Climate Variability of the Tropical Western Atlantic Storms: Is it hinged to Intra-Americas Seas climate processes?

The proposal seeks to understand the low frequency variability of the Tropical Western Atlantic Storms1 (TWAS) and its relationship with Intra-Americas Seas (IAS) climate processes. Traditionally simulations and predictions beyond the NWP range for tropical Atlantic storms have largely been on their frequency of occurrence throughout the basin over the 6-month period from June through November. This type of forecast or simulation has limited application although they have demonstrated admirable skill on seasonal time scales and on longer time scales in their rendition of the 20th century variability. The success of this study could be a harbinger for attempting predictions of a subset of the tropical Atlantic storms that are geographically more limited in the basin (western Atlantic). Furthermore a majority of TWAS make landfall over continental North America. In addition, the TWAS climatologically has a characteristic dominance of genesis in June and November, which could also be potentially exploited if we understand their causality. Thus this proposal is relevant to NOAA’s NGSP mission on climate adaptation and mitigation to the threat of potential land falling tropical storms in North America.

The proposed work will employ high-resolution (~10km) coupled oceanatmosphere model centered over the IAS in an attempt to resolve the TWAS, the Caribbean Low Level Jet (CLLJ), air-sea fluxes in the IAS, the diurnal variations in the region and capture the associated, intricate sub-surface ocean structure. In addition several sensitivity experiments are also proposed to understand the influence on the genesis and lifecycle of TWAS. This framework of regional coupled ocean-atmosphere modeling is deliberately chosen to afford the high resolution for multi-decadal integrations and limit the model drift by forcing the regional system with credible largescale reanalysis (NCEP CFSR). The coupled GCM’s have shown acute climatological bias in the IAS region with poor depiction of the associated variability in the boreal summer season.

The central objective of the proposal is to understand whether (and followed by how) IAS climate processes like the evolution of the IAS SST and sub-surface ocean evolution from the prior seasons, variability of CLLJ, air-sea fluxes in IAS, overlying atmospheric meridional cell can influence TWAS. The basis for this investigation is buttressed by several related observational evidence, a clear working knowledge of the models to be employed with its demonstration of use over another domain, and availability of computing resources to conduct the proposed integrations.