Structural characteristics of North Indian Ocean tropical cyclones during 1999–2017: a scatterometer observation-based analysis

The climatology and numerical modeling of tropical cyclones (TCs) both are the primary focus area of research over the North Indian Ocean (NIO); however, the size determination and variation are a less emphasized topic. Therefore, the present study deals with the determination of the size of TCs over NIO mainly by following the vorticity-based approach and using scatterometer data sets. It assesses the ability of this data set to determine the size of the NIO TCs. Different parameters such as Rmax, Rvor, R34 (i.e., the radius of 34 knots winds; 1 knot = 0.514444 ms−1), R50 (i.e., the radius of 50 knots winds), and R64 (i.e., the radius of 64 knots winds) are determined for the said purpose. The error between TC center determined by the vorticity-based approach and India Meteorological Department (IMD) data is in the range of 30–105 km (mean value is 76.34 km) and with Joint Typhoon Warning Centre (JTWC) is within 25–115 km (mean value 79.77 km) when all of the observations are considered. However, if the observations with the smallest time gap of < 30 min are considered, the corresponding mean error values become 30.12 km (± 20.83 km) and 36.47 km (± 20.21 km). The comparison of Rmax with JTWC observation is having a correlation value of ~ 0.75 with RMSE of ~ 7.6 km. The radial parameter Rmax varies in the range of 15–90 km, R64 varies within 15–60 km, R34 lies in the range of 80–300 km, R50 varies within 15–60 km, and Rvor is within 190–485 km for the NIO region that is comparable with the JTWC data. Larger size TCs are observed near the higher latitude of the NIO region, and the size of systems increases with an increase in latitude. The size of the pre-monsoon season TCs is found to be larger in comparison to post-monsoon season systems over NIO. An empirical relationship is also established based on the linear regression method to determine the size of TCs using SCATSAT-1 data. The results presented in this work indicate that scatterometer wind data with the spatial resolution of ~ 6 to 25 km would be handy enough to study the structural characteristics of NIO TCs.