On the Robustness of Recent Lower Stratospheric Ozone Trends in Specified Dynamics Model Simulations

A recent analysis of satellite-based ozone measurements has reported that near-global lower stratospheric ozone has continued to decline since the late 1990s. In contrast to this lower stratospheric ozone decline, flat or increasing lower stratospheric ozone trends over the same time period were found in specified dynamics (SD) Chemistry-Climate Model (CCM) simulations nudged to reanalysis wind/temperature fields with historical ODSs. This presentation assesses the representation of dynamical changes in SD-CCM simulations as a possible explanation for the apparent discrepancy between SD-CCMs and observations. We assess the ability of a Whole Atmosphere Community Climate Model (WACCM)-SD simulation to reproduce the dynamical trends present in its input reanalysis, and find that under a commonly-used configuration, WACCM-SD fails to reproduce the underlying tropical upwelling changes present in its input reanalysis. This failure to properly reproduce the input significantly impacts the simulated ozone trends. Finally, we present a new method of specified dynamics nudging aimed at ameliorating the dynamical inconsistency, and discuss the impact on simulated ozone trends.