In this paper,features for the evolution of the East Asia/Pacific(EAP) events and their association with high-and mid-latitude Rossby waves during the Meiyu period are analyzed on the medium-range time scale.It is sho...In this paper,features for the evolution of the East Asia/Pacific(EAP) events and their association with high-and mid-latitude Rossby waves during the Meiyu period are analyzed on the medium-range time scale.It is shown that life cycles of the positive and negative EAP events cannot be simply regarded as "mirror" each other.In the upper troposphere,downward propagations of Rossby wave packets both over high-and mid-latitude regions of Eurasian continent and over the Asian jet region are responsible for generating basic patterns of high-and mid-latitude anomaly centers of the events.In this layer,Rossby wave packets also propagate from the mid-latitude anomaly center to the high-latitude one.In the middle and lower troposphere,the formation of the subtropical anomaly center of the event is mainly attributed to the anomalous convective activity in the tropical Pacific warm pool.The northward Rossby wave energy dispersion from this center is favorable to the enhancement and maintenance of the mid-latitude anomaly center in the same layer.Finally,it might be hypothesized that typical features of the positive and negative EAP events in their mature phase result from the interaction between(or phase-locking of) respective anomalous circulations induced both by quasi-zonal Rossby wave packets embedded in upper troposphere westerly and by quasi-meridional Rossby wave packets in the background flow of the East Asian summer monsoon in the middle and lower troposphere.展开更多
Based on the NCEP DOE AMIP II daily reanalysis data （1979-2005）, the evolution of the East Asia/Pacific （EAP） teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time s...Based on the NCEP DOE AMIP II daily reanalysis data （1979-2005）, the evolution of the East Asia/Pacific （EAP） teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as ＂mirrors＂ to each other with simply reversed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern significantly affects the rainfall over the region south of the Yangtze River. The positive （negative） EAP pattern tends to cause positive （negative） precipitation anomalies in that region. This is different from the earlier research findings based on monthly mean data.展开更多
基金Supported jointly by the 973 Project (Grant No. 2006CB403601)the National Natural Science Foundation of China (Grant Nos. 40523001 and 40575024)
文摘In this paper,features for the evolution of the East Asia/Pacific(EAP) events and their association with high-and mid-latitude Rossby waves during the Meiyu period are analyzed on the medium-range time scale.It is shown that life cycles of the positive and negative EAP events cannot be simply regarded as "mirror" each other.In the upper troposphere,downward propagations of Rossby wave packets both over high-and mid-latitude regions of Eurasian continent and over the Asian jet region are responsible for generating basic patterns of high-and mid-latitude anomaly centers of the events.In this layer,Rossby wave packets also propagate from the mid-latitude anomaly center to the high-latitude one.In the middle and lower troposphere,the formation of the subtropical anomaly center of the event is mainly attributed to the anomalous convective activity in the tropical Pacific warm pool.The northward Rossby wave energy dispersion from this center is favorable to the enhancement and maintenance of the mid-latitude anomaly center in the same layer.Finally,it might be hypothesized that typical features of the positive and negative EAP events in their mature phase result from the interaction between(or phase-locking of) respective anomalous circulations induced both by quasi-zonal Rossby wave packets embedded in upper troposphere westerly and by quasi-meridional Rossby wave packets in the background flow of the East Asian summer monsoon in the middle and lower troposphere.
基金Supported jointly by the 973 Project under Grant No. 2006CB403601the National Natural Science Foundation of Chinaunder Grant Nos. 40523001 and 40575024
文摘Based on the NCEP DOE AMIP II daily reanalysis data （1979-2005）, the evolution of the East Asia/Pacific （EAP） teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as ＂mirrors＂ to each other with simply reversed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern significantly affects the rainfall over the region south of the Yangtze River. The positive （negative） EAP pattern tends to cause positive （negative） precipitation anomalies in that region. This is different from the earlier research findings based on monthly mean data.
