Wave Activity Budget and the Variabilities of the Extratropical Climate

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Upper-level weather charts typically show large-scale wave patterns which are closely associated with the surface fronts, cyclones, and anticyclones that make up daily weather in the middle latitudes. The movements of these waves, and the surface weather patterns connected to them, is driven in large measure by the mean westerly jet streams along which they propagate. The mean jet streams are in turn strongly affected by the behavior of the waves, thus the topic of wave-mean flow interaction is essential for understanding and predicting midlatitude weather. Classical wave-mean flow interaction theory offers powerful insights, but it is based on linear wave dynamics and thus is only formally valid for small amplitude, or infinitesimal, waves. This is a substantial limitation given the waviness of the real-world atmosphere, and the PI has devoted considerable effort to the development of a more general theory which holds for waves of finite amplitude (see AGS-1151790 and AGS-0750916). The present work applies this theory to several topics in atmospheric dynamics, including the 20-30 day oscillation found in the eddy kinetic energy of the Southern Hemisphere storm track (see AGS-1343080). Preliminary work suggests that the oscillation satisfy a wave action conservation relationship and the periodicity is related to wave-induced poleward surface heat flux. Another topic is the dynamics of atmospheric blocking episodes, and a localized version of the wave-mean flow framework is developed to address this problem. Other topics include the roles of boundary layer damping and condensational heating in wave-mean flow interaction. The work is conducted through a combination of analysis of meteorological data (from reanalysis products) and simulations with various configurations of the Community Atmosphere Model (the atmospheric component model of the Community Earth System Model).The work has broader impacts in both a scientific and societal sense, as the conceptual framework developed by the PI can be used by researchers to study a variety of phenomena related to climate variability and change. Further downstream the improved understanding provided by the framework can benefit weather prediction on monthly to seasonal timescales and contribute to better understanding of the results of future climate projections used for decision support. Beyond the benefits of the research itself, the project supports education through a summer school on atmospheric dynamics attended by about 30 graduate students and early career scientists. The summer school includes a combination of lectures, demonstrations, and hands-on activities. In addition, the project supports a graduate student and a postdoc, thereby training the next -generation workforce in this research area.