Aircraft observations of rapid meridional transport from the tropical tropopause layer into the lowermost stratosphere: Implications for midlatitude ozone

In situ measurements of water vapor, CH₄, and N₂O, acquired aboard the NASA ER-2 aircraft during January-March 2000 in a campaign to survey the Arctic vortex, are used to examine transport into the lowermost stratosphere in the context of middle- and high-latitude ozone declines observed over the last several decades.

Analysis of tracer-tracer correlations of H2O + 2*CH₄ and N₂O indicates that rapid, poleward isentropic transport from the lower tropical stratosphere coupled with diabatic descent between the subtropical and polar jet streams delivers very young air to the high-latitude lowermost stratosphere during winter, while descent of older air from the vortex and subsequent transport to lower latitudes is very limited. From middle to late winter, mixing ratios of H2O + 2*CH₄ decrease by about 1 ppmv immediately outside the vortex, consistent with rapid transport of the winter phase of the seasonal cycle in water vapor to high latitudes from the lower tropical stratosphere.