Mechanisms of ENSO‐forcing of hemispherically symmetric precipitation variability
Mechanisms of ENSO‐forcing of hemispherically symmetric precipitation variability
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DOI：
10.1256/qj.04.96
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发表时间：
2005-04
影响因子：
8.9
通讯作者：
R. Seager;N. Harnik;W. Robinson;Y. Kushnir;M. Ting;Huei-Ping Huang;Jennifer Velez
中科院分区：
文献类型：
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作者：
R. Seager;N. Harnik;W. Robinson;Y. Kushnir;M. Ting;Huei-Ping Huang;Jennifer Velez
北半球冬季和春季厄尔尼诺-南方涛动强迫的降水异常模式具有显著的半球对称性，在中纬度地区具有显著的纬向对称性。对全球降水变率和大气再分析中的水汽收支的观测结果进行了检验，认为纬向对称分量是由副热带急流中的瞬变涡旋和热带强迫变化相互作用造成的。在厄尔尼诺事件期间，两个半球的急流增强，并向赤道方向移动。副热带急流的变化会影响瞬变涡动动量通量和涡动驱动的平均经向环流。在厄尔尼诺事件期间，每个半球中纬度的涡旋驱动上升伴随着低层辐合，并带来降水增加。瞬变涡水汽通量和定常涡水汽通量的这些变化几乎完全相互抵消，总之，不会对纬向平均降水异常有贡献。异常驻波的传播破坏了纬向对称性。较深的阿留申低压周围的气流和太平洋急流的东延为北太平洋东部和美国西海岸的降水增加提供了水汽，而瞬变-涡旋水汽辐合为美国南部的降水增加提供了水汽。在每种情况下，降水增加从根本上都是由异常热通量和涡度通量强迫的异常上升造成的。版权所有(C)2005皇家气象学会
The patterns of precipitation anomalies forced by the El Niño–Southern Oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and, in the midlatitudes, have a prominent zonally symmetric component. Observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically‐forced changes in the subtropical jets. During El Niño events the jets strengthen in each hemisphere and shift equatorward. Changes in the subtropical jet influence the transient‐eddy momentum fluxes and the eddy‐driven mean meridional circulation. During El Niño events, eddy‐driven ascent in the midlatitudes of each hemisphere is accompanied by low‐level convergence and brings increased precipitation. These changes in the transient‐eddy and stationary‐eddy moisture fluxes almost exactly cancel each other and, in sum, do not contribute to the zonal‐mean precipitation anomalies. Propagation of anomalous stationary waves disrupts the zonal symmetry. Flow around the deeper Aleutian Low and the eastward extension of the Pacific jet stream supply the moisture for increased precipitation over the eastern North Pacific and the western seaboard of the United States, while transient‐eddy moisture convergence supplies the moisture for increased precipitation over the southern United States. In each case, increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes. Copyright © 2005 Royal Meteorological Society