|Title||All-sky Assimilation of AMSU-A Window Channels|
|Series/Collection||EUMETSAT/ECMWF Fellowship Programme Research Report|
|Type||Eumetsat Fellowship Programme Research Report|
|Authors||Duncan, D, Bormann, N, Geer, AJ|
Following the activation of AMSU-A temperature sounding channels in all-sky conditions at ECMWF,
All-sky assimilation of the AMSU-A window channels is shown to be similar to that of microwave imagers when adequate quality control and observation error modelling are applied; different observation error models are tested, with a 50 GHz-based cloud proxy yielding the best results. The choice of observation error model has a modest effect on the assimilation, though smaller than that of the additional data itself. Experiments using a depleted observing system indicate that active use of these window channels can impart a good fraction of the impact provided by four microwave imagers. When compared to a full observing system, the addition of AMSU-A window channels provides a small but significant improvement in background fits to observations of winds and humidity. These benefits are most notable in the tropics, where the addition of AMSU-A window channels fills in temporal sampling gaps left by the imagers. Signals in the analysis-based verification are small and more mixed, with improvement seen for columnar humidity in the tropics out to day 2 but degradation of low-level temperature forecasts in the southern hemisphere out to day 4. Further testing will be performed to ascertain the suitability of assimilating the AMSU-A window channels in a future operational cycle.