Joint Session on Air-Sea Interaction Paper #: J3.3 and the Coastal Environment Coupled modeling of eddy-wind interaction in the California Current System — Impact on eddy kinetic energy and Ekman pumping Hyodae Seo Woods Hole Oceanographic Institution Art Miller & Joel Norris Scripps Institution of Oceanography AMS Annual Meeting, Phoenix January 5, 2015
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o |
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o | U a = U ab + U aSST Satellite observations: Xie 2004 Correlation (SST & wind): high-passed
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o | U a = U ab + U aSST Satellite observations: Xie 2004 Correlation (SST & wind): high-passed An anticyclonic eddy in the Southern Ocean (Chelton 2013) a b Surface temperature SST and SSH Ekman velocity with contour interval = 0.5 cm da and height surface temperature 2 2 0.5 6 d D ⊖ 1 1 0.25 s 3 τ 0 0 0 0 U ⊕ –0.25 –1 –3 –1 –0.5 –6 –2 –2 –2 –1 0 1 2 –2 –1 0 1 2 2 northward propagation of an anticyclonic eddy
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o | U a = U ab + U aSST U o = U ob + U oe Satellite observations: Xie 2004 Correlation (SST & wind): high-passed An anticyclonic eddy in the Southern Ocean (Chelton 2013) a b Surface temperature SST and SSH Ekman velocity with contour interval = 0.5 cm da and height surface temperature 2 2 0.5 6 d D ⊖ 1 1 0.25 s 3 τ 0 0 0 0 U ⊕ –0.25 –1 –3 –1 –0.5 –6 –2 –2 –2 –1 0 1 2 –2 –1 0 1 2 2 northward propagation of an anticyclonic eddy
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o | U a = U ab + U aSST U o = U ob + U oe Satellite observations: Xie 2004 Correlation (SST & wind): high-passed An anticyclonic eddy in the Southern Ocean (Chelton 2013) a b Surface temperature SST and SSH Ekman velocity with contour interval = 0.5 cm da and height surface temperature 2 2 0.5 6 d D ⊖ 1 1 0.25 s 3 τ 0 0 0 0 U ⊕ –0.25 –1 –3 –1 –0.5 –6 –2 –2 –2 –1 0 1 2 –2 –1 0 1 2 2 with contour interval = 0.5 cm da 2 northward propagation 6 of an anticyclonic eddy 1 3 Upwelling at the center: U ⊕ 0 0 decaying of an anticyclonic eddy –3 –1 W e = τ /[ ρ (f+ ζ )] –6 –2 2 –2 –1 0 1 2
Eddy-wind interaction τ = ρ C D (U a − U o ) |U a − U o | U a = U ab + U aSST U o = U ob + U oe Satellite observations: Xie 2004 Correlation (SST & wind): high-passed An anticyclonic eddy in the Southern Ocean (Chelton 2013) a b Surface temperature SST and SSH Ekman velocity with contour interval = 0.5 cm da and height surface temperature 2 2 0.5 6 d D ⊖ 1 1 0.25 s 3 τ 0 0 0 0 U ⊕ –0.25 –1 –3 –1 –0.5 Different feedbacks due to –6 –2 –2 –2 –1 0 1 2 –2 –1 0 1 2 2 with contour interval = 0.5 cm da SST - and current-induced 2 northward propagation 6 eddy-wind interactions! of an anticyclonic eddy 1 3 Key question: Upwelling at the center: U ⊕ 0 0 decaying of an relative impact of τ SST and τ cur anticyclonic eddy –3 –1 on the eddy dynamics? W e = τ /[ ρ (f+ ζ )] –6 –2 2 –2 –1 0 1 2
Previous studies on impacts of τ SST and τ cur • Previous ocean-modeling studies show weakened eddy variability with inclusion of τ SST and τ cur . uncoupled SST - τ coupled SST SST uncoupled EKE U o - τ coupled EKE effect of τ SST : Jin et al. (2009) effect of τ cur : Eden and Dietze (2009) • This study examines the relative importance of τ SST vs τ cur using a fully coupled regional model.
Scripps regional coupled model and experiments Scripps regional coupled model • Seo et al. 2007, 2014 Ocean • 7 km O-A resolutions Atmosphere WRF or bulk physics • 6-yr integration (2005-2010) τ (Q & FW) WRF 6-h coupling ROMS SST & U sfc 6-h NCEP FNL monthly SODA
Scripps regional coupled model and experiments Scripps regional coupled model • Seo et al. 2007, 2014 Ocean • 7 km O-A resolutions Atmosphere WRF or bulk physics • 6-yr integration (2005-2010) τ (Q & FW) WRF 6-h coupling ROMS SST & U sfc SST & U sfc Removal of eddies with 5° loess filter 6-h NCEP FNL monthly SODA (Putrasahan et al. 2013) T b T e Exps τ formulation τ form ation includ ncludes CTL T b T e U b U e U b U e noT e T b U b U e noU e T b T e U b
EKE significantly reduced by current effect on wind stress Drifter climatology CTL noT e cm 2 s -2 Marchesiello et al. 2003 noU e • T e no impact • 25% weaker EKE with U e - Surface current dissipates the EKE JAS 2005-2010
Eddy kinetic energy budget ! ! ! ! ! ! ! ! Ke t + U ⋅ Ke + # u ⋅ Ke + ∇⋅ ( # u # p ) = ∇ ∇ ! ! u ⋅ ! " + ρ o ( − ! " u ⋅ ( ! " w + ! " u ⋅ U )) − g " " ∇ ρ τ + ε K m → K e P e → K e Eddy-Wind terms: barotropic baroclinic Wind work (P) if positive conversion conversion Eddy drag ( ε ) if negative (BT) (BC)
Reduced EKE is primarily due to enhanced eddy drag ← lower EKE CTL=0.58 BC noT e =0.58 ← higher EKE noU e= 0.51 CTL: somewhat higher level of BC: cannot explain the lower EKE. [10 -5 kgs -1 m -3 ] With U e , 42% CTL= - 0.47 stronger eddy noT e = - 0.53 u ′τ x ′ drag noU e= - 0.33 v ′τ y ′ CTL=1.74 With U e , 16% noT e =1.86 reduction in wind work noU e= 1.90 cross-shore distance (km)
Eddy-induced Ekman pumping velocity Stern (1965) & Gaube et al. (2014) ✓ ◆ 1 τ τ τ W tot = r ⇥ ( f + ζ ) ρ o r ⇥ τ τ ⇥ r ˜ background wind stress = W cur + W SST W tot ✓ ◆ τ x r ⇥ ˜ τ τ τ 1 τ y ∂ζ τ x ∂ζ β ˜ + r ⇥ τ τ τ 0 SST = ˜ ∂ x � ˜ + . � (10) ρ o ( f + ζ ) 2 ρ o ( f + ζ ) 2 ρ o ( f + ζ ) ρ o ( f + ζ ) ∂ y | {z } | {z } | {z } | {z } ˜ W SST W lin W SST W ζ ˜ W β ˜ W c W ζ W β Curl-induced Vorticity gradient-induced linear Ekman pumping nonlinear Ekman pumping β Ekman pumping (negligible) SST -induced Ekman pumping (Chelton et al. 2004)
Eddy-induced Ekman pumping velocity Stern (1965) & Gaube et al. (2014) ✓ ◆ 1 τ τ τ W tot = r ⇥ ( f + ζ ) ρ o r ⇥ τ τ ⇥ r ˜ background wind stress = W cur + W SST W tot ✓ ◆ τ x r ⇥ ˜ τ τ τ 1 τ y ∂ζ τ x ∂ζ β ˜ + r ⇥ τ τ 0 τ SST = ˜ ∂ x � ˜ + . � (10) ρ o ( f + ζ ) 2 ρ o ( f + ζ ) 2 ρ o ( f + ζ ) ρ o ( f + ζ ) ∂ y | {z } | {z } | {z } | {z } ˜ W SST W lin W SST W ζ ˜ W β ˜ W c W ζ W β Curl-induced Vorticity gradient-induced linear Ekman pumping nonlinear Ekman pumping β Ekman pumping ▽ X τ′ vs ▽ c T ʹ (negligible) CTL OBS SST -induced Ekman α c =0.8 α c =0.6 pumping (Chelton et al. 2004) noT e noU e ≈ α c ∇ c SST W SST = ∇× # τ SST α c =0.6 ( ) ( ) ρ o f + ζ ρ o f + ζ α c =0
Ekman pumping velocity JAS climatology OBS (QuikSCAT & AVISO) W sst W lin W tot W ζ CTL (with both eddy current and temperature) W sst W lin W tot W ζ JAS 2005-2009 m/day
SST - and current-induced Ekman pumping velocity Wek vs ▽ c T ʹ CTL-noTe CTL Wek W ctl -W noTe r=-0.06 Wek ▽ c T ʹ Wek vs ζ CTL-noUe • SST and current induce W ctl -W noUe perturbation Wek of comparable magnitudes r=-0.3 Wek but with distinctive spatial patterns. - indicative of different feedback processes ζ JAS 2005-2009
Summary • Surface EKE is weakened almost entirely due to mesoscale current effect on wind stress. - SST has no impact (at odds with some previous studies) - EKE budget: eddies primarily enhance the eddy drag, and weaken the wind work of secondary importance. • Change in eddy drag means changes in Ekman pumping velocities - Eddy-current and eddy-SST produce Ekman pumping velocity climatologies of comparable magnitudes and different distributions. - Implying different feedback processes, a subject of ongoing study.
Thanks! hseo@whoi.edu This study gratefully acknowledges NSF OCE-09060770.
Ekman pumping velocity JAS climatology noT e (without eddy temperature) W sst W lin W tot W ζ noU e (without eddy current) W sst W lin W tot W ζ JAS 2005-2009 m/day
Summertime EKE budget in CTL BT u · τ BC P y =v ′τ y ′ • Eddy wind work is a primary P x =u ′τ x ′ source • BC secondary and BT negligible • v’ τ y ’: Source of EKE nearshore • u’ τ x ’: Dissipating EKE in the upwelling zone
Summertime EKE budget in CTL BT u · τ BC P y =v ′τ y ′ • Eddy wind work is a primary P x =u ′τ x ′ source • BC secondary and BT negligible • v’ τ y ’: Source of EKE nearshore • u’ τ x ’: Dissipating EKE in the along-shore averages upwelling zone
Recommend
More recommend
