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1 Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the Southern California Coastal Regions (Santa Ana Winds and Air-Sea Interaction)

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Presentation on theme: "1 Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the Southern California Coastal Regions (Santa Ana Winds and Air-Sea Interaction)"— Presentation transcript:

1 1 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 Roads Scripps Institution of Oceanography UCSD, 0224 La Jolla, CA th International RSM workshop Yonsei University, Seoul, Korea July 12-16, 2004

2 2 Outline What is the Santa Ana? : Observational evidence Numerical Simulations: : Oceanic and atmospheric response (coupled and uncoupled simulations) Conclusions/Ongoing work

3 3 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

4 4 RSM simulation: Feb. 7 ~ 16, 2002 In San Diego U10m(m/s) V10m(m/s) RH2m(%) FWI(%) 3 hourlyDaily averaged Santa Ana Episode

5 5 925mb winds(m/s) and FWI(%) Increased likelihood of wildland fires Feb 8 3Z ~ Feb 13Z 2002

6 6 850mb winds(m/s) and Low Level Cloudiness(%) Large scale clearing of low- level marine layer clouds Feb 8 3Z ~ Feb 13Z 2002

7 7 Forcing from RSM(1): zonal windstress(N/m2) SCBFAR OFFSHORE Santa Ana Forcing Climatology forcing difference

8 8 Forcing from RSM(2): surface net heatflux (W/m2) SCBFAR OFFSHORE Santa Ana Forcing difference Climatology forcing

9 9 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 (enhanced res. near top and bathymetry) Curvilinear horizontal grid (~12km and ~5km resolution) Momentum flux, Net surface heat, freshwater flux : 3 hourly

10 10 Forcing from RSM: SHFLUX(W/m2) Shflux(W/m2) =swrad+lwrad-lhtfl-shtfl Heat-flux Correction: Q’=Q+dQdSST*(T_mod-SST) dQdSST~-40(W/m2/C)

11 11 Oceanic Response(1): SST(C) FAR OFFSHORESCB response to Santa Ana response to climatology

12 12 Cross-shore Component Ekman Mass Transport(kg/s/m) Measure of Upwelling intensity FAR OFFSHORE SCB response to Santa Ana response to climatology

13 13 Oceanic Response(2): Meridional surface current(V, m/s) FAR OFFSHORE SCB INLAND response to climatology response to Santa Ana

14 14 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

15 15 Atmospheric Response(1): Zonal 10m forced w/ ROMS SST forced w/ OBS SST difference

16 16 Atmospheric Response(2): meridional winds(V, 10m forced w/ ROMS SST forced w/ OBS SSTdifference

17 17 Atmospheric Response(3): surface net heatflux (W/m2) forced w/ OBS SST forced w/ ROMS SST difference

18 18 FWI(%): RSM’s Response to ROMS SST vs Reanalysis SST forced w/ OBS SST forced w/ ROMS SST San Diego

19 19 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.

20 20 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.


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