Revisiting the Precursors of Cyclonic Systems in the CORDEX RCM REMO2009 Simulations.

The Tropical Cyclonic Disturbances (TCDs) over the Bay of Bengal (BoB) have always disrupted life, economy and environment across the coastal regions. The present study evaluates the ability of COoordinated Regional Climate Downscaling Experiment (CORDEX) constituting regional climate model (here REMO2009) in simulating the behaviour of some precursors of TCDs, frequency of TCDs and their intensity over the BoB. Furthermore, the impacts of El Niño Southern Oscillations (ENSO) and Indian Ocean Dipole (IOD) are addressed to determine the sensitivity of the model in capturing large-scale ocean-atmosphere coupled phenomena. The model outputs (resolution 0.44° × 0.44°) are evaluated against the recorded observations of India Meteorological Department and ERA-Interim reanalysis (resolution 0.25° × 0.25°) over the time period 1979–2005. Evaluation of TCD frequencies and intensities on a year-to-year basis shows the model performing reasonably well against observations but intensity is largely reduced. Also, we find an overestimated number of TCDs in the model as pre-monsoon (post-monsoon) shows + 195% (+ 80%) more TCDs. The large-scale environmental fields associated with TCDs show spatiotemporal biases of varying magnitudes in the model however are consistent in capturing TCDs and their behaviours. The mean climatology shows clear differences in environmental fields during days with TCDs and without TCDs. The genesis geolocations in observations are coherent with their environmental fields and are firmly reproduced in the model albeit with spatial differences. The intensity in the model is found to be mostly low showing weak TCDs besides overestimating (underestimating) TCDs of moderate (high) intensities. The REMO2009 model is found satisfactorily simulating the TCDs (year-to-year basis) and associated large-scale environmental fields against the observations and reanalysis. The impacts of large climatic teleconnections (ENSO and IOD) are also captured in the model with warm ENSO phase suppressing the TCDs activities while cold phase triggering the TCDs. On the similar watch, a negative dipole over the Indian Ocean triggers the TCDs while a positive dipole suppresses the TCDs formation in the model. The present study using the regional climate model (RCM) REMO2009 is moreover a needed baseline for the future projections and evaluation of other RCMs under the CORDEX domains. [ABSTRACT FROM AUTHOR]