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We are pleased to announce an update of the processing chain which calculates the model-based atmospheric corrections, associated with a vertical resolution increase of the ECMWF model.

 We are pleased to announce an update of the processing chain which calculates the model-based atmospheric corrections, associated with a vertical resolution increase of the ECMWF model. The number of model levels increases from the current 91 levels to 137 levels. The upgrade is planned to take place on June 25. The first operational run using the new resolution will be the 12 UTC June 25 assimilation and forecast run. For more information, please visit the ECMWF dedicated web page:<link http: www.ecmwf.int products changes ifs_cycle_38r2>www.ecmwf.int/products/changes/ifs_cycle_38r2/.

The increased number of levels enables a better representation of physical processes, clouds, inversions and vertically propagating gravity waves. For altimetric atmospheric corrections, we generally use the model data integrated from 3D to 2D to have model values at sea level.

Impact studies have been carried out on both vertical resolutions using Jason-2 products, by looking specifically at the following parameters: wet tropospheric correction, dry tropospheric correction, U and V model wind components, sea surface pressure and the Dynamic Atmospheric Correction. On average, the differences are rather small (a few hPa for pressure fields, 0.5 m/s for winds, a few mm for tropospheric correction). Only locally high discrepancies, mainly due to shifts in the location of highs, lows and fronts, can be expected.

The results on OGDR products indicate differences on the order of only tens of cm/s rms on model wind speed components, and less than 1 mm rms for the range corrections. The significant wave height is not significantly affected. On IGDR and GDR products, where the Dynamic Atmospheric Correction is applied, we have observed additionally range differences of 1-2cm rms over the ocean.