Quasi‐Two‐Day Waves in the Northern Hemisphere Observed by TIMED/SABER Measurements During 2002–2019

The quasi‐two‐day waves (QTDWs) with westward‐propagating wavenumbers 2 (W2), 3 (W3), and 4 (W4) during the boreal summers were statistically examined using TIMED/SABER temperature observation datasets during 2002–2019 with a 6‐day two‐dimensional least‐squares fitting window. The W4 (W3) and W2 QTDWs were observed at ∼67–73 km and ∼30–40°N, and ∼89–95 km and ∼20–30°N, respectively. The W4 mode occurred 57 times over the past 18 years compared to 43 (52) times for the W3 (W2) QTDWs. The W4 QTDW reached maximum amplitudes of ∼9–10 K during 2006, 2009, and 2017, whereas W3 and W2 QTDWs attained maximum amplitudes of ∼8 K during 2017 and 2012. In addition, W4, W3, and W2 occurred more frequently with periods of 41–44 hr, 47–53 hr, and 44–50 hr, respectively. QTDW events with longer periods took place later than those events with shorter periods. Statistically, the W4 (W2) QTDW events were significantly more frequent during days 195–210 (165–180). In contrast, the W3 QTDW tended to occur during days 180–195 but was only slightly less frequent during days 195–210 and 210–225. Diagnostic analysis of the modern‐era retrospective analysis for research and applications ‐2 reanalysis dataset indicates that the attribution variations of the QTDWs, including their amplitudes and periods, were intimately related to the corresponding variabilities of the background zonal wind. Key Points The W3 and W4 quasi‐two‐day waves (QTDWs) show clear amplitude and period variations in the middle atmosphere during the boreal summers The W4 QTDW dominates the QTDW behaviors during boreal summers with the largest amplitude of ∼9–10 K The periods of QTDWs are relatively stable during early and middle stages of the boreal summers but become longer during late boreal summers