Model analysis of the tropospheric ozone trend over Reunion Island from 1992 to 2011

Thursday, 18 December 2014: 1:55 PM
Junhua Liu1, Jose M Rodriguez2, Anne M Thompson2, Anne R Douglass2, Mark A Olsen3, Stephen D Steenrod1 and Jennifer A Logan4, (1)NASA GSFC/USRA GESTAR, Greenbelt, MD, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)NASA GSFC/MSU GESTAR, Greenbelt, MD, United States, (4)Harvard Univ, Cambridge, MA, United States
Analysis of the long-term ozonesonde measurements has shown a statistically significant positive trend in the middle and upper troposphere over Reunion Island (21°S, 55°E) in July-September from 1992 to 2011. Here we examine the potential causes of these observed ozone trends using hindcast simulations from the GMI chemical transport model (CTM), driven by assimilated MERRA meteorological fields. The GMI hindcast simulation reproduces the morphology of observed trends showing more positive trends during the austral winter months (July-September) than during the summer months (December-February), notably in middle and upper troposphere. The simulations include a stratospheric ozone tracer; analysis of this tracer simulation identified an increase in the stratospheric contribution to tropospheric ozone at Reunion over austral winter months from 1992 to 2011, suggesting that changes in stratospheric ozone contribution play a major role in the observed trend. Noting that Reunion is located at the boundary of subtropical jets, where strong stratosphere troposphere exchange (STE) occurs due to shear and folding, we discuss analyses of the dynamics to examine processes impacting the stratospheric ozone contribution over this region.