基于自组织映射的长江中下游夏季天气分型及其降水特征

Synoptic classification and precipitation characteristics in summer over the Yangtze River Basin based on self-organizing map

利用欧洲中心1979—2015年夏季6—8月ERA-Interim逐日再分析资料和国家气候中心CN05.1格点化降水观测数据集,引入基于自组织映射SOM(Self-Organizing Maps)方法进行长江中下游地区夏季海平面气压空间距平场的客观分型,得到该地区25种地面天气型及其系统演变特征,发现天气型的稳定、转移与天气系统强弱有关。高低压系统越强,天气型停滞频率越高,天气型越稳定;反之,天气型越不稳定。基于SOM天气型转移概率,发现三条与局地降水联系的系统演变路径,其中1号路径暖空气势力强盛,副高北上,推动锋面北抬,产生江北降水型,多发生在7月;路径2反映冷空气势力强盛推动锋面南下的天气过程,产生沿江降水型,该天气型在6、7月均易发生;路径3表现为台风移动变化对长江下游江南地区降水的影响,为江南降水型,且集中在8月。通过引入SOM方法对逐日天气尺度环流进行分型,从气候态上捕捉与降水有关的天气系统的移动变化特征,体现SOM方法在模拟天气系统演变的优势。

Based on the ERA-Interim reanalysis data from the European Center and CN05.1 gridded Precipitation observation data from the National Climate Center during the summer from June to August during 1979—2015,the Self-Organizing Maps(SOM)method is introduced to classify objectively sea level pressure fields over the Yangtze River Bain,and 25 surface synoptic patterns and their characteristics of evolution in the area is obtained.It s found that the stability and shift of synoptic patterns are related to the strength of the weather systems.The stronger high and low pressure system,the higher stagnation frequency of synoptic patterns,and the more stable synoptic patterns.On the contrary,the synoptic pattern is more unstable.Three systematic evolution paths associated with local precipitation are found on the basis of the SOM synoptic patterns transition probability.Among them,warm air force on the first path is strong and push the front northward with subtropical pacific high pressure northward,which brings Northern Yangtze River Rainfall Pattern(NYRP)mostly occurring in July.The second path reflects that the cold air forces spurs the southward of the front,resulting in Yangtze River Rainfall Pattern(YRP),which is likely to occur in June and July.Path three represents the influence of the typhoon movement to the precipitation in the Jiangnan region of lower reaches of the Yangtze River,which forms Southern Yangtze River Rainfall Pattern(SYRP)concentrated in August.In this study,the SOM method is used to classify the daily atmospheric circulation and capture the movement characteristics of the weather system related to the precipitation from the climate state,which reflects the advantages of the SOM method in simulating the evolution of the weather system.