Downscaling Global Warming with a Regional Ocean- Atmosphere Model over the Tropical Atlantic Role of equatorial ocean dynamics: equatorial upwelling and ocean mesoscale variability Hyodae Seo and Shang-Ping Xie International Pacific Research Center University of Hawaii AGU December 16, 2009 Also thanks to Raghu Murtugudde, Markus Jochum, and Art Miller
Introduction: Weakening of Walker circulation and ocean heat transport Multi-model ensemble change (A1B-20C) in ω (500hPa) Vecchi and Soden 2007
Introduction: Weakening of Walker circulation and ocean heat transport 123$ !" $ ! %1&!"""34$ ! '()*4$ ! +,-.1&!""34$ ! //01&!"3 #" Multi-model ensemble change u x ′ >0 !" (A1B-20C) in ω (500hPa) ! +,-.&!"" ! //0&!" τ x ′ >0 " !" $ % &!""" ! '()* ! !" zonal + vertical 153$ ! 1 ! 167087%9:7087;33 " "C"< 23 27 2 1 25 29 23 21 17 9 1 "C"D ! !"" 2 7 15 25 7 1 23 1 5 "C"B 19 ! #"" "C"# Themocline feedback zonal 1.3$ ! 1 ! 67087%3 " 2 23 7 DEPTH "C"! 2 5 9 2 3 2 7 2 5 2 ! !"" 1 7 21 " 17 23 19 δ (-u ∂ T/ ∂ x) 5 1 21 ! "C"! 19 ! #"" vertical Equatorial upwelling ! "C"# 173$ ! 1 ! :7087;3 " $ 23 27 29 25 ! "C"B 3 2 21 9 1 19 23 ! !"" 25 17 27 ! "C"D Vecchi and Soden 2007 15 δ (-w ∂ T/ ∂ z) 1 5 7 21 1 ! #"" $ ! "C"< !<"= !>"= !<"? !#"? @"? A"? B"? "= GFDL CM2.1 10-member ensemble Change in ocean heat transport (2046-2050) - (1996-2000)
• Tropical Instability Waves (TIWs) are the undulations of equatorial SST front in the Pacific and Atlantic. • Generated by oceanic intrinsic instability. • Primarily sub-seasonal, but important for low-frequency tropical climate. • Not well-resolved in the IPCC-AR4 models. So we need to downscale .
Model and Experiments Scripps Coupled Ocean-Atmosphere Regional Model * Atmosphere: Regional Spectral Model (Scripps RSM) Ocean: Regional Ocean Modeling System (ROMS) CTL • CTL : RSM (NCEP2 6hrly) + ROMS (SODA monthly) ➜ ➜ Flux • 25 km ROMS + 50 km RSM ROMS RSM ➜ ➜ SST • Daily coupling ➜ ➜ • 28-yr. integration: 1980-2007 SODA NCEP2 * Seo, Miller and Roads, 2007 : The Scripps Coupled Ocean-Atmosphere Regional (SCOAR) model, with applications in the eastern Pacific sector. Journal of Climate
Model and Experiments Scripps Coupled Ocean-Atmosphere Regional Model * Atmosphere: Regional Spectral Model (Scripps RSM) Ocean: Regional Ocean Modeling System (ROMS) CTL • CTL : RSM (NCEP2 6hrly) + ROMS (SODA monthly) ➜ ➜ Flux • 25 km ROMS + 50 km RSM ROMS RSM ➜ ➜ SST • Daily coupling ➜ ➜ • 28-yr. integration: 1980-2007 SODA NCEP2 GW • δ =GFDL CM2.1 monthly difference: ➜ ➜ Flux • (2045-2050: A1B)-(1996-2000: 20C) ROMS RSM ➜ ➜ SST • GW : RSM (NCEP2 6-hrly + δ ) + ROMS (SODA ➜ ➜ monthly + δ ) NCEP2+ δ SODA+ δ * Seo, Miller and Roads, 2007 : The Scripps Coupled Ocean-Atmosphere Regional (SCOAR) model, with applications in the eastern Pacific sector. Journal of Climate
Model and Experiments Scripps Coupled Ocean-Atmosphere Regional Model * Atmosphere: Regional Spectral Model (Scripps RSM) Ocean: Regional Ocean Modeling System (ROMS) CTL • CTL : RSM (NCEP2 6hrly) + ROMS (SODA monthly) ➜ ➜ Flux • 25 km ROMS + 50 km RSM ROMS RSM ➜ ➜ SST • Daily coupling ➜ ➜ • 28-yr. integration: 1980-2007 SODA NCEP2 GW • δ =GFDL CM2.1 monthly difference: ➜ ➜ Flux • (2045-2050: A1B)-(1996-2000: 20C) ROMS RSM ➜ ➜ SST • GW : RSM (NCEP2 6-hrly + δ ) + ROMS (SODA ➜ ➜ monthly + δ ) NCEP2+ δ SODA+ δ Quasi-steady state * Seo, Miller and Roads, 2007 : The Scripps Coupled Ocean-Atmosphere Regional (SCOAR) model, with applications in the eastern Pacific sector. Journal of Climate
Simulation of present-day climate and global warming response: Annual mean SST, surface winds, and precip.
Simulation of present-day climate • Zonal SST gradient and equatorial cold tongue in SCOAR
Simulation of present-day climate GW response • Reduced warming in the equator • Intensified cross-equatorial meridional winds • Zonal SST gradient and equatorial cold tongue in SCOAR
Change in equatorial zonal currents and equatorial instability SCOAR CTL Mean U SCOAR δ U • EUC is more realistic SEC (stronger) in SCOAR. EUC • Stronger cross- equatorial wind ➡ Stronger EUC GFDL 20C Mean U GFDL δ U ( Philander and Delecluse, 1983 ) ➡ Enhanced Barotropic and baroclinic instability ➡ Stronger TIWs
Strengthening of TIWs ( 20-40 day band-pass filtered EKE and SST variance) CTL EKE GW EKE (a) CTL EKE (b) GW EKE 120 5N 5N 100 80 2.5N 2.5N 60 40 EQ EQ 20 2.5S 2.5S 0 40W 20W 0E 40W 20W 0E • EKE and TIW-SST GW SST Variance CTL SST Variance (c) CTL SST VAR (d) GW SST VAR variance all become 5N 5N stronger during the 0.1 0.08 cold season. 2.5N 2.5N 0.06 0.04 EQ EQ 0.02 2.5S 2.5S 40W 20W 0E 40W 20W 0E Seasonal cycle of EKE Seasonal cycle of SST Variance 0.1 (f) Climatology of SST VAR 150 (e) Climatology of EKE CTL CTL GW GW 100 0.05 50 0 0 1 3 5 7 9 11 1 3 5 7 9 11 month month
Annual mean mixed layer ocean heat budget (30W-10W) δ Eddy-NET δ Upwelling • Equatorial upwelling (cooling) increases • Increased w’ acting on climatological dT/dz >> Climatological <w> acting on dT’/dz due to radiative forcing. • Net eddy heat flux (warming) increases, damping the effect of upwelling.
Conclusion and Discussion • Downscaling is also important for study of oceanic role in weather and climate. • Advantages: Better capture equatorial currents and mesoscale variabilities • Exploratory research: Coupled downscaling of the IPCC climate change scenarios • Upwelling increases. TIWs increase. Impact the mean state. • Need to monitor TIW heat flux(zonal) for detection of warming signal. • Need to resolve high-freq. processes in the model for global warming research.
Thanks!
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