Stratospheric and tropospheric contributions to extreme ozone minimum events over the Tibetan Plateau during winters 1987-2001 (Invited)

Wintertime extreme ozone minima in the total column ozone over the Tibetan Plateau (TP) between 1978 and 2001 are analyzed using observations from the Total Ozone Mapping Spectrometer (TOMS), Global Ozone Monitoring Experiment (GOME), and reanalysis data from both NCEP and ECMWF. Results show that total column ozone reduction in nine selected events can be substantially attributed to ozone reduction in the upper troposphere and lower stratosphere region (below 25 km). As in our previous study, this reduction is generally caused by uplift of the local tropopause and northward transport of tropical ozone-poor air associated with an anomalous anticyclone in the upper troposphere. And these anticyclonic anomalies are closely related to anomalous tropical deep convective heating, however, not necessarily phase-locked with the tropical Madden-Julian Oscillation as in our earlier case study. Moreover, five of the nine events are also coupled with contributions from stratospheric dynamics between 25 and 40 km, i.e., 15-40 % derived from GOME observations for events in November 1998, February 1999 and December 2001. Based on all the selected events, stratospheric column ozone reduction over the TP region can be attributed to the dynamics (development and/or displacement) of the two main stratospheric systems, i.e., the polar vortex and the “low-ozone pocket” inside the Aleutian High. And the latter may be regarded as a unique mechanism for total column ozone reduction in the North Pacific/East Asian sector.