at the Space Applications Centre, Indian Space Research Organisation, the operational derivation of AMVs (infrared winds and water vapor winds) from the Indian geostationary satellite Kalpana-1 has been initiated a few years back. Recently, an L-band radar lower atmosphere wind profiler (LAWP) has been installed at the National Atmospheric Research Laboratory, Gadanki located at (13.58°N, 79.28°E) for continuous high-resolution wind measurements in the lower atmosphere. In this study, a comparison of Kalpana-1 AMVs with wind measurements from LAWP and radiosonde has been carried out for a period of one and a half years. The performances of Kalpana-1 AMVs are also assessed by a separate comparison of Meteosat-7 AMVs, derived at the European Organisation for the Exploitation of Meteorological Satellites, with wind measurements from LAWP and radiosonde. Both sets of comparison show that AMVs from Kalpana-1 and Meteosat-7 are comparable over the Indian Ocean region.  相似文献   

Height Assignment Improvement in Kalpana-1 Atmospheric Motion Vectors   总被引：1，自引：0，他引：1  

S. K. Deb  Steve Wanzong  C. S. Velden  Inderpreet Kaur  C. M. Kishtawal  P. K. Pal  W. P. Menzel 《Journal of the Indian Society of Remote Sensing》2014,42(4):679-687

The real-time operational use of atmospheric motion vectors (AMVs) at numerical weather prediction (NWP) centers in India are being adversely affected due to inaccurate height assignment of cloud tracers, especially in thin semi-transparent clouds. In India, the operational derivation of AMVs from the Indian geostationary satellite Kalpana-1 began few years ago. A statistical empirical method (SEM) of height assignment, based on a genetic algorithm, is currently used to estimate the height of the retrieved vectors from Kalpana-1. This method has many limitations. In this paper, attempts have been made to implement the widely used and well tested height assignment methods such as the infrared window (WIN) technique, the H₂O intercept, and the cloud base method in the Kalpana-1 AMV retrieval algorithm. The new height assignment algorithm significantly improves the statistics of the retrieved winds when compared to radiosondes, especially in high and mid levels winds.  相似文献   

Radon as seismic precursor: new data with well water of Jalpaiguri,India     

Dipak Ghosh  Argha Deb  Swarup Ranjan Sahoo  Subrata Haldar  Rosalima Sengupta 《Natural Hazards》2011,58(3):877-889

This paper reports the measurement of radon concentration in well water at the site of Jalpaiguri (26°32′N, 88°46′E) near the active fault zone of West Bengal, India. Radon concentration has been measured in well water with the help of solid-state nuclear track detectors (SSNTD). The study indicates a positive correlation between radon anomaly and earthquake. The data of radon content in well water have been compared with that in soil gas at the same site.  相似文献