| 西南地区汛期降水次季节变化主模态的低频环流传播路径特征 |
| |
| 作者姓名： | 白慧 严小冬 池再香 王瑾 |
| |
| 作者单位： | 贵州省气候中心,贵州省山地气象科学研究所,贵州省山地气象科学研究所,贵州省山地气象科学研究所 |
| |
| 基金项目： | 国家自然科学基金青年项目（42305051）；国家自然科学基金地区项目（41965010）；贵州省科技计划项目（黔科合支撑[2021]一般 508）；贵州省科技计划项目（黔科合基础-ZK[2022]一般 273） |
| |
| 摘 要： | 【目的】本文探讨中国西南地区汛期（5~9月）降水次季节变化的主模态，以及中高纬和热带次季节波动如何影响该地区持续性异常低频降水，以期能为了解和预测西南地区汛期降水的次季节变化提供参考。【方法】利用西南地区111个地面气象站1961~2015年逐日降水资料和JRA-55再分析环流场资料，采用EOF经验证交分解方法，分析西南地区汛期降水次季节变化主模态的低频环流特征和传播路径。【结果】西南地区汛期逐日降水主模态的空间分布为南北纬向型分布，空间特征向量高值区域分布在西南地区的南部和东南部，其高值区对应的SWDR与PC1的相关系数达0.991（通过0.05信度检验），PC1气候平均值的显著周期为12.9 d，且逐年PC1的显著周期主要集中在10~20 d时段，占比为60.0%；在PC1的典型低频年中，汛期季节内及其各分月的PC1均能较好地表征对应降水异常分布型的时间演变特征，且二者低频分量的正相关性更高（通过0.05信度检验），即PC1低频分量均能更好地把握SWDPI低频分量的准双周振荡特征，尤其在6、7和8月，这可能与影响主模态降水异常分布型的同期大气低频环流信号更为稳定有关；PC1的季节内变化不仅与中国东南部和南海形成的对流异常偶极子有关，还与在西南地区对流层高层形成的位势高度异常偶极子息息相关，该对流异常偶极子的形成与前期菲律宾以东OLR正异常的西北向传播和巴尔喀什湖东南部OLR负异常的东南向传播有关，并且菲律宾以东被抑制的对流向西北方向传播总是伴随着低层的局部反气旋，而西南地区的西南部对流的增强（抑制）总是伴随着高层北部的负（正）位势高度异常，同时，西南地区对流层高层的位势高度异常偶极子的形成，与中高纬对流层高层类似Rossby低频波列东南向传播过程中在青藏高原东侧顺时针转向有关。【讨论】从气候背景看，影响PC1季节内变化的低频波列传播主要与两个方面的因子有关，一方面为对流层高层西风急流轴主体位置的南压和强度的增强，通过影响中高纬类似Rossby低频波列的东传南下，从而影响在西南地区对流层高层形成位势高度异常偶极子型分布，另一方面为印度季风槽的北抬加强了南海至菲律宾海域异常反气旋西北侧的西南气流，促使了西南地区低层异常气旋的形成，同时东亚季风槽的增强也利于热带西太平洋低频对流发展并向西北传播，从而影响在中国东南部和南海的形成的对流异常偶极子型分布。
|
| 关 键 词： | 降水 次季节 低频环流 传播路径 西南地区 |
| 收稿时间： | 2024/2/4 0:00:00 |
| 修稿时间： | 2024/2/4 0:00:00 |
Characteristics of Low-frequency Circulation Propagation Path of the Main Modes of Sub-seasonal Variation of Precipitation in Rainy Season in Southwest China |
| |
| Authors: | baihui YAN Xiaodong CHI Zaixiang and WANG Jin |
| |
| Institution: | Guizhou Climate Center,Guizhou Institute of Mountain Meteorological Science,Guizhou Institute of Mountain Meteorological Science,Guizhou Institute of Mountain Meteorological Science |
| |
| Abstract: | This paper discusses the main modes of sub-seasonal variation of precipitation in the rainy season (May-September) in Southwest China, and how the sub-seasonal atmospheric oscillations of mid-high latitudes and tropics affect the persistent abnormal low-frequency precipitation in Southwest China for the purpose of providing some references for understanding and forecasting the sub-seasonal variation of precipitation in the flood season in this region. The daily precipitation data from 111 surface weather stations and JRA-55 reanalysis circulation field data in Southwest China during 1961-2015 as well as the EOF empirical orthogonal decomposition method are adopted in analyzing the features of low-frequency circulation propagation path of the main modes of sub-seasonal variation of rainy-season precipitation in Southwest China. The results show that the main modes of daily precipitation in rainy season in Southwest China are distributed in a North-South zonal pattern. The high-value region of the spatial feature vector is in the south and southeast of Southwest China, and the correlation coefficient between SWDPI and PC1 in the high-value region is 0.991, which has passed the 0.05 confidence test. The significant period of PC1 climate mean is 12.9 d, and the significant period of annual PC1 is mainly concentrated in the 10-20 d period, accounting for 60.0%. In the typical low-frequency years of PC1, the PC1 in rainy season and each month can well represent the temporal evolution characteristics of the corresponding precipitation anomaly distribution pattern, with the positive correlation of the low-frequency components of the two becoming even higher and having passed the 0.05 confidence test. That is, the low-frequency components of PC1 can better grasp the quasi-biweekly oscillation characteristics of the low-frequency components of SWPDI, especially in June, July and August, which might be related to the more stable low-frequency atmospheric circulation signals that affect the anomaly distribution pattern of the main-mode precipitation in the corresponding period. The sub-seasonal variation of PC1 is not only linked to the convective anomaly dipole in Southeast China and the South China Sea, but also associated with the anomaly dipole of geopotential height in the upper troposphere in Southwest China. The formation of the convective anomaly dipole is caused by the northwest propagation of the positive OLR anomaly in the area east of the Philippines and the southeast propagation of the negative OLR anomaly in the southeast of Balkhash Lake. In addition, the suppressed northwesterly propagation east of the Philippines is always accompanied by local anticyclones in low level, while the southwest convection enhancement (suppression) in Southwest China is always accompanied by the negative (positive) geopotentical height anomaly in the north of upper troposphere. Meanwhile, the formation of anomaly dipole in the upper troposphere in Southwest China is correlated to the clockwise turn of the Rossby-like low-frequency wave train in the upper troposphere in the mid-high latitudes in the east side of the Tibetan Plateau. From the perspective of climate background, the low-frequency wave train propagation that affects the sub-seasonal variation of PC1 is mainly related to two factors. On the one hand, the main position of westerly jet shifts southward and the strength is enhanced in the upper troposphere, causing the Rossby-like low-frequency wave train to spread eastward and southward in the mid-high latitudes and affecting the distribution of the geopotential height anomaly dipole in the upper troposphere in Southwest China. On the other hand, the northward shifting of the Indian monsoon trough strengthens the southwest airflow in the northwest side of the anomalous anticyclones from the South China Sea to the Philippines, promoting the formation of the low-level anomalous cyclones in Southwest China. Meanwhile, the strengthening of the East Asian monsoon trough also facilitates the development and northwestward propagation of low-frequency convection in the tropical western Pacific, thus affecting the distribution of the convective anomaly dipole in Southeast China and the South China Sea. |
| |
| Keywords: | precipitation sub-seasonal low-frequency circulation propagation path southwest China |
|
| 点击此处可从《》浏览原始摘要信息 |
| 点击此处可从《》下载免费的PDF全文 |
|
