Impact of high resolution sea surface temperature on tropical cyclone characteristics over the Bay of Bengal using model simulations

Abstract

The Advanced Weather Research and Forecasting (WRF‐ARW) model is used to carry out three simulations to examine the response of varying resolution of the sea surface temperature (SST) on tropical cyclone characteristics up to 72 hr lead time. They are named CNTL (Control, with default SST), SST1 (with SST data at 0.5° × 0.5°) and SST2 (with SST data at 0.083° × 0.083°). It is found that a lower SST (~0.2–0.4 K) within the effective radius (i.e. 2.5 times the radius of the maximum wind) of the storm leads to a weaker storm (about 7 hPa) for SST2 than for CNTL. The storm size in SST2 is about 5 km larger than in CNTL during the 24–72 forecast hours. The reduced storm size and enhanced diabatic heating in the core region facilitate a stronger storm for CNTL compared with SST1 and SST2. As a result, the central pressure of the tropical cyclone deepens further with a stronger radial pressure gradient, leading to a more rapid intensification in the CNTL than the others. A daily update of SST improved the storm track and intensity by 37% and 41% for SST2 and 9% and 20% for SST1 respectively in comparison to CNTL. The study demonstrates that SST with a higher horizontal resolution (0.083° × 0.083°) serves as a useful input parameter for the model to improve the prediction of a cyclone’s track and intensity.

Impact of Assimilation of Satellite Retrieved Ocean Surface Winds on the Tropical Cyclone Simulations Over the North Indian Ocean

“…Rainfall intensity and radial distribution is also improved in the simulations with observed SST. The model's initialization using the dynamic SST shows improvement in intensity and track prediction in the model (Mandal et al, 2007;Bongirwar et al, 2011;Rai et al, 2019). Pothapakula et al, 2017 studied the impact of SSTs on the translational speed of TCs and the TC-induced SST changes.…”

Simulations of Bay of Bengal tropical cyclones in a regional convection-permitting atmosphere–ocean coupled model

“…Atmosphere-only (uncoupled) NWP models generally assume constant SST over the forecast, derived from ocean analysis systems, which has been the operational 80 practice for TC prediction over the Bay of Bengal (Mohanty et al, 2015;Osuri et al, 2017;Routray et al, 2017;Srinivas et al, 2013;Nadimpalli et al, 2020). Updating SST during simulations with SST observations has been shown to improve track and intensity predictions (Mohanty et al, 2019;Rai et al, 2019). In an operational setting, it is possible to use the forecast SST from a regional ocean model as an updating lower boundary condition (Mahmood et al, 2021), but this is not common operational practice.…”

“…Previous studies suggest that the biases in ATM might deteriorate if SST were instead persisted throughout model runs: Rai et al (2019) conducted simulations of TC Phailin (October 2013, Bay of Bengal) with persisted 685 and daily updating SST. Using the daily updating SST improved storm track and intensity estimates by 37% and 41%, respectively.…”

The Regional Coupled Suite (RCS-IND1): application of a flexible regional coupled modelling framework to the Indian region at kilometre scale

“…For example, Vellinga et al (2020), based on assessment of global coupled UM forecasts, showed differences of the order of 10 hPa between central pressure in coupled and uncoupled simulations across different ocean basins by 168 h into a forecast, although with extreme cases having differences of order 20 hPa. Rai et al (2019) showed that use of a relatively cooler (0.2-0.4 K cooler than control) timeevolving SST data product could lead to about 7 hPa more intense storms after 78 h forecast time over the Bay of Bengal in atmosphere-only experiments. It should be noted, however, that SST differences between ATMfix and AOW of up to 2 K develop in the RCS-IND1 simulations, initialized around 3-4 d ahead of the deepest cyclone intensity, and based on different initial ocean states.…”

“…Routray et al, 2017;Mahmood et al, 2021). The relevance of spatial resolution of SST boundary conditions for atmosphere-only simulation of TC Phailin was examined by Rai et al (2019), who found improved performance of the order of 30 %-40 % when using a higher-resolution (0.083 • × 0.083 • ) SST analysis. Beyond the well-documented impacts of TC multi-hazards on lives and livelihoods (e.g.…”