Rong-Hua Zhang

Funded partly by NASA PO Program, ….

Applications of Remotely Sensed High-

resolution SST Data to Representing

Tropical Instability Wave

(TIW)-Induced Surface Wind Response

University of Maryland, College Park, Maryland, USA

Outline

• Introduction

• Representing TIW-induced wind forcing & feedback

• A hybrid coupled ocean-atmosphere model (HCMOGCM

) Atmosphere: Wind stress: SVD-based;

Ocean: The Cane-Gent OGCM

• Ocean model experiments: with and without TIW wind forcing

• Coupled ocean-atmos experiments: TIW wind feedback

• Summary

TIW=0.0 TIW=2.0

τTIW = TIW Svd ( SSTTIW )

Tropical Instability Waves (TIWs)July 27-Aug. 3 1998(a) SST

(b) Ocean Chlorophyll (Chl) from satellite

Effects of TIWs on the Tropical Pacific Climate & Marine Ecosystem

Heat and momentum budget & balance Mean ocean and atmosphere states Seasonal modulation Interannual variations

e.g., as a stochastic forcing to modulate ENSO ? …….

High resolution modeling evidence:

Model improvements, biases, … => TIW effects

Challenges: TIW-induced wind forcing and feedback

Resolving TIW wind signals: high resolution Studies mostly on diagnostic analyses, less on

solutions Uncertainty in representing TIW wind forcing in

observations & data products TIW wind forcing not adequately represented in

ocean and coupled modeling Mechanisms for atmos wind responses: still in debate

e.g.: vertical mixing vs pressure gradients Poor understanding of interactions between TIWs

and large-scale processes A clean & clear assessment of TIW-induced wind

forcing & feedback => still lacking …. …..

IPCC AR4 climate models & ENSO forecast models

TIW-induced wind feedback NOT

taken into account

Different ways TIW-induced wind forcing is represented in the Atmos for ocean-related modeling

Not resolved at low resolution e.g.: global climate models; atmos re-analysis climate products

=> Biases

High resolution wind data (e.g.,: directly from satellite obs. ) e.g.: prescribed wind data : A forced ocean modeling without feedback from the ocean to the atmos

=> Biases

TIW resolving coupled air-sea models at TIW scales Regional models: Scripps; IPRC => regional !! Global climate model => expensive; not affordable now !!

Biases can be introduced by TIW-induced wind forcing

ocean ocean modelsmodels

τTIW

Taking into account TIW-induced wind forcing & feedback

Using satellite data to explore statistical modeling for TIW wind

=> another application of satellite data to climate modeling;

A simple parameterization for TIW winds; A modeling tool for interactions between TIWs

and large-scale processes; A clean assessment for the effects of TIW wind

forcing & feedback on ocean & coupled modeling; Understanding basic processes involved, the role in

biases of SST simulation; …. Improving climate simulations & prediction;

This work

An empirical mpdel for τTIW

• TMI SST & QuikSCAT winds

• Daily data during 2000-2007;

• Filtered for TIW signals

• SVD analyses: dominant modes

• Relationship between SSTTIW & τTIW

• Given SSTTIW => τTIW fields

τTIW = TIW Svd ( SSTTIW )

τTIW = TIW Svd ( SSTTIW )

An SVD-based Empirical Model for τTIW

Svd ( SSTTIW )=τTIW

Svd ( SSTTIW ) = τTIWYear 1999

OGCM

SSTTIWSST

τ=τclim+ τTIW

Feedback

Empirical model (SVDmodes, αTIW)

Representing Tropical Instability Waves (TIWs)-induced Wind Forcing & Feedback in Climate Models

Assessing TIW-induced wind forcing/feedback effects in ocean and coupled models Not clearly examined; mostly diagnostic analyses; Difficulty in representing/isolating TIW wind forcing part: e.g.: satellite data contaminated by non-TIW wind signals High resolution models: include everything, not clean & clear A simple, clean, clear way to do this: add-on/off approach An empirical model for TIW wind part:

τTIW = TIW Svd ( )

τ = τclim + τTIW

modTIWSST

τTIW = 0.0

τTIW = observed wind directly from satellite obs.

SST differences at (140W,0): τTIW= TIW Svd (SSTTIW)

Hybrid Coupled Model at ESSIC/UMD

• The Gent-Cane ocean model A sigma-layer, reduced-gravity OGCM with

(1) A hybrid mixing scheme Chen, Rothstein & Busalacchi (1995)

(2) Coupling to an advective atmos mixed layer model (Murtugudde, Seager & Busalacchi 1995)

(3) Model specifications: Tropical Pacific domain: 25N-25S; 31-layers; Resolution: 1 deg in longitude and 0.5 deg in latitude

• An empirical atmospheric wind stress anomaly model (SVD-based)

TIW-induced wind forcing & feedback experiments

OGCM

SSTTIW

SSTinter=SST-SSTclim

τ=τclim+ + τTIWτinter

Effects induced in ocean & coupled ocean-atmos models

Ocean modeling: Cooling effects on SST; However: over-cooling in ocean modeling directly forced by atmos wind without TIW feedback Interannual variability in coupled ocean-atmos models Enhanced ENSO amplitude

Shortened oscillation periods

How to adequately represent the TIW wind feedabck

Using satellite SST data to represent tropical instability wave

(TIW)-induced surface wind forcing

An empirical modeling approach:

can be used to adequately represent TIW-induced

wind feedback for climate modeling

Critical to SST data: resolution, error, ….

τTIW = TIW Svd ( SSTTIW )

ObservatioObservatio

nsns SimulationsSimulations

Sensitivity to spatial resolution of SSTTIW: SSTTIW variance along 3N

Concluding remarks• An empirical model for TIW-induced wind forcing;

• Large effects identified on ocean and coupled simulations

e.g.: cooling effects; Modulation of ENSO ;

=> Importance of TIW wind forcing but significant uncertainties in representing it in climate models & reanalysis data;

• A clear feedback induced by TIW wind forcing: Processes identified….

• A clear source for biases; this forcing component adequately be taken

into account for better climate simulation & prediction • A new way to use satellite data for climate modeling:

physical parameterizations data assimilation

• ……

Interactions between TIWs and large-scale processes

mixed layer

Thermocline

Pre

Freshwater Flux

Ocean BiologyTropical Instability Waves (TIWs)

Interactions between TIWs and large-scale processes

mixed layer

Thermocline

Pre

Freshwater Flux

Ocean BiologyTropical Instability Waves (TIWs)

Atmospheric response

Interactions between TIWs and large-scale processes

mixed layer

Thermocline

Pre

Freshwater Flux

Ocean BiologyTropical Instability Waves (TIWs)

Atmospheric response

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