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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2018-43
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Model description paper
23 Mar 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
Observational operators for dual polarimetric radars in variational data assimilation systems
Takuya Kawabata1, Thomas Schwitalla2, Ahoro Adachi1, Hans-Stefan Bauer2, Volker Wulfmeyer2, Nobuhiro Nagumo1, and Hiroshi Yamauchi3 1Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, 3050052, Japan
2Institute of Physics and Meteorology, University of Hohenheim, Stuttgart, 70599, Germany
3Japan Meteorological Agency, Tokyo, 1008122, Japan
Abstract. We developed two observational operators for dual polarimetric radars and implemented them in two variational data assimilation systems: WRF Var, the Weather Research and Forecasting Model variational data assimilation system, and NHM-4DVAR, the nonhydrostatic variational data assimilation system for the Japan Meteorological Agency nonhydrostatic model. The operators consist of a space interpolator, two types of variable converters as well as their linearized and transposed (adjoint) operators. The space interpolator takes account of the effects of radar-beam broadening in both vertical and horizontal directions and climatological beam bending. The first variable converter emulates polarimetric parameters with model prognostic variables and includes attenuation effects, and the second one derives rainwater content from the observed polarimetric parameter (specific differential phase). We developed linearized and adjoint operators for the space interpolator and variable converters and then assessed whether the linearity of the linearized operators and the accuracy of the adjoint operators were good enough for implementation in variational systems. The results of a simple assimilation experiment showed good agreement between assimilation results and observations with respect to reflectivity and specific differential phase but not with respect to differential reflectivity.
Citation: Kawabata, T., Schwitalla, T., Adachi, A., Bauer, H.-S., Wulfmeyer, V., Nagumo, N., and Yamauchi, H.: Observational operators for dual polarimetric radars in variational data assimilation systems, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-43, in review, 2018.
Takuya Kawabata et al.
Takuya Kawabata et al.
Takuya Kawabata et al.

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Short summary
We developed two observational operators for dual polarimetric radars and implemented them in two variational data assimilation systems: WRF Var and NHM-4DVAR. The operators consist of a space interpolator and two types of variable converters. The first variable converter emulates polarimetric parameters with model prognostic variables, and the second derives rainwater content from the observed polarimetric parameter. The system worked properly in verification and assimilation tests.
We developed two observational operators for dual polarimetric radars and implemented them in...
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