Impact of period and timescale of FDDA analysis nudging on the numerical simulation of tropical cyclones in the Bay of Bengal
KAUST DepartmentEarth Science and Engineering Program
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AbstractIn this study, the impact of four-dimensional data assimilation (FDDA) analysis nudging is examined on the prediction of tropical cyclones (TC) in the Bay of Bengal to determine the optimum period and timescale of nudging. Six TCs (SIDR: November 13–16, 2007; NARGIS: April 29–May 02, 2008; NISHA: November 25–28, 2008; AILA: May 23–26, 2009; LAILA: May 18–21, 2010; JAL: November 04–07, 2010) were simulated with a doubly nested Weather Research and Forecasting (WRF) model with a horizontal resolution of 9 km in the inner domain. In the control run for each cyclone, the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) analysis and forecasts at 0.5_ resolution are used for initial and boundary conditions. In the FDDA experiments available surface, upper air observations obtained from NCEP Atmospheric Data Project (ADP) data sets were used for assimilation after merging with the first guess through objective analysis procedure. Analysis nudging experiments with different nudging periods (6, 12, 18, and 24 h) indicated a period of 18 or 24 h of nudging during the pre-forecast stage provides maximum impact on simulations in terms of minimum track and intensity forecasts. To determine the optimum timescale of nudging, two cyclone cases (NARGIS: April 28–May 02, 2008; NISHA: November 25–28, 2008) were simulated varying the inverse timescales as 1.0e-4 to 5.0e-4 s−1 in steps of 1.0e-4 s−1. A positive impact of assimilation is found on the simulated characteristics with a nudging coefficient of either 3.0e-4 or 4.0e-4 s−1 which corresponds to a timescale of about 1 h for nudging dynamic (u,v) and thermodynamical (t,q) fields.
CitationYesubabu V, Srinivas CV, Ramakrishna SSVS, Hari Prasad KBRR (2014) Impact of period and timescale of FDDA analysis nudging on the numerical simulation of tropical cyclones in the Bay of Bengal. Natural Hazards 74: 2109–2128. Available: http://dx.doi.org/10.1007/s11069-014-1293-2.
SponsorsAuthors sincerely thank Dr. Satyamurty Director, EIRSG, Dr. B. Venkatrman, AD, RSEG and Dr. R. Baskaran Head, RIAS for their encouragement and support in carrying out the study. The first author acknowledges the Space Applications Centre, Ahmadabad for the award of the Junior Research Fellowship under MeghaTropiques-Utilization Project under which this research was carried out. The WRF-ARW model was obtained from NCAR. The NCEP GFS analysis and forecasts were downloaded from NCEP. The QSCAT data were obtained from NASA. The prepbufr surface upper air observations are taken from the online archives of NCAR. Authors thank the anonymous reviewers for critical reviews and valuable comments, which helped to improve the manuscript.