IMPLICATIONS OF 3-DIMENSIONAL TRACER STUDIES FOR 2-DIMENSIONAL ASSESSMENTS OF THE IMPACT OF SUPERSONIC AIRCRAFT ON STRATOSPHERIC OZONE

A two-dimensional (2D) model, which uses a residual circulation and di ffusion, and a three-dimensional (3D) model, which uses winds from a s tratospheric data assimilation system, have been used to estimate the transport and dispersion of aircraft exhaust (tracer) in the lower str atosphere. Four month calculations using the 2D model with tracer inje cted continuously between 40-degrees - 50-degrees north and south lati tudes are compared with similar 3D calculations for the same time peri od. The seasonal behavior of the tracer fields in the two models is si milar. The zonal mean of the 3D tracer distribution resembles the 2D d istribution when the 2D calculation uses a residual circulation derive d from the assimilated wind fields, but the 3D distribution indicates more rapid vertical mixing. The similarity of the 2D and 3D tracer dis tributions suggests the similarity of the seasonal mean mass transport in both models. However, there is a significant difference in the pla cement of stratosphere/troposphere exchange in the two models. In the 2D model, tracer transport to the troposphere takes place mostly at hi gh latitudes. In the 3D model, most tracer transport takes place at mi ddle latitudes, and is clearly associated with synoptic scale events. This may be particularly important to assessment calculations, as the pollutant source is mostly in middle latitudes. The 3D model is also u sed to consider the buildup of tracer in oceanic flight corridors. Nor th Atlantic (Boston-London), north Pacific (Los Angeles - Tokyo) and t ropical (Los Angeles-Sydney) corridors are considered. For northern he misphere winter, the tracer distributions remain zonally asymmetric. T he tracer from Boston-London is largely excluded from the Aleutian ant i-cyclone, and the tracer from Los Angeles - Tokyo is largely containe d within the anticyclone. The tropical tracer distribution is also asy mmetric; the time scale for zonal mixing is long compared to the time for meridional transport processes due to weak zonal winds. Although m ore of the tracer injected in the tropical corridor is transported to higher altitude than for the other corridors, the transfer of mass fro m the stratosphere to the troposphere is nearly the same for the three corridors. There are no systematic differences that suggest that one corridor is inherently more or less polluting than another.