Development of Doppler radar wind data assimilation
for the HIRLAM 3D-Var
M. Lindskog, H. Järvinen, D. B. Michelson
Abstract
A three-dimensional variational data assimilation (3D-Var) scheme has been
developed for the HIgh Resolution Limited Area Model (HIRLAM). The
HIRLAM 3D-Var minimizes a cost function measuring the distance of the
analysis to the background field and to the observations.
Each source of information is weighted according to
its estimated error covariance. Radar wind observations can be
input for HIRLAM 3D-Var either as radial wind super-observations or as
vertical profiles of horizontal wind obtained with the Velocity Azimuth
Display (VAD) technique. Background error standard deviation (sb)
of wind and radial wind have been estimated by
applying a randomization method, in which the background state
is perturbed with
Gaussian errors. The derived values of sb are used in the quality
control of observations,
and also in the assignment of radar wind observation error standard deviations
(so).
Parallel data assimilation and forecast
experiments confirm reasonably well-tuned error statistics and indicate a
slightly positive impact of radar wind data on the verification scores,
regardless of whether the radar wind information is input as
radial wind super-observations or as VAD wind profiles.
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