Qualification: 
Ph.D
dhanyam@am.amrita.edu

Dr. Dhanya M. currently serves as Assistant Professor at the Department of Physics, Amrita School of Arts and Sciences and Assistant Professor at Amrita WNA.

Publications

Publication Type: Journal Article

Year of Publication Publication Type Title

2016

Journal Article

Dr. Dhanya M. and Chandrasekar, A., “Impact of variational assimilation using multivariate background error covariances on the simulation of monsoon depressions over India”, Annales Geophysicae, vol. 34, pp. 187–201, 2016.

2016

Journal Article

Dr. Dhanya M., Gopalakrishnan, D., Chandrasekar, A., Singh, S. Kumar, and Prasad, V. S., “The impact of assimilating MeghaTropiques SAPHIR radiances in the simulation of tropical cyclones over the Bay of Bengal using the WRF model”, International Journal of Remote Sensing, vol. 37, pp. 3086–3103, 2016.[Abstract]


The present study aims to investigate the impact of assimilating SAPHIR (Sounder for Probing Vertical Profiles of Humidity) radiances in the simulation of tropical cyclones over the Indian region by the Weather Research and Forecasting (WRF) model. Three tropical cyclones which formed over the Bay of Bengal are chosen as the case studies. Since SAPHIR is a humidity microwave sensor, it is interesting to assess the impact of these observations in simulating cyclones which depend significantly on moist-convective processes. The study makes use of the three-dimensional variational (3DVar) assimilation technique of the WRF variational assimilation system. The results of the study indicate that the assimilation of SAPHIR radiances do have a positive impact on the simulation of tropical cyclones considered here. Two model simulations are performed – a control run (Ctrl) with only conventional and satellite wind observations assimilated, and a SAPH run (SAPH) where SAPHIR radiances are also assimilated in addition to conventional and satellite wind observations. Both these simulations are compared to each other and to observations from the India Meteorological Department (IMD), Joint Typhoon Warning Centre (JTWC), and Tropical Rainfall Measurement Mission (TRMM), as well as analysis fields from Global Forecast System (GFS) from the National Centres for Environmental Prediction (NCEP). Comparison of minimum sea level pressure and maximum wind speed simulated by the model with the IMD and JTWC observations shows that the SAPHIR assimilation has a moderate impact on the simulation of these features by the model. Track prediction of the model is also improved at initial forecast times, as evidenced by the reduced track errors in the model run with SAPHIR radiances assimilated. The warm core structure, as well as the relative vorticity structure of the cyclones, are also impacted in a moderate manner by the assimilation of SAPHIR radiances. The assimilation also positively impacted the rainfall simulation of the model. This is seen from the higher equitable threat score, lower false alarm ratio, and higher probability of detection estimated with respect to TRMM observations, in the SAPH run as compared to the Ctrl run. More »»

2014

Journal Article

Dr. Dhanya M. and Chandrasekar, A., “Improved Rainfall Simulation by Assimilating Oceansat-2 Surface Winds Using Ensemble Kalman Filter for a Heavy Rainfall Event over South India”, IEEE Transactions on Geoscience and Remote Sensing, vol. 52, pp. 7721-7726, 2014.[Abstract]


This paper describes the improvements in the simulation of a heavy rainfall event due to the assimilation of surface wind observations from the Oceansat-2 scatterometer using ensemble Kalman filter (EnKF) technique. A heavy rainfall event over the southern peninsular region of India during the northeast Indian monsoon season is investigated in this paper using the Advanced Research Weather Research and Forecasting model. A control (CTRL) run where no surface wind observations are assimilated, as well as a 3-D variational (3DVar) run and an EnKF run wherein surface wind observations are assimilated using the 3DVar and EnKF techniques, is performed. Results indicate that the EnKF assimilation run simulates various meteorological fields, including precipitation fields during the rainfall event, better than the CTRL and the 3DVar runs. Qualitative and quantitative comparisons with Tropical Rainfall Measurement Mission precipitation observations indicate that the rainfall simulation shows improvement due to EnKF assimilation as compared with the other two model runs. Vertical profiles of area-averaged and time-averaged relative vorticities and temperature anomalies around the low-pressure system are also better reproduced in the EnKF experiment. Considering the importance of accurate real time simulations of heavy rainfall events associated with the Indian monsoon season, this paper provides encouraging results on the utility of EnKF technique as applied over the Indian region. More »»

Publication Type: Conference Proceedings

Year of Publication Publication Type Title

2016

Conference Proceedings

Dr. Dhanya M., Gopalakrishnan, D., Chandrasekar, A., Singh, S. Kumar, and Prasad, V. S., “Impact of Megha-Tropiques SAPHIR radiance assimilation on the simulation of tropical cyclones over Bay of Bengal”, Remote Sensing and Modeling of the Atmosphere, Oceans, and Interactions VI, 98820E (3 May 2016). 2016.[Abstract]


Impact of SAPHIR radiance assimilation on the simulation of tropical cyclones over Indian region has been investigated using the Weather Research and Forecasting (WRF) model. Three cyclones that formed over Bay of Bengal have been considered in the present study. Assimilation methodology used here is the three dimensional variational (3DVar) scheme within the WRF model. With the initial and boundary conditions from Global Forecasting System (GFS) analyses from the National Centres for Environmental Prediction (NCEP), a control run (CTRL) without assimilation of any data and a 3DVar run with the assimilation of SAPHIR radiance have been performed. Both model simulations have been compared with the observations from India Meteorological Department (IMD), Tropical Rainfall Measurement Mission (TRMM), and analysis fields from GFS. Detailed analysis reveals that, the SAPHIR radiance assimilation has led to significant improvement in the simulation of all the three cyclones in terms of cyclone track, intensity, accumulated rainfall. The simulation of warm core structure and relative vorticity profile of each cyclone by 3DVar run are found to be more closer to GFS analyses, when compared with the CTRL run. More »»

Publication Type: Conference Paper

Year of Publication Publication Type Title

2013

Conference Paper

A. Chandrasekar and Dr. Dhanya M., “3DVAR Assimilation of Saphir Radiance from Meghatropiques : Case Study of A Heavy Rainfall events over South Indian Peninsula”, in High Impact Weather Events and their prediction over the SAARC Region, At New Delhi, India, March 2013, 2013.

2012

Conference Paper

Dr. Dhanya M. and Chandrasekar, A., “Impact of assimilating Oceansat2 and Quikscat wind observations on the simulation of weather systems during north east monsoon over India”, in IITM Golden jubilee International Conference on Opportunities and Challenges in Monsoon prediction in Changing Climate (OCHAMP) 21-25 February, 2012 , Indian Institute of Tropical Meteorology , Pune, 2012.

2012

Conference Paper

Dr. Dhanya M. and Chandrasekar, A., “The impact of variational assimilation of Oceansat-2 wind observations on the numerical simulation of heavy rainfall events during northeast Indian monsoon”, in 39th COSPAR Scientific Assembly 2012 - 14-22 July 2012., 2012.

2008

Conference Paper

Dr. Dhanya M., Anjali, B., and T.N., V., “Analysis of monsoon rainfall and wind simulations on flosolver using the varsha 1.2 GCM”, in International Conference on Aerospace Science and Technology, Bangalore,India, 2008.[Abstract]


The present work was intented to assess the ability of the GCM Varsha 1.2 of Flosolver , NAL to forecast the features of all India rainfall and 850 hpa wind during south west13; monsoon. The model was integrated for 30 days of each of the four monsoon months June, July, August and September with five different initial conditions for each. The study has been done for 21 years (1986-2006). Simulated wind and rainfall climatologies have been compared with observed13; ones. One month simulation for the monsoon months are studied to determine the skill of the model in simulating large scale features and organized rainfall. The correlations are calculated for simulated wind and rainfall with the observed values. The results show that the all India rainfall and 850 hpa wind compare reasonably well with that of the observation. More »»

Faculty Research Interest: 
207
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AMRITA
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