Study pre- and post-monsoon storms over NIO region using high resolution IMDAA reanalysis dataset

This study analyzed the suitability of using high resolution IMDAA reanalysis for understanding the tropical storms in the North Indian Ocean (NIO). The study evaluates the performance of IMDAA reanalysis by considering 197 storms at different categories (depression to super-cyclone) during the period 1979-2018 over the NIO. It is considered (i) oceanic basins (ii) season of occurrence, (iii) straight movers and recurving/looping storms and (iv) storm intensities. The location and intensity errors of the storms represented in IMDAA are calculated against IMD's best-estimated tracks. The distribution of genesis points of storms has been calculated using the Kernel density estimation approach (KDE). It is noticed that the distribution of storm genesis locations over both the NIO basins, Arabian Sea (AS) and Bay of Bengal (BoB), are displaced in IMDAA reanalysis, both latitudinally and longitudinally, from the observed genesis location. It is also noticed that mean genesis errors are high in the pre-monsoon season as compared to the post-monsoon, in both basins. But the errors are lesser in BoB compared to AS storms in both the cyclone seasons. The IMDAA reanalysis well represented the storm movement with fewer track errors in the case of higher intensity categories of the storm than the low (weaker intensity) category of storms. The right or eastward bias and fast movement of cyclones are observed in the IMDAA reanalysis, which are reduced steadily in the higher categories of TCs mainly in the BoB, and NIO as a whole. The landfall errors (position and time) of the storms are reasonably reduced in recent decades in IMDAA over all the basins than past decades, which may be due availability of more satellite observations. IMDAA reanalysis captured the translation speed of storms from NIO and BoB reasonably well in most of the cases mainly at higher categories of TCs. It is comprehended that the TC intensities are considerably underestimated in IMDAA reanalysis as compared to the observations. Overall, the tracks of the storms are well represented but the intensity and properties associated with the TC environments are not as good in IMDAA reanalysis.