Evaluation and assimilation of ATMS data in the ECMWF system

TitleEvaluation and assimilation of ATMS data in the ECMWF system
Publication TypeMiscellaneous
Year of Publication2012
AuthorsBormann, N, Fouilloux, A, Bell, W
Secondary TitleTechnical Memorandum
Number689
Abstract

This memorandum reports on the first experiences with ATMS data at ECMWF, both in terms of the contribution to the calibration/validation exercise, and in terms of initial assimilation trials. Comparisons in brightness temperature space against short-term forecasts are used to establish the fidelity of the data. Monitoring of ATMS data against short-term forecasts show that the data are generally of good quality, with a noise performance that is well within specification and, after appropriate averaging, comparable to or better than that of AMSU-A. Biases vary smoothly with scan-positions, even before an appropriate antenna pattern correction has been established, and ATMS looks better than AMSUA in this regard. Outer scan positions can be assimilated without restrictions due to biases, and together with the wider swath this leads to a much improved coverage from ATMS compared to one AMSU-A. There are indications of larger inter-channel and spatial error correlations in ATMS data than for AMSU-A, possibly linked to a weak cross-track striping effect. The analysis and forecast impact in initial assimilation trials over two seasons are significantly positive in the short-range over the Southern Hemisphere and in the long range over the Northern Hemisphere, with an otherwise overall neutral impact.