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Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the Southern California Coastal Regions (Santa

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 92093 5 th International RSM workshop

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Preliminary Simulation of the Regional Coupled Atmosphere-Ocean Model in the Southern California Coastal Regions (Santa

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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) Hyodae Seo, Art Miller, John Roads Scripps Institution of Oceanography UCSD, 0224 La Jolla, CA 92093 5th International RSM workshop Yonsei University, Seoul, Korea July 12-16, 2004

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

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

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

  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. Forcing from RSM(1): zonal windstress(N/m2) Climatology forcing Santa Ana Forcing difference FAR OFFSHORE SCB

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

  9. Atmosphere and Ocean Model and their Exchange of Forcing ATMOSPHERE ECPC’ RSM: 20km resolution Momentum flux, Net surface heat, freshwater flux : 3 hourly 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)

  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. Oceanic Response(1): SST(C) response to Santa Ana response to climatology FAR OFFSHORE SCB

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

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

  14. Atmosphere and Ocean Model and their Exchange of Forcing Atmosphere: ECPC RSM: 20km resolution Momentum flux, Net surface heat, freshwater flux : 3 hourly SST: daily 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)

  15. Atmospheric Response(1): Zonal winds(U,m/s) @ 10m forced w/ OBS SST difference forced w/ ROMS SST

  16. Atmospheric Response(2): meridional winds(V, m/s) @ 10m forced w/ OBS SST difference forced w/ ROMS SST

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

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

  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. 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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