Zonal Asymmetry of the Quasi-Biennial Oscillation

Abstract Zonal asymmetry in the amplitude of the Quasi-Biennial Oscillation (QBO) is investigated using JRA-55 reanalysis data and in-situ IGRA radiosonde observations. In addition to the previously reported asymmetry near 10 hPa, significant longitudinal variation with the largest amplitudes over the western and central Pacific is found around 70 hPa. Unlike the dominant wavenumber-1 pattern near 10 hPa, the structure at 70 hPa exhibits more localized variations. Longitudinal differences in the QBO zonal wind at 70 hPa reach up to 30%, indicating that the descent of the QBO into the lower stratosphere and upper troposphere exhibits pronounced longitudinal variation. The asymmetry results were confirmed in five additional reanalysis datasets. Similar zonal variation of QBO amplitudes is also identified in radiosonde observations and in both CMIP6 and QBOi models that explicitly simulate the QBO. These results demonstrate that the longitudinal structure of the 70-hPa QBO amplitude is a robust feature across observations, reanalyses, and climate models.