Independent and joint influences of eastern Pacific El Nino-southern oscillation and quasi-biennial oscillation on Northern Hemispheric stratospheric ozone

Using ozone observations, reanalysis data, and climate model simulations, this study investigates in detail the independent and joint influences of the eastern Pacific (EP) El Nino-Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO) on stratospheric ozone in the Northern Hemisphere (NH) during winter. Statistically, the stratospheric ozone in the NH in winter increases during El Nino events but decreases during La Nina events. Stratospheric ozone increases in the east wind phases of the QBO (EQBO) and decreases in the west wind phases of the QBO (WQBO). The stratospheric ozone anomalies in the middle and high latitudes caused by ENSO activities are clearly larger than those related to the QBO phase. Since the phases of wave-1 and wave-2 planetary waves anomalies related to ENSO activities are broadly similar to those of QBO phases, the joint effect of ENSO and QBO on stratospheric ozone is approximately equal to the linear superposition of their independent impacts. This means that during EQBO phases, the stratospheric ozone anomalies are increased during El Nino events but reduced during La Nina events, and vice versa during WQBO phases. Numerical sensitivity experiments are performed to further investigate the independent and joint influences of EP ENSO and QBO on stratospheric ozone in the NH during winter. The results from simulations agree well with the results from statistical analysis.