Performance of weather research and forecasting model with variable horizontal resolution     

Prashant Kumar  Satya P. Ojha  Randhir Singh  C. M. Kishtawal  P. K. Pal 《Theoretical and Applied Climatology》2016,126(3-4):705-713

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Tropical Indian Ocean surface salinity bias in Climate Forecasting System coupled models and the role of upper ocean processes     

Anant Parekh  Jasti S. Chowdary  Ojha Sayantani  T. S. Fousiya  C. Gnanaseelan 《Climate Dynamics》2016,46(7-8):2403-2422

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Modifications in aerosol physical,optical and radiative properties during heavy aerosol events over Dushanbe,Central Asia     

Dipesh Rupakheti  Maheswar Rupakheti  Xiufeng Yin  Julian Hofer  Mukesh Rai  Yuling Hu  Sabur F.Abdullaev  Shichang Kang 《地学前缘(英文版)》2021,12(6):299-312

The location of Central Asia,almost at the center of the global dust belt region,makes it susceptible for dust events.The studies on atmospheric impact of dust over the region are very limited despite the large area occupied by the region and its proximity to the mountain regions(Tianshan,Hindu Kush-Karakoram-Himalayas,and Tibetan Plateau).In this study,we analyse and explain the modification in aerosols'phys-ical,optical and radiative properties during various levels of aerosol loading observed over Central Asia utilizing the data collected during 2010-2018 at the AERONET station in Dushanbe,Tajikistan.Aerosol epi-sodes were classified as strong anthropogenic,strong dust and extreme dust.The mean aerosol optical depth(AOD)during these three types of events was observed a factor of～3,3.5 and 6.6,respectively,higher than the mean AOD for the period 2010-2018.The corresponding mean fine-mode fraction was 0.94,0.20 and 0.16,respectively,clearly indicating the dominance of fine-mode anthropogenic aerosol during the first type of events,whereas coarse-mode dust aerosol dominated during the other two types of events.This was corroborated by the relationships among various aerosol parameters(AOD vs.AE,and EAE vs.AAE,SSA and RRI).The mean aerosol radiative forcing(ARF)at the top of the atmosphere(ARFTOA),the bottom of the atmosphere(ARFBOA),and in the atmosphere(ARFATM)were-35±7,-73±16,and 38±17 Wm-2 during strong anthropogenic events,-48±12,-85±24,and 37±15 Wm-2 during strong dust event,and-68±19,-117±38,and 49±21 Wm-2 during extreme dust events.Increase in aerosol loading enhanced the aerosol-induced atmospheric heating rate to 0.5-1.6 K day-1(strong anthropogenic events),0.4-1.9 K day-1(strong dust events)and 0.8-2.7 K day 1(extreme dust events).The source regions of air masses to Dushanbe during the onset of such events are also identified.Our study con-tributes to the understanding of dust and anthropogenic aerosols,in particular the extreme events and their disproportionally high radiative impacts over Central Asia.  相似文献   

Scale length of the galactic thin disk     

D. K. Ojha 《Journal of Astrophysics and Astronomy》2000,21(1-2):53-59

This paper presents an analysis of the first 2MASS (The Two Micron All Sky Survey) sampler data as observed at lower Galactic latitude in our Galaxy. These new near-infrared data provide insight into the structure of the thin disk of our Galaxy, The interpretation of star counts and color distributions of stars in the near-infrared with the synthetic stellar population model, gives strong evidence that the Galactic thin disk density scale length,h _R , is rather short (2.7 ± 0.1 kpc).  相似文献   

Turbulence characteristics of flow region over a series of 2-D dune shaped structures     

Satya P. Ojha  B.S. Mazumder 《Advances in water resources》2008

This paper addresses the development of a flow region associated with turbulence and stress characteristics over a series of 2-D asymmetric dunes placed successively at the flume surface. Experiments were conducted over twelve asymmetric dunes of mean length 32 cm, crest height 3 cm and the dune width almost as wide as width of the flume, using 3-D Micro-ADV at the Indian Statistical Institute, Calcutta. The variations of turbulence statistics along the flow affected by the wavy bottom roughness have been studied. Quadrant decomposition of the instantaneous Reynolds shear stress has been adopted to calculate the contribution of ejection and sweeping events in shear stress generation. The relative dominance of two events are found to contribute in a cyclic manner (spatially) in the near bed region, whereas such phenomenon seems to be disappeared towards the main flow.  相似文献   

Role of upper ocean processes in the seasonal SST evolution over tropical Indian Ocean in climate forecasting system     

Jasti S. Chowdary  Anant Parekh  Sayantani Ojha  C. Gnanaseelan 《Climate Dynamics》2015,45(9-10):2387-2405

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Evaluation of linear regression methods as downscaling tools in temperature projections over the Pichola Lake Basin in India   总被引：1，自引：0，他引：1  

Manish Kumar Goyal  C. S. P. Ojha 《水文研究》2011,25(9):1453-1465

In this paper, downscaling models are developed using various linear regression approaches, namely direct, forward, backward and stepwise regression, for obtaining projections of mean monthly maximum and minimum temperatures (Tmax and Tmin) to lake‐basin scale in an arid region in India. The effectiveness of these regression approaches is evaluated through application to downscale the predictands for the Pichola lake region in the state of Rajasthan in India, which is considered to be a climatically sensitive region. The predictor variables are extracted from (i) the National Centers for Environmental Prediction (NCEP) reanalysis dataset for the period 1948–2000 and (ii) the simulations from the third‐generation Canadian Coupled Global Climate Model (CGCM3) for emission scenarios A1B, A2, B1 and COMMIT for the period 2001–2100. The selection of important predictor variables becomes a crucial issue for developing downscaling models as reanalysis data are based on a wide range of meteorological measurements and observations. A simple multiplicative shift was used for correcting predictand values. Direct regression was found to yield better performance among all other regression techniques for the training data set, while the forward regression technique performed better in the validation data set, explored in the present study. For trend analysis, the Mann–Kendall non‐parametric test was performed. The results of downscaling models show that an increasing trend is observed for Tmax and Tmin for A1B, A2 and B1 scenarios, whereas no trend is discerned with the COMMIT scenario by using predictors. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Self-similar MHD shock waves for a rotating atmosphere under the force of gravitation     

Onkar Nath  S. N. Ojha  H. S. Takhar 《Astrophysics and Space Science》1993,200(1):27-34

A study has been made of self-similar magnetohydrodynamic spherical shock waves for a rotating atmosphere taking into account the effect of self-gravitation. The energy is assumed to vary with some power of time. A study has been made to investigate the effects of magnetic field in the presence and absence of gravitation. The variation of flow variables is shown in tables for several different cases of physical interest.  相似文献   

Tropical Indian Ocean subsurface temperature variability and the forcing mechanisms     

Ojha Sayantani  C. Gnanaseelan 《Climate Dynamics》2015,44(9-10):2447-2462

The first two leading modes of interannual variability of sea surface temperature in the Tropical Indian Ocean (TIO) are governed by El Niño Southern Oscillation and Indian Ocean Dipole (IOD) respectively. TIO subsurface however does not co-vary with the surface. The patterns of the first mode of TIO subsurface temperature variability and their vertical structure are found to closely resemble the patterns of IOD and El Niño co-occurrence years. These co-occurrence years are characterized by a north–south subsurface dipole rather than a conventional IOD forced east–west dipole. This subsurface dipole is forced by wind stress curl anomalies, driven mainly by meridional shear in the zonal wind anomalies. A new subsurface dipole index (SDI) has been defined in this study to quantify the intensity of the north–south dipole mode. The SDI peaks during December to February (DJF), a season after the dipole mode index peaks. It is found that this subsurface north–south dipole is a manifestation of the internal mode of variability of the Indian Ocean forced by IOD but modulated by Pacific forcing. The seasonal evolution of thermocline, subsurface temperature and the corresponding leading modes of variability further support this hypothesis. Positive wind stress curl anomalies in the south and negative wind stress curl anomalies in the north of 5°S force (or intensify) downwelling and upwelling waves respectively during DJF. These waves induce strong subsurface warming in the south and cooling in the north (especially during DJF) and assist the formation and/or maintenance of the north–south subsurface dipole. A thick barrier layer forms in the southern TIO, supporting the long persistence of anomalous subsurface warming. To the best of our knowledge the existence of such north–south subsurface dipole in TIO is being reported for the first time.  相似文献   

Post-outburst phase of McNeil's nebula (V1647 Orionis)     

D. K. Ojha  S. K. Ghosh  A. Tej  R. P. Verma  S. Vig  G. C. Anupama  D. K. Sahu  P. Parihar  B. C. Bhatt  T. P. Prabhu  G. Maheswar  H. C. Bhatt  B. G. Anandarao  V. Venkataraman 《Monthly notices of the Royal Astronomical Society》2006,368(2):825-836

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