Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT
<p>This paper analyzes the differences between ERA-Interim and ERA5 surface winds fields relative to Advanced Scatterometer (ASCAT) ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress-equivalent winds (U10S) and air–sea relative m...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-06-01
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| Series: | Ocean Science |
| Online Access: | https://www.ocean-sci.net/15/831/2019/os-15-831-2019.pdf |
| Summary: | <p>This paper analyzes the differences between ERA-Interim
and ERA5 surface winds fields relative to Advanced Scatterometer (ASCAT) ocean vector wind
observations, after adjustment for the effects of atmospheric stability and
density, using stress-equivalent winds (U10S) and air–sea relative motion
using ocean current velocities. In terms of instantaneous root mean square (rms) wind speed
agreement, ERA5 winds show a 20 % improvement relative to ERA-Interim
and a performance similar to that of currently operational ECMWF forecasts.
ERA5 also performs better than ERA-Interim in terms of mean and transient wind
errors, wind divergence and wind stress curl biases. Yet, both ERA products
show systematic errors in the partition of the wind kinetic energy into
zonal and meridional, mean and transient components. ERA winds are
characterized by excessive mean zonal winds (westerlies) with too-weak mean
poleward flows in the midlatitudes and too-weak mean meridional winds (trades)
in the tropics. ERA stress curl is too cyclonic in midlatitudes and high latitudes,
with implications for Ekman upwelling estimates, and lacks detail in the
representation of sea surface temperature (SST) gradient effects (along the equatorial cold tongues
and Western Boundary Current (WBC) jets) and mesoscale convective airflows (along the Intertropical Convergence Zone and the warm
flanks for the WBC jets). It is conjectured that large-scale mean wind
biases in ERA are related to their lack of high-frequency (transient wind)
variability, which should be promoting residual meridional circulations in
the Ferrel and Hadley cells.</p> |
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| ISSN: | 1812-0784 1812-0792 |