Dynamics of eddy-driven North Atlantic Oscillations in a localized shifting jet: zonal structure and downstream blocking |
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Authors: | Dehai Luo Wen Zhou Ke Wei |
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Institution: | (1) College of Physical and Environmental Oceanography, Ocean University of China, 266003 Qingdao, China;(2) CityU-IAP Laboratory for Atmospheric Sciences, Department of Physics and Material Sciences, City University of Hong Kong, Hong Kong, China;(3) Center for Monsoon System Research, IAP, Chinese Academy of Science, Beijing, China |
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Abstract: | In a weakly nonlinear model how an initial dipole mode develops to the North Atlantic Oscillation (NAO) in a localized shifting
jet under the prescribed eddy forcing is examined. It is found that the zonal structure of the eddy-driven NAO anomaly is
not only dominated by the longitudinal distribution of the preexisting Atlantic storm track, but also by the initial condition
of the NAO anomaly itself associated with the interaction between a localized shifting jet and a topographic standing wave
over the Atlantic basin. When both the initial NAO anomaly and the eddy vorticity forcing in the prior Atlantic storm track
are more zonally localized, the subsequent eddy-driven NAO anomaly can be more zonally isolated and asymmetric. But, it seems
that the shape of the initial NAO anomaly associated with the latitudinal shift of a prior Atlantic jet plays a more important
role in producing the zonal asymmetry of subsequent NAO patterns. The zonal asymmetry of the NAO anomaly can be enhanced as
the height of topography increases. In addition, it is further found that blocking events occur easily over the Europe continent
through the decaying of positive-phase NAO events. However, prior to the positive-phase NAO life cycle the variability in
each of three factors: the Atlantic jet, the eddy vorticity forcing in the Atlantic storm track and the initial NAO anomaly
can result in a variation in the blocking activity over the Europe sector in strength, duration, position and pattern. |
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Keywords: | |
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