[PAOCQ] Marianna Linz (Harvard)

“A Variety of Perspectives on Stratospheric Mixing”

The global stratospheric circulation can be separated into two parts: a slower component in which air rises in the tropics and sinks in the mid- to high latitudes, and a faster component with rapid quasi-horizontal exchange of air between lower and higher latitudes. This second component, the horizontal mixing, is critical for the distribution of trace gases and the spread of aerosols from volcanoes or wildfires. The balance between horizontal mixing and downwelling from above also sets the ozone concentrations in the extratropical lower stratosphere, where air is transported into the troposphere and affects atmospheric chemistry and radiative forcing. The horizontal mixing component varies substantially across different chemistry climate models, and comparing with observations is a challenge. I will present a variety of perspectives on stratospheric mixing, including Lagrangian and Eulerian metrics. The different methods are complimentary, and I will use them to show the vertical and seasonal structure of stratospheric mixing. I will then present a comparison of stratospheric mixing across different generations of chemistry climate models, and where possible, the comparison with observations or reanalysis products as well. Over time, models have improved in their agreement both with each other and with observations, though improvements are modest.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

Contact: paoc-colloquium-comm@mit.edu