摘要:基于GRAPES-REPS（Global and Regional Assimilation and Prediction Enhanced System-Regional Ensemble Prediction System）区域集合预报模式和集合变换卡尔曼滤波（Ensemble Transform Kalman Filter，ETKF）初值扰动方法，对2015年6月1~15日10 km与15 km水平分辨率分别进行集合预报试验，通过分析ETKF初值扰动分量、初值扰动方差准确率、动能谱、扰动能量演变、日变化及集合离散度、均方根误差等特征，揭示GRAPES-REPS区域集合预报ETKF初值扰动结构及增长特征。结果表明：（1）ETKF初值扰动方案产生的扰动能够保持所有正交、不相关方向的误差方差，且ETKF分量α参数值及放大因子具有较好的稳定性。（2）ETKF初值扰动方法生成的扰动场以大尺度扰动为主，扰动结构及能量具有随流型依赖特征，低层以内能扰动为主，高层以动能扰动为主，且集合扰动可以有效捕捉预报误差的结构。（3）GRAPES区域集合预报初值扰动总能量和集合离散度随预报时效的延长均呈发展趋势，但离散度增长率小于均方根误差增长率，即集合预报总体存在集合离散度不足的问题。（4）水平分辨率提高可以增加中高层大尺度扰动波谱能量，明显改进等压面及近地面风场及温度场的集合预报效果。值得指出的是，GRAPES-REPS区域集合预报低层内能扰动能量存在明显的日变化特征，特别是青藏高原地区更加显著，需要进一步研究青藏高原初值扰动结构的合理性。
关键词:区域集合预报/
GRAPES模式/
初值扰动结构/
扰动增长特征
Abstract:Using the GRAPES-REPS (Global and Regional Assimilation and Prediction Enhanced System-Regional Ensemble Prediction System) model and ETKF (Ensemble Transform Kalman Filter) initial perturbation method, ensemble forecast experiments at 10 km and 15 km horizontal resolutions were conducted from 1 to 15 June 2015. By analyzing ETKF characteristics of initial perturbation components, variance accuracy, kinetic energy spectrum, perturbation energy evolution, daily variation and ensemble spread, root mean square error, characteristics of initial perturbation structures and its growth rate in the regional ensemble prediction system of GRAPES-REPS are revealed in the present study. The preliminary experimental results indicate:(1) The ETKF initial ensemble perturbations can maintain even distribution to the orthogonal and uncorrelated ensemble directions, while the value of α parameter and inflation factor of the ETKF component are stable. (2) The perturbation field derived from the ETKF initial perturbation schemes is mainly large-scale with a flow dependent structure. The internal perturbation energy and the kinetic perturbation energy are the prevailing perturbation energy in the lower and higher levels, respectively. In addition, the ensemble perturbation can effectively capture the structure of forecast error. (3) The total energy of initial perturbation and ensemble spread can keep appropriate growth rate at all forecast lead times. However, the growth rate of ensemble spread is lower than that of root mean square error, indicating that there still exist problems of insufficient ensemble spread. (4) The increase in horizontal resolution can increase the large-scale perturbation spectrum energy at the middle and high levels, and contribute to the improvement of ensemble forecast results at isobaric levels and near the surface, such as forecast of temperature and wind. It is worth pointing out that the internal perturbation energy in the lower levels shows obvious diurnal variation characteristics in GRAPES-REPS, especially over the Qinghai-Tibet Plateau. It is necessary to further explore the rationality of initial perturbation structure over the Qinghai-Tibet Plateau.
Key words:Regional ensemble forecast/
GRAPES model/
Initial perturbation structures/
Characteristics of perturbation growth rate
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