STRATOSPHERIC TROPOSPHERIC EXCHANGE AFFECTING THE NORTHERN WETLANDS REGIONS OF CANADA DURING SUMMER 1990/

The Arctic Boundary Layer Expedition (ABLE) 3B was conducted over the northern wetlands region of Canada during July and August 1990. Severa l stratospheric/tropospheric exchange events were noted by zenith-look ing airborne lidar and in situ measurements of ozone and other trace g as species. Isentropic trajectories and potential vorticity analyses a re utilized to determine the frequency of stratospheric inputs which w ould have affected the tropospheric column over the Moosonee and Schef ferville regions and to describe the favored pathways of transport of stratospheric air arriving at these locations. At the 310 K potential temperature level (middle troposphere), trajectories having ''aged str atospheric'' values of potential vorticity at some point in their 5-da y history arrived at Moosonee or Schefferville roughly 40% of the time during the ABLE 3B study period, most often via large-scale subsidenc e enroute from ''stratospheric input regions'' over the Arctic Ocean o r northern and central Canada. At 325 K (upper troposphere), ''fresh'' stratospheric input was evident on about 80% of the trajectories, mos t often associated with jet streaks within the polar and Arctic jet st reams. A case study is presented which illustrates both of these gener al stratospheric input processes.