Waves breaking on rocks

EPS/ASCAT ocean wind assessment

Waves breaking on rocks
Waves breaking on rocks

The objective of the study is the assessment of the impact and further development of the assimilation strategy of ASCAT products on the Metop satellites at the European Centre for Medium-Range Weather Forecasts (ECMWF).

Last Updated

05 March 2021

Published on

30 October 2018

The study also aims to take into account the EPS-SG scatterometer (SCA) features, in particular the better representation of high winds and the higher spatial resolution.


Objectives

The main goals of this study are:

  • To better understand how to handle and take maximum benefit of very high wind speeds, this study aims to improve the QC to allow an inclusion of extreme observations.
  • To investigate the optimal observation sampling strategies by testing different thinning procedures and observation errors.
  • To assess the impact on tropical cyclones (TC) based on the swath coverage and on TC cyclogenesis.
  • To test the sensitivity of the NWP system to different products resolutions.
  • To assess the impact of ASCAT winds on the modeled ocean parameters by using a coupled ocean-atmosphere system.

Overview

The European Centre for Medium-Range Weather Forecasts (ECMWF) conducted this study to provide support for the assessment and further development of ASCAT related products from the Advanced Scatterometer on board the METOP satellites for the EUMETSAT Polar System (EPS). Specifically, the study addressed:

  • The characterization of the ASCAT wind error, the wind speed distribution and the analysis and background departures. The use of the current ‘Gaussian plus flat’ VarQC distribution for variational quality control within 4D-Var was compared to different settings of the Huber norm VarQC distribution.
  • Sensitivity tests on the use of a reduced thinning and an inflated observation error standard deviation were performed (see Figure 1).
  • The impact of scatterometer winds on the TC developing stage and on the impact of a partial storm coverage by the ASCAT swath were evaluated.
  • An analysis on the use of the ASCAT 12.5 km products, replacing the current 25 km ones used in operations, was carried out.
  • Another analysis, related to the sensitivity of the system to product resolutions, was performed on the assimilation of experimental ASCAT products providing wind observations at low resolutions of 50 km, 62.5 km and 100 km. These products were generated by ICM-CSIS in the framework of a NWP SAF project.
  • The impact of ASCAT winds assimilation on a coupled atmosphere ocean system was evaluated over 2014.
 ASCAT-A wind used observations for a case study on TC Kilo for the cycle 8 September 2015 12UTC for the experiments on Huber norm (HN) and reduced thinning (Thin): “CTRL” (a), “VarQC/Thin=2” (b), “HN” (c), “NH/Thin=2” (d).
Figure 1: ASCAT-A wind used observations for a case study on TC Kilo for the cycle 8 September 2015 12UTC for the experiments on Huber norm (HN) and reduced thinning (Thin): “CTRL” (a), “VarQC/Thin=2” (b), “HN” (c), “NH/Thin=2” (d).