Surface Pressure Semidiurnal Tides and the Stratospheric Quasi-Biennial Oscillation: Synchronization and Disruption

Abstract

Atmospheric surface pressure provides valuable information on the vertical dynamical structure of the atmosphere. Previous studies have reported that among the waves observed in surface pressure, semidiurnal tides (SDTs) are significantly affected by the stratospheric Quasi-Biennial Oscillation (QBO). Using historical surface-pressure observations and the Earth-system model MRI-ESM2.0, this study confirms that SDTs and the QBO are synchronized, such that SDT amplitude increases or decreases, respectively, at a rate of ∼1 Pa per 20 ms⁻¹ during westerly or easterly phases of the QBO at 30 hPa. Our numerical simulations and a linear analytical model support the QBO-SDT relationship being dynamically forced by background zonal winds rather than by anomalous ozone radiative heating. We also find that the QBO-SDT relationship was notably disturbed by the volcanic eruptions of Mount Agung in 1963 and Mount Pinatubo in 1991, during which increased shortwave radiative absorption caused by stratospheric aerosol enhanced the SDT amplitude. Short-lived El Nino events also occurred, moistening the upper troposphere to provide extra solar heating when volcanic aerosol was transported to higher latitudes. The influence of volcanic eruptions and El Nino events overlap with the QBO frequency band, jointly working as “noise” in QBO-SDT synchronization.