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Age of Air and the Circulation of the Stratosphere

Marianna Linz, Ph.D., 2017
Alan Plumb, Advisor

The circulation of air in the stratosphere is important for the distribution of radiatively important trace gases, such as ozone and water vapor, and other chemical species. Age of air is an idealized tracer with unique mathematical properties, which we exploit to derive a theory for the relationship of tracer observations to the stratospheric circulation. We show that the meridional age difference is a measure of the global diabatic circulation, the total overturning strength through an isentropic surface, and apply the theory to satellite data to derive the first observationally-based estimates of the global meridional overturning circulation strength at all levels in the stratosphere.  To understand the relationship between the diabatic circulation and other metrics of the circulation, we calculate it in a state-of-the-science atmospheric model and in three different reanalysis data products. The global diabatic circulation covaries with one typical circulation metric, and it is correlated with total column ozone. We develop a metric for the adiabatic mixing, showing that it is related to the meridional age difference and the vertical gradient of age. A picture of global average stratospheric circulation could thus be obtained using age of air data, given reliable long-term records.