Observation error statistics for Doppler radar radial wind superobservations assimilated into the DWD COSMO-KENDA system

Waller, J. A., Bauernschubert, E., Dance, S. L. ORCID: https://orcid.org/0000-0003-1690-3338, Nichols, N. K. ORCID: https://orcid.org/0000-0003-1133-5220, Potthast, R. ORCID: https://orcid.org/0000-0001-6794-2500 and Simonin, D. (2019) Observation error statistics for Doppler radar radial wind superobservations assimilated into the DWD COSMO-KENDA system. Monthly Weather Review, 147. pp. 3351-3364. ISSN 0027-0644 doi: 10.1175/MWR-D-19-0104.1

Abstract/Summary

Currently in operational numerical weather prediction (NWP) the density of high-resolution observations, such as Doppler radar radial winds (DRWs), is severely reduced in part to avoid violating the assumption of uncorrelated observation errors. To improve the quantity of observations used and the impact that they have on the forecast requires an accurate specification of the observation uncertainties. Observation uncertainties can be estimated using a simple diagnostic that utilises the statistical averages of observation-minus-background and observation-minus-analysis residuals. We are the first to use a modified form of the diagnostic to estimate spatial correlations for observations used in an operational ensemble data assimilation system. The uncertainties for DRW superobservations assimilated into the Deutscher Wetterdienst convection-permitting NWP model are estimated and compared to previous uncertainty estimates for DRWs. The new results show that most diagnosed standard deviations are smaller than those used in the assimilation, hence it may be feasible assimilate DRWs using reduced error standard deviations. However, some of the estimated standard deviations are considerably larger than those used in the assimilation; these large errors highlight areas where the observation processing system may be improved. The error correlation length scales are larger than the observation separation distance and influenced by both the superobbing procedure and observation operator. This is supported by comparing these results to our previous study using Met Office data. Our results suggest that DRW error correlations may be reduced by improving the superobbing procedure and observation operator; however, any remaining correlations should be accounted for in the assimilation.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/84712
Item Type	Article
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Mathematics and Statistics Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Meteorological Society
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