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 fluxes will not be correct, but their variability might be reliable Data: all VOS data from ICOADS ( )

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

Sampling errors in fluxes: Double exponential distribution (2ePDF)   ×1 0 -3

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

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 1 st guess for the thresholds on the parameters  then – repeat the procedure again

123-yr ( ) climatology

Climatological differences between 2ePDF-derived and traditionally averaged fluxes

Linear tends, sensible + latent, winter

Regional time series of winter sensible + latent heat flux

Winter (JFM) EOFs

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

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

Canonical correlation of the heat fluxes with HADSLP for different periods

Conclusions: 5-degree 123-yr homogeneous time series of turbulent fluxes ( ) were derived using 2ePDF integration – multi-decadal variability is visible Product is available at 2-degree resolution for and 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 Forcing long-term runs of ocean GCMs in [still] coarse resolution Potential application

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

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

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

Effect in latent heat flux estimates: RMS = 7 W/m 2 Slope = Intercept = W/m 2

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

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