Moisture sources for the genesis of tropical cyclones over the Bay of Bengal using the lagrangian FLEXPART model

Sources of moisture-feeding for the incipient tropical cyclones (TCs) over the Bay of Bengal (BoB) are least explored. Using a three-dimensional Lagrangian model running with NCEP-FNL data, the present work identified various source locations and major transport routes that contributed moisture to pre- and post-monsoon TCs genesis (TCG) over the BoB. The clustered mean trajectories identified using the k-means method demonstrated that moisture transport towards the TCG region during pre-monsoon is dominated by intense low-level westerly/south-westerly trajectories propagating across the North Indian Ocean covering the Somalia coast and the Arabian Sea. Meanwhile, during post-monsoon, north-easterly/easterly trajectories are more prevalent and bring moisture to the BoB TCG region from the South China Sea and North-West Pacific. Moreover, the study highlights the spatiotemporal variations of moisture uptake (MU) pattern and its contribution and demonstrates that robust MU with a contribution of 20–90% occurs locally before three days of TCG. Meanwhile, remote sources contribute a moisture amount of ≤ 20%. Furthermore, the composite analysis of different diagnostic parameters confirms that identified MU at the local scale is attributed to an evaporation process in association with a dynamic uplifting mechanism caused by an anomalous cyclonic circulation, which provides moisture for TCG, while the horizontal advection is the mechanism, which gradually builds moisture required for the TCG from the remote sources.