Chasing the Outflow

by Frank Flocke (NCAR/ACD)

Late last week we took advantage of the chance to do our first outflow chasing flight. One of the science goals for DC3 is to assess the impact of deep convection on the upper tropospheric chemistry and composition. Since the air continues to be photo-chemically processed (during the day) as well as mixed with surrounding air as it is transported away, it is important to try and sample the air again the following day to see how it has changed and whether we can explain these changes with what we know about the processes in the upper troposphere.

NSF/NCAR GV sampling outflow during RF04 over Oklahoma. Photo by Chris Cantrell.

Friday, May 25 & Saturday, May 26 presented the chance to do that. We had flown an isolated, large area of convection on Friday over Oklahoma. Extensive sampling of the storm outflow at around 11-12 km altitude had given us a pretty good idea what the air mass lofted by the convection looked like. The meteorological and chemical transport models predicted winds in that region of the atmosphere that would transport the air we sampled on Thursday to an area over central Illinois reaching South into western KY/TN, and located at 35,000-40,000 feet altitude. This is an area we can easily reach with our aircraft and the models showed that the air mass was going to be reasonably well defined.

NSF/NCAR GV “bowtie” loops over the central US.

So off we went again on Saturday afternoon to try and find the air over the area predicted by the models. Both aircraft flew large bowtie-shaped patterns centered over southwestern Illinois, aligned slightly differently and flown at different altitudes covering the predicted altitude range of the air mass. Both aircraft were able to sample air that had the chemical signature we would expect from convective influence and the sampled air also was a match with respect to some of the chemical species sampled the day prior. Precise analysis of the data will tell us more about the outcome of this endeavor, but it was likely successful and we can now more confidently plan for the next plume chase in the coming days and weeks.

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