Prediction of Indian summer monsoon in short to medium range time scale with high resolution global forecast system (GFS) T574 and T382     

V. R. Durai  S. K. Roy Bhowmik 《Climate Dynamics》2014,42(5-6):1527-1551

Performance of national centers for environmental prediction based global forecast system (GFS) T574/L64 and GFS T382/L64 over Indian region has been evaluated for the summer monsoon season of 2011. The real-time model outputs are generated daily at India Meteorological Department, New Delhi for the forecasts up to 7 days. Verification of rainfall forecasts has been carried out against observed rainfall analysis. Performance of the model is also examined in terms of lower tropospheric wind circulation, vertical structure of specific humidity and precipitable water content. Case study of a monsoon depression is also illustrated. Results obtained show that, in general, both the GFS T382 and T574 forecasts are skillful to capture climatologically heavy rainfall regions. However, the accuracy in prediction of location and magnitude of rainfall fluctuates considerably. The verification results, at the spatial scale of 50 km resolution, in a regional spatial scale and country as a whole, in terms of continuous skill score, time series and categorical statistics, have demonstrated superiority of GFS T574 against T382 over Indian region. Both the model shows bias of lower tropospheric drying and upper tropospheric moistening. A bias of anti-cyclonic circulation in the lower tropospheric level lay over the central India, where rainfall as well as precipitable water content shows negative bias. Considerable differences between GFS T574 and T382 are noticed in the structure of model bias in terms of lower tropospheric wind circulation, vertical structure of specific humidity and precipitable water contents. The magnitude of error for these parameters increases with forecast lead time in both GFS T574 and T382. The results documented are expected to be useful to the forecasters, monsoon researchers and modeling community.  相似文献   

Sensitivity of seasonal precipitation extremes to model configuration of the Canadian Regional Climate Model over eastern Canada using historical simulations     

Philippe Roy  Philippe Gachon  René Laprise 《Climate Dynamics》2014,43(9-10):2431-2453

This study analyzes the uncertainty of seasonal (winter and summer) precipitation extremes as simulated by a recent version of the Canadian Regional Climate Model (CRCM) using 16 simulations (1961–1990), considering four sources of uncertainty from: (a) the domain size, (b) the driving Atmosphere–Ocean Global Climate Models (AOGCM), (c) the ensemble member for a given AOGCM and (d) the internal variability of the CRCM. These 16 simulations are driven by 2 AOGCMs (i.e. CGCM3, members 4 and 5, and ECHAM5, members 1 and 2), and one set of re-analysis products (i.e. ERA40), using two domain sizes (AMNO, covering all North America and QC, a smaller domain centred over the Province of Québec). In addition to the mean seasonal precipitation, three seasonal indices are used to characterize different types of variability and extremes of precipitation: the number of wet days, the maximum number of consecutive dry days, and the 95th percentile of daily precipitation. Results show that largest source of uncertainty in summer comes from the AOGCM selection and the choice of domain size, followed by the choice of the member for a given AOGCM. In winter, the choice of the member becomes more important than the choice of the domain size. Simulated variance sensitivity is greater in winter than in summer, highlighting the importance of the large-scale circulation from the boundary conditions. The study confirms a higher uncertainty in the simulated heavy rainfall than the one in the mean precipitation, with some regions along the Great Lakes—St-Lawrence Valley exhibiting a systematic higher uncertainty value.  相似文献   

Detection of Rain/Cloud Pixels by Ka-band AltiKa Altimeter over the Tropical Region: Development of a Rain/Cloud Flag Algorithm and its Validation     

Partha Roy  Rakesh Mohan Gairola 《Marine Geodesy》2015,38(3):86-106

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Effect of ion kinematic viscosity on large amplitude dust ion acoustic solitary waves     

Kaushik Roy  Taraknath Saha  Prasanta Chatterjee 《Astrophysics and Space Science》2014,349(2):745-751

Nonlinear dust ion acoustic solitary waves (DIASW) in dusty plasma are studied incorporating kinematic viscosity, using Sagdeev’s pseudopotential approach. The effects of kinematic viscosity and the nonextensive parameter q on the features of DIASW are investigated in some detail.  相似文献   

RETRACTED ARTICLE: Observing the result of external magnetic field with nonextensivity on DA waves for two temperature electrons in a dusty plasmas     

M. S. Zobaer  N. Roy  A. A. Mamun 《Astrophysics and Space Science》2014,350(1):231-236

This theoretical investigation has been made on dust-acoustic (DA) waves containing nonextensivity of electrons being two different temperatures, negatively charged dust grains, and Maxwellian ions. The Zakharov-Kuznetsov (Z-K) equation has been derived and numerically solved to analysis the basis features. It is observed that the characteristics of the DA solitary waves (DASWs) are significantly modified by the external magnetic field with the different temperatures for electrons followed by the nonextensive distribution. The results obtained from this analysis can be employed in understanding the nature of plasma waves both in laboratory and space plasma system.  相似文献   

Shock waves in a dusty plasma having q-nonextensive electron velocity distribution     

Kaushik Roy  Prasanta Chatterjee  S. S. Kausik  C. S. Wong 《Astrophysics and Space Science》2014,350(2):599-605

The dust-acoustic shock waves have been theoretically investigated using reductive perturbation technique. An unmagnetized four-component dusty plasma system consisting of nonextensive q-distributed electrons, Boltzmann distributed ions, and negatively as well as positively charged dust particles has been considered. The solution of Burgers equation in planar geometry is numerically analyzed. It has been observed that the nonextensive q-distribution of electrons has a significant role in the formation of shock waves. The relevance of our results to astrophysics as well as laboratory plasmas are briefly discussed.  相似文献   

Snowpack and runoff response to climate change in Owens Valley and Mono Lake watersheds     

Mariza Costa-Cabral  Sujoy B. Roy  Edwin P. Maurer  William B. Mills  Limin Chen 《Climatic change》2013,116(1):97-109

Precipitation from the Eastern Sierra Nevada watersheds of Owens Lake and Mono Lake is one of the main water sources for Los Angeles’ over 4 million people, and plays a major role in the ecology of Mono Lake and of these watersheds. We use the Variable Infiltration Capacity (VIC) hydrologic model at daily time scale, forced by climate projections from 16 global climate models under greenhouse gas emissions scenarios B1 and A2, to evaluate likely hydrologic responses in these watersheds for 1950–2099. Comparing climate in the latter half of the 20th Century to projections for 2070–2099, we find that all projections indicate continued temperature increases, by 2–5 °C, but differ on precipitation changes, ranging from ?24 % to +56 %. As a result, the fraction of precipitation falling as rain is projected to increase, from a historical 0.19 to a range of 0.26–0.52 (depending on the GCM and emission scenario), leading to earlier timing of the annual hydrograph’s center, by a range of 9–37 days. Snowpack accumulation depends on temperature and even more strongly on precipitation due to the high elevation of these watersheds (reaching 4,000 m), and projected changes for April 1 snow water equivalent range from ?67 % to +9 %. We characterize the watershed’s hydrologic response using variables integrated in space over the entire simulated area and aggregated in time over 30-year periods. We show that from the complex dynamics acting at fine time scales (seasonal and sub-seasonal) simple dynamics emerge at this multi-year time scale. Of particular interest are the dynamic effects of temperature. Warming anticipates hydrograph timing, by raising the fraction of precipitation falling as rain, reducing the volume of snowmelt, and initiating snowmelt earlier. This timing shift results in the depletion of soil moisture in summer, when potential evapotranspiration is highest. Summer evapotranspiration losses are limited by soil moisture availability, and as a result the watershed’s water balance at the annual and longer scales is insensitive to warming. Mean annual runoff changes at base-of-mountain stations are thus strongly determined by precipitation changes.  相似文献   

A megacity in a changing climate: the case of Kolkata     

Susmita Dasgupta  Asvani K. Gosain  Sandhya Rao  Subhendu Roy  Maria Sarraf 《Climatic change》2013,116(3-4):747-766

Projections by the Intergovernmental Panel on Climate Change suggest that there will be an increase in the frequency and intensity of climate extremes in the 21st century. Kolkata, a megacity in India, has been singled out as one of the urban centers vulnerable to climate risks. Modest flooding during monsoons at high tide in the Hooghly River is a recurring hazard in Kolkata. More intense rainfall, riverine flooding, sea level rise, and coastal storm surges in a changing climate can lead to widespread and severe flooding and bring the city to a standstill for several days. Using rainfall data, high and low emissions scenarios, and sea level rise of 27 cm by 2050, this paper assesses the vulnerability of Kolkata to increasingly intense precipitation events for return periods of 30, 50, and 100 years. It makes location-specific inundation depth and duration projections using hydrological, hydraulic, and urban storm models with geographic overlays. High resolution spatial analysis provides a roadmap for designing adaptation schemes to minimize the impacts of climate change. The modeling results show that de-silting of the main sewers would reduce vulnerable population estimates by at least 5 %.  相似文献   

The rapid growth and decay of severe cyclone JAL (2010) over the Bay of Bengal     

S. D. Kotal  S. K. Bhattacharya  S. K. Roy Bhowmik  P. K. Kundu 《Meteorology and Atmospheric Physics》2013,121(3-4):161-179

This study investigates the life cycle of Bay of Bengal cyclone JAL, characterized by a rapid fluctuation in its intensity during 60-h interval. The cyclone JAL underwent a period of rapid intensification during 24-h from 0000 UTC 05 November to 0000 UTC 06 November 2010. It was quasi-static during subsequent 24 h followed by a 12-h period of unusually rapid decay. During the rapid cyclogenesis phase, the system intensified (by 25 kt) from deep depression (DD) to severe cyclonic storm (SCS) and weakened (by 30 kt) from SCS to DD during the 12-h period of rapid cyclolysis. European Centre for Medium Range Weather Forecasts (ECMWF) model analysis field is used to analyze the Q vectors, K index and potential vorticity (PV) to diagnose the life cycle of this unusual cyclone. The analysis reveals that the 500–700 hPa column-averaged Q-vector convergence above the surface cyclone had strengthened and very high values of the K index produced a burst of heavy precipitation during the development stage of the cyclone. The associated latent heat release produced a substantial diabatic positive PV anomaly in the lower and middle troposphere that caused rapid cyclogenesis. The rapid cyclolysis is coincident with the weakening of the upper and lower PV anomalies and the westward shearing of the upper PV from the cyclone centre. Thus, the very latent heat release that assisted the rapid development of the cyclone also played an important role in its subsequent rapid decay. ECMWF model forecast for track and intensity is also verified.  相似文献   

Spatial patterns of diurnal variations in summer-season lightning activity across the tropical and subtropical regions of the Northern Hemispheric Americas     

Shouraseni Sen Roy  Robert C. Balling Jr. 《Meteorology and Atmospheric Physics》2013,121(3-4):199-206

Hourly lightning data were obtained from the Tropical Rainfall Measuring Mission dataset collected through the Lightning Imaging Sensor instrument from 1998 to 2011 to analyze the diurnal pattern of lightning activity in the tropical and subtropical northern hemispheric Americas. The majority of the lightning strikes occurred over land, with relatively lower strike rates over the oceanic areas. The results of our studies showed substantial spatial variations in the time of maximum and strength of the diurnal cycle in the study area. A clockwise progression in the time of maximum was observed across most of the study area, particularly over North America where an east–west orientation was observed. The findings of our study were mainly a result of the interaction between local topography such as the Andes and Rocky mountains, and surface level atmospheric circulations. The strength of the observed diurnal cycle was greatest in the Gulf of Mexico region.  相似文献