P2.45
Development of a mesoscale 4-dimensional variational data assimilation (4D-Var) system at JMA
Yoshihiro Ishikawa, Japan Meteorological Agency, Tokyo, Japan
The JMA is developing a 4-dimensional variational data assimilation (4D-Var) system for a hydrostatic mesoscale model (MSM) with a horizontal resolution of 10km and 40 vertical levels. The system is planned to be operational from early 2002 with three-hour assimilation windows. Since it is aimed to provide MSM products within one and half hours from observation times, an incremental approach will be taken to save computational time, using a 20km version of MSM for inner loop calculation of 4D-Var.
The cost function consists of a background term, observation terms, and a penalty term for reducing gravity wave noise. The control variables are the initial and boundary conditions of unbalanced wind, temperature, surface pressure, and specific humidity. The background error statistics are obtained by using the NMC method. The horizontal background error correlations are assumed to be homogeneous and of Gaussian type to significantly reduce memory requirement. The forward model is a full-physics model, while physics of the adjoint model include moist processes, simplified boundary layer processes, and horizontal diffusion only.
Experiments have been carried out to assess the performance of the 4D-Var system using the 20km version of MSM, and comparisons have been made with the current operational forecast using the same model. Assimilated observations are conventional meteorological data and radar-AMeDAS one-hour precipitation data. In the operational analysis, 3-dimensional optimal interpolation and physical initialization are used for assimilating the conventional data and the precipitation data, respectively. It is found that significant improvements in precipitation and wind forecast are obtained even without assimilating the precipitation data. Assimilation of the precipitation data leads to further improvements in precipitation forecast.
Poster Session 2, Summer Storms (Poster session)
Tuesday, 16 January 2001, 2:30 PM-5:30 PM
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