MERCATOR OCEAN JOURNA:
SEPTEMBER 2021
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igure 2: Annual mean meridional (a) wind speed difference and (b) transient wind speed difference between scatterometer (Metop-A ASCAT)
and collocated ECMWF ERAB5 for 2018
1.3 Improved ocean wind forcing products
ın order to reduce systematic biases in the numerical
weather prediction model (NWP) wind fields, a
scatterometer-based correction was derived. Temporally-
averaged differences between geolocated scatterometer
wind data and ECMWF re-analysis fields (Figure 3) were
applied tooriginal ECMWF winds to produce a bias-corrected
ocean wind forcing product, ERA* (ERA star, Trindade
et al., 2020). Verified against independent observations,
the variance of differences was reduced by 20% in ERA*
compared to uncorrected NWP fields. A combination of
at least two scatterometers with complimentary orbits
and a temporal averaging window of two to three days
were found to be the best balance between preserving
small-scale temporal and spatial variability and smooth
correction fields. Further development and testing of ERA*
is 0ngoing to produce improved wind forcing products, that
zan be added to the CMEMS catalogue. Improved hourly
wind vector fields can be used for wave models, storm
surge prediction and ocean forcing alike. They, furthermore,
avercome problems with scatterometer data assimilation,
atmospheric model dynamical closure and weak ocean
:oupling of atmospheric models. In addition, a comparison
and validation of ERAb5* and Ifremer L4 products is being
carried out.
