The role of wave cyclones in the vertical transport of lower tropospheric air during the spring 2001 NASA /TRACE -P experiment

Transport of air from low altitudes to the free troposphere by cyclones during NASA's TRAnsport and Chemical Evolution over the Pacific (TRACE-P) experiment is investigated. Airstreams responsible for lower tropospheric venting are diagnosed using results from a high-resolution meteorological model (MM5) together with in situ and remotely sensed chemical data. Hourly wind data from the MM5 are used to calculate 3-D grids of backward air trajectories. A reverse domain filling (RDF) technique then is employed to examine the Lagrangian characteristics of airstreams over the computational domain, and to isolate airstreams ascending from below 850 hPa to the free troposphere during the previous 36-hours. Two cases are examined in detail.;Results show that airstreams originating at low altitudes differ considerably from those described by classic conceptual models and in the recent literature. In addition, airstreams sampled by the TRACE-P aircraft are found to exhibit large variability in chemical concentrations. This variability is due to differences in the altitude histories of individual airstreams with respect to anthropogenic sources over continental Asia and Japan. Complex interactions between successive wave cyclones also are found to be important features determining the chemical composition of the airstreams. Particularly important is the process of post-cold frontal polluted air being rapidly transported offshore and recirculated into ascending airstreams of upstream cyclones.