Low-ozone events and three-dimensional transport at midlatitudes of South America during springs of 1996 and 1997

Sudden and transient decreases of ozone column values were detected over th e midlatitudes of South America during the springs of 1996 and 1997 by a ne twork of ground instruments. These low-ozone events were accompanied by air temperature decreases in the lower stratosphere. The analysis of the event s suggests a connection with the springtime Antarctic ozone hole. Three-dim ensional isentropic back trajectories showed that vertical motion also cont ributed to the decreases of total ozone observed at the midlatitudes of Sou th America.