Ocean frontal-scale air-sea interaction

1. Ocean frontal-scale air-sea interaction A Subgroup of the CLIVAR Working group on Western Boundary Current Ocean-Atmosphere Coupling Participants: Bond, Cronin, Kelly, Samelson, Small, Thompson

2. Some questions • On what scales do ocean and atmosphere interact near WBCs? • How do Gulf Stream and Kuroshio compare? • Are models (global and/or regional) getting the interaction right? • To what depth in atmosphere does effect extend? • How do storms respond to SST fronts? Does this feedback onto mean circulation?

3. Overview • Analysis of synoptic storms and the Gulf stream by Kelly, Thompson et al • Regional modeling of atmospheric response to Gulf Stream by Small et al • Tropical-extratropical cyclone transitions – Bond and Cronin • Air-Sea coupling in coastal upwelling by Samelson et al

4. Response of MABL to ocean fronts • 2 ways MABL may respond: • 1. Directly, via influence of surface fluxes on MABL only • Heat fluxes alter thermodynamic structure, stratification, clouds etc. • Momentum mixing and pressure anomalies alter wind profile • 2. Indirectly, via influence of surface fluxes on extratropical storms which will then change boundary layer (and much deeper) properties

5. Analysis of synoptic storms and Gulf Stream Kathie KellyLuAnne ThompsonJimmy BoothJerome Patoux University of Washington , Seattle

6. Intensity of Storms Passing over the Gulf Stream Histogram of storm intensity Storms passing to the north of the Gulf Stream (red) are more intense than those passing to the south (green) Jones, Kelly, Patoux, & Thompson University of Washington

7. Storm Tracks and the North Atlantic Oscillation Storms that occurred in DJFM that passed through the box (dashed line) NAO strongly negative NAO strongly positive Booth, Kelly, Patoux, & Thompson University of Washington

8. Regional atmospheric modeling of response to Gulf Stream R. Justin Small, Yuqing Wang, Shang-Ping Xie International Pacific Research Center, University of Hawaii

9. Regional Atmospheric Modeling • Regional Atmospheric Model of Yuqing Wang (IPRC) • Hydrostatic, sigma coordinate, primitive equation • Lateral boundary conditions NCEP/NCAR reanalysis • ½ degree and 1/3 degree simulations, 28 vertical levels • Surface boundary conditions daily evolving AMSR SST • Run for up to 4 months of winter season, Jan-April 2003 • ****Previous high-resolution studies of atmospheric and storm response over Gulf Stream just consider a few case studies and short time periods –here we extend this to 4 months – to get reliable statistics (mean and synoptic variance).

10. Regional Atmospheric Model Mean situation Jan-Apr

11. Rain rate and deep response • Hobbs (GRL, 1987) introduced the ‘Gulf Stream Rainband’, a quasi-stationary band with associated lightning strikes. Trunk and Bosart (1990) mapped the mean radar echos off Cape Hatteras to confirm.

12. Synoptic variability: 2-8 day bandpass MODEL OBSERVATIONS CLOSE-UP CLOSE-UP

13. Vertical structure of variance (MODEL)

14. Tropical-Extratropical Cyclone TransitionsNick Bond --  University of Washington JISAOMeghan Cronin -- NOAA Pacific Marine Environmental Laboratory • Common in western North Pacific and western North Atlantic • Source of substantial forecast uncertainty regionally and far downstream • Focus for THORPEX in terms of targeted atmospheric observations • Potentially sensitive to underlying ocean; to be assessed in upcoming NWP experiments on recent western Pacific events

15. General Decrease in Forecast Skill for ET Storms ET Tracks Forecast Skill Bifurcation From Jones et al., 2003: Wea. And Forecasting

16. 19 Oct 27 Oct Tokage- Downstream Increase in Uncertainty ECMWF EPS 500 hPa Standard Deviation Forecast from 16 October Forecast from 18 October 17 Oct 25 Oct 0 0 0 180 0 180 Hovmoller diagrams of the standard deviation in 500 mb geopotential height among the individual members of an ensemble of ECMWF model forecasts. The rate of spread in the forecasts (i.e., error growth) becomes relatively large near the time of Tokage’s transition. From a presentation for the Pacific Asian Regional Campaign (PARC-2008) at the NOAA THORPEX PI meeting, 19 Jan 2006, NCEP

17. Coastal Boundary Layer Air-Sea Coupling in Coastal UpwellingRoger Samelson, Eric Skyllingstad, Natalie PerlinCOAS, Oregon State University Reduced SAT and Winds

18. Numerical Simulations of Air-Sea CouplingDuring Coastal Upwelling (Perlin et al., JPO, 2007) Idealized two-dimensional (cross-shore and vertical) simulations of wind-driven coastal upwelling Atmosphere: 15 m/s northerly geostrophic wind Ocean: Stratified, at rest Sloping bathymetry 72-hour coupled and uncoupled simulations Initial model atmospheric potential temperature, water vapor mixing ratio, and ocean temperature and salinity profiles Ocean bathymetry

19. Surface Atmospheric Forcing and Ekman Transport

20. Atmospheric Boundary Layer Structure and SST SST SST

21. Coastal Boundary Layer Warm, offshore flow Heat Cooling ~10-30 km

22. from Long-EZ, November 14, 1999 Vickers et al. (2001) Aircraft Data Momentum flux (u*, shaded) Offshore velocity (u, solid contours) Coast

23. COAMPS Barrier Island Simulation Turbulent Kinetic Energy Neutral Heating Cooling q = 293 q = 283 q = 287

24. offshore velocity (u) momentum flux (u*) Barrier Island flow: models vs. observations COAMPS LES Observations