数字滤波初始化方案在高分辨率GRAPES区域模式中的应用研究

高分辨率同化系统中引入的高频率高密度观测信息会造成分析变量之间的不平衡，因而在模式积分中产生的虚假重力波会严重影响模式预报质量和运行稳定。为了抑制虚假重力波在模式中快速增长，文中通过在高分辨率GRAPES区域模式中应用非绝热数字滤波和增量数字滤波初始化方案，研究不同滤波截断周期的初始化方案对分析预报的影响。试验结果表明，不同初始化方案的分析预报效果依赖于截断周期，截断周期越长滤除的高频信息越多，对于3 km分辨率模式，30 min与15 min截断周期的初始化方案既滤除了高频噪音，也基本保留了有意义的分析信息。不同截断周期的数字滤波方案在GRAPES-MESO系统中对气象要素预报场的影响基本可忽略；而在GRAPES-RAFS系统中，初始化方案对分析和预报的影响会逐渐累积，15 min截断周期的初始化方案比2 h截断周期的初始化方案的风场预报和降水预报质量更优。 

A study on digital filter initialization in high-resolution GRAPES regional model

The imbalance of the analysis variables created by introducing irregular high frequency and high density observations into the high-resolution analysis gives rise to unphysical gravity-inertia waves in the model integration, and thus affects the forecast quality and stability of operational models. In this paper, the diabatic digital-filtering initialization and incremental digital filter initialization are applied to 3 km resolution GRAPES regional model to suppress noises in the early forecast hours, and the impact on analysis and forecast with different cutoff periods of initializations are evaluated. The analysis and forecast experiments show that the filtering effect relies on the cutoff period. If the cutoff period is longer, more high frequency signals are removed. In the 3 km resolution modelling, both 30 min and 15 min cutoff periods initialization can remove high frequency noises and retain meaningful analysis information. The impact produced by different cutoff period initialization schemes in the GRAPES-MESO system on the model variables can be neglected, whereas the accumulated effects of initialization schemes are gradually observed in the GRAPES-RAFS system. The results show that wind and precipitation forecast qualities are obviously improved with a 15 min cutoff period initialization compared to that with the 2 h cutoff period. The impact of digital filter initialization scheme on high-resolution model prediction depends on the cutoff period. The cutoff period of 30 min or 15 min is suitable for 3 km resolution model, and the initialization scheme of incremental digital filter demonstrates obvious advantages.