Figure 8. NOAA Hazard Management System (HMS) and Smoke Product analysis of smoke (a) 21 Aug 2013 and (b) 30 Aug 2013. Below, three-day backward FLEXPART-WRF trajectories corresponding to each episode is provided (c) 21 Aug 2013 and (d) 30 Aug 2013. Additional trajectories are placed in the data archive at https://tropo.gsfc.nasa.gov/seacions/.
4.5.1. 17-21 August 2013: Evidence of biomass burning advected by a cutoff low
The meteorological map provided in Figure 6a-c indicates biomass burning transported by a cut-off low originating on 17 August 2013 00:00 UTC at 500 hPa over central Missouri. In this case the cut-off low was created by a closed upper-level low pressure system that was cut off from a westerly current (14 August 06:30 UTC) and it began moving independently. The cut-off low remained nearly stationary until 19 August 00:00 UTC, at which time the trough filled in and moved eastward. Due to the nature of the quasi-stationary system, the westerly flow of air propagated the western fire plumes over the central U.S. and southeast U.S. Figure 7a and 7c present a cross section and plane view of the resulting low. Due to the low pressure system the trajectory analysis indicated that smoke flowed from various fire locations to the St. Louis area (see Figure 8). Figure 9a-c depicts the vertical ozone and meteorological profiles representative of this time period (21 August). Refer to Figure 2 for corresponding ozonesonde curtain plots.