The Argo Steering Team

GODAE Final SymposiumNice, 12-15 November 2008

Argo: the challenge of continuing 10 years of progress.

Outline

• The evolution of Argo.

• Argo’s effectiveness.

• The Argo-era global ocean.

• Argo and ocean surface data.

• The future of Argo.

Ocean Data Assimilation is a key application for Argo.

Please submit comments and questions for the Argo Roundtable.

Argo deployment training with N.Z. Minister of Research, Science and Technology, October 2007. Photo by A. Blackwell (NIWA)

•In the 1990s, a global survey required many years of research vessel effort.

•Today high quality data can be collected anywhere in the world without a ship being present at the time. (continuous, global data)

In the WOCE global survey, ~8000 CTD profiles were collected by RVs from 1991-1997.

Argo obtains 9000 CTD profiles per month.

A technology revolution:

An idea to a global array in 10 years.

The key factors were:•The enabling technology.•An international partnership of science and agencies.•An open data policy, with free and immediate access.GODAE is one of Argo’s “parents”.

400,000 high quality profiles have been collected during 2004-2008.

Left: profiles per 1o box, 2004-2008.

3000 floats obtain 9000 profiles per month.

Argo 3o x 3o design

Argo present distribution

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Equal area distribution

Red dots: Winter 1950-2000 (WOD) Black dots: Winter 2008 (Argo)

Argo obtains more winter T,S profiles in a single year than in all pre-Argo winters combined.

Nevertheless, Argo has not yet achieved its designed coverage in the southern hemisphere, where an additional 750 floats are needed.

The shortfall will impact many applications.

Argo’s impact is greatest in the southern hemisphere.

How effective is Argo for large-scale variability?

Argo SST anomaly, Dec 2006

NOAA OI SST anomaly, Dec 2006

Argo mapping error can be estimated in several ways:

•Formal OI error estimates.•Maps from subsets of Argo data.•Altimetric height subsampling experiments.•Comparison to independent datasets such as SST.

Niño 3.4 (Argo)

Niño 3.4 (NOAA OI)NO

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Altimetric height subsampling experiment:Zonally averaged variance of large-scale (10o x 10o x 3 months) anomalies (mean and annual cycle removed):

Black: Signal variance from 15-year AVISO dataset, 1993-2007.

Blue: Signal variance from 4-year dataset, 2004-2007.

Thick red: Noise upper bound, SSH minus steric height, 2004-2007.

Thin red: Noise lower bound, SSH minus subsampled and re-mapped SSH, 1993-2007.

Argo/ NOAA OI SST comparison:Black: Signal variance from 15-year dataset, 1993-2007.

Blue: Signal variance from 4-year dataset, 2004-2007.

Red: Noise upper bound, NOAA OI SST minus Argo SST, 2004-2007.

The large-scale signal and Argo sampling noise:

SIGNAL

SIGNAL

NOISE

NOISE

Argo is most effective in the tropics.More floats are needed in the southern hemisphere.

Systematic errors?

(Right) Willis et al. (2008) noted that the increase in global sea level is not seen in 4-year records of steric sea level and ocean mass.

How accurate is the global mean temperature and steric height from Argo?

A highest priority for Argo is to identify and correct systematic errors (e.g. p0 drift) and to estimate their impact.

Global mean sea level variability (top), steric component from Argo (middle), mass component from GRACE (bot). Grey lines represent the residual of the other two measurements. From Willis, Chambers, and Nerem (GRL, 2008).

New techniques are being developed for error detection.

Testing the Argo dataset.

Altimetric height is used to flag anomalies in Argo steric height for expert examination(Guinehut et al., 2008).

Here a problem is detected in data from Float 5900984.

Argo and shipboard transects show similar and consistent decadal signals in temperature along 24.5oN in the Atlantic.

(Vélez-Belchí, Hernández-Guerra and Fraile-Nuez, 2008).

Argo - IGY

Testing the Argo dataset.

Argo - WOCE

RAPID - IGY

RAPID - IGY

The Argo dataset, 2004-2008, provides an accurate 5-year mean and annual cycle for the global ocean. Argo can be compared to past datasets and is a baseline for observing future evolution.

Maps of Argo-minus-WOA01 steric height highlight the large and deep density changes south of 30oS.Roemmich and Gilson (2008)

The Argo-era ocean.

The Argo-era ocean.

• The southern hemisphere ocean is warmer and fresher in the Argo era than in WOA01.

• The northern hemisphere is warmer and saltier.

• Heat gain is dominated by the southern hemisphere (larger area).

• The surface layer stratification is increased.

• The Argo ocean is fresher in high rainfall regions, saltier in high evaporation regions (increase in the global hydrological cycle?)

Zonal averages of T, S, and σθ from Argo (contours), and the Argo- minus-WOA01 differences (colors). Roemmich and Gilson (2008).

Global averages of Argo-minus-WOA01 T and S

Argo-minus-WOA01 salinity differences on density surfaces, excluding the upper 200m.

•Subsurface waters are fresher in the SH intermediate waters (all oceans) and below the ITCZ.

•Subsurface waters are saltier below evaporative regions and NH intermediate waters (Atlantic).

The Argo-era ocean.

Argo SH

Argo zonally-averaged annual cycle is compared to altimetric height, SST, and air-sea flux.

Argo and ocean surface datasets.

AVISO SSH Argo SST NOAA OI SST

Argo A-S flux NOC A-S flux

Argo and ocean surface datasets.

Argo SH AVISO SSH Difference Argo SST NOAA OI SST

Hemispheric and global annual cycles are compared for consistency and for complementary information.

SH: southern hemisphereNH: northern hemisphereGL: global

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Argo heat gain NOC A-S flux

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Sea Surface Height

Air-Sea flux

Sea Surface Temperature

Sea Surface Salinity

Argo SSS WOA01 SSS

Argo’s future: two paths forward.

1. Improved implementation for Argo’s original objectives:– Increased float lifetime.– Enhanced float capabilities.– Better coverage in the southern

hemisphere.– Detection/correction of systematic errors.

Float lifetimes continue to improve through technical innovation and careful handling.

Right: A 6–year record, with stable salinity, by a UW float in the Indian Ocean (fig. provided by A. Wong).

Argo’s future: two paths forward.

2. Potential objectives to increase Argo’s value:– Abyssal floats to sample the full water column.– New sensors: biological, geochemical, surface layer, …– Regional arrays in marginal seas.– High latitude floats under seasonal ice.– Glider sampling in boundary currents.

Argo was designed for the ice-free oceans, but there are now many floats in the seasonal ice zones.

A UW float is deployed through the ice on a cruise by R/V Aurora Australis. Photo: G. Williams

Argo’s future: the planning process.

• This GODAE F.S. Argo paper is intended to initiate a review of Argo’s status and a discussion of its future priorities. Contribute via the Argo Round Table.

• Argo’s 3rd Science Workshop, “The Future of Argo” will be held in Hangzhou in March 2009. http://www.argo.ucsd.edu/ASW3.html .

• Broad input and participation are invited (including ODA Argo users).

• A Community White Paper for OceanObs09 will be developed.