The impacts of two types of El Niño on global ozone variations in the last three decades

Abstract

The effects of El Nino Modoki events on global ozone concentrations are investigated from 1980 to 2010 El Nino 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 90°S to 90°N. These changes in ozone concentrations reduce stratospheric column ozone. The reduction in stratospheric column ozone during El Nino 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 60°W and 120°W. Because of the decrease in stratospheric column ozone during El Nino 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 Nino Modoki events are associated with the primary EOF modes of both time series. We also found that El Nino Modoki events can affect global ozone more significantly than canonical El Nino events. These results imply that El Nino Modoki is a key contributor to variations in global ozone from 1980 to 2010.