Coupling between leading modes in the troposphere-stratosphere interaction

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Studies about the stratosphere have been performed from the framework of the zonal mean and deviations from it, and their interaction. However, there are many cases that cannot be explained from this framework, and thereby a new framework is needed. It is the framework of time mean (non-uniform zonal field) and deviations from it. The present study is the first comprehensive research from this framework. In particular, no numerical study from this standpoint has been done, therefore this research is the first in the world.Data analyses about the coupling between the troposphere and stratosphere show the followings : The Pacific-North American pettern (PNA) in the troposphere vertically propagates into the stratosphere, causing the wavenumber 1 (W1) pattern. The dominance of the PNA in the troposphere via the excitation of the W1 mode amplifies the annular mode in the stratosphere. In some cases, this coupling causes sudden warmings. These sequences are clearly different from the AO.Next, by using numerical models, we successfully simulate phenomena in which dominant wavenumbers are different between the troposphere and stratosphere. For this success, a non-uniform zonal field is indispensable. Furthermore, the coupling from the PNA in the troposphere via W1 to the AM in the stratosphere can be simulated by a time integration model.We further proceed to the study about the reality of dominant modes in the troposphere. The conclusion is that although the North Atlantic Oscillation (NAO) and PNA are independent, dominant oscillations in the troposphere, the AO apparently appears due to the spatial correlation of the NAO and PNA. This conclusion verifies our approach that the PNA and NAO are treated in the troposphere.The predictability of the sudden warming is also studied. As a result, we show that sudden warmings caused by wavenumbers 2 or 3 are more difficult in their prediction than those caused by wavenumber 1.