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IORAS activities for DRAKKAR in 2006

IORAS activities for DRAKKAR in 2006. General topic: Development of long-term flux data set for interdecadal simulations with DRAKKAR models Task: Using 2ePDF to derive homogeneous time series of turbulent fluxes at least in the North Atlantic. What means “homogeneous”?

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IORAS activities for DRAKKAR in 2006

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  1. IORAS activities for DRAKKAR in 2006 • General topic:Development of long-term flux data set for interdecadal simulations with DRAKKAR models • Task: Using 2ePDF to derive homogeneous time series of turbulent fluxes at least in the North Atlantic. • What means “homogeneous”? • Sampling in 1960s+ should be as bad as before WW2 • Impact of parameterizations should be minimized to the extent possible • Impact of changes in observational practices should be minimized as well • Result expected: The fluxeswill not be correct, but their variabilitymight be reliable • Data: all VOS data from ICOADS (1880-2005)

  2. Homogenization of sampling in space: 6-hourly NWP individual variables Random sampling error Bulk parameteri-zations Random VOS-like sub-sampling Real-time VOS-like sub-sampling Total sampling error Objective analysis error Re-computation of surface fluxes using bulk formulae

  3. Sampling errors in fluxes: Double exponential distribution (2ePDF)   ×10-3

  4. Homogenization of sampling in time: per 5°x5° box MC-sub-sampling for n=7,15,25,50 per 5°x5°, 2°x2° box

  5. Parameterizations: • COARE-3.0 (no skin, no free convection, instead - 4/3 convection scheme for calm winds, no mature turbulence scheme) Parameters: • Wind – Beaufort only, WMO1100 => to Lindau (1995) scale • SST – buckets only, no engine intakes • Air temperature – all Production – iterative run for every month: • 1st guess - 2eWPDF derivation of monthly means for 10-degree boxes south of 40N and for gerrymander network north of 40N • 2ePDF computation for 5x5 degree boxes, if the PDF does not fit at 95% level, use the 1st guess for the thresholds on the parameters • then – repeat the procedure again

  6. 123-yr (1880-2002) climatology

  7. Climatological differences between 2ePDF-derived and traditionally averaged fluxes

  8. Linear tends, sensible + latent, winter

  9. Regional time series of winter sensible + latent heat flux 3 1 2 4

  10. Winter (JFM) EOFs

  11. 95% sign. lev. Link of the leading mode in turbulent fluxes with NAO index: 30-yr running correlation changes over time considerably

  12. NAO-related τ, Q, E-P Control NAO-related heat flux only NAO-based NAO is a dominant signal in driving NA circulation? NAO-based reconstructions of forcing are possible Eden and Willebrand 2001, Eden and Jung 2001 Reconstruction for 1865-1997: MHT, 48N Eden and Jung 2001, J. Climate Eden and Willebrand 2001, J. Climate HEAT FORCING IS IMPORTANT

  13. Canonical correlation of the heat fluxes with HADSLP for different periods

  14. Conclusions: 5-degree 123-yr homogeneous time series of turbulent fluxes (1880-2002) were derived using 2ePDF integration – multi-decadal variability is visible Product is available at 2-degree resolution for 1910-1940 and 1948-2005 Individual variables are also available, so that use of forcing based on bulk formulae is possible During the period 1915/20 – 1950/55 winter surface turbulent fluxes are just loosely connected with NAO, being closely related to NAO during the decades before and after this period Potential application Forcing long-term runs of ocean GCMs in [still] coarse resolution

  15. Other activities: validation of NOAA blended satellite winds 11 satellites, 0.25x0.25 resolution, global, 1987-onwards, 6-hourly – effectively from 1994 Zhang et al. 2006

  16. Validation of NOAA blended satellite winds 06:00 Much more detailed structure than ERA40 More reliable tropical winds than in both NCEP and ERA40 Good representation of coastal patterns 18:00

  17. Computation of humidity: Strategy: • Statistical multiregression approach (not a neural network yet) for the decade of 1960s • Deviations from seasonal climatology are considered • Exponential functions + polynomials for Ta, V, SLP • Done locally, for every month and every box

  18. Effect in latent heat flux estimates: RMS = 7 W/m2 Slope = 0.996 Intercept = + 1.4 W/m2

  19. Precipitation from NWP: Threshold on small precipitation, associated with the spin-up effect: 0.02 – 0.1 mm/day – up to 10-12 mm/month in subpolar latitudes CMORPH – 0.25x0.25, daily, satellites + model, 2001-onwards

  20. Winds Cardone (Oceanweather Inc.) kinematically corrected winds, up to 0.2 degree, 3-hourly (wind workstation)

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