东亚季风区集合预报扰动增长的时空不均匀特征分析

Characteristics of Spatio-temporal Inhomogeneities in the Growth of Ensemble Forecast Perturbations in East Asian Monsoon Region

关键词:  集合预报  增长特征  季节特征  纬度带差异

Key words:  ensemble forecast  growth characteristics  seasonal characteristics  latitudinal zone differences

摘要:

为深入认识东亚季风区集合预报扰动增长的时空变化特征，以更好地改进该区域集合预报扰动结构，基于中国气象局区域集合预报模式(CMA-REPS)，利用 2021 年 1—12 月集合预报结果，选取扰动能量、离散度和集合一致性等评估指标，对比分析不同纬度风场和温度场集合预报扰动增长的时空变化特征，并分析了一次典型降水过程的集合预报扰动增长特征。(1) 集合预报扰动增长过程中集合离散度时空分布具有纬度带差异和季节特征。离散度大小呈现由北向南递减趋势。在 45～60 °N、30～45 °N区域，集合预报离散度的最大值通常出现在春季，这与大气环流季节转换、冷暖空气交汇等相关，具有明显的流依赖特征，而在 15～30 °N 低纬区域的集合预报离散度最大值则通常出现在夏季，这与台风活动有关。同时值得关注的是青藏高原地区表现为一个集合离散度大值区，可能与青藏高原大地形对预报扰动增长影响有关。(2) 预报扰动增长过程中，集合一致性的时空分布特征与离散度基本一致。45～60 °N、30～45 °N 中高纬度区域的集合一致性在春季更接近1；在 15～30 °N 低纬地区，集合一致性夏季更接近 1，但各季节一致性均明显偏小。(3) 集合预报扰动能量及其增长率的垂直分布同样具有显著的纬度差异和季节差异。在 45～60 °N、30～45 °N中高纬度区域，扰动总能量在高层和低层存在大值区，最大值出现在春季；在 15～30 °N低纬区域扰动总能量偏小且随高度变化不明显，而且各季节扰动能量增长率也偏小，说明需要特别发展低纬区域集合预报扰动方法。集合预报扰动增长表现出的季节性、流依赖性和区域变化等特征，表明东亚季风区的集合扰动方法需要针对不同纬度和不同季节进行分别研究，尤其需要关注低纬区域集合预报扰动结构调整。

Abstract:

This study aims to gain a deeper understanding of the spatio-temporal evolution characteristics of the growth of ensemble perturbations so as to better improve the structure of ensemble forecast perturbations in the East Asian monsoon region. Using the China Meteorological Administration-Regional Ensemble Prediction System (CMA-REPS) and ensemble forecast results from January to December 2021, we analyzed and compared the spatio-temporal characteristics of perturbation growth in wind and temperature fields at different latitudes. Evaluation indexes such as perturbation energy, ensemble spread, and ensemble consistency were employed. Moreover, the growth characteristics of ensemble forecast perturbations during a typical precipitation event were examined. The results show that: (1) The spatio- temporal distribution of ensemble spread in the process of ensemble forecast perturbations growth showed latitude zone difference and seasonal characteristics. The value of the ensemble spread showed a decreasing trend from north to south. In the 45-60 ° N and 30-45 ° N regions, the maximum value of ensemble spread usually occurred in spring, which was related to seasonal transitions in atmospheric circulation and the convergence of cold and warm air masses. This demonstrated a clear flow-dependence in the evolution of ensemble spread. However, the maximum value of ensemble spread in the 15-30 °N low-latitude region usually appeared in summer, which was related to typhoon activities. Notably, the Qinghai-Tibet Plateau exhibited a region of high ensemble spread, likely due to the influence of its topography on perturbation growth. (2) The spatio-temporal distribution of ensemble consistency during the perturbation growth process was highly consistent with the spread. The ensemble consistency was closer to 1 in the spring in the 30-45 °N and 45-60 °N mid- to high-latitude regions, and the ensemble consistency was closer to 1 in the summer in the low-latitude region of 15-30 °N. By contrast, the consistency in all seasons was significantly smaller. (3) The vertical distribution of ensemble forecast perturbation energy and its growth rate also exhibited significant latitudinal and seasonal differences. In the 30-45 °N and 45-60 °N mid- to high-latitude regions, perturbation energy showed high values in both upper and lower levels, with the maximum occurring in spring; in the low-latitude region of 15-30 °N, the total perturbation energy was small and did not change significantly with height, and the growth rate of the perturbation energy in all seasons was relatively small, indicating the need for the development of specific ensemble forecast perturbation methods for low-latitude regions. The observed seasonal, flow-dependent, and regional variations in ensemble perturbation growth highlight the necessity of conducting separate studies for different latitudes and seasons in the East Asian monsoon region, particularly with regard to adjusting the ensemble perturbation structure in low-latitude regions.