Tracer‐tracer relationships and lower stratospheric dynamics: CO₂ and N₂O correlations during SPADE

Abstract

Simultaneous measurements of CO 2 and N 2 O from the NASA ER‐2 aircraft during SPADE deployments in November 1992, April/May 1993, and October 1993 provide new information on transport rates in the lower stratosphere. The tropospheric seasonal cycle in CO 2 , superimposed on the long‐term trend, is observed to propagate into the stratosphere. The compact correlations observed between CO 2 and N 2 O indicate that meridional transport is sufficiently rapid to create a uniform set of relationships over the northern hemisphere up to at least 21 km even though CO 2 changes significantly on a time scale of 8 to 12 weeks. The observed seasonal dependence of the correlations indicates that vertical transport above 20 km is slower in northern summer than in winter and slow throughout the year between 19 km and the tropopause. The inferred amplitude of the seasonal CO 2 oscillation in the stratosphere, viewed relative to N 2 O, places constraints on the mean latitude for air entering the stratosphere.