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Impact of Microphysics Scheme Complexity on the Propagation of Initial Perturbations

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  • 1 National Center for Atmospheric Research,* Boulder, Colorado
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Abstract

The study of evolution characteristics of initial perturbations is an important subject in four-dimensional variational data assimilation (4DVAR) and mesoscale predictability research. This paper evaluates the impact of microphysical scheme complexity on the propagation of the perturbations in initial conditions for warm-season convections over the central United States. The Weather Research and Forecasting Model (WRF), in conjunction with four schemes of the Morrison microphysics parameterization with varying complexity, was used to simulate convective cases using grids nested to 5-km horizontal grid spacing. Results indicate that, on average, the four schemes show similar perturbation evolution in amplitude and spatial pattern during the first 2 h. After that, the simplified schemes introduce significant error in amplitude and spatial pattern. The simplest (liquid only) and most complex schemes show almost the same growth rate of initial perturbations with different amplitudes during 6-h forecast, suggesting that the simplest scheme does not reduce the nonlinearity in the most complex scheme. The evolution of vertical velocity and total condensates is more nonlinear than horizontal wind, temperature, and humidity, which suggest that the observations of cloud variables and vertical velocity should have a shorter time window (less than 1 h) compared to horizontal wind, temperature, and humidity observations. The simplified liquid-only microphysics scheme can be used as an acceptable substitute for the more complex one with a short time window (less than 1 h).

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Dr. Hongli Wang, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307. E-mail: hlwang@ucar.edu

Abstract

The study of evolution characteristics of initial perturbations is an important subject in four-dimensional variational data assimilation (4DVAR) and mesoscale predictability research. This paper evaluates the impact of microphysical scheme complexity on the propagation of the perturbations in initial conditions for warm-season convections over the central United States. The Weather Research and Forecasting Model (WRF), in conjunction with four schemes of the Morrison microphysics parameterization with varying complexity, was used to simulate convective cases using grids nested to 5-km horizontal grid spacing. Results indicate that, on average, the four schemes show similar perturbation evolution in amplitude and spatial pattern during the first 2 h. After that, the simplified schemes introduce significant error in amplitude and spatial pattern. The simplest (liquid only) and most complex schemes show almost the same growth rate of initial perturbations with different amplitudes during 6-h forecast, suggesting that the simplest scheme does not reduce the nonlinearity in the most complex scheme. The evolution of vertical velocity and total condensates is more nonlinear than horizontal wind, temperature, and humidity, which suggest that the observations of cloud variables and vertical velocity should have a shorter time window (less than 1 h) compared to horizontal wind, temperature, and humidity observations. The simplified liquid-only microphysics scheme can be used as an acceptable substitute for the more complex one with a short time window (less than 1 h).

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Dr. Hongli Wang, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307. E-mail: hlwang@ucar.edu
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