The role of water vapor and its associated latent heating in extreme Beaufort coastal storm surge events

During the rather limited ice-free season that typically may occur from late July through early October, the Beaufort Sea region is susceptible to extreme windstorms, many of which produce damaging storm surges to low-lying coastal communities. During the most recent years, the ice-free season has lengthened, suggesting an increased vulnerability of coastal communities to cyclogenesis-related windstorms. Therefore, our research focuses on the dynamic and thermodynamic mechanisms responsible for significant surface wind events during the ice-free season in this region.

Our analysis methodology includes the detailed synoptic-dynamic analysis, including numerical experiments, on a case of an especially long-lived extreme storm surge that occurred in September 1999. We utilize conventional surface and upper-air station data, along with satellite and ground-based water vapor data. We also utilize global and regional reanalysis data to document the synoptic-scale and mesoscale environments associated with the cyclogenesis events. Our numerical experiments with the Weather Research and Forecasting (WRF) model include sensitivity testing with COSMIC-derived water vapor data, and sensitivity tests to illustrate the relative roles that latent heating plays in the storm surge event, at various stages in its lifecycle.

A particularly important finding of our research on the devastating September 1999 storm surge event is that a relatively rare case of explosive cyclogenesis in the Gulf of Alaska is a key player in this Beaufort storm surge. The deep-tropospheric latent heating during the explosive cyclogenesis generates a dynamic tropopause ridge. This ridge in turn induces surface ridging that contributes to the strong west-northwesterlies associated with the storm surge.

We find that a significant synoptic-scale signature to several Beaufort coastal cyclone events includes surface anticylonic ridging northward of the Alaskan Brooks Mountain Range. The associated cold surge is associated with surface coastal frontogenesis, and subsequent cyclogenesis. This synoptic-scale signature is often conditioned by the presence of anomalously-warm and moist air to the southeast of the cold surge. The associated strong frontogenesis, along with latent heating, provides a significant mesoscale trigger to the frontal cyclone. We also examine other cyclogenetic mechanisms, including predictability issues, for this presentation.