Journal of Geophysical Research (ASHOE/MAESA special issue), 102, 13119-13134, 1997

Mixing of polar vortex air into middle latitudes as revealed by tracer-tracer scatter plots

D.W. Waugh1, R.A. Plumb2, J.W. Elkins3, D.W. Fahey4, K.A. Boering5, G.S. Dutton3,6, E.Keim4,6, R.-S. Gao6, B.C. Daube5, S. C. Wofsy5, M. Loewenstein7, J. R. Podolske7, K.R. Chan7, M.H. Proffitt4, K. K. Kelly4, P.A. Newman8, L.R. Lait8

1. Cooperative Research Centre for Southern Hemisphere Meteorology (CRCSHM)
2. Massachusetts Institute of Technology
3. NOAA Climate Monitoring and Diagnostics Laboratory (CMDL)
4. NOAA Aeronomy Laboratory (AL)
5. Harvard University
6. Cooperative Institute for Research in Environmental Sciences (CIRES)
7. NASA Ames Research Center (ARC)
8. NASA Goddard Space Flight Center (GSFC)


Abstract

The occurrence of mixing of polar vortex air with mid-latitude air is investigated by examining the scatter plots of in-situ measurements of the long-lived tracers N2O, NOy, CCl3F (F11), and CO2 from the NASA ER-2 aircraft during the SPADE (April, May 1993; northern hemisphere) and ASHOE/MAESA (March-October 1994; southern hemisphere) campaigns. The tracer-tracer scatter plots from SPADE form correlation curves which differ from those measured during previous aircraft campaigns (AAOE, AASE, AASE-II) and from two-dimensional chemical transport models. It is argued that these anomalous linear correlation curves are ``mixing lines'' resulting from the recent mixing of polar vortex air into the middle latitude environment. Further support for this mixing scenario is provided by contour advection calculations and calculations with a simple one-dimensional strain-diffusion model. The scatter plots from the mid-winter deployments of ASHOE/MAESA are consistent with those from previous mid-winter measurements (i.e., no mixing lines), but the spring CO2:N2O scatter plots form altitude-dependent mixing lines which indicate that air from the vortex edge region (but not from the inner vortex) is mixing with mid-latitude air during this period. These results suggest that at altitudes above about 16 km the mixing of polar vortex air into middle latitudes varies with season: in northern and southern mid-winter this mixing rarely occurs, in southern spring mixing of vortex-edge air occurs, and after the vortex breakup mixing of inner vortex air occurs.