Numerical Investigation of Air- Sea Interactions During Winter Extratropical Storms Presented by Jill Nelson M.S. Marine Science Candidate Graduate Research Seminar December 3, 2010

Economic and Societal Impacts  Rough seas  Coastal storm surge and erosion  Dangerous conditions for commercial and recreational fishers  Widespread rain and snowfall  Wind gusts and wind chills  Power outages  School and business closings

Climatology of Winter Storms  January: 2 – 4 storms develop along east coast  Favorable regions for development and intensification – northern wall of the Gulf Stream – southeastern New England Number of January Storms Zishka and Smith (1980)

Ocean-Atmosphere Feedbacks  Feedbacks that occur when a cold, dry air mass encounters much warmer Atlantic waters dfg  Large heat flux from the ocean to the atmosphere  Development/strengthening of atmospheric circulation  Cooling of ocean surface  Modified SSTs feedback and weaken the passing storm Atmospheric ResponseOceanic Response Increasing air temperatureHeat is lost from upper ocean Enhanced wind speedsChanges in velocity structure

Modeling Experiments  Approach: Perform hindcast from Jan 15-31, 2005 to investigate the effects of SST gradients on the overlying air masses  Uncoupled Model Solutions Provide atmosphere model (WRF) with a low resolution SST field based on satellite observations  Coupled Model Solutions 2-way coupling between atmosphere and ocean models using the COAWST system (WRF ROMS)

Atmospheric Model Design Surface Temperatures  WRF v  Initial and boundary conditions from larger scale WRF parent domain  3 km horizontal resolution  48 vertical layers  1/2° RTG-SST product WRF Physics WSM 5-class microphysics Monin-Obukhov surface layer MYJ surface TKE scheme No cumulus scheme Kain-Fritsch in parent domain

Oceanic Model Design Sea Surface Temperatures  Regional Ocean Modeling System (ROMS)  Initial and boundary conditions from global 1/12° HYCOM  2 km horizontal resolution  36 vertical layers  Atmospheric forcing from WRF model

COAWST Modeling System Weather Research & Forecasting Model WRF v3.1.1 Regional Ocean Modeling System (ROMS) SST τ and Net Heat Flux Coupled-Ocean-Atmosphere-Wave-Sediment-Transport Model

Study Area  Unique geography:  Gulf Stream boundary current  Large horizontal temperature gradients  Model solutions are compared against in-situ observations  One strong marine cyclone on January 22-23, 2005 Locations of In-situ Buoys

Model-Data Comparison Observed Uncoupled Coupled January 2005 Sunset Beach, NC

Modeled Heat Flux January 2005 Upward Latent Heat Flux Upward Sensible Heat Flux W m

Coupled Latent Heat Flux

Ongoing Research  Quantify the effects of air-sea coupling on winter extratropical cyclones  Introduce wave activity into the current COAWST configuration for a fully coupled model experiment

Conclusions  Uncoupled and coupled COAWST model solutions are used to examine air-sea feedbacks during the passage of a winter storm over the Atlantic Ocean  Air-sea coupling provides more realistic ocean surface temperature gradients to force atmospheric circulations  Higher surface heat flux produced by coupled model due to better representation of ocean environment

Questions