Estimates of the seasonal cycle of mass and ozone transport at high northern latitudes

Zonally averaged transport of mass and ozone into high northern latitudes e xhibits a pronounced annual cycle. During summer, downwelling is at a minim um, and horizontal bulk advection and eddy fluxes of ozone and mass are fou nd to be significant. This study examines in detail the ozone budget betwee n 58 and 67 kPa in a meridional annulus ranging from 60 degrees to 70 degre es N during summer. The area of the study was chosen to correspond with the Photochemistry of Ozone Loss in the Arctic Region in Summer high-altitude aircraft experiment based in Fairbanks, Alaska, from April to September, 19 97. It is found that the seasonal cycle in transport is an important contri butor to the resultant seasonal march of ozone at high latitudes. The horiz ontal eddy contribution to the ozone tendency at high latitudes in the lowe r stratosphere is found to be large and negative (reducing ozone) during mi ddle and late summer, where it more than offsets the increasing ozone tende ncy due to advection by the residual circulation. During early summer, the high-latitude air mass appears to be relatively isolated, with in situ chem ical processes driving the ozone tendency.