Ocean-wave coupled modeling in COAMPS-TC: A study of Hurricane Ivan (2004)

•Fully-coupled air/sea/wave tropical cyclone (TC) modeling is demonstrated.•New SWAN input/dissipation source terms and drag formulation are implemented.•Ocean to wave model coupling and new SWAN source terms improve wave properties.•Wave to ocean model coupling includes the Stokes' Drift Current (SDC).•10-25% of the total near surface current velocity is attributed to SDC in TC conditions.

Tropical cyclone ocean-wave model interactions are examined using an ESMF - (Earth System Modeling Framework) based tropical cyclone (TC) version of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®1). This study investigates Hurricane Ivan, which traversed the Gulf of Mexico (GOM) in September 2004. Several oceanic and wave observational data sets, including Acoustic Doppler Current Profilers (ADCPs), National Oceanic and Atmospheric Administration (NOAA) buoys, satellite altimeter data, and Scanning Radar Altimeter (SRA) data, allow for a unique analysis of the coupled atmosphere, ocean (Navy Coastal Ocean Model, NCOM), and wave (Simulating WAves Nearshore, SWAN) models in COAMPS-TC. To determine the feasibility of coupling NCOM to SWAN in high-wind conditions during Hurricane Ivan, near-surface currents in NCOM were first compared to near-surface ADCP observations. Recent modifications to SWAN, including new wind-to-wave energy input and wave-breaking energy dissipation source functions, as well as a new ocean surface drag coefficient formulation appropriate for high-wind conditions, significantly improved the forecast wave field properties, such as significant wave height (SWH), in TC conditions. Further results show that the ocean-to-wave model coupling, which allows for the strong, hurricane-induced, surface currents in NCOM to interact with SWAN, provided additional improvements to the forecast SWH field. Additionally, wave-to-ocean model coupling, which included the input of the Stokes Drift Current (SDC) calculated from the SWAN wave spectra to NCOM, is examined. The models indicate that the SDC was on the order of 10-25% of the near-surface Eulerian current during Ivan. Recent studies of the importance of the SDC and the resulting Langmuir turbulence on vertical ocean mixing in TCs is also discussed.