LAUSR

Abstract This paper studies the influence of Rossby wave breaking (RWB) on ozone variations in the upper troposphere and lower stratosphere on isentropic surfaces between 330 K and 370 K during 1985–2015 over two U.S. sites (Boulder in Colorado and Wallops Island in Virginia), using the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalysis data and ozonesonde measurements. We have analyzed the occurrence of elevated ozone days and its association with the two types of RWB: anticyclonic wave breaking (AWB) and cyclonic wave breaking (CWB). Our results show that AWB and CWB are associated with higher ozone levels in summer at isentropic surfaces below 350 K, and the ozone enhancement associated with AWB is more significant than with CWB. Together, AWB and CWB account for 20–30% of elevated ozone days. Both AWB and CWB are associated with lower ozone levels in winter at all the isentropic surfaces, and such an effect is more significant at Boulder than at Wallops Island.