Stratospheric Ozone Depletion in CESM

7 Observations show an increase in maximum precipitation extremes and a decrease in 8 maximum temperature extremes over southeastern South America (SESA) in the second 9 half of the 20th century. The Community Earth System Model (CESM) Large Ensemble 10 (LE) experiments are able to successfully reproduce the observed trends of extreme precip11 itation and temperature over SESA. Careful analysis of a smaller ensemble of CESM-LE 12 single forcing experiments reveals that the trends of extreme precipitation and temperature 13 over SESA are mostly caused by stratospheric ozone depletion. The underlying dynamical 14 mechanism is investigated, and it is found that, as a consequence of stratospheric ozone 15 depletion and the resulting southward shift of tropospheric jet streams, anomalous easterly 16 flow and more intense cyclones have occurred over SESA, which are favorable for heavier 17 rainfall extremes and milder heat extremes. 18 Purdue University, West Lafayette, IN, 47907 E-mail: [email protected] 1