Recurvature and movement processes of tropical cyclones over the Bay of Bengal. (25th August 2021)

• Record Type: Journal Article
• Authors: Akter, Nasreen; Tsuboki, Kazuhisa
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 147:Number 740(2021)
• Page Start: 3681
• Page End: 3702
• Publication Date: 2021-08-25
• Subjects: premonsoon dryline -- recurvature -- steering flow -- vertical wind shear; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.4148
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract: Active bimodal tropical cyclones (TCs) are embedded in nonuniform flows over the Bay of Bengal (BoB). More than half of the TCs that occurred from 1990 to 2019 recurved from their original path due to the influence of 500–300 hPa steering flows. Premonsoon TCs have a tendency to turn right and make landfall on the right‐side coastal areas of the BoB. On the other hand, most of the TCs that occurred in the postmonsoon season crossed the left coast or east coast of India, despite being left or right from their path. The simulation shows that Cyclone Roanu (2016) was driven by a warm, moist, unstable southwesterly that was blocked and diverted by the hot, dry stable air masses of northerlies and northwesterlies. As a result, the TC moved along the dry–moist boundary, keeping a constant distance of ∼400 km between the eye and dryline. Conversely, the combined steering of moist southeasterly and southward‐moving upper‐level westerly jets controlled the track of postmonsoon Cyclone Madi (2013), encompassing a left turn of ∼150°. In addition to the primary steering mechanism, TC vortex propagation can be explained by the strong vertical shear (>30 m·s −1 ) offered by the dryline during the premonsoon period and near the monsoon trough in the postmonsoon period. This vertical shear causes the upper‐level anticyclone to tilt downshear, resulting in the forward motion of the TC vortex. The deep convection and associated mesovortices, especially those that are more prominent along the dryline, additionally influence asymmetric diabatic heating, contributing to the advection of TC potential vorticity. Abstract : Premonsoon Cyclone Roanu was steered by the 500‐hPa southwesterly wind, which was blocked and diverted from the synoptic‐scale dryline formed aloft in the north and northwest regions of the Bay of Bengal. Vertical shear associated with this dryline can explain the vortex motion of the cyclone. The postmonsoon season does not have a dryline; the environments related to monsoon troughs are responsible for cyclone movement in these periods.