Mixing between the troposphere and lowermost stratosphere indicated by HIRDLS measurements of isentropic tracer-tracer correlations

Correlations between pairs of tracers are often used in the analysis of aircraft measurements to characterize regions of mixing in the UTLS, seen primarily in the local vertical direction. Here we show plots of ozone (stratospheric source) versus CFC12 (tropospheric source) on isentropic surfaces in the UTLS to present an alternate view of these regions, including their temporal variations and preferred locations. Version 5 tracer data from the High Resolution Dynamics Limb Sounder (HIRDLS), which has a vertical resolution of ~ 1 km, are interpolated to isentropic surfaces from ~ 340 to 410 K. Subsequently tracer equivalent latitudes and Nakamura equivalent lengths are calculated. Regions around the barriers, where equivalent lengths are small, show details of the smooth transition from stratosphere-like to troposphere-like mixing ratios. These regions are more distinct in winter, and vary in latitude and width with isentropic level. These features are in reasonable agreement with those from the NCAR Whole Atmosphere Community Climate Model (WACCM).