摘要
利用西风波导结构以及波作用通量,探讨了夏季欧亚一类中高纬持续异常环流所对应的Rossby波的能量频散特征。中高纬度对流层上层存在结构较为复杂的弱波导,Rossby波能量频散过程基本上与该弱波导结构一致。Rossby波传播特征在不同时期以及两种环流型(E型和C型)之间存在显著差异:(1)在梅雨前期,与E型环流对应,Rossby波从南欧气旋式异常环流中心传播到乌拉尔山正高度异常中心,并且波作用通量在乌拉尔山西侧辐合,形成该地区正高度异常环流。乌拉尔山持续异常中心东侧重新激发出Rossby波,并传播至贝加尔湖和鄂霍次克海地区,维持对应的异常环流。与C型异常环流对应,Rossby波活动非常活跃。该型三个活动中心呈现高纬-中纬-高纬的分布特征,这与波导结构密切相关。(2)在梅雨期,Rossby波的传播对两类持续异常环流的作用更加明显,其传播路径基本上在处于极区和偏向中纬度一侧的两个"波障碍区"之间的带状西风波导区中。Rossby波从乌拉尔山活动中心向东传播,最终形成贝加尔湖和鄂霍次克海地区的持续异常环流。在C型维持过程中则还存在另一种强迫因子。在C型中,Rossby波从乌拉尔山活动中心向中纬度传播,并在亚洲急流中向东传播至东亚地区。(3)在后汛期,在欧亚大陆上纬向"波障碍区"的增加使得Rossby波活动减弱。E型异常环流型的鄂霍次克海活动中心向东扩展到北太平洋,但来自上游的Rossby波传播只作用于该活动中心的西北侧部分。C型中Rossby波的传播在乌拉尔山活动中心地区变弱。在夏季各个时期,E和C型持续异常环流对应着不同位相的EAP(或PJ)型,但并没有Rossby波从中纬度向北传播至鄂霍次克海地区的现象。
The energy dispersion feature of the Rossby wave in association with the summertime persistent anomaly events of mid- and high-latitude Eurasia is investigated in terms of the westerly waveguide structure and a wave-activity flux. In the upper troposphere, there is a weak waveguide with a complicated structure over the mid-high latitude region, and it is basically consistent with the Rossby wave propagation in this region. The characteristics of Rossby wave propagation, however, are significantly different in different periods of summertime and between different persistent anomaly circulations, i. e. , E- and C-type circulations. （1） In the pre- Meiyu period, for the E-type circulation, Rossby waves propagate from southern Europe to the Urals, acting to maintain the positive height anomaly circulation over the Urals. The Rossby wave emanates again from the eastern side of the Urals and propagetes to Lake Baikal and the Sea of Okhotsk region, which is responsible for the mainte- nance of the corresponding height anomalies. For the C-type circulation, the Rossby wave is very active and the distribution of the corresponding height anomaly centers shows a geographical location of high- mid - high latitudes, respectively, consistent with the Rossby wave propagation and waveguide structue. （2） In the Meryu period, the impact of the Rossby wave propagation on the persistent anomaly circulations becomes even more important. The Rossby wave propagation is consistent with a zonally elongated westerly waveguide, which is embeded between two wave barriers, one over the polar side and the other over the mid-latitude side. Rossby wave propagation connects three anomalous centers of action of E- and C-type circulations. Another forcing mechanism is also partly responsible for the maintenance of C-type circulation. During this period, the Rossby wave propagates from the center of action aroud the Urals to the mid-latitude region, then continues to propagate along the Asian jet stream. （3） In the post- Meiyu period, due to the increased zonally elongated wave barrier regions over Eurasia, the Rossby wave propaga- tion becomes weak. In the E-type circulation, the center of action aroud the Sea of Okhotsk extends to the North Pacific, but the incoming Rossby wave only reaches the northwestern portion of this center of action. In the C-type circulation, the center of action aroud the Urals corresponds to a relatively weak Rossby wave propagation. Finally, the authors find that during different periods of summertime the EAP （or PJ） pattern in its different phases accompanies the E- and C-type circulations. However, it is not find that Rossby waves propagate from the mid-latitude region to the high-latitude region around the Sea of Okhotsk.
出处
《大气科学》
CSCD
北大核心
2008年第3期615-628,共14页
Chinese Journal of Atmospheric Sciences
基金
国家重点基础研究发展规划项目2006CB403601
国家自然科学基金资助项目40523001、40575024
