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

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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

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


Sampling errors in fluxes:

Double exponential

distribution

(2ePDF)

×10-3


Homogenization of sampling in time:

per 5°x5° box

MC-sub-sampling for n=7,15,25,50 per 5°x5°, 2°x2° 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 1st guess for the thresholds on

    the parameters

  • then – repeat the procedure again


123-yr (1880-2002) climatology


Climatological differences between

2ePDF-derived and traditionally

averaged fluxes


Linear tends, sensible + latent, winter


Regional time series of

winter sensible + latent

heat flux

3

1

2

4


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-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


Canonical correlation

of the heat fluxes with

HADSLP for different

periods


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


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

Much more detailed

structure than ERA40

More reliable tropical

winds than in both

NCEP and ERA40

Good representation

of coastal patterns

18:00


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/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


Winds

Cardone (Oceanweather Inc.) kinematically corrected

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


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