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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. Some questions. On what scales do ocean and atmosphere interact near WBCs?

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Ocean frontal scale air sea interaction

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

Some questions
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?


  • 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

Response of mabl to ocean fronts
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

Analysis of synoptic storms and gulf stream

Analysis of synoptic storms and Gulf Stream

Kathie KellyLuAnne ThompsonJimmy BoothJerome Patoux

University of Washington , Seattle

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

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

Regional atmospheric modeling of response to gulf stream

Regional atmospheric modeling of response to Gulf Stream

R. Justin Small,

Yuqing Wang, Shang-Ping Xie

International Pacific Research Center, University of Hawaii

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).

Regional atmospheric model mean situation jan apr
Regional Atmospheric Model Mean situation Jan-Apr

Rain rate and deep response
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.

Synoptic variability 2 8 day bandpass
Synoptic variability: 2-8 day bandpass





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

General Decrease in Forecast Skill for ET Storms

ET Tracks

Forecast Skill Bifurcation

From Jones et al., 2003: Wea. And Forecasting

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







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

Coastal Boundary Layer

Air-Sea Coupling in Coastal UpwellingRoger Samelson, Eric Skyllingstad, Natalie PerlinCOAS, Oregon State University

Reduced SAT

and Winds

Numerical simulations of air sea coupling during coastal upwelling
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

Coastal boundary layer
Coastal Boundary Layer

Warm, offshore flow



~10-30 km

Aircraft data

from Long-EZ, November 14, 1999

Vickers et al. (2001)

Aircraft Data

Momentum flux (u*, shaded)

Offshore velocity (u, solid contours)


Coamps barrier island simulation
COAMPS Barrier Island Simulation

Turbulent Kinetic Energy




q = 293

q = 283

q = 287

Barrier island flow models vs observations

offshore velocity (u)

momentum flux (u*)

Barrier Island flow: models vs. observations