Observing climate variability and change in the global oceans: The - PowerPoint PPT Presentation

Observing climate variability and change in the global oceans: The Argo Program. Dean Roemmich Scripps Institution of Oceanography, UCSD droemmich@ucsd.edu Greenhouse 2011: The Science of Climate Change Cairns, April 4 ‐ 8, 2011

Outline • The Argo Program – how autonomous instruments are revolutionizing global ocean observations. • What are we learning from Argo? � Mean temperature, salinity, and circulation } Argo era � Seasonal-to-interannual variability � Multi-decadal trends } Argo + historical data � Centennial change – Challenger to Argo • The future of global ocean observations.

The profiling float: revolutionizing ocean observations 3200 free-drifting Argo floats collect high-quality Temperature/Salinity (TS) profiles, 0 – 2000 m, and velocity at 1000 m, every 10 days. The heat (T) and water (from S) balance are fundamental indicators of climate. In future, Argo will measure not only T and S, but also oxygen, nutrients, pH, and biological parameters. No nation could do Argo by itself; cooperation is essential. Schematic of an Argo float cycle. The U.S. and Australia are the largest contributors of Argo floats. All of the data are freely and immediately available (www.argo.net).

The profiling float: revolutionizing ocean observations Throughout the history of oceanography, subsurface data collection required a ship to be present. The profiling float removed this limitation. Conventional Oceanography: Today’s Oceanography: Research vessels collected ~10,000 Argo floats collect 10,000 T/S T/S profiles in 3,000 ship-days at sea, profiles every month, with nearly 1991-1997, during the World Ocean uniform distribution. Circulation Experiment (WOCE). WOCE ship tracks, 1991-1997. Argo float profiles from 1 month

The significance of global coverage Pre-Argo August Before Argo: All August T,S profiles > 1000 m. Argo August 2004-2010: Argo August T,S profiles > 1000 m. The global nature of Argo makes it possible to: • Combine with other global observations (e.g. satellite altimetry) • Observe the patterns and evolution of global climate variability (e.g.: El Niño) • Compare the modern ocean with previous “transect” data (e.g.: WOCE, Challenger, …)

The value of Argo Operational applications Research Papers per year Over 750 research papers have used Argo data: http://www.argo.ucsd.edu/Bibliography.html Research topics include water-mass properties and formation, air-sea interaction, ocean Operational centers around the world circulation and transport, mesoscale eddies, use Argo data in ocean state ocean dynamics, and seasonal-to-decadal climate estimation, short-term forecasting variability and change. and seasonal to decadal prediction. http://www.argo.ucsd.edu/Use_by_Operational.html Also: Education and Outreach See: http://www.argo.ucsd.edu/Educational_Use.html

Argo and WOCE “mean fields” Potential temperature ( o C) 500 m WOCE Pacific Atlas, Talley (2007) Argo 2004-2010 mean From a few hundred thousand profiles: From a few thousand profiles: Argo provides both time means and snapshots, WOCE produced neither a snapshot or a with realistic error estimates. (Inset plot: time mean, but rather a multi-year composite standard deviation of monthly temperatures) of snapshots from many transects. The sampling errors are difficult to estimate.

Argo trajectory data compared with Argo steric height Mapping the Indo-Pacific “super-gyre”: Absolute pressure: Argo Trajectories Relative pressure: Argo Steric Height Top: 1000 m geostrophic pressure from Katsumata and Yoshinari (2010) Bottom: 1000/2000 dbar steric height from Roemmich and Gilson (2009)

Mean sea surface height from Argo and surface drifters Absolute sea surface height, 1993-2002 , from surface drifter and wind data (Maximenko et al, 2009, Method B) Absolute sea surface height, 2004- 2009, from Argo : based on 1000 m geostrophic pressure from Katsumata and Yoshinari, 2010, plus 0/1000 steric height from Roemmich and Gilson, 2009) The similarity of these independent estimates of SSH demonstrate the capability of the observing system.

Global sea surface height: Altimetry, Argo, and ocean mass Closing the global SSH budget Steric + mass is critical for understanding sea Measured level rise: JASON measuring total SSH. Argo measuring steric height. GRACE measuring ocean mass. Blue lines are observed values; red are residuals from the other 2 components. (Merrifield et al , 2010 update of Leuliette and Miller, 2009)

The global imprint of El Niño/La Niña from Argo Although we’ve known the global pattern of El Niño in SST and sea level, Argo now reveals those patterns in surface salinity and in subsurface properties, needed for better understanding and prediction. For example…

Global El Niño/La Niña variability from Argo Tropical temperature anomalies do not average out in global means. 10x Global T 160 anomaly 10x Global SST anomaly Moreover, surface layer (0-100m) T ( o C) anomalies are opposite to the 100- 200m layer. Nino 3.4 SST anomaly The interannual heat content fluctuations in the individual layers are ~ 10 22 J/yr, larger than the rate due to decadal warming. Depth (m) (Left: Time-series of globally- averaged temperature versus depth, based on Roemmich and Gilson, 2009)

Decadal variability: Argo and the historical data archive Heat gain by the ocean The oceans dominate (~90%) heat gain in the climate system (e.g. Bindoff et al, 2007, IPCC; blue is 1961-2003, red is 1993-2003). 50-yr heat gain by the oceans: ~0.3 x 10 22 J/yr (0-700 m) Levitus et al. (2009) Most of the global heat gain is south of 30 o S (e.g. Sutton and Roemmich 2011, in press) Upper right: Zonal average of temperature change ( o C), Argo-minus-World Ocean Atlas 2001. From Roemmich and Gilson (2009). Lower right: Zonal and 0-2000 m depth integral of heat content change, Argo-minus-WOA01 (10 16 J/m). Decadal change estimates have large uncertainty due to the sparse spatial coverage of historical data.

Decadal variability: Argo and the historical data archive Salinity change indicates an increase in the global hydrological cycle. Surface layer salinity has increased in the salty Salinity change regions and decreased in the fresh regions, (Argo minus climatology SSS) indicating an increase in global rates of evaporation and precipitation, by about 4% Hosoda et al. (2009). Also Helm et al (2010), Durack and Wijffels (2010). Salinity climatology Argo minus climatological salinity, 0-100 m avg, Roemmich and Gilson (2009) E-P climatology Zonal averages, from Hosoda et al. 2009

Centennial change: Argo and Challenger Voyage of HMS Challenger 1872-1876 Challenger temperature section, New York-St Thomas (Worthington 1976) In the first global oceanographic expedition, HMS Challenger obtained 263 temperature profiles, 1872 – 1876, using pressure-protected min/max thermometers. Since Argo measures temperature everywhere, we have 263 profiles of “Argo-minus-Challenger” temperature difference. Challenger-to-Argo is the maximum time interval possible (> 130 years) for the instrumental record of (subsurface) ocean temperature change. Min/max protected thermometer from HMS Challenger (Fig from Tait, 1881)

Centennial change: Argo and Challenger Argo – Challenger SST Mean 0.72 ± 0.07 o C Mean ± Std err Depth (m) 100 fathoms 183 m Mean 0.37 ± 0.12 o C Temperature difference o C Right: ∆ T at 0 and 100 fathoms (red(+)/blue(-), tenths o C) Left: Global mean ∆ T vs depth. Uncertainties remain regarding depths and T versus pressure corrections of Challenger measurements. Heat gain, 0-1000 m: 0.3 x 10 22 J/yr

The future of global ocean observations • It is critical to sustain new capabilities for observing the global ocean, providing critical climate datasets. (Argo, repeat shipboard hydrography, moored arrays, satellites, surface drifters, …) • Enhancing Argo will further increase its value to science and society: – Increase sampling at high latitudes (seasonal ice) and all marginal seas. – Develop deep floats for sampling to the ocean bottom. – Add new sensors (O 2 , pH, Chl, carbon, nitrate, …) to observe ecosystem and geochemical impacts of climate. – Implement 2-way high bandwidth communication. – Build boundary current arrays using floats and gliders in combination. • The era of global oceanography has arrived, as autonomous instruments are revolutionizing the ocean observing system. What we see today is just the beginning!