Evidence from aircraft field campaigns over the past 20 years showing the ubiquity of stratospheric intrusions (SIs) reaching deep into the free troposphere throughout the subtropics and mid-latitudes. Aircraft-based estimates attribute a quarter of the summertime mid-latitude tropospheric ozone budget to such events. SIs even have the power to influence atmospheric composition near the surface, particularly in the western United States. Despite their importance, SIs remain extremely challenging to model, both at regional and global scales. Regional models often struggle with representing the large scale environmental conditions associated with SIs, while global models have typically been run at coarse resolutions which do not adequately represent the chemical and composition effects in the lower troposphere. New capabilities make it feasible for global simulations of with horizontal resolutions of 25-50 km, enabling accurate determination of SI impacts on tropospheric composition and improved simulation of trace gas gradients in the upper troposphere/lower stratosphere. This seminar will highlight work from NASA’s Goddard Earth Observing System (GEOS) model that sheds new light on the frequency of SIs and their impacts throughout the troposphere. This will include examples of how SIs manifest in NASA aircraft field campaigns and satellite observations, as well as a discussion of implications for air quality forecasting and our understanding of carbon sources and sinks.