The Impacts of Two Types of El Nio on Global Ozone Variations in the Last Three Decades

The effects of El Nio Modoki events on global ozone concentrations are investigated from 1980 to 2010 El Nio Modoki events cause a stronger Brewer-Dobson (BD) circulation which can transports more ozone-poor air from the troposphere to stratosphere, leading to a decrease of ozone in the lower-middle stratosphere from 90S to 90N. These changes in ozone concentrations reduce stratospheric column ozone. The reduction in stratospheric column ozone during El Nio Modoki events is more pronounced over the tropical eastern Pacific than over other tropical areas because transport of ozone-poor air from middle-high latitudes in both hemispheres to low latitudes is the strongest between 60W and 120W. Because of the decrease in stratospheric column ozone during El Nio Modoki events more UV radiation reaches the tropical troposphere leading to significant increases in tropospheric column ozone An empirical orthogonal function (EOF) analysis of the time series from 1980 to 2010 of stratospheric and tropospheric ozone monthly anomalies reveals that: El Nio Modoki events are associated with the primary EOF modes of both time series. We also found that El Nio Modoki events can affect global ozone more significantly than canonical El Nio events. These results imply that El Nio Modoki is a key contributor to variations in global ozone from 1980 to 2010.