Migrating diurnal tide anomalies during QBO disruptions in 2016 and 2020: morphology and mechanism

Abstract. The stratosphere Quasi-Biennial Oscillation (QBO) modulates the migrating diurnal tide (DW1) in mesosphere and lower thermosphere (MLT). DW1 amplitudes are larger during QBO westerly (QBOW) than during easterly (QBOE) phases. Since QBO’s discovery in 1953, two rare QBO disruption events occurred in 2016 and 2020. During these events, anomalous westerly winds propagate upward, disrupting normal downward propagation of easterly phase and producing a persistent westerly wind layer. In this study, global responses of DW1 amplitudes and phases in MLT to these QBO disruptions, as well as the excitation sources are investigated, using SABER/TIMED observations, MERRA-2 reanalysis and SD-WACCM-X simulations. Similarity of the DW1 responses to these two events is that DW1 phases and wavelengths exhibit weak responses to these events, whereas the amplitudes show significant responses. Relative to regular QBOE, DW1 amplitudes increase by ~20.5 % at equator and 14.4 % at 30° N/S during the 2016 event, but by only ~6.0 % and 2.0 % during the 2020 event. Water vapour radiative heating, ozone radiative heating and latent heating are enhanced by ~10 %, ~6.6 % and ~22 % relative to QBOE in 2016 event. In 2020, water vapour radiative heating shows a clear increase (~9 %), whereas ozone heating and latent heating remain nearly unchanged to the QBOE. In summary, the simultaneous amplification of water vapour, ozone and latent heating could account for the pronounced DW1 amplitude increase in 2016 event, while the enhancement of water vapour heating may explain the weaker response in 2020 event.