SGER: Stratosphere-Troposphere Transfer of the Zonal Angular Momentum Associated with the Global Mass Circulation

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Recent observational studies reveal that changes in the wintertime stratospheric circulation are followed by changes in the troposphere. This apparent downward influence is an active area of research. Under this Small Grant for Exploratory Research (SGER), Cai will investigate the dynamics of troposphere-stratosphere coupling in an unconventional framework, analyzing the mass circulation using the potential temperature as the vertical coordinate. Terms in the zonal mean angular-momentum balance will be calculated from daily analyses. The results will be used to explore the mechanisms responsible for the poleward and downward propagation of angular momentum anomalies in the stratosphere and, as revealed in Cai's recent published work, their equatorward propagation near Earth's surface. The results will provide a preliminary test of Cai's controversial hypothesis that the propagation of these features results from their advection by a global mass circulation that is ultimately driven by heating. Broader impacts of this work are in its potential implication for predictability on extended timescales, since the angular momentum anomalies take about 50 days to propagate in the stratospheres from the tropics to high latitudes, and then opposite signed anomalies take about the same amount of time to propagate in the troposphere from high latitudes to the subtropics. A graduate student and a post-doc will participate in the research.