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The RAPID ocean observation array at 26.5°N in the HadCM3 model

The RAPID ocean observation array at 26.5°N in the HadCM3 model. Leon Hermanson, Rowan Sutton, Keith Haines, Doug Smith, Jo ël Hirschi. Content. Introduction to RAPID-WATCH and VALOR The RAPID observation array Getting an MOC from the observations Creating an analogous array in HadCM3

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The RAPID ocean observation array at 26.5°N in the HadCM3 model

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  1. The RAPID ocean observation array at 26.5°N in the HadCM3 model Leon Hermanson, Rowan Sutton, Keith Haines, Doug Smith, Joël Hirschi

  2. Content • Introduction to RAPID-WATCH and VALOR • The RAPID observation array • Getting an MOC from the observations • Creating an analogous array in HadCM3 • Can models reproduce MOC without RAPID? (but including other observations, eg. ARGO) • Seasonal cycles in the model and observations • Assimilating the RAPID observations

  3. Introduction to RAPID-WATCH • The RAPID climate change programme ran from 2001—2008 • Aim was to improve our ability to quantify the probability and magnitude of future rapid change in climate, with a focus on the role of the Atlantic Ocean's Thermohaline Circulation • RAPID-WATCH follows on from RAPID and will run until 2014 • Aim is to continue monitoring the MOC using the moored array in the North Atlantic and also exploit the data being collected • Observations will be used to: • determine and interpret recent changes in the Atlantic MOC • assess the risk of rapid climate change due to changes in the MOC • investigate the potential for predicting the MOC and its impacts on climate.

  4. Value of the RAPID array (VALOR) • Aim is to assess the value of the RAPID array observations for predictions of the Atlantic MOC and its impact on climate • Will provide information for an assessment of the RAPID array late 2011 • The project will explore a range of issues concerning the design of a potential MOC prediction system • There are four main activities: • Ocean synthesis • Hindcast experiments • Ensemble design • Pseudo-observations

  5. Located at approximately 26°N Between Florida and Morocco Reasons for choosing this latitude: Gulf Stream is mainly found in Florida Straits and has been measured there since 1981 High correlation between MOC and ocean heat transport Steep continental slope in the West Strong, steady trade winds The RAPID array • Downside: • Low decadal signal to noise ratio

  6. Gulf Stream MOC Transport (Sv) Ekman Upper mid-ocean Meridional transports at 26°N in the Atlantic 1 Sv = 106 m3 s-1

  7. Gulf Stream transport

  8. Ekman transport

  9. Upper mid-ocean transport

  10. Meridional Overturning Circulation

  11. 26.25°N W1 W2 MARW MARE E Resolution: 1¼° x 1¼° The RAPID array and HadCM3

  12. 76.25W 76.25W Meridional velocity at 26.25 °N

  13. 76.25W 76.25W Meridional velocity at 28.8°N

  14. Monthly means Δ RAPID array • - 26.25°N 28.8°N Comparison of MOC components

  15. Wind stress HadCM3 control NOC1.1 Jan July

  16. Average correlation 0.3 (0.4) 0.6 (0.6) 0.9 (0.8) -0.3 (0.0) Using all obs except RAPID DPS2 PPE Assimilation Monthly means

  17. Component correlations

  18. Seasonal cycle of MOC at 26°N

  19. Seasonal cycle of upper mid-ocean

  20. Seasonal cycle of Gulf Streamand Ekman Gulf Stream transport Ekman transport

  21. Assimilating RAPID observations • Four years of twice-daily temperature and salinity at five merged profile locations • Too high frequency • Need to split up some profiles • Differences in mean states • Given the large amount of ARGO and other observations 2004—2008, will RAPID have an impact? • Eastern boundary poor in current assimilation (without RAPID) • In NEMO deep observations project onto MOC • Alternative methods

  22. Salinity 1951-2006 Potential Temp 1951-2006 HadCM3 ABW Levitus 05

  23. Correlations with transport 1000m Lag -5 months

  24. Scientific summary • The way the observed MOC is calculated is particular to the unusual bathymetry at 26°N • As most of Florida is missing in HadCM3, the components of the MOC are difficult to reproduce • There are no compelling reasons to move the model array to 28.8°N • Assimilating all observations except RAPID creates an unrealistic seasonal cycle • RAPID observations may have a large impact at eastern boundary and at deep levels • RAPID transports could possibly be assimilated through their covariance with temperature and salinity

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