Effects of Ocean-Atmosphere Coupling in a Modeling Study of Coastal Upwelling in the Area of Orograp...
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Effects of Ocean-Atmosphere Coupling in a Modeling Study of Coastal Upwelling in the Area of Orographically-Intensified Flow. Natalie Perlin, Eric Skyllingstad, and Roger Samelson. College of Oceanic and Atmospheric Sciences, Oregon State University. 2007 ROMS/TOMS Workshop October 1-3, UCLA.

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Natalie perlin eric skyllingstad and roger samelson

Effects of Ocean-Atmosphere Coupling in a Modeling Study of Coastal Upwelling in the Area of Orographically-Intensified Flow

Natalie Perlin, Eric Skyllingstad, and Roger Samelson

College of Oceanic and Atmospheric Sciences,

Oregon State University

2007 ROMS/TOMS Workshop

October 1-3, UCLA


Outline of the talk

Outline of the talk

  • Background : observations, theory, modeling

  • Recent modeling efforts: study design, test cases

  • Modeling results

  • Conclusions, discussion, future work


Background

Background

  • Three phenomena/processes involved:

  • Flow intensification downwind of major capes along the Oregon-California coastline – satellite, in-situ observations, atm. modeling

  • Wind-driven coastal upwelling in the summertime – observations, theories, ocean and coupled ocean-atmosphere modeling

  • Mesoscale air-sea interaction affecting boundary layers in both ocean and atmosphere – observations, theories, coupled modeling


Wind intensification downwind of major capes off the u s west coast

Enriquez and Friehe (1995)

Wind intensification downwind of major capes off the U.S. West coast

Enriquez and Friehe, 1995

Perlin et al., 2004


Wind driven coastal upwelling

Wind-driven coastal upwelling

Satellite SST

Coastal Ekman transport at the ocean boundary:

Huyer et al., 2005


Air sea interaction in the marine boundary layer airborne observations

Air-sea interaction in the marine boundary layer : airborne observations

Duck, North Carolina

Oregon coast, COAST experiment

Momentum flux and wind speed

Potential temp. (K) and v-wind (m/s)

Courtesy of John Bane, UNC

Vickers et al., 2001


First results from a coupled model

First results from a coupled model

Courtesy of John Bane, UNC

Perlin et al., 2007


Numerical study design for a coupled model

Numerical study design for a coupled model

coastal bend

  • Coupled ocean-atmosphere model,

  • COAMPS (atm.) and ROMS (ocean)

  • Horiz. domain 160 x 210, 3-km grid

  • Vertical: 47 lvs. (atm.) and 40 (ocean)

  • Time step: 5 s (atm) and 100 s (ocean)

  • Atm. model is driven by 15 m/s geostrophic wind in the atm. boundary layer; 5 m/s above 2000 m.

  • Ocean model: initially at rest, stratified in temp. and salinity

  • Periodic N-S boundary conditions in both atm. and ocean models; the domain becomes a periodic channel

  • Open W-E boundary conditions; eastern wall in ROMS


Wind stress control case

Wind stress: control case


Surface currents and sst

Surface currents and SST


Marine boundary layer height

Marine boundary layer height

  • Atmospheric boundary layer grows over most of the domain

  • The localized region of low boundary layer height (<200m) is sustained

  • throughout the run


Potential temperature and meridional wind component cross sections

Potential temperature and meridional wind component cross-sections

control case


Three more study cases considered

Three more study cases considered

  • Case 1:

    a) Run a coupled model for 36 hours, save the output for restart

    b) Use 36-h wind stress to re-start ocean model and run for 108 h (4.5 days)

    c) Re-couple the models and run them for 36 h (total of 72 hours for the atmosphere, or 180 h for the ocean)

  • Case 2:

  • a) Use a coupled 36-h run to determine wind stress 100 km offshore

  • b) Force the ocean model with spatially and temporarily invariable wind stress, run for 72 hours

  • Case 3

  • a) Use a 36-h forecast of the wind stress from the coupled model

  • b) Force the ocean model with spatially variable, but constant in time wind forcing; run for 72 hours


Sea surface temperatures

Sea surface temperatures

control case

case 1


Sea surface temperatures1

Sea surface temperatures

case 2

case 3


Natalie perlin eric skyllingstad and roger samelson

SST: Case 1 extension to 22 days

  • Further widening of cold water area near the coast

  • SST front remains relatively sharp

  • Beginning of eddy formation, more robust in the offshore region downstream of an initial coastal bend


Wind stress sst coupling

Wind stress-SST coupling

H. Hashizume et al., J. Climate. 15, 3379 (2002).

(Figure courtesy of Dudley Chelton, COAS)


Sst and wind stress case 1

SST and wind stress: case 1


Conclusions

Conclusions

  • Marine boundary layer structure in the area of wind intensification was simulated well in the case study

  • Onset of upwelling circulation occurred sooner in the area of wind acceleration, downstream of the first coastal bend

  • Coastal jet develops instabilities with time, more pronounced in the area of wind acceleration

  • No definite relationship between wind stress curl and SST gradient has been found in the coastal region (on meso-alpha scale)


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