# Presentation: 578669

## Ocean exchanges with the atmosphere 

- Peter K. Taylor
- Southampton Oceanography Centre UK

**...****.did we learn anything during WOCE?**

## Overview

- What surface fluxes were needed for WOCE

- How the flux estimates are obtained

- How far have we progressed during the WOCE period

- Future Flux Observing System

**“****Separately for...”**

## The Goals of WOCE

## The important Air-Sea fluxes for WOCE 

**“****Net heat flux**
** ****is sum of...”**

## The important Air-Sea fluxes for WOCE 

**“****but little in this talk**
**on precipitation**
** ****since accuracy **
**still poor” **

## The important Air-Sea fluxes for WOCE 

## Goal 2 of WOCE

## Air-Sea Flux aims for WOCE

- Produce estimates of the global air-seafluxes of heat, freshwater and momentumon a range of time and space scales

- Work toward definition of an on-going observing system for the surface fluxes

- Produce climatological fields for these fluxes

## How surface fluxes are determined

- Budget methods give total heat flux:

- divergence of ocean heat transport (e.g. Ganachaud & Wunsch, 2000)

- atmospheric flux divergence with top of atmosphere radiative balance ...the “residual” method(e.g. Trenberth et al. 2001 )

## Determining the individual flux components

- Turbulent fluxes from *in situ* data, models, and satellites, are based on meteorological variables (temperature, wind, etc.) and the bulk formulae

- SW and LW Radiative fluxes can be obtained from Satellite data and from NWP models

## Example of Bulk FormulaLatent heat flux (W/m2)

- Flux  =

- Transfer    x   Wind  x humidityCoefficient    speed    difference

## Determining the Transfer Coefficient 

**GARP Air-Sea Interaction experiments :****BOMEX, AMTEX, IFYGL**

**“****SeaSat coincided**
**with JASIN”**

## The Legacy of GARP: 

- Budget experiments are difficult!

- Experimental data on transfer coefficients was available

- Satellite scatterometers could define wind forcing

- We must continue to maintain (and improve) the *in situ* observing systems

**The Legacy of SeaSat:**

## Developing the Voluntary Observing Ship (VOS) system

**Developing the Voluntary Observing Ship (VOS) system**

- Mean random errors in ship SST obs ( C )1970 - 1997 (Kent, 2002)

- The random and systematic errors in VOS data are much better known

- Due to research during the WOCE period (partly funded by TOGA and WOCE):

- Now greater emphasis on meta-data ....how the observations are obtained

**“****we can now plot**
** ****a map of error values**
** ****like this one”**

## Wind Stress

- The choice of Drag Coefficient, *C**D10n*

- Effect of using other *C**D10n* values

- Climatic variations in mean wind stress

- Effect of poor sampling in the SO

## The variation of the Drag Coefficient with wind speed

**The variation of the Drag Coefficient with wind speed**

**“****Before WOCE:**
**Smith (1980)”**

**“****Smith (1988) ...used for **
**TOGA and scatterometer**
**Data on WOCE DVD”**

**“****WOCE Southern Ocean **
**Cruises confirmed **
**Smith (1980)” **

**“****but some models are**
**still using these**
**higher values”   **

## Comparison of the zonal mean wind stress

- ( Josey et al. 2002, J.Phys.Oceanogr.                                     **32**,1993 - 2019)

## Comparison of the zonal mean wind stress

- ( Josey et al. 2002, J.Phys.Oceanogr.                                     **32**,1993 - 2019)

## Change in wind stress with NAO

**Change in wind stress with NAO**

**SOC**

**H&R**

**“****SOC & H&R wind**
**stress fields**
**look similar”**

## Change in wind stress with NAO

**Change in wind stress with NAO**

**SOC**

**H&R**

**1949-79**

**NCEP**

**1980-93**

**“****but NCEP has lower**
** ****stress for period**
**representing most**
** ****of H&R data” **

**“****Scaling H&R by Cd**
**ratio gives values**
**similar to NCEP”**

**“****Apparent agreement**
**between H&R & SOC**
**was due to NAO**
**variations” **

**‘****remaining differences **
**between NCEP, H&R **
**and SOC may be due **
**to bad sampling”**

## Comparison of the zonal mean wind stress

- ( Josey et al. 2002, J.Phys.Oceanogr.                                     **32**,1993 - 2019)

## Zonal Wind stress in the Southern Ocean: July mean values

**SOC Climatology**

**ECMWF**

**ERS-1**
**AMI**

**“****ECMWF ERA and **
**scatterometer winds **
**show extensive belt **
**of high winds in SO”**

**“****Where data is lacking **
**values are extrapolated **
**from other regions”**

## Summary: Wind stress 

**The WOCE cruises have helped confirm the ****Smith (1980) C****D10n ****to U****10n**** relationship**

**H&R (and Oberhuber) over-estimate the wind stress over much of the world ocean: by around 30%**

*...**.but we knew that  (e.g. Harrison, 1989)**...so why do models still use these stress fields?*

**The magnitude and patterns of wind stress varies significantly  between different periods: WOCE will not ****be “typical” of other decades**

**WOCE helped implement satellite scatterometer missions which are now coming to fruition**

## Heat Fluxes

**Global Heat balance for in situ climatologies **

**Adjustment using WOCE hydrography**

**Comparison with other estimates: Reanalyses, Residual Method **

**Comparison of the implied latent heat flux distributions**

## Annual heat input to Ocean (W/m2)(SOC Climatology, Josey et al. 1999)

**Annual heat input to Ocean (W/m****2****)****(SOC Climatology, Josey et al. 1999)**

- 30           90           150         -150         -90          -30          30

- 75   60  45   30   15      0   -15   -30  -45   -60   -75

- -100   -50     0      50   100  W/m2

**“****This annual mean is **
**deceptive with regard **
**to regions of **
**heating and cooling”**

## Monthly heat input to Ocean (W/m2)(SOC Climatology, Josey et al. 1999)

**Monthly heat input to Ocean (W/m****2****)****(SOC Climatology, Josey et al. 1999)**

**“****Heating occurs over **
**most of summer **
**Hemisphere” **

**“****we will use **
**January fields in **
**following comparisons”**

## Before and after WOCE

- (Esbensen & Kushnir  1981)

**Before and after WOCE**

- -500           -250               0               250 W/m2

## Comparison of SOC & OSU climatologies

- SOC has:
- Correct flux averaging method

*( Fluxes calculated from individual **observations and then averaged**i.e. “sampling” rather than “classical” )*

- Higher resolution

- More information: revised version of COADS with observations corrected on a ship by ship basis

- Larger Global Heat Budget imbalance

## Comparison of ClimatologiesNet Heat Flux for January and Mean Annual imbalance (W/m2)

- -500           -250               0               250 W/m2

**“****there is obviously **
**more summer heating **
**in SOC fields”**

## The Heat Budget problem

- Unless adjusted, climatologies show too much heat flux into the ocean(e.g. Bunker et al. 1982, Isemer et al. 1989,          DaSilva et al. 1984, Josey et al. 1999)

- This heat imbalance varies little year to year ( few W/m2 )

- Adjusting the heat fluxes degrades the comparisons with buoy data(Josey et al. 1999)

## Can WOCE help?

**Can WOCE help?**

**Heat Transports in PW****(adapted from Grist & Josey, 2002)**

**0.002       Aagard & Greisman (1975)     0.1**

**-0.09 ( R & McC. 89)**

**0.76 (Bryden et al. 91)**

**0.70 (Wijffels et al. 96)**

**0.90 (Wijffels et al. 2001)**

**1.22 (Hall & Bryden 82)**

**1.22**

**1.18**

**(Klein et al. 95)**

**0.60 (Speer et al. 96)**

**0.29 (Holfort & Siedler 01)**

**0.46 (McDonagh 02)**

**“****Grist & Josey (see poster)**
**have adjusted SOC **
**climatology  using**
** ****WOCE section data”**

## Effect of Constraining Heat Budget

## Comparison of Constrained SOC & UWM heat fluxes

**(adapted from ****Grist & Josey, 2002)**

**“****Fields look similar but DaSilva **
**(UWM) has e.g. stronger cooling over**
**Gulf Stream, greater heating in**
**summer hemisphere;  this causes **
**small differences in implied **
**ocean heat transport... ”       **

## Comparison of other Flux fields

**Comparison of other Flux fields**

**-2**

**-4**

**6**

**1**

**“****some differences are obvious, **
**for example the el Nino region”**

## Atlantic Zonal Mean Values

**Atlantic Zonal Mean Values**

**(adapted from Grist & Josey, 2002)**

**“****compared to SOC,**
**there is  slightly more **
**heating in the UWM **
**climatology, hence less **
**ocean transport”       **

**“****in Residual method,**
**more cooling over the **
**Gulf Stream implies **
**greater ocean heat **
**transport northward”**

**“****in contrast NCEP cooling **
**occurs in the Trade Wind**
**zone rather than higher **
**latitudes”    **

**“****lack of net heat input**
**in ERA implies too large**
**ocean heat transport **
** ****in Southern Ocean”**

## Atlantic OceanMean area heat fluxClimatology - WOCE( W/m2 )

**Atlantic Ocean****Mean area heat flux****Climatology**** - ****WOCE****( W/m****2**** )**

**(adapted from****Grist & Josey, 2002)**

**“****area mean air-sea **
**flux can be calculated **
**from difference in **
**ocean heat transport **
**between hydrographic **
**lines”                      **

**“****Bar plot shows difference **
**from this mean for the **
**flux fields listed”   **

**“****original SOC climatology **
**has too much heat **
**input everywhere”  **

**“****compared to hydrography, **
**rest have too little cooling at**
**high latitudes, too little heat**
**input in low latitudes”**

## Pacific & Indian Oceans: Mean area heat fluxClimatology - WOCE  ( W/m2 ) 

**Pacific & Indian Oceans: Mean area heat flux****Climatology**** - ****WOCE  ( W/m****2**** )**** **

**(Grist & Josey, 2002)**

**“****any such pattern in the **
**Pacific is less clear”**

## The Residual Method gives the best agreement with Hydrography

**The  *****in situ***** climatologies can be adjusted to give agreement with Hydrography**

**But have the individual heat flux components been properly adjusted?**

## Transfer Coefficient for water vapour

## Errors in estimating Latent Heat flux

**Air-Sea interaction experiments suggest that *****C******E10n***** is known to 10% or better**

**Inverse analyses suggest that the Flux is underestimated by nearly 20%**

**Do the errors in the observations explain this difference?**

**“****possibly but we need **
**independent verification”**

## Independent sources for Evaluating Bias Errorsin Latent Heat Flux Estimates

- Satellite based estimates of Latent Heat Flux

- Flux fields from models

- Reference data sets - buoys and ships

- Freshwater Budget - but precipitation???

## Annual mean zonal Latent Heat Flux

- ( from Curry et al. 2002      and Kubota et al. 2002 )** **

**“****Constrained UWM/COADS**
**would be similar to  ERA**
**...****model fluxes bridge **
**original and constrained **
**values”**

**“****The ‘SeaFlux’ group**
**have performed**
**flux field comparisons**
**...****these are original **
**UWM/COADS values” **

## Example of a Satellite Flux field Product

- Climatological mean (1988 - 1996) Latent Heat Fluxin January from the HOAPS (Grassl et al. 2000) Atlas

## Annual mean zonal Latent Heat Flux

- ( from Curry et al. 2002      and Kubota et al. 2002 )** **

**“****satellite derived flux fields **
**also show a range of values”**

## Comparison of SOC Climatology and WHOI Buoy deployments

**“****Only for FASINEX is the **
**constrained field (solid colour) **
**closer to the buoy values”**

## Comparison of SOC Climatology and WHOI Buoy deployments

**“****but for short wave**
**heating it is TOGA **
**that is brought into**
** ****better agreement”     **

## Summary 

**Increasing the Latent Heat flux gives similar evaporation to the reanalysis results**

**BUT...comparison with reference data suggests the models over-estimate evaporation  **

**We need more in situ reference data**

**Satellite data doesn’t help!**

## Beyond WOCE:the Observing System

## Future Surface Flux estimation

**Move toward global fields from NWP models and/or Remote sensing ****(wind stress, shortwave, sst, latent heat? longwave? )**

**Role of *****in situ***** data is increasingly for verification:**
**“****Flux reference” Buoys**
**Improved ship data (the VOS Climate project, VOSClim)**

## Using “Flux Reference” Data

## The J-COMM VOS Climate Project VOSClim

- VOSClim initially aims to improve the meta-data available from the ships

- Observations during 2001 from ships recruited to the VOSClim Project

- P&O Nedlloyd Southampton - a VOSClim ship

## Have We Learnt Anything? 

**During WOCE we have learnt much about the error characteristics of our flux estimates**

**Mean net heat flux fields can be brought into agreement with ocean heat transport values**

**But we still don’t have distributions of the component heat fluxes which give a balanced budget **

## However...

**For Surface Flux studies,  the full dividend of WOCE is still to come:**

**Continuing analysis of WOCE data**

**The full exploitation of satellite data**

**The Global Ocean Observing System**

**New NWP reanalysis experiments**

## Acknowledgements

**The content of this talk was based on the conclusions of the joint WCRP/SCOR Working Group on Air-Sea Fluxes****1****.  However the specific examples shown were obtained from the SOC Meteorology team****2****, in particular Simon Josey and Jeremy Grist;  the IRI/LDEO Climate Data Library****3****;  and the SeaFlux group****4****.  Bob Marsh supplied the title page graphic.**

- 3 http://ingrid.ldeo.columbia.edu/

- 4 http://paos.colorado.edu/~curryja/ocean/

- 1 http://www.soc.soton.ac.uk/JRD/MET/WGASF/

- 2 http://www.soc.soton.ac.uk/JRD/MET/

## THE  END