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This study updates a body of literature that aims to separate atmospheric disturbances into standing and traveling zonal wave components. Classical wavenumber-frequency analysis decomposes longitude- and time-dependent signals into contributions from distinct spatial and temporal scales. Here, an additional decomposition of the spectrum into standing and traveling components is described. Previous methods decompose the power spectrum into standing and traveling parts with no explicit allowance for covariance between the two. This study provides a simple method to calculate the variance of each of these components and the covariance between them. It is shown that this covariance is typically a significant portion of the variance of the total signal. The approach also preserves phase information and allows for the reconstruction of the real-space standing and traveling components. The technique is applied to reanalysis wintertime geopotential height anomalies in the Northern Hemisphere in order to investigate planetary wave interference effects in stratosphere-troposphere coupling. The results show that for planetary waves 1-3, standing waves explain the largest portion of the variance at low frequencies. An exception is for wave 1 in the high-latitude troposphere, where there is a strong westward-traveling wave. Furthermore, the antinodes of the standing waves have preferred longitudes that tend to align with the extremes of the climatological wave, suggesting that standing waves contribute to a linear interference effect that has been shown to be an important part of stratosphere-troposphere interactions. [ABSTRACT FROM AUTHOR]

An exceptionally strong stratospheric sudden warming (SSW) that spontaneously occurs in a very simple stratosphere–troposphere AGCM is discussed. The model is a dry, hydrostatic, primitive equation model without planetary stationary waves. Transient baroclinic wave–wave interaction in the troposphere thus provides the only source of upward-propagating wave activity into the stratosphere. The model’s SSW is grossly similar to the Southern Hemisphere major SSW of 2002: it occurs after weaker warmings “precondition” the polar vortex for breaking, it involves a split of the polar vortex, and it has a downward-propagating signature. These similarities suggest that the Southern Hemisphere SSW of 2002 might itself have been caused by transient baroclinic wave–wave interaction. The simple model used for this study also provides some insight into how often such extreme events might occur. The frequency distribution of SSWs in the model has exponential, as opposed to Gaussian, tails. This suggests that very large amplitude SSWs, though rare, might occur with higher frequency than might be naively expected. [ABSTRACT FROM AUTHOR]