The AEROCE'96 Springtime Intensive sought to quantify the sources of tropospheric ozone and other trace gases transported to the western North Atlantic Ocean atmosphere. The month-long investigation utilized near-daily ozonesondes launched from Purdue University, IN; Charlottesville, VA; and Bermuda. The Wyoming King Air flew several missions, and a fully instrumented tower on Bermuda made continuous chemical measurements in the marine boundary layer. Stratospheric ozone intrusions were observed behind 8 cold fronts over the eastern U.S. throughout the month of the intensive, several of these fronts subsequently penetrated to the latitude of Bermuda. Here we investigate the temporal and spatial evolution of a particularly strong tropopause fold which traversed the eastern United States on April 30. The fold was defined by a strong polar jet, and was clearly identified by a gradient of isentropic potential vorticity in the upper troposphere and a region where surfaces of constant potential temperature crossed from the polar stratosphere into the subtropical troposphere. Positioned behind the surface cold front and associated with a synoptic scale upper-level long-wave trough, the fold was clearly visible in GOES-8 water vapor imagery as a band of dry air in the mid- to upper troposphere. Over a 60 hour period, ozone increased in the mid- to upper troposphere as the fold passed over Purdue and Charlottesville. A Charlottesville ozonesonde was timed to fly into the leading edge of the fold at 2200 UTC, April 30, revealing two ozone laminae of 120 ppb in the mid troposphere. Twelve hours later a layer of enhanced ozone (150 ppb) was still present over Charlottesville. An ozonesonde from Wallops Island, VA (1400 UTC) and aircraft measurements off the coast of New Jersey (1800 UTC) showed this enhancement extended nearly 850 km east of Charlottesville, becoming diluted over space and time. Back trajectories and atmospheric cross sections are utilized to discern the origin and structure of the tropopause fold, and to estimate the amount of ozone exchanged. In addition to being a source for mid tropospheric ozone, this event was also significant because the associated surface system that developed in conjunction with the upper-level trough lofted polluted boundary layer air rich in CO and NOy from the Midwest. Satellite imagery indicates rapid transport of this air to the lower-troposphere over Bermuda on April 28, two days before the tropopause fold traversed the eastern U.S
Symposium on Interdisciplinary Issues in Atmospheric Chemistry