IORAS activities for DRAKKAR in 2006
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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

  • 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)

Homogenization of sampling in space:

6-hourly NWP individual variables

Random sampling error









Total sampling error


analysis error


of surface fluxes

using bulk formulae

Sampling errors in fluxes:

Double exponential




Homogenization of sampling in time:

per 5°x5° box

MC-sub-sampling for n=7,15,25,50 per 5°x5°, 2°x2° box


  • COARE-3.0 (no skin, no free convection, instead -

    4/3 convection scheme for calm winds, no mature

    turbulence scheme)


  • 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

Climatological differences between

2ePDF-derived and traditionally

averaged fluxes

Regional time series of

winter sensible + latent

heat flux





95% sign. lev.

Link of the leading mode in turbulent fluxes

with NAO index:

30-yr running correlation changes over time considerably

NAO-related τ, Q, E-P


NAO-related heat flux only


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



Canonical correlation

of the heat fluxes with

HADSLP for different



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

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


Much more detailed

structure than ERA40

More reliable tropical

winds than in both

NCEP and ERA40

Good representation

of coastal patterns


Computation of humidity:


  • 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/m2

Slope = 0.996

Intercept = + 1.4 W/m2

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


Cardone (Oceanweather Inc.) kinematically corrected

winds, up to 0.2 degree, 3-hourly (wind workstation)