We found that the interannual difference of the W3 and W4 Q2DW is significantly correlated with the Quasi-Biennial Oscillation westerly (QBOW) and easterly (QBOE) phase, identified from the analysis of the 2003 to 2020 MERRA-2 and SABER atmospheric data. The amplitude of the zonal wind in the QBOE phase is approximately ∼10 m/s stronger than that in the QBOW phase. Mean zonal easterly winds are stronger in the QBOE phase than in the QBOW phase, while westerly winds are stronger in the QBOW phase. The Q2DW is present in the summer, and the background wind is easterly in both hemispheres. The mean temperature amplitudes of W3 and W4 in the QBOW phase are stronger than those in the QBOE phase, and the difference is ~2 K and ~3 K (in the Southern Hemisphere); ~2 K and ~3 K (in the Northern Hemisphere), respectively. The mean wave period of W4 in the QBOW phase in the Northern Hemisphere is shorter than that in the QBOE phase. The W3 mode is modulated by atmospheric eigenmodes in both hemispheres and shows slight differences in the QBOW and QBOE phases, while the W4 mode is more likely to show significant differences in the different QBO phases. Our diagnostic analysis suggests that the amplification of the QBOW phases W3 and W4 may be due to stronger mean-flow instabilities and background winds in the mesosphere. In addition, planetary waves gain stronger source activity during the QBOW phase to provide sufficient energy for propagation and amplification.

Quasi-2-Day Planetary Waves; QBO Phases; background wind; instability; source activity