A New Coupled Ocean‐Waves‐Atmosphere Model Designed for Tropical Storm Studies: Example of Tropical Cyclone Bejisa (2013–2014) in the South‐West Indian Ocean

Abstract

Ocean‐Waves‐Atmosphere (OWA) exchanges are not well represented in current Numerical Weather Prediction (NWP) systems, which can lead to large uncertainties in tropical cyclone track and intensity forecasts. In order to explore and better understand the impact of OWA interactions on tropical cyclone modeling, a fully coupled OWA system based on the atmospheric model Meso‐NH, the oceanic model CROCO, and the wave model WW3 and called MSWC was designed and applied to the case of tropical cyclone Bejisa (2013–2014). The fully coupled OWA simulation shows good agreement with the literature and available observations. In particular, simulated significant wave height is within 30 cm of measurements made with buoys and altimeters. Short‐term (< 2 days) sensitivity experiments used to highlight the effect of oceanic waves coupling show limited impact on the track, the intensity evolution, and the turbulent surface fluxes of the tropical cyclone. However, it is also shown that using a fully coupled OWA system is essential to obtain consistent sea salt emissions. Spatial and temporal coherence of the sea state with the 10 m wind speed are necessary to produce sea salt aerosol emissions in the right place (in the eyewall of the tropical cyclone) and with the right size distribution, which is critical for cloud microphysics.

The effect of atmosphere–ocean coupling on the prediction of 2016 western North Pacific tropical cyclones

“…Air–sea coupling is one of the key factors contributing to the prediction skill of subseasonal to seasonal forecast systems, related to improved skill in capturing the sea‐surface temperature (SST) variations that are important for predicting intraseasonal climate variability, such as the Madden–Julian oscillation (MJO: Vitart et al, ). Following the same concept, coupled models have been investigated for operational synoptic weather forecasts (usually <10 days: Bender and Ginis, ; Yablonsky and Ginis, ; Wu et al, ; Mogensen et al, ; Pianezze et al, ). In June 2018, ECMWF launched its first operational atmosphere–ocean coupled NWP model for global weather forecasts (Buizza et al, ).…”

An evaluation of tropical cyclone forecast in the Southwest Indian Ocean basin with AROME‐Indian Ocean convection‐permitting numerical weather predicting system

“…In parallel, additional developments aiming at improving TC forecasting are also investigated using a research configuration of the model, used since 2012 to test and evaluate improvements to be potentially implemented in operations-several studies based on this research configuration have already been achieved within the last few years (e.g., Pianezze et al, 2018;Colomb et al, 2019). In this study, the potential of a high-resolution EPS based on an experimental configuration of AROME-IO was demonstrated on a case of lowpredictability TC, which passed over Reunion Island in April 2018.…”

The orographic effect of Reunion Island on tropical cyclone track and intensity

“…Very recently, observations (Figure b) and numerical simulations of TC Berguitta (January 2018) also showed an intriguing change of track when the storm moved close to Reunion Island, which surprised the TC operational forecasters. A similar behavior was also observed during TC Bejisa (Pianezze et al ., ; December 2013–January 2014, Figure b) and TC Dina in January 2002 (Roux et al ., ; Jolivet et al ., ), as they passed nearby La Reunion.…”