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   

A cyclone over Saudi Arabia on 5 January 2002: A case study     

A. Chakraborty  M. Mujumdar  S. K. Behera  R. Ohba  T. Yamagata 《Meteorology and Atmospheric Physics》2006,93(1-2):115-122

Summary A shallow and short-lived subsynoptic cyclone is discussed as one of typical events causing natural disasters over Saudi Arabia on 5 January 2002 using the Japan Meteorological Agency global analysis dataset. The main cause for its formation was vorticity stretching. On the same day widespread rainfall over Saudi Arabia with enhanced precipitation over the mountainous Jeddah region was also observed using the Global Precipitation Climatology Project dataset. Owing to eastward-moving wintertime synoptic-scale Mediterranean disturbances, this rainfall was associated with frontal activity, modified by the local orography.  相似文献   

Role　of　Triad　Kinetic　Energy　Interactions　for　Maintenance　of　Upper　Tropospheric　Low　Frequency　Waves　during　Summer　Monsoon　　1988     

D.R. Chakraborty  N.K. Agarwal 《大气科学进展》1996,13(1):91-102

ＲｏｌｅｏｆＴｒｉａｄＫｉｎｅｔｉｃＥｎｅｒｇｙＩｎｔｅｒａｃｔｉｏｎｓｆｏｒＭａｉｎｔｅｎａｎｃｅｏｆＵｐｐｅｒＴｒｏｐｏｓｐｈｅｒｉｃＬｏｗＦｒｅｑｕｅｎｃｙＷａｖｅｓｄｕｒｉｎｇＳｕｍｍｅｒＭｏｎｓｏｏｎ１９８８Ｄ．Ｒ．Ｃｈａｋｒａｂｏｒｔｙａ...  相似文献   

Mg tracer diffusion in synthetic forsterite and San Carlos olivine as a function of P,T and fO2   总被引：1，自引：0，他引：1  

Sumit Chakraborty  John R. Farver  Richard A. Yund  David C. Rubie 《Physics and Chemistry of Minerals》1994,21(8):489-500

We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo₁₀₀) and San Carlos olivine (Fo₉₂) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ/mol (96 kcal/mol) and 275 (±25) kJ/mol (65 kcal/ mol) in forsterite and San Carlos olivine, respectively, along [001] at a fO₂ of 10^–12 bars. There is no change in activation energy of Mg tracer diffusion within this temperature range. Mg tracer diffusion in a nominally pure forsterite is found to be anisotropic (D_c > D_a > D _b) and a function of fO₂. This fO₂ dependence is different from that in olivine containing Fe as a major element, which suggests that the diffusion mechanism of Mg in forsterite is different from that in Fe-bearing olivine at least over some range of fO₂. The diffusion mechanism in nominally pure forsterites may involve impurities present below the limits of detection or alternately, Si or Fe³⁺ interstitial defects, Fe being present as impurity (ppm level) in forsterite. Pressure dependence of Mg tracer diffusivity in forsterite measured to 10 GPa in a multianvil apparatus yields an activation volume of approximately 1–3.5 cm³/ mol. It is found that presence of small amounts of hydrogen bearing species in the atmosphere during diffusion anneal (f_H2 0.2 bars, f_H20 0.24 bars) do not affect Mg tracer diffusion in forsterite within the resolution of our measurement at a total pressure of 1 bar. The observed diffusion process is shown to be extrinsic; hence extrapolation of the diffusion data to lower temperatures should not be plagued by uncertainties related to change of diffusion mechanism from intrinsic to extrinsic.  相似文献   

Depositional Record of Tidal-Flat Sedimentation in the Permian Coal Measures of Central India: Barakar Formation, Mohpani Coalfield, Satpura Gondwana Basin   总被引：1，自引：0，他引：1  

Chandan Chakraborty  Sanjoy Kumar  Ghosh  Tapan Chakraborty 《Gondwana Research》2003,6(4):817-827

The Permian Barakar Formation in the Mohpani coalfield, Satpura Gondwana basin, is composed of three broad lithologies that occur repetitively and are iterdigitated: (1) several metres thick coarse- to medium-grained sandstone bodies with scoured bases, (2) 5-20 m thick medium- to fine-grained sandstone bodies and (3) 5-20 m thick mudstone-dominated packages with variable proportions of centimetre- to decimetre-scale, fine- to medium-grained sandstone, carbonaceous shale and coal. The Barakar strata were previously interpreted as deposits of braided rivers and associated inter-channel flood basin in a continental setting. However, this study recognizes signatures of tidal current from the mudstone-dominated packages implying marine influence during Barakar sedimentation.

The mudstone-dominated sediment bodies are the focus of this paper and comprise of three lithofacies that bear imprints of tidal processes during Barakar sedimentation: (1) heterolith, (2) sandstone, and (3) coal-carbonaceous shale, which alternate with one another within individual bodies. The heterolithic facies show interlayering of sandstone and claystone resembling flaser, wavy and lenticular bedding, as well as pinstripe stratification. Successive sandstone-mudstone couplets indicate periodic waxing and waning of flows. Within individual heterolithic packages, the sandstone:claystone ratio along with the bedding style, varies cyclically upwards giving rise to alternate sandstone-dominated and claystone-dominated intervals suggesting tidal velocity fluctuation reflective of spring-neap lunar cycle. Thickness plots of successive sand-mud couplets also reveal cyclic variation with a conspicuous periodicity of around 12 couplets per cycle, which corroborates the spring-neap-spring (or neap-spring-neap) lunar cycle. Presence of abundant desiccation cracks indicates periodic emergence and points towards an intertidal setting. The sandstone facies is characterized by a variety of wave-generated features such as bundled and chevron upbuilding of lamina, bi-directional foreset orientations, offshooting and draping laminae, scour-and-drape feature, swollen lens-like geometries suggesting their emplacement under storm-induced combined-flow on the tidal-flat. The coal-carbonaceous shale facies represent supratidal marsh environment.  相似文献   

Geochemistry of some banded iron-formations of the Archean supracrustals,Jharkhand-Orissa region,India     

H. N. Bhattacharya  Indranil Chakraborty  Kaushik K. Ghosh 《Journal of Earth System Science》2007,116(3):245-259

Banded iron-formations (BIF) form an important part of the Archean supracrustal belts of the Jharkhand-Orissa region, India. Major, trace and REE chemistry of the banded iron-formation of the Gandhamardan, Deo Nala, Gorumahisani and Noamundi sections of the Jharkhand-Orissa region are utilized to explore the source of metals and to address the thermal regime of the basin floor and the redox conditions of the archean sea. Hydrothermal fluids of variable temperatures might have contributed the major part of the Fe and other trace elements to the studied banded iron-formations. Diagenetic fluids from the sea floor sediments and river water might have played a subdued role in supplying the Fe and other elements for the banded iron-formations.  相似文献   

Variability of tropical error characteristics in the NCEP (MRF) lower tropospheric wind forecasts during two contrasting seasons     

S. De  D. R. Chakraborty 《Meteorology and Atmospheric Physics》2007,98(3-4):175-194

  相似文献   

Influence of fluvial‐tidal interactions on the nature of cross‐stratified packages in a deltaic setting: examples from the Barakar Coal Measure (Permian), Satpura Gondwana Basin,central India     

Sanjoy Kumar Ghosh  Chandan Chakraborty  Tapan Chakraborty 《Geological Journal》2005,40(1):65-81

Nine different types of cross‐stratified packages from the coal‐bearing, deltaic succession of the Barakar Formation (Permian) of the Satpura Gondwana Basin, central India, are described. The deposits are characterized by periodic mudstone drapes, reactivation surfaces including all other features suggestive of deposition from periodically unsteady, tidally‐influenced flows. The inferred flow patterns varied from purely bidirectional to pulsating unidirectional. The different types of cross‐stratified packages are interpreted to have resulted from superimposition of ebb‐oriented, steady, unidirectional fluvial currents of variable strength on the tidal flow in a deltaic setting. The study helps to distinguish cross‐strata that may develop in settings where fluvial and tidal currents interact. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Erratum to: Characterizing slope morphology using multifractal technique: a study from the western continental margin of India     

Chakraborty  Bishwajit  Karisiddaiah  S. M.  Menezes  A. A. A.  Haris  K.  Gokul  G. S.  Fernandes  W.  Kavitha  G. 《Natural Hazards》2015,77(1):127-127

  相似文献   

Discrimination between Babul plantations and Mustard crop using Polarimetric C- and L- band data     

R. L. Mehta  N. Parihar  A. Sinha  B. P. Shastri  M. Chakraborty 《Journal of the Indian Society of Remote Sensing》2014,42(2):439-444

Radar sensors can be used for large-scale vegetation mapping and monitoring using backscattering coefficients in different polarizations and wavelength bands. C-band space borne SAR is widely used for the classification of agricultural crops, but can only perform a limited discrimination of various tree species. This paper presents the results of discrimination between mustard crop and babul plantation (Prosopis sp.) using quad polarisation Radarsat 2 and ALOS PALSAR data. Study area is comprised of dense babul plantation along the canal, mustard crop on one side of the canal and Fallow land near to Ramgarh village of Jaisalmer district. Three bands of Radarsat (HH, HV and VV) acquired during peak mustard crop growth stage were integrated with four polarizations (HH, HV, VH and VV) of ALOS PALSAR acquired when crop cover was absent. Using only Radarsat data Jefferies-Matusita (JM) separability between mustard crop and babul plantation was found to be poor (710). Where as in the seven band combination the separability was observed to be high (1374). Among the different polarizations three layer combination, highest separability was observed using cross polarizations (HV and VH) of L-band with any one of the Radarsat Polarisation (HH/HV/VV). This combination of C- and L-band resulted in easy separation of mustard and babul plantation which was otherwise difficult using only Radarsat data.  相似文献