# Exact calculation of u\_10 and v\_10 wind components on ERA5 single levels

**URL:** <https://forum.ecmwf.int/t/exact-calculation-of-u-10-and-v-10-wind-components-on-era5-single-levels/2924>\
**Category:** C3S - Datasets and Usage\
**Tags:** carra, era5\
**Created:** [4 June 2024 16:14 UTC](https://forum.ecmwf.int/t/exact-calculation-of-u-10-and-v-10-wind-components-on-era5-single-levels/2924 "2024-06-04T16:14:23Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Paul\_Meyer](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/p/f9ae1b/32.png) [@Paul\_Meyer](https://forum.ecmwf.int/u/Paul_Meyer)\
**Post date:** [4 June 2024 16:14 UTC](https://forum.ecmwf.int/t/exact-calculation-of-u-10-and-v-10-wind-components-on-era5-single-levels/2924/1 "2024-06-04T16:14:23Z")

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Hi all,

I am trying to find out, how u\_10 and v\_10 are retrieved on the single levels in ERA5. Comparing to the model levels indicates an overestimation of the velocities at 10m. I assumed that they are interpolated from the model levels, however, i cannot reconstruct the same values from the model levels.

For the CARRA dataset, some information is given regarding the 10 m winds calculation, but I am missing something similar for ERA5.  
[Copernicus Arctic Regional Reanalysis (CARRA): Data User Guide - Copernicus Knowledge Base - ECMWF Confluence Wiki](https://confluence.ecmwf.int/display/CKB/Copernicus+Arctic+Regional+Reanalysis+%28CARRA%29%3A+Data+User+Guide#CopernicusArcticRegionalReanalysis(CARRA):DataUserGuide-Variablesat10-metreheight)

The same applies for the 100 m wind components, although they are much closer to the model-level interpolated values.

Has anyone experienced something similar?

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**Author:** ![remi\_gandoin](https://forum.ecmwf.int/user_avatar/forum.ecmwf.int/remi_gandoin/32/709_2.png) [@remi\_gandoin](https://forum.ecmwf.int/u/remi_gandoin)\
**Post date:** [12 June 2024 08:45 UTC](https://forum.ecmwf.int/t/exact-calculation-of-u-10-and-v-10-wind-components-on-era5-single-levels/2924/2 "2024-06-12T08:45:43Z")

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Hi Paul, in ERA5 the 10m is a diagnostic parameter computed using a roughness length of 3cm. It does not necessarily correspond to the model 10m wind. See Section 3.10.2 in [IFS Documentation CY41R2 - Part IV: Physical Processes | ECMWF](https://www.ecmwf.int/en/elibrary/79697-ifs-documentation-cy41r2-part-iv-physical-processes). All the best from Denmark. Rémi, C2Wind.