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 Seasonal-to-interannual variability Multi-decadal trends Centennial change – Challenger to Argo

• The future of global ocean observations.

} Argo era } Argo + historical data

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.

The profiling float: revolutionizing ocean observations

Schematic of an Argo float cycle. No nation could do Argo by itself; cooperation is essential. The U.S. and Australia are the largest contributors of Argo floats. All of the data are freely and immediately available (www.argo.net).

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

The profiling float: revolutionizing ocean observations

The significance of global coverage

2004-2010: Argo August T,S profiles > 1000 m.

Pre-Argo August Argo August

Before Argo: All 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, …)

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 circulation and transport, mesoscale eddies,

• cean dynamics, and seasonal-to-decadal climate

variability and change.

Also: Education and Outreach

See: http://www.argo.ucsd.edu/Educational_Use.html

The value of Argo

Research

Operational centers around the world use Argo data in ocean state estimation, short-term forecasting and seasonal to decadal prediction.

http://www.argo.ucsd.edu/Use_by_Operational.html

Operational applications

Papers per year

From a few thousand profiles: WOCE produced neither a snapshot or a time mean, but rather a multi-year composite

• f snapshots from many transects. The

sampling errors are difficult to estimate. From a few hundred thousand profiles: Argo provides both time means and snapshots, with realistic error estimates. (Inset plot: standard deviation of monthly temperatures)

WOCE Pacific Atlas, Talley (2007)

Potential temperature (oC) 500 m Argo 2004-2010 mean

Argo and WOCE “mean fields”

Top: 1000 m geostrophic pressure from Katsumata and Yoshinari (2010) Bottom: 1000/2000 dbar steric height from Roemmich and Gilson (2009)

Argo trajectory data compared with Argo steric height

Absolute pressure: Argo Trajectories Relative pressure: Argo Steric Height

Mapping the Indo-Pacific “super-gyre”:

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.

Mean sea surface height from Argo and surface drifters

Closing the global SSH budget is critical for understanding sea 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)

Global sea surface height: Altimetry, Argo, and ocean mass

Steric + mass Measured

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…

Tropical temperature anomalies do not average out in global means. Moreover, surface layer (0-100m) anomalies are opposite to the 100- 200m layer. The interannual heat content fluctuations in the individual layers are ~ 1022 J/yr, larger than the rate due to decadal warming. (Left: Time-series of globally- averaged temperature versus depth, based on Roemmich and Gilson, 2009)

Depth (m) 10x Global SST anomaly 10x Global T160 anomaly Nino 3.4 SST anomaly T (oC)

Global El Niño/La Niña variability from Argo

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).

Decadal variability: Argo and the historical data archive

Heat gain by the ocean

Upper right: Zonal average of temperature change (oC), 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 (1016 J/m). Decadal change estimates have large uncertainty due to the sparse spatial coverage of historical data.

Most of the global heat gain is south of 30oS (e.g. Sutton and Roemmich 2011, in press)

50-yr heat gain by the oceans: ~0.3 x 1022 J/yr (0-700 m) Levitus et al. (2009)

Salinity change indicates an increase in the global hydrological cycle.

Zonal averages, from Hosoda et al. 2009

E-P climatology Salinity climatology Salinity change (Argo minus climatology SSS)

Argo minus climatological salinity, 0-100 m avg, Roemmich and Gilson (2009)

Decadal variability: Argo and the historical data archive

Surface layer salinity has increased in the salty regions and decreased in the fresh regions, 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).

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)

• cean temperature change.

Centennial change: Argo and Challenger

Min/max protected thermometer from HMS Challenger (Fig from Tait, 1881)

Voyage of HMS Challenger 1872-1876

Challenger temperature section, New York-St Thomas (Worthington 1976)

Right: ∆T at 0 and 100 fathoms (red(+)/blue(-), tenths oC) 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 1022 J/yr

Temperature difference oC Depth (m) Mean ± Std err

100 fathoms 183 m

Mean 0.37 ± 0.12 oC

Centennial change: Argo and Challenger

Argo – Challenger SST Mean 0.72 ± 0.07 oC

The future of global

• cean 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 (O2, 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!

References

Bindoff, N.L. and co-authors, 2007: "Observations: Oceanic Climate Change and Sea Level." In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. Durack, P. J. and S. E. Wijffels, 2010: Fifty-Year Trends in Global Ocean Salinities and Their Relationship to Broad-Scale Warming. Journal

• f Climate, 23, 4342-4362.

Helm, K. P., N. L. Bindoff, and J. A. Church, 2010: Changes in the global hydrological-cycle inferred from ocean salinity. Geophys. Res. Lett., 37, L18701. Hosoda, S., T. Suga, N. Shikama, and K. Mizuno, 2009: Global Surface Layer Salinity Change Detected by Argo and Its Implication for Hydrological Cycle Intensification. Journal of Oceanography, 65, 579-586. Katsumata, K. and H. Yoshinari, 2010: Uncertainties in global mapping of Argo drift data at the parking level. Journal of Oceanography, 66, 553-569. Leuliette, E. W., & L. Miller, 2009: Closing the sea level rise budget with altimetry, Argo, and GRACE, Geophys. Res. Lett., 36, L04608, doi:10.1029/ 2008GL036010. Levitus, S., J. I. Antonov, T. P. Boyer, R. A. Locarnini, H. E. Garcia, and A. V. Mishonov, 2009: Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems, Geophys. Res. Lett., 36, L07608, doi:10.1029/2008GL037155. Maximenko, N., P. Niiler, M-H. Rio. O. Melnichenko, L. Centurioni, D. Chambers V. Zlotnicki, & B. Galperin, 2009: Mean dynamic topography of the ocean derived from satellite and drifting buoy data using three different techniques. J. Atmos. Oceanic. Technol, DOI: 10.1175/2009JTECHO672.1 D Merrifield, M. and co-authors, 2010: Sea level variations. In State of the Climate in 2009, D.S. Arndt, M.O. Baringer and M.R. Johnson, Eds, Bulletin of the American Meteorological Society, 91, s69 – s71. Roemmich D. and J. Gilson, 2009: The 2004–2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo Program. Progress in Oceanography, doi:10.1016/j.pocean.2009.03.004 Sutton, P. and D. Roemmich, 2011: Decadal steric and sea surface height changes in the Southern Hemisphere. Geophys. Res. Lett., doi:10.1029/2011GL046802, in press. Tait, P.G., 1881: The pressure errors of the Challenger thermometers. Challenger Narrative, v. II, Appendix A. (Reprinted by Cambridge University Press, 1898, as Scientific Papers by P.G. Tait) Talley, L.D., 2007: Hydrographic Atlas of the World Ocean Circulation Experiment (WOCE). Volume 2: Pacific Ocean (eds. M. Sparrow, P. Chapman and J. Gould), International WOCE Project Office, Southampton, U.K., ISBN 0-904175-54-5. Worthington, L.V., 1976: On the North Atlantic circulation, Oceanographic Studies, The John Hopkins University, Baltimore, MD, 6, 1-110.