Coupled modeling of eddy-wind interaction in the California Current - - PowerPoint PPT Presentation

Hyodae Seo Woods Hole Oceanographic Institution Art Miller & Joel Norris Scripps Institution of Oceanography

Coupled modeling of eddy-wind interaction in the California Current System

— Impact on eddy kinetic energy and Ekman pumping

Joint Session on Air-Sea Interaction and the Coastal Environment

AMS Annual Meeting, Phoenix January 5, 2015

Paper #: J3.3

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Ua = Uab + UaSST

Satellite observations: Xie 2004 Correlation (SST & wind): high-passed

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Ua = Uab + UaSST

Satellite observations: Xie 2004 Correlation (SST & wind): high-passed northward propagation

• f an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2 surface temperature 2 2 1 1 –1 –2 –2 –1

U⊕ D⊖ τ

Ekman velocity

d s

Surface temperature and height 2

a b

2 1 1 0.5 –0.5 0.25 –0.25 –1 –2 –2 –1

An anticyclonic eddy in the Southern Ocean (Chelton 2013) SST and SSH

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Ua = Uab + UaSST

Satellite observations: Xie 2004 Correlation (SST & wind): high-passed northward propagation

• f an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2 surface temperature 2 2 1 1 –1 –2 –2 –1

U⊕ D⊖ τ

Ekman velocity

d s

Surface temperature and height 2

a b

2 1 1 0.5 –0.5 0.25 –0.25 –1 –2 –2 –1

An anticyclonic eddy in the Southern Ocean (Chelton 2013) SST and SSH

Uo = Uob + Uoe

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Ua = Uab + UaSST

Satellite observations: Xie 2004 Correlation (SST & wind): high-passed northward propagation

• f an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2 surface temperature 2 2 1 1 –1 –2 –2 –1

U⊕ D⊖ τ

Ekman velocity

d s

Surface temperature and height 2

a b

2 1 1 0.5 –0.5 0.25 –0.25 –1 –2 –2 –1

An anticyclonic eddy in the Southern Ocean (Chelton 2013) SST and SSH

Uo = Uob + Uoe

We=τ/[ρ(f+ζ)]

2 2 1 1 –1 –2 –2 –1

U⊕

Upwelling at the center: decaying of an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2

Eddy-wind interaction

τ = ρ CD (Ua− Uo) |Ua − Uo|

Ua = Uab + UaSST

Satellite observations: Xie 2004 Correlation (SST & wind): high-passed

Different feedbacks due to SST

• and current-induced

eddy-wind interactions! Key question: relative impact of τSST and τcur

• n the eddy dynamics?

northward propagation

• f an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2 surface temperature 2 2 1 1 –1 –2 –2 –1

U⊕ D⊖ τ

Ekman velocity

d s

Surface temperature and height 2

a b

2 1 1 0.5 –0.5 0.25 –0.25 –1 –2 –2 –1

An anticyclonic eddy in the Southern Ocean (Chelton 2013) SST and SSH

Uo = Uob + Uoe

We=τ/[ρ(f+ζ)]

2 2 1 1 –1 –2 –2 –1

U⊕

Upwelling at the center: decaying of an anticyclonic eddy

with contour interval = 0.5 cm da 6 3 –3 –6 2

Previous studies on impacts of τSST and τcur

• Previous ocean-modeling studies show weakened eddy

variability with inclusion of τSST and τcur.

uncoupled SST SST

• τ coupled SST

Uo-τ coupled EKE uncoupled EKE

effect of τSST: Jin et al. (2009) effect of τcur: Eden and Dietze (2009)

• This study examines the relative importance of τSST vs τcur

using a fully coupled regional model.

Scripps regional coupled model and experiments

• Seo et al. 2007, 2014
• 7 km O-A resolutions
• 6-yr integration (2005-2010)

WRF or bulk physics τ (Q & FW)

Ocean

6-h NCEP FNL monthly SODA

WRF ROMS

Scripps regional coupled model

6-h coupling

Atmosphere

SST & Usfc

Scripps regional coupled model and experiments

• Seo et al. 2007, 2014
• 7 km O-A resolutions
• 6-yr integration (2005-2010)

WRF or bulk physics τ (Q & FW)

Ocean

6-h NCEP FNL monthly SODA

WRF ROMS

Scripps regional coupled model

6-h coupling

Atmosphere

SST & Usfc

Te Tb Removal of eddies with 5° loess filter (Putrasahan et al. 2013)

SST & Usfc

Ub Ue

Exps τ form τ formulation ation includ ncludes CTL Tb Te Ub Ue noTe Tb Ub Ue noUe Tb Te Ub

• Te no impact
• 25% weaker EKE with Ue
• Surface current dissipates the EKE

JAS 2005-2010

EKE significantly reduced by current effect on wind stress

Drifter climatology

Marchesiello et al. 2003

CTL noTe

cm2s-2

noUe

Eddy kinetic energy budget

Pe → Ke baroclinic conversion (BC) Km → Ke barotropic conversion (BT) Eddy-Wind terms: Wind work (P) if positive Eddy drag (ε) if negative

Ket + ! U ⋅ ! ∇ ! Ke+ # ! u ⋅ ! ∇ ! Ke+ ! ∇⋅( # ! u # p ) =

+ρo(−!" u ⋅(!" u ⋅ ! ∇ ! U))− g " ρ " w + !" u ⋅ !" τ +ε

Reduced EKE is primarily due to enhanced eddy drag

CTL=0.58 noTe=0.58 noUe=0.51 CTL: somewhat higher level of BC: cannot explain the lower EKE. ← higher EKE ← lower EKE [10-5kgs-1m-3]

BC

u′τx′ v′τy′

With Ue, 16% reduction in wind work With Ue, 42% stronger eddy drag

cross-shore distance (km)

CTL=-0.47 noTe=-0.53 noUe=-0.33 CTL=1.74 noTe=1.86 noUe=1.90

˜ Wtot = Wcur + WSST = r ⇥ ˜ τ τ τ ρo (f + ζ) | {z }

˜ Wc

• 1

ρo (f + ζ)2 ✓ ˜ τ y ∂ζ ∂x ˜ τ x∂ζ ∂y ◆ | {z }

˜ Wζ

+ β˜ τ x ρo (f + ζ)2 | {z }

˜ Wβ

+ r ⇥ τ τ τ 0

SST

ρo (f + ζ) | {z }

WSST

. (10) Wtot = 1 ρo r ⇥ ✓ τ τ τ (f + ζ) ◆ r ⇥ τ τ ⇥ r

Stern (1965) & Gaube et al. (2014)

Eddy-induced Ekman pumping velocity

background wind stress Wlin Wζ Wβ WSST

Curl-induced linear Ekman pumping Vorticity gradient-induced nonlinear Ekman pumping β Ekman pumping (negligible) SST

• induced Ekman

pumping (Chelton et al. 2004)

˜ Wtot = Wcur + WSST = r ⇥ ˜ τ τ τ ρo (f + ζ) | {z }

˜ Wc

• 1

ρo (f + ζ)2 ✓ ˜ τ y ∂ζ ∂x ˜ τ x∂ζ ∂y ◆ | {z }

˜ Wζ

+ β˜ τ x ρo (f + ζ)2 | {z }

˜ Wβ

+ r ⇥ τ τ τ 0

SST

ρo (f + ζ) | {z }

WSST

. (10) Wtot = 1 ρo r ⇥ ✓ τ τ τ (f + ζ) ◆ r ⇥ τ τ ⇥ r

Stern (1965) & Gaube et al. (2014)

Eddy-induced Ekman pumping velocity

background wind stress Wlin Wζ Wβ WSST

Curl-induced linear Ekman pumping Vorticity gradient-induced nonlinear Ekman pumping β Ekman pumping (negligible) SST

• induced Ekman

pumping (Chelton et al. 2004)

WSST = ∇× # τ SST ρo f +ζ

( )

≈ αc∇cSST ρo f +ζ

( )

αc=0.6 αc=0.8

OBS CTL ▽Xτ′vs ▽cTʹ noTe noUe

αc=0.6 αc=0

Ekman pumping velocity JAS climatology

OBS (QuikSCAT & AVISO)

Wlin Wζ Wsst Wtot Wlin Wζ Wsst Wtot

CTL (with both eddy current and temperature)

JAS 2005-2009

m/day

▽cTʹ Wek Wek vs ▽cTʹ

Wctl-WnoTe

r=-0.06 ζ Wek vs ζ Wek

Wctl-WnoUe

r=-0.3 JAS 2005-2009 CTL Wek CTL-noTe CTL-noUe

SST

• and current-induced Ekman pumping velocity
• SST and current induce

perturbation Wek of comparable magnitudes but with distinctive spatial patterns.

• indicative of different

feedback processes

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 noTe (without eddy temperature) noUe (without eddy current)

Wlin Wζ Wsst Wtot Wlin Wζ Wsst Wtot JAS 2005-2009

m/day

• v’τy’: Source of EKE nearshore
• u’τx’: Dissipating EKE in the

upwelling zone

BC BT Px=u′τx′ Py=v′τy′ Summertime EKE budget in CTL

• Eddy wind work is a primary

source

• BC secondary and BT

negligible

u·τ

• v’τy’: Source of EKE nearshore
• u’τx’: Dissipating EKE in the

upwelling zone

BC BT Px=u′τx′ Py=v′τy′ Summertime EKE budget in CTL

along-shore averages

• Eddy wind work is a primary

source

• BC secondary and BT

negligible

u·τ