Dynamic and thermodynamic characteristics of the Bay of Bengal cyclones during 2001–20 and impact of scatterometer winds through composite analysis

Abstract

This study comprehensively investigates the dynamic, and thermodynamic characteristics associated with pre-monsoon and post-monsoon tropical cyclones (TCs) over the Bay of Bengal during 2001–20. For this purpose, numerical simulations using Weather Research and Forecasting model (called CTRL) and the outputs with assimilation through three-dimensional variational data assimilation techniques (called DA) are used. The DA experiments considered modified initial conditions that are generated by employing assimilated scatterometer winds. Accordingly, a total of 74 model simulations are carried out for 37 TCs categorized as Cyclonic Storm (CS), Severe Cyclonic Storm (SCS), and Highly Intensified Cyclonic Storm (HICS), for preparing the composites. Composite analysis involving different category TCs is performed, where the simulated results are compared against India Meteorological Department observations and the Indian Monsoon Data Assimilation and Analysis (IMDAA). The comparison provides an insight regarding the model performance, where DA demonstrates improved estimation of maximum sustained wind, minimum sea level pressure and cyclone track. The seasonal variations of the dynamic characteristics consisting of vertical wind shear, vorticity, and tangential and radial winds are found to strengthen along with TC intensity. Also, an increase in the rate of convergence supported by well-defined wind fields is realized at the TC center. In most instances, both experiments demonstrate similar trends, but DA exhibits improvement in the estimations, specifically for SCS and HICS categories. However, a limited impact of scatterometer wind data assimilation is realized on the dynamic behavior of CS category TCs. The impact is also found to be limited on the thermodynamic properties of all three categories, although the seasonal variation reveals a consistent increasing trend of temperature anomalies with TC intensity, indicating an association with the intensification process.