05 July 2017

Wintertime Atmospheric Buoyancy Forcing and Oceanic Response During Strong Wind Events Around Southeastern Greenland in the Regional Arctic System Model (RASM) for 1990-2010

Assess the impact of strong mesoscale wind events on ocean convection

Science

This research uses the Regional Arctic System Model (RASM) to analyze the impact of the strong mesoscale wind events along the southeastern coast of Greenland on ocean heat loss, buoyancy flux, and mixed layer depth change. This is the first high-resolution, fully coupled, realistically forced simulation of these coupled mesoscale atmosphere - ocean processes.

Impact

The results presented in this paper demonstrate the capabilities of high resolution coupled regional system models for studying climatically important processes such as ocean convection. We show that strong wind events with westerly or northerly flow are associated with large buoyancy loss from the ocean, through turbulent heat loss, and that this results in mixed layer deepening on both event and seasonal time scales.

Summary

Strong, mesoscale tip jets and barrier winds that occur along the southeastern Greenland coast have the potential to impact deep convection in the Irminger Sea. The self-organizing map (SOM) training algorithm was used to identify 12 wind patterns that represent the range of winter [November–March (NDJFM)] wind regimes identified in the fully coupled Regional Arctic System Model (RASM) during 1990–2010. For all wind patterns, the ocean loses buoyancy, primarily through the turbulent sensible and latent heat fluxes; haline contributions to buoyancy change were found to be insignificant compared to the thermal contributions. Patterns with westerly winds at the Cape Farewell area had the largest buoyancy loss over the Irminger and Labrador Seas due to large turbulent fluxes from strong winds and the advection of anomalously cold, dry air over the warmer ocean. Similar to observations, RASM simulated typical ocean mixed layer depths (MLD) of approximately 400 m throughout the Irminger basin, with individual years experiencing MLDs of 800 m or greater. The ocean mixed layer deepens over most of the Irminger Sea following wind events with northerly flow, and the deepening is greater for patterns of longer duration. Seasonal deepest MLD is strongly and positively correlated to the frequency of westerly tip jets with northerly flow. 

Contact
John Cassano
University of Colorado at Boulder