Joint impacts of ENSO Modoki and QBO on stratospheric ozone in winter in the Northern Hemisphere

Composite analysis is applied in the present study to investigate independent and joint impacts of the second type of El Niño-Southern Oscillation (ENSO Modoki) and the Quasi-biennial Oscillation (QBO) on stratospheric ozone in the Northern Hemisphere (NH) in winter using observed ozone data and reanalysis data. The analysis reveals that stratospheric ozone in the NH in winter increases during El Niño Modoki events but decreases during La Niña Modoki events. Stratospheric ozone in the NH in winter increases during the east wind phase of the QBO (EQBO) and decreases during the west wind phase of the QBO (WQBO). In contrast, stratospheric ozone anomalies in the middle and high latitudes caused by ENSO activities are evidently larger than those related to the QBO phases. Further analysis indicates that during the EQBO phase, stratospheric ozone anomalies in the NH are amplified during El Niño Modoki events but reduced during La Niña Modoki events. During the WQBO phases, El Niño Modoki events only slightly increase the stratosphere ozone concentration in the NH in winter, while the ozone concentration is greatly reduced during La Niña Modoki events. Therefore, the EQBO enhances the effect of El Niño Modoki events on stratospheric ozone in the NH, but weakens the effect of La Niña Modoki events. The WQBO weakens the effect of El Niño Modoki events but intensifies the effect of La Niña Modoki events on stratospheric ozone in the NH.