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Global modeling and assimilation

A GEOS-5 simulation of a stratospheric intrusion that affected
several western states on April 6 and 7, 2012.
Credit: NASA GSFC/GMAO

In collaboration with meteorologists and atmospheric scientists at NASA’s Goddard Space Flight Center, SSAI atmospheric scientists are conducting leading-edge simulations of the chemical composition of the troposphere and stratosphere with the Goddard Earth Observing System Model, Version 5 (GEOS-5). Recent improvements implemented by SSAI’s team of software developers have enabled GEOS-5, with its comprehensive stratosphere-troposphere chemistry module, to be run at spatial resolutions down to 25 kilometers. This capability allows researchers to simulate and study the movement and chemical evolution of dozens of trace gases, such as ozone, carbon monoxide, and volatile organic compounds, in finer detail than heretofore possible, and to generate chemical signatures of important transient weather events, including tropical storms and, as described here, stratospheric intrusions.

The animation illustrates GEOS-5’s replication of stratospheric intrusions over the United States in 2012.¬† The most spectacular event peaked in April, when ozone in the intrusion was, in fact, detected by the ground ozone observation network. GEOS-5 shows how filaments of stratospheric air are stretched and twisted by sheared wind fields, and are eventually mixed or dispersed into surrounding tropospheric air.

Successfully simulating the intrusions is important because it demonstrates that GEOS-5 has the potential to illuminate the complex dynamics of intrusions, and to support new and more accurate studies of their frequency and how they contribute to the ozone budget of the troposphere. GEOS-5 emerges as an additional tool to help air quality officials demonstrate when intrusions, rather than local pollution, are the cause of surface ozone concentrations that exceed EPA standards. SSAI is also helping to explore the efficacy of forecasting stratospheric intrusions, with the objective of developing a prototype of an operational product in GEOS-5.