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Discussion papers
https://doi.org/10.5194/os-2018-160
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2018-160
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Jan 2019

Research article | 15 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

Characterizing ERA-interim and ERA5 surface wind biases using ASCAT

Maria Belmonte Rivas1,2 and Ad Stoffelen1 Maria Belmonte Rivas and Ad Stoffelen
  • 1Royal Netherlands Meteorology Institute (KNMI), de Bilt, 3731GA, The Netherlands
  • 2Instituto de Ciencias del Mar (ICM), Consejo General de Investigaciones Cientificas (CSIC), Barcelona, 08003, Spain

Abstract. This paper analyses the differences between ERA-Interim and ERA5 surface winds fields relative to 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 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 defective mean poleward flows at mid-latitudes, and defective mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic at mid and high latitudes, with implications for Ekman upwelling estimates, and lack detail in the representation of SST gradient effects (along the equatorial cold tongues and WBC jets) and mesoscale convective airflows (along the ITCZ 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 Ferrell and Hadley cells.

Maria Belmonte Rivas and Ad Stoffelen
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Maria Belmonte Rivas and Ad Stoffelen
Maria Belmonte Rivas and Ad Stoffelen
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Latest update: 22 Feb 2019
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Short summary
This paper describes the differences between ocean surface winds provided by ERA reanalyses and satellite scatterometer observations. This work is motivated by the widespread use of reanalysis winds for ocean forcing in marine forecasting centers, and the application of scatterometer observations as a means to characterize reanalysis wind errors, which we conjecture are related to deficiencies in the physics of the underlying assimilating model.
This paper describes the differences between ocean surface winds provided by ERA reanalyses and...
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