Wednesday, 25 January 2017
4E (Washington State Convention Center )
Stratosphere-troposphere exchange (STE) influences tropospheric column ozone (O3) significantly, and quantifying its contribution to surface O3 is crucial within the context of understanding the impacts of ozone precursor emission reductions. Here, the online coupled WRF-Chem model is used to simulate O3 during FRAPPE (Front Range Air Pollution and Photochemistry Experiment), July-August, 2014. Continetal scale (12km resolution) and regional scale (4km resolution) simulations were performed using 4 different strategies for O3 lateral boundary and initial conditions (BC/IC). Aircraft, ozonesonde, tower and surface data from FRAPPE are used for evaluation. The case using a simple climatological profile demonstrates that model O3 biases within the boundary layer (BL) are highly correlated with biases well above the BL introduced by the IC/BCs. When IC/BCs are specified according to the larger scale global model or the O3 derived from data assimilation within NWS/NCEP Global Forecast System, overall statistics show little bias, but transient multi-day features in observed upper level O3 are not well reproduced. The case with upper level IC/BCs partitioned according to potential vorticity (PV) allows O3 to be specified according to finer scale thermodynamic properties associated with STE. Resolved features as small as 80km horizontally and 2 km vertically demonstrate effective downward transport of O3 from intrusion events, O3 laminae over the western U.S., and helps explain some of the transient features observed in the upper-level O3 observations. The exchange between upper-level and BL O3 within the context of terrain induced wave forcing within the model is also discussed.
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