A pre-operational variational data assimilation system for a non-hydrostatic model at the Japan Meteorological Agency: Formulation and preliminary results
A pre-operational variational data assimilation system for a non-hydrostatic model at the Japan Meteorological Agency: Formulation and preliminary results
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DOI：
10.1256/qj.05.132
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发表时间：
2005-10-01
影响因子：
8.9
通讯作者：
Tsuyuki, T.
中科院分区：
文献类型：
--
作者：
Honda, Y.;Nishijima, M.;Tsuyuki, T.
日本气象厅正在开发一个新的非静力模式变分数据同化系统，以供业务使用。JMA非静力模式变分资料同化系统（JNoVA）主要作为一个四维变分资料同化系统，但也可以作为一个三维系统使用，控制变量集包括不平衡水平风、大尺度位温和地面气压、不平衡温度和伪相对湿度等初始条件。在控制变量转换中，显式地考虑了静力平衡和地转平衡，隐式地考虑了地面摩擦的影响。在用NMC方法计算背景误差协方差时，引入了低通滤波器来去除潜在温度和表面压力中的噪声，这些噪声降低了平衡风的质量。低通滤波器的截止波长设置为300 km，这是模式动能谱过渡到表征中尺度运动的较浅斜坡的尺度。虽然对某些物理过程进行了简化，但除辐射外的所有物理过程都被考虑在内。结果表明，定量降水预报（在强度，时间和位置的事件）从分析由JNoVA的改进，从分析预测的四维变分系统，采用JMA流体静力学谱模式。
A new variational data assimilation system for a non-hydrostatic model is being developed at the Japan Meteorological Agency (JMA) for operational use. Known as the JMA non-hydrostatic model variational data assimilation (JNoVA) system, it mainly functions as a four-dimensional variational data assimilation system, although it has an option to be used as a three-dimensional system.The set of control variables consists of initial conditions of unbalanced horizontal winds, large-scale components of potential temperature and surface pressure, unbalanced temperature and pseudo relative humidity. In the control variable transformation, hydrostatic balance and geostrophic balance are considered explicitly and the effect of the surface friction is also considered implicitly. When calculating the background-error covariances by the NMC method, a low-pass filter is introduced to remove noise in potential temperature and surface pressure that degrades the quality of the balanced winds. The cut-off wavelength of the low-pass filter is set to 300 km, which is the scale at which the model's kinetic energy spectrum transits to the shallower slope characterizing mesoscale motions.An adjoint model of the JMA non-hydrostatic model has been developed from scratch by hand for this system. Although some of the physics are simplified, all physical processes except the radiation are considered.A preliminary data assimilation experiment with the JNoVA has been done for a heavy rainfall event. The results show that the quantitative precipitation forecast (in terms of the intensity, timing and position of the event) from the analysis by the JNoVA is improved over the forecast from the analysis by a four-dimensional variational system that employs the JMA hydrostatic spectral model.