Impact of Vortex Initialization in Prediction of Tropical Cyclones over Bay of Bengal with NCUM Model     

Ashish Routray  Vivek Singh  Ankur Gupta  Devajyoti Dutta  John P. George 《Marine Geodesy》2019,42(2):201-226

The present study evaluates the impact of vortex initialization (VI) scheme within the NCMRWF Global Unified model (NCUM-G) for prediction of tropical cyclones (TCs) formed over Bay of Bengal (BoB). For this purpose, two numerical experiments such as control simulation (CNTL) without using VI scheme and VOTX simulation using the VI scheme in the NCUM-G are performed by considering four landfalling TCs formed over BoB basin during the year 2016–17. The results suggest that even though TCs are large synoptic systems, the introduction of VI scheme has a positive impact on the prediction of the location, movement, intensity and development of rain bands associated with the TCs. The initial vortex position and landfall position errors are reduced by ～64% and ～39% in VOTX simulations over CNTL, respectively. The mean track errors of all the four TCs are reasonably improved by ～58% in VOTX over CNTL. The equitable threat score (ETS) and frequency bias are significantly improved in the VOTX for all the TC cases as compared to CNTL. Study results provide a positive proof of concept that the VI scheme within the NCUM-G can help to improve the simulation of track and intensity of TCs over BoB.  相似文献   

Why is Indian Ocean warming consistently?     

Suryachandra A. Rao  Ashish R. Dhakate  Subodh K. Saha  Somnath Mahapatra  Hemantkumar S. Chaudhari  Samir Pokhrel  Sobhan K. Sahu 《Climatic change》2012,110(3-4):709-719

Observations have shown that the Indian Ocean is consistently warming and its warm pool is expanding, particularly in the recent decades. This paper attempts to investigate the reason behind these observations. Under global warming scenario, it is expected that the greenhouse gas induced changes in air–sea fluxes will enhance the warming. Surprisingly, it is found that the net surface heat fluxes over Indian Ocean warm pool (IOWP) region alone cannot explain the consistent warming. The warm pool area anomaly of IOWP is strongly correlated with the sea surface height anomaly, suggesting an important role played by the ocean advection processes in warming and expansion of IOWP. The structure of lead/lag correlations further suggests that Oceanic Rossby waves might be involved in the warming. Using heat budget analysis of several Ocean data assimilation products, it is shown that the net surface heat flux (advection) alone tends to cool (warm) the Ocean. Based on above observations, we propose an ocean-atmosphere coupled positive feedback mechanism for explaining the consistent warming and expansion of IOWP. Warming over IOWP induces an enhancement of convection in central equatorial Indian ocean, which causes anomalous easterlies along the equator. Anomalous easterlies in turn excite frequent Indian ocean Dipole events and cause anti-cyclonic wind stress curl in south-east and north-east equatorial Indian ocean. The anomalous wind stress curl triggers anomalous downwelling oceanic Rossby waves, thereby deepening the thermocline and resulting in advection of warm waters towards western Indian ocean. This acts as a positive feedback and results in more warming and westward expansion of IOWP.  相似文献   

The hemispheric asymmetry of solar activity during the last century and the solar dynamo     

Ashish Goel Arnab Rai Choudhuri 《中国天文和天体物理学报》2009,9(1)

We believe the Babcock-Leighton process of poloidal field generation to be the main source of irregularity in the solar cycle. The random nature of this process may make the poloidal field in one hemisphere stronger than that in the other hemisphere at the end of a cycle. We expect this to induce an asymmetry in the next sunspot cycle. We look for evidence of this in the observational data and then model it theoretically with our dynamo code. Since actual polar field measurements exist only from the 1970s, we use the polar faculae number data recorded by Sheeley (1991, 2008) as a proxy of the polar field and estimate the hemispheric asymmetry of the polar field in different solar minima during the major part of the twentieth century. This asymmetry is found to have a reasonable correlation with the asymmetry of the next cycle. We then run our dynamo code by feeding information about this asymmetry at the successive minima and compare the results with observational data. We find that the theoretically computed asymmetries of different cycles compare favorably with the observational data, with the correlation co-efficient being 0.73. Due to the coupling between the two hemispheres, any hemispheric asymmetry tends to get attenuated with time. The hemispheric asymmetry of a cycle ei-ther from observational data or from theoretical calculations statistically tends to be less than the asymmetry in the polar field (as inferred from the faculae data) in the preceding minimum. This reduction factor turns out to be 0.43 and 0.51 respectively in observational data and theoretical simulations.  相似文献   

Synergizing community-based forest monitoring with remote sensing: a path to an effective REDD+ MRV system     

M. S. R. Murthy  Hammad Gilani  Bhaskar Singh Karky  Eklabya Sharma  Marieke Sandker  Upama Ashish Koju  Shiva Khanal  Mohan Poudel 《Carbon balance and management》2017,12(1):19

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Evaluation of TRMM multi-satellite precipitation analysis (TMPA) against terrestrial measurement over a humid sub-tropical basin,India     

Dheeraj?KumarEmail author  Amar?Kant?Gautam  Santosh?S?Palmate  Ashish?Pandey  Shakti?Suryavanshi  Neha?Rathore  Nayan?Sharma 《Theoretical and Applied Climatology》2017,129(3-4):783-799

To support the GPM mission which is homologous to its predecessor, the Tropical Rainfall Measuring Mission (TRMM), this study has been undertaken to evaluate the accuracy of Tropical Rainfall Measuring Mission multi-satellite precipitation analysis (TMPA) daily-accumulated precipitation products for 5 years (2008–2012) using the statistical methods and contingency table method. The analysis was performed on daily, monthly, seasonal and yearly basis. The TMPA precipitation estimates were also evaluated for each grid point i.e. 0.25° × 0.25° and for 18 rain gauge stations of the Betwa River basin, India. Results indicated that TMPA precipitation overestimates the daily and monthly precipitation in general, particularly for the middle sub-basin in the non-monsoon season. Furthermore, precision of TMPA precipitation estimates declines with the decrease of altitude at both grid and sub-basin scale. The study also revealed that TMPA precipitation estimates provide better accuracy in the upstream of the basin compared to downstream basin. Nevertheless, the detection capability of daily TMPA precipitation improves with increase in altitude for drizzle rain events. However, the detection capability decreases during non-monsoon and monsoon seasons when capturing moderate and heavy rain events, respectively. The veracity of TMPA precipitation estimates was improved during the rainy season than during the dry season at all scenarios investigated. The analyses suggest that there is a need for better precipitation estimation algorithm and extensive accuracy verification against terrestrial precipitation measurement to capture the different types of rain events more reliably over the sub-humid tropical regions of India.  相似文献   

Soil and water conservation measures improve soil carbon sequestration and soil quality under cashews   总被引：2，自引：1，他引：1  

Gopal Ramdas Mahajan  Bappa Das  Sandrasekaran Manivannan  Begur Lakshminarasimha Manjunath  Ram Ratan Verma  Sujeet Desai  Rahul Mukund Kulkarni  Ashish Marotrao Latare  Reshma Sale  Dayesh Murgaonkar  Kiran Puna Patel  Shaiesh Morajkar  Ashwini Desai  Natasha Barnes  Heena Mulla 《国际泥沙研究》2021,36(2):190-206

Land degradation is becoming a serious problem in the west coast region of India where one of the world's eight biodiversity hotspots,the‘Western Ghats’,is present.Poor land management practices and high rainfall have led to increasing problems associated with land degradation.A long-term(13-year)experiment was done to evaluate the impact of soil and water conservation measures on soil carbon sequestration and soil quality at three different depths under cashew nut cultivation on a 19%slope.Five soil and water conservation measures-continuous contour trenches,staggered contour trenches,halfmoon terraces,semi-elliptical trenches,and graded trenches all with vegetative barriers of Stylosanthes scabra and Vetiveria zizanoides and control were evaluated for their influence on soil properties,carbon sequestration,and soil quality under cashews.The soil and water conservation measures improved significantly the soil organic carbon,soil organic carbon stock,carbon sequestration rate and microbial activity compared to the control condition(without any measures).Among the measures tested,continuous contour trenches with vegetative barriers outperformed the others with respect to soil organic carbon stock,sequestration rate,and microbial activity.The lower metabolic quotient with the measures compared to the control indicated alleviation of environmental stress on microbes.Using principal component analysis and a correlation matrix,a minimum dataset was identified as the soil available nitrogen,bulk density,basal soil respiration,soil pH,acid phosphatase activity,and soil available boron and these were the most important soil properties controlling the soil quality.Four soil quality indices using two summation methods(additive and weighted)and two scoring methods(linear and non-linear)were developed using the minimum dataset.A linear weighted soil quality index was able to statistically differentiate the effect of soil and water conservation measures from that of the control.The highest value of the soil quality index of 0.98 was achieved with continuous contour trenches with a vegetative barrier.The results of the study indicate that soil and water conservation measures for cashews are a potential strategy to improve the soil carbon sequestration and soil quality along with improving crop productivity and reducing the erosion losses.  相似文献   

Diagnosis of boreal summer intraseasonal oscillation in high resolution NCEP climate forecast system     

S. Abhik  P. Mukhopadhyay  R. P. M. Krishna  Kiran D. Salunke  Ashish R. Dhakate  Suryachandra A. Rao 《Climate Dynamics》2016,46(9-10):3287-3303

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