Assimilation of water vapor lidar observations: impact study on the COPS precipitation forecasts and hindcasts

E. Richard, S. Bielli, M. Grzeschik, C. Flamant, C. Kiemle, M. Dorninger

The Convective and Orographically-driven Precipitation Study carried

out in summer 2007 over northeastern France and southwestern Germany

provided a fairly comprehensive description of the low-troposphere water

vapour field thanks, in particular, to the deployment of two airborne

differential absorption lidar systems. These lidar observations were

assimilated using the 3D VAR assimilation system of the Application of

Research to Operations at MEsoscale (AROME) numerical weather prediction

mesoscale model. The assimilation was carried out for the period of 4

July-3 August by running a 3-hour forward intermittent assimilation

cycle. First, the impact of the lidar observations was assessed by

comparing the analyses with a set of more than 200 independent

soundings. The lidar observations were found to have a positive impact

on the analyses by reducing the dry bias in the first 500 m above ground

level and by diminishing the root mean square error by roughly 15% in

the first km. Then, the impact of the lidar observations was

assessed by comparing the AROME precipitation forecasts (obtained with

and without the lidar observations for the period of 15 July-2 August)

with the gridded precipitation observations provided by the Vienna

Enhanced Resolution Analysis. In general, the impact was found to be

positive but not significant for the 24h precipitation, and positive

and significant for the 6h precipitation with an improvement lasting up

to 24h. Additional experiments performed with the Meso-NH research

model showed that the results were improved when the model was run in

hindcast mode and indicated that the model 24h-precipitation was more

sensitive to boundary conditions errors than to initial condition errors

in the moisture field.

Institut für Meteorologie und Geophysik
Externe Organisation(en)
Université Toulouse III Paul Sabatier, Eberhard Karls Universität Tübingen, Université Paris VI - Pierre-et-Marie-Curie, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
Geophysical Research Abstracts
Anzahl der Seiten
ÖFOS 2012
105206 Meteorologie
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