Atmospheric chemical transport based on high-resolution model-derived winds: A case study

Flight 10 of NASA's Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Exp eriment (SONEX) extended southwest of Lajes, Azores. A variety of chemical signatures was encountered. These signatures are examined in detail, relati ng them to meteorological data from a high-resolution numerical model havin g a horizontal grid spacing of 30 and 90 km with 26 vertical levels. The me teorological output at hourly intervals is used to create backward trajecto ries from the locations of the chemical signatures. Four major categories o f chemical signatures are discussed: stratospheric, lightning, continental pollution, and a mixed chemical layer. The strong stratospheric signal is e ncountered just south of the Azores in a region of depressed tropopause hei ght. Three chemical signatures at different altitudes in the upper troposph ere are attributed to lightning. Backward trajectories from these signature s extend to locations of cloud-to-ground lightning, Specifically, results s how that the trajectories pass over regions of lightning 1-2 days earlier o ver the eastern Gulf of Mexico and off the southeast coast of the United St ates. The lowest leg of the flight exhibits a chemical signature consistent with continental pollution. Trajectories from this signature are found to pass over the highly populated Northeast Corridor of the United States. Sur face-based pollution apparently is lofted to the altitudes of the trajector ies by convective clouds along the East Coast that did not contain lightnin g. Finally, a mixed layer is described. Its chemical signature is intermedi ate to those of lightning and continental pollution. Backward trajectories from this layer pass between the trajectories of the lightning and pollutio n signatures. Thus they likely are impacted by both sources.