Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the Southern California...
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Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the
Southern California Coastal Regions(Santa Ana Winds and Air-Sea Interaction)
Hyodae Seo, Art Miller, John RoadsScripps Institution of Oceanography
UCSD, 0224 La Jolla, CA 92093
5th International RSM workshopYonsei University, Seoul, Korea
July 12-16, 2004
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Outline
• What is the Santa Ana? : Observational evidence• Numerical Simulations: : Oceanic and atmospheric response
(coupled and uncoupled simulations)• Conclusions/Ongoing work
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The Santa Ana: Devil’s breath
• Interaction with topography• Dry and warm due to adiabatic heating
• Wildfires • Clearing of marine stratiform clouds• Dust/Aerosols transport to the ocean
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RSM simulation: Feb. 7 ~ 16, 2002
In San DiegoU10m(m/s) V10m(m/s)
RH2m(%)
FWI(%)
3 hourly Daily averaged
Santa Ana Episode
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925mb winds(m/s) and FWI(%)
Increased likelihood of wildland firesFeb 8 3Z ~ Feb 13Z 2002
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850mb winds(m/s) and Low Level Cloudiness(%)
• Large scale clearing of low-level marine layer cloudsFeb 8 3Z ~ Feb 13Z 2002
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Forcing from RSM(1): zonal windstress(N/m2)
SCBFAR OFFSHORE
Santa Ana Forcing
Climatology forcing
difference
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Forcing from RSM(2): surface net heatflux (W/m2)
SCBFAR OFFSHORE
Santa Ana Forcing
difference
Climatology forcing
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Atmosphere and Ocean Model and their Exchange of Forcing
ATMOSPHEREECPC’ RSM: 20km resolution
OCEAN
The Regional Ocean Modeling System (ROMS)
Primitive equation ocean model (Song and Haidvogel, 1994)Sigma vertical coordinate (enhanced res. near top and bathymetry)
Curvilinear horizontal grid (~12km and ~5km resolution)
Momentum flux,
Net surface heat, freshwater flux
: 3 hourly
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Forcing from RSM: SHFLUX(W/m2)
Shflux(W/m2) =swrad+lwrad-lhtfl-shtflHeat-flux Correction:Q’=Q+dQdSST*(T_mod-SST)dQdSST~-40(W/m2/C)
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Oceanic Response(1): SST(C)
FAR OFFSHORE SCB
response to Santa Ana
response to climatology
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Cross-shore Component Ekman Mass Transport(kg/s/m)Measure of Upwelling intensity
FAR OFFSHORESCB
response to Santa Anaresponse to climatology
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Oceanic Response(2): Meridional surface current(V, m/s)
FAR OFFSHORE
SCB
INLAND
response to climatology
response to Santa Ana
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Atmosphere and Ocean Model and their Exchange of Forcing
Atmosphere: ECPC RSM: 20km resolution
Ocean:
The Regional Ocean Modeling System(ROMS)
Primitive equation ocean model (Song and Haidvogel, 1994)Sigma vertical coordinate
Curvilinear horizontal grid (~12km and ~5km resolution)
Momentum flux,
Net surface heat, freshwater flux
: 3 hourly
SST: daily
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Atmospheric Response(1): Zonal winds(U,m/s) @ 10m
forced w/ ROMS SST
forced w/ OBS SST
difference
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Atmospheric Response(2): meridional winds(V, m/s) @ 10m
forced w/ ROMS SST
forced w/ OBS SST difference
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Atmospheric Response(3): surface net heatflux (W/m2)
forced w/ OBS SST
forced w/ ROMS SST
difference
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FWI(%): RSM’s Response to ROMS SST vs Reanalysis SST
forced w/ OBS SST
forced w/ ROMS SST
San Diego
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Conclusion/Ongoing work(1)
• Both RSM and ROMS reproduce qualitatively well the atmospheric extreme and typical oceanic response in terms of spatial intensity and temporal evolution.
• Oceanic response indicates that Santa Ana winds forcing modifies the Ekman dynamics of the ocean surface layer by decreasing upwelling, and thereby increasing SST.
• ROMS could not resolve any small scale cold tongues and chlorophyll blooms adjacent to the coastlines.
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Conclusion/Ongoing Work(2)• Coupled RSM run with ROMS shows less intense Santa Ana event,
mainly because the ocean surface from ROMS is warmer.
• Higher Surface Heatflux (Stronger Winds) from RSM Warmer SST from ROMS lower Heatflux(weaker winds) from RSM ( and presumably colder SST from ROMS?): possibility of stable integration.
• Coupled model requires higher resolution (up to 5km) and better description of coastlines in order to resolve the small scale and short-lived features.
• Sensitivity of Southern California Current System to atmospheric forcing: Use of bulk parameterizations to provide feedback, implementation of 3D NPZD ecosystem model.