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. We use the Specified Dynamics version of the Whole Atmosphere Community Climate Model Extended (SD-WACCMX) tomodel the descent of nitric oxide (NO) and other mesospheric tracers in the extended, elevated stratopausephase of the 2013 sudden stratospheric warming (SSW). The dynamics are specified with a high-altitude version of the Navy Global Environmental Model (NAVGEM-HA). Consistent with our earlier published results, we find that using a high-altitude meteorological analysis to nudge WACCMX allows for a realistic simulation of the descentof lower-thermospheric nitric oxide down to the lower mesosphere, near 60 km. This is important because these simulations only included auroral electrons and did not consider additional sources of NO from higher-energyparticles that might directlyproduce ionization, and hence nitric oxide, below 80–85 km. This suggests that theso-called energetic particleprecipitation indirect effect (EPP-IE) can be accurately simulated, at least in years of low geomagneticactivity, such as 2013, without the need for additional NO production, provided the meteorology is accuratelyconstrained. Despite the general success of WACCMX in bringing upper-mesospheric NO down to 55–60 km, a detailed comparisonof the WACCMX fields with the analyzed NAVGEM-HA H2O and satellite NO and H2O data from the SolarOccultation for Ice Experiment (SOFIE) and the Atmospheric Chemistry Experiment-Fourier TransformSpectrometer (ACE-FTS)reveals significant differences in the latitudinal and longitudinal distributionsat lower altitudes.This stems from the tendency for WACCMX descent to maximize at sub-polar latitudes, and while such sub-polar descent is seen in the NAVGEM-HA analysis, it is more transient than in the WACCMX simulation. These differencesare linked to differences in the transformed Eulerian mean (TEM) circulation between NAVGEM-HA and WACCMX, most likely arising from differences in how gravity wave forcing is represented.To attempt to compensate for the differing distributionsof model vs. observed NO and to enable us to quantify the total amount of upper-atmospheric NO delivered to the stratopause region, we use potential vorticity and equivalent latitude coordinates.Preliminary results suggest both model and observations are generally consistent with NO totalsin the range of 0.1–0.25 gigamoles (GM).

atmospheric chemistry and physics

Two- and three-dimensional structures of the descent of mesospheric trace constituents after the 2013 sudden stratospheric warming elevated stratopause event