effects of ocean-atmosphere coupling in a modeling study of coastal upwelling in the area of...
TRANSCRIPT
Effects of Ocean-Atmosphere Coupling in Effects of Ocean-Atmosphere Coupling in
a Modeling Study of Coastal Upwelling in a Modeling Study of Coastal Upwelling in
the Area of Orographically-Intensified Flowthe Area of Orographically-Intensified Flow
Natalie Perlin, Eric Skyllingstad, and Roger Samelson
College of Oceanic and Atmospheric Sciences, Oregon State University
2007 ROMS/TOMS Workshop2007 ROMS/TOMS WorkshopOctober 1-3, UCLAOctober 1-3, UCLA
Outline of the talk
• Background : observations, theory, modeling
• Recent modeling efforts: study design, test cases• Modeling results• Conclusions, discussion, future work
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
Enriquez and Friehe (1995)Enriquez and Friehe (1995)
Wind intensification downwind of major capes off the U.S. West coast
Perlin et al., 2004
Enriquez and Friehe, 1995Enriquez and Friehe, 1995
Wind-driven coastal upwelling
Satellite SST
Huyer et al., 2005
Coastal Ekman transport at Coastal Ekman transport at the ocean boundary:the ocean boundary:
fM ys
cE
Air-sea interaction in the marine boundary layer : airborne observations
Courtesy of John Bane, UNC Vickers et al., 2001
Potential temp. (K) and v-wind (m/s)
Oregon coast, COAST experimentOregon coast, COAST experiment Duck, North CarolinaDuck, North Carolina
Momentum flux and wind speed
First results from a coupled model
Perlin et al., 2007
Courtesy of John Bane, UNC
Numerical study design for a coupled model
• 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
coastal bend
Wind stress: control case
Surface currents and SST
Marine boundary layer height
1. Atmospheric boundary layer grows over most of the domain
2. The localized region of low boundary layer height (<200m) is sustained
throughout the run
Potential temperature and meridional wind component cross-sections
control case
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 temperaturescontrol case case 1
Sea surface temperaturescase 2 case 3
SST: Case 1 extension to 22 days
1. Further widening of cold water
area near the coast
2. SST front remains relatively
sharp
3. Beginning of eddy formation,
more robust in the offshore
region downstream of an initial
coastal bend
Wind stress-SST coupling
(Figure courtesy of Dudley Chelton, COAS)
H. Hashizume et al., J. Climate. 15, 3379 (2002).
SST and wind stress: case 1
s
s
s
k
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)