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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-9
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-9
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Feb 2019

Submitted as: research article | 11 Feb 2019

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.

All-sky assimilation of infrared radiances sensitive to mid- and upper-tropospheric moisture and cloud

Alan J. Geer1, Stefano Migliorini2, and Marco Matricardi1 Alan J. Geer et al.
  • 1ECMWF, Shinfield Park, Reading RG2 9AX, UK
  • 2Met Office, FitzRoy Road, Exeter EX1 3PB, UK

Abstract. All-sky assimilation of infrared (IR) radiances has not yet become operational at any weather forecasting centre but it promises to bring new observations in sensitive areas and it avoids the need for cloud detection. A new all-sky IR configuration gives results comparable to (and in some areas better than) clear-sky assimilation of the same data, meaning that operational implementation is now feasible. The impact of 7 upper-tropospheric water vapour (WV) sounding channels from the Infrared Atmospheric Sounding Interferometer (IASI) is evaluated in both all-sky and clear-sky approaches. All-sky radiative transfer simulations (and the forecast model’s cloud fields) are now sufficiently accurate that systematic errors are comparable to those of clear-sky assimilation outside of a few difficult areas such as deep-convection. All-sky assimilation brings 65 % more data than clear-sky assimilation globally, with the biggest increases in midlatitude storm tracks and tropical convective areas. However all-sky gives slightly less weight to any one observation than in the clear-sky approach. In the midlatitudes, all-sky and clear-sky assimilation have similarly beneficial impact on mid- and upper-tropospheric dynamical forecast fields. Here the addition of data in cloudy areas is offset by the slightly lower weight given to the observations. But in the tropics, all-sky assimilation is significantly more beneficial than clear-sky assimilation, with improved dynamical short-range forecasts throughout the troposphere and stratosphere.

Alan J. Geer et al.
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Alan J. Geer et al.
Alan J. Geer et al.
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Short summary
Satellite radiance observations are used to initialise weather forecasts, but only recently have the data been used in conditions of cloud and precipitation. By starting to fill this gap in coverage of the earth's atmosphere using data taken in the microwave part of the spectrum, the quality of operational forecasts has been improved. The current work shows that cloudy infrared data, with its stronger and more nonlinear sensitivity, can also benefit operational-quality forecasts.
Satellite radiance observations are used to initialise weather forecasts, but only recently have...
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