Planetary Wave Breaking in the Polar Winter Middle Atmosphere and Extreme Temperature Event
We investigate the dynamical mechanisms responsible for USLM disturbances using the above mentioned observations in addition to model outputs from the Whole Atmosphere Community Climate Model (WACCM4). Results indicate that WACCM reliably reproduces USLM disturbances. Analysis of planetary wave breaking and EP-flux of individual and composite USLM events indicate an increase in breaking near the 0.1 hPa level, approximately 10 km above the extreme thermal anomaly at the stratopause in the days leading up to the peak of the event. Vertical coupling of the atmosphere during this event is illustrated in the progression of these events and their impact on the thermal structure, zonal mean wind, polar vortex and conditions that have the potential to support a secondary baroclinic instability (including the Charney-Stern criteria for instability the role of baroclinic/barotropic instabilities). In addition, USLM disturbances appear to have front-like behavior analogous to the troposphere. Broader impacts of these disturbances and the dynamics associated with them influence gravity wave generation/propagation, vertical air motion, chemical tracer transport, precondition of the atmosphere for SSWs and the potential to couple with the thermosphere through tides.