HR: 08:00h
AN: A51C-01    [PDF]
TI: Evidence of Deep Convective Transport of Reactive Constituents to the Tropical Tropopause Layer Using Convective Influence Calculations
AU: * Selkirk, H B
EM: hselkirk@mail.arc.nasa.gov
AF: Bay Area Environmental Research Institute, NASA-Ames Research Center, M/S 245-5, Moffett Field, CA 94035-1000 United States
AU: Pfister, L
EM: pfister@mindego.arc.nasa.gov
AF: NASA-Ames Research Center, M/S 245-5, Moffett Field, CA 94035-1000 United States
AU: Ridley, B A
EM: ridley@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Atlas, E
EM: atlas@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AB: Isentropic convective influence calculations are performed to identify upstream convective systems impacting air sampled just below the subtropical and tropical tropopause on a flight of the NASA WB-57F from Houston, Texas south to 5$\deg$N during the September 1999 airborne mission Atmospheric Chemistry of Combustion Effects Near the Tropopause (ACCENT). Interpretation of ensembles of in situ tracer measurements, in particular NO$_{y}$, O$_{3}$, and CH$_{3}$I, have indicated that much of the air sampled on this flight had been recently injected by deep convection, although from non-pristine marine boundary layers. In addition there were more limited stretches of the flight track with evidence of biomass burning and industrial sources. Consistent with this finding, convective influence calculations indicate that the great majority of the parcels along the flight track had been affected by deep convective events at some time in the seven days preceding the flight; the majority of these were oceanic systems. Under the anticyclonic upper tropospheric flow pattern prevailing north of $\sim$11$\deg$N, the marine convective influence came from systems in the Gulf of Mexico, around Cuba and over the waters east of the Bahamas. Influence from continental systems was sporadic except for one extended portion of the track with air that the calculations indicated had been injected by land-based systems over Guatemala within the previous 12-24 hours. South of $\sim$11$\deg$N, a group of systems east of the Lesser Antilles were major contributors of marine influence. However, as the aircraft approached its turnaround at 5$\deg$N, the calculations also show influence from land-based systems over Colombia, consistent with the tracer measurements. One important feature of the results is that the convective influence over the course of the 2600-km flight track is derived from a relatively small number of systems. This is a direct result of the minimal dispersion of the trajectories, particularly those emanating from the marine systems. This can be understand as a consequence of the weak shears in this anticyclonic, summer hemisphere circulation and suggests that, in the tropical troposphere layer at least, the tracer profiles of individual air masses are likely to persist far longer than in the dynamical rough and tumble near the jet streams and other more strongly sheared or vertically mixed environments.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting