Examining the Influence of Caribbean Sea Upper Ocean Variability on Hurricane Ivan (2004) Using Uncoupled and Coupled Simulations

Upper ocean variability and its impact on tropical cyclone (TC) intensity is well-documented in literature in several ocean basins through observational studies. The Caribbean Sea contains significant upper ocean variability including multiple large warm core eddies (WCE) and the Amazon-Orinoco river plume. Several major TCs have passed through the Caribbean Sea in the last decade and forecast models have missed numerous rapid intensification events when storms pass over these ocean features. Moreover, only a few observational studies have investigated the impact of the basin’s ocean thermal and haline variability on upper ocean dynamics and air-sea processes during TC passage. The sparsity of in situ data in this region makes it difficult to assess the full impact of the river plume and WCEs on air-sea processes and TC intensity. Thus, numerical experiments are needed to examine the importance of pre-existing ocean structure on air-sea interaction and TC intensity in this basin.

In this study, the Weather Research and Forecasting (WRF) model is used for the case of Hurricane Ivan (2004) as the storm passes through the Caribbean Sea. Three different experiments are run to examine the influence of upper ocean structure on sea surface temperature (SST) response, air-sea fluxes, and TC intensity and track within this basin. These experiments include holding SST constant, updating SST every six hours, and including one-dimensional (1-D) ocean physics. Ocean mixed layer depths are extracted from the Systematically Merged Atlantic Regional Temperature and Salinity climatology and integrated into WRF such that ocean variability is accurately represented. Preliminary results indicate intensity errors are less over the river plume region for the static SST simulation whereas they are less over WCE regions for the 1-D ocean physics simulation. This result suggests a sensitivity in intensity error based on upper ocean representation. Results from WRF are subsequently compared to those from the Coupled Ocean-Atmospheric-Wave-Sediment-Transport (COAWST) model to examine the influence of a 1-D ocean to a three-dimensional (3-D) ocean. The comparison between WRF with a 1-D ocean and COAWST underscores the significance of representing 3-D ocean structure and dynamics in a coupled model for such a complex ocean basin. In this context, the importance of horizontal advection, upwelling, and shear-induced mixing within the stratified river plume and WCEs is evaluated with respect to mixed layer response, SST cooling, air-sea fluxes, and TC intensity change.