Fig. 4

a–c Same as Fig. 3 but for westward travelling normal atmospheric modes with periods 4, 5, 7, 10, and 16 days (panels from the top to the bottom, respectively) Figures 3 and 4 show that in many cases, accounting OGW dynamical and thermal effects in the MUAM results in changes in the amplitudes of stationary PWs and travelling NAMs. Depositions of OGW momentum and heat have primary effects directly modifying general circulation and planetary waves and secondary effects of influence of modified mean flow on the wave propagation conditions. Changes in the zonal wind direction in the middle atmosphere over the equator during different QBO phases modify the general circulation (see Fig. 1) and change PW and NAM propagation conditions. They can substantially affect PW amplitudes and other parameters up to higher altitudes described in some previous publications (Holton 1984; McLandress 2002; Ortland and Alexander 2006; Watanabe and Miyahara 2009; Mayr et al. 2011; Hoffmann et al. 2012). Inhomogeneities of orographic wave sources and conditions of OGW propagation may lead to the generation of additional PW modes, which could have contributed to the results in Figs. 3, 4, and 5 (e.g., Holton 1984; McLandress and McFarlane 1993; Watson and Gray 2015; Gavrilov et al. 2013b)