The role of tropical upwelling in explaining discrepancies between recent modeled and observed lower-stratospheric ozone trends

Using a suite of SD simulations with alternative nudging configurations, it is shown that short-term (similar to 2-decade) lower-stratospheric ozone trends scale linearly with short-term trends in tropical lower-stratospheric upwelling near 85 hPa. How-ever, none of the simulations fully capture the recent ozone decline, and the ozone and upwelling scaling in the WACCM simulations suggests that a large short-term upwelling trend (similar to 6 % decade(-1)) would be needed to explain the observed satellite trends.

The strong relationship between ozone and upwelling, coupled with both the large range of reanalysis upwelling trend estimates and the inability of WACCM-SD simulations to repro-duce upwelling from their input reanalyses, severely limits the use of SD simulations for accurately reproducing recent ozone variability. However, a free-running version of WACCM using only surface boundary conditions and a nudged quasi-biennial oscillation produces a positive decadal-scale lower-stratospheric upwelling trend and a negative near-global lower-stratospheric column ozone trend that is in closest agreement with the ozone observations.