Atmosphere Ocean Science Colloquium

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Large-Scale Tropospheric Transport: Constraints from Models and Observations

Speaker: Clara Orbe, NASA

Location: Warren Weaver Hall 1302

Date: Wednesday, November 15, 2017, 3:30 p.m.

Synopsis:

The transport of chemicals is a major uncertainty in the modeling of tropospheric composition. A natural way to quantify tropospheric transport is in terms of the distribution of transit times from the Northern Hemisphere (NH) midlatitude surface, where various greenhouse gases and ozone-depleting substances are emitted. Here, we show that the transit-time distribution (TTD), or more generally the Green's function of the transport operator, is characterized by mean transit times or “mean ages” that are significantly larger than their corresponding modal transit times. We show that this behavior holds for flows simulated by a hierarchy of models, ranging from an idealized dry dynamical core to a comprehensive atmospheric general circulation model. Idealized loss and mean age tracers are then used to constrain different TTD timescales both from observations (e.g. sulfur hexafluoride and chlorofluorocarbons) and from a broad range of models participating in the Chemistry Climate Modeling Initiative. A comparison among simulations using the Goddard Earth Observing System Chemistry Climate Model and the Whole Atmosphere Community Climate Model, wherein the large-scale flow is constrained to reanalysis meteorology, reveals large (~30-40%) differences in interhemispheric transport that are related to large differences in parameterized convection over the oceans. Our results indicate that more attention needs to focus on convective parameterizations in models and the methods by which they are applied in simulations using analyzed winds.