A Multiscale Dynamics Diagnosis Of The Stratospheric Sudden Warming In The Winter Of 2012~2013

Using a newly developed analysis tool, multiscale window transform (MWT),and the MWT-based localized multiscale energetics analysis, the January 2013 stratospheric sudden warming (SSW) is diagnosed for an understanding of the underlying dynamics. The fields are first reconstructed onto three scale windows, i.e.,mean window, sudden warming window or SSW window, and synoptic window.According to the reconstructions the major warming period may be divided into three stages, namely, the stages of rapid warming, maintenance, and decay, each with different controlling dynamics. It is found that the explosive growth of temperature in the rapid warming stage (December 28 - January 10) results from the collaboration of a strong poleward heat flux and canonical transfers through baroclinic instabilities in the polar region, which extract available potential energy(APE) from the mean-scale reservoir. In the course, a significant portion of the acquired APE is converted to and stored in the SSW-scale kinetic energy (KE),leading to a reversal of the polar night jet. In the stage of maintenance (January 11-25), the mechanism for the warming is completely different: First the previously converted energy stored in the SSW-scale KE is converted back, and most importantly in this time a strong barotropic instability happens over Alaska,which extracts the mean-scale KE to maintain the high temperature, while the mean-scale KE is mostly from the troposphere, in conformity with the classical paradigm of mean flow-wave interaction with the upward propagating planetary waves.Afterwards, the warming decays and the system resumes to its normal state.