1.Center for Earth System Modeling and Prediction of CMA;2.Chinese Academy of Meteorological Sciences;3.Chengdu University of Information Technology
对流尺度数值预报对初始场的微小扰动非常敏感，且初始扰动的演变具有模式依赖、环流依赖和尺度依赖特征，如何构建合理的初始扰动场是国内外对流尺度集合预报领域尚未解决的难点问题和研究前沿。本文基于中国气象局3km水平分辨率的GRAPES（Global/Regional Assimilation and Prediction Enhanced System，GRAPES）对流尺度模式，利用其同化分析系统的背景误差和一个二维随机型，构建大、中、小三个尺度的初始扰动场，并选取中国夏季一次典型的多区域强降水天气个例，开展对流尺度集合预报试验，对比分析了大、中、小尺度初始扰动能量的时空演变和谱分解特征，以期为构建适用于GRAPES对流尺度集合预报的初始扰动场提供依据。研究结果表明，在GRAPES 3km对流尺度模式中：（1）大、中、小尺度初始扰动总能量的增长过程具有明显差异：大尺度初始扰动总能量随着模式积分呈增长趋势，尤以对流层中高层的持续增长为甚；而中、小尺度初始扰动总能量随着模式积分以日变化为主，表现为下午至傍晚（夜晚至清晨），扰动总能量显著增加（减小），且扰动总能量小尺度分量的日变化占主导，这可能是由于太阳辐射引起地表加热，使得白天的对流活动比夜晚活跃，且对流直接影响了扰动总能量小尺度分量的变化。此外，大、中、小尺度初始扰动总能量增长均以扰动动能增长为主，且扰动位能在对流层低层的增长不可忽略。（2）大、中、小尺度初始扰动总能量增长具有环流依赖特征：对北支气流控制的中高纬天气区，在斜压不稳定较强的低槽区，大尺度初始扰动总能量增长突出，而在槽后西北气流区，大、中、小尺度初始扰动总能量均不增长；对南北气流交汇区，仍以大尺度初始扰动总能量增长最为明显；对南海夏季风影响区，大、中、小尺度初始扰动总能量发展均较弱，扰动位能增长与区域降水大值率演变有较好的对应关系。（3）大、中、小尺度初始扰动总能量的谱分析结果显示，不同积分时段扰动总能量的多尺度串级特征有差异：在积分前3h主要为扰动总能量的大尺度分量向小尺度分量的降尺度串级，积分6h后则为中、小尺度分量的升尺度串级。上述研究结果表明，在天气系统复杂、动力不稳定时空分布不均匀的区域（如中国区域）发展对流尺度集合预报时，有必要针对不同的不稳定天气区，构建具有尺度依赖和环流依赖的初始扰动结构。
The convective-scale numerical weather prediction (NWP) is sensitive to the initial minor perturbation and the evolution of initial perturbation (hereafter IP) is model-dependent, flow-dependent, and scale-dependent. And it has always been difficult to construct a reasonable initial perturbation for the convection-permitting ensemble prediction systems. Based on the GRAPES 3km convective-scale model of Center for Earth System Modeling and Prediction of CMA, we use a two-dimensional random function and background error of assimilation system in GRAPES 3km to construct the large, meso, and small scale stochastic initial perturbation field. Based on the constructed different scale initial perturbations, three convective-scale ensemble forecast experiments are conducted for a typical weather process of multi-regional heavy precipitation in summer in China. The spatial-temporal evolution and spectral decomposition characteristics of perturbation energy for three IP experiments are analyzed to understand the evolution characteristics of different scale initial perturbations in a convective scale model, to provide a reference for constructing an optimal initial perturbation in GRAPES convection-permitting ensemble prediction systems. Results show that: in the GRAPES 3km convective-scale model, (1) There are significant differences in the evolution of difference total energy (DTE) in three IP experiments. The DTE of large-scale IP increases with model integration, especially in the middle and upper troposphere. However, the DTE evolution of meso and small-scale IP experiments shows an apparent diurnal cycle characteristic. Specifically, it exhibits a significant increase (decrease) from afternoon to evening (from night to morning) when the convection is active (passive), and the diurnal cycle is mainly caused by the diurnal cycle of the small-scale component of DTE. The diurnal cycle of DTE may be due to the surface heating caused by solar short wave radiation, which makes the convection more active during the day than at night, and the convection directly affects the small-scale component of the DTE. In addition, the DTE of three IP experiments increases mainly by the development of difference kinetic energy (DKE), and the difference potential energy (DPE) cannot be neglected in the lower troposphere. (2) The DTE evolution of large, meso, and small-scale IP experiments is flow-dependent. Specifically, in the mid-high latitudes, the DTE increases of large-scale IP is dominant in the region where the baroclinic instability is strong (e.g., trough region), and the DTE of large, meso, and small-scale IP experiments does not develop in the region with relatively weak baroclinic instability (e.g., the northwest flow behind trough). In the confluence region of the north and south airflow, the DTE increases of large-scale IP is still dominant. However, the DTE of all three IP experiments hardly develops in the region affected by the South China Sea summer monsoon, and there is a relatively consistent relationship between the DPE(difference potential energy) development and the ratio of large precipitation rate in this region. (4) The DTE spectrum shows that the multi-scale cascade characteristics of DTE change with integration periods. The downscaling cascade of DTE from the large-scale component to the small-scale component in the first 3 hours is powerful. However, for lead times after 6 hours, the upscale DTE growth from meso and small-scale components becomes the main characteristic of the DTE spectrum. In conclusion, it is necessary to construct a scale-dependent and flow-dependent initial perturbation structure for different unstable weather regions, especially when we build the convection-permitting ensemble prediction in regions with complex weather systems and non-uniform spatial-temporal distribution dynamic instability (such as China).