“…Vertical wavelengths of them range from 40 to 110 km (Pancheva et al, 2004). In the Southern Hemisphere (SH), their periods and wavenumbers are about 48 h and −3 (minus means westward propagation), respectively, while in the Northern Hemisphere (NH), periods contain 53-56, 48-50 and 42-43 h, with corresponding wavenumbers −2, −3 and −4 (Craig et al, 1980;Pancheva et al, 2004;Malinga and Ruohoniemi, 2007). Moreover, numerous observations have verified the nonlinear interactions between QTDWs and other PWs (Pancheva et al, 2004;Babu et al, 2011;Li and Ning, 2011), which can partly explain the short-term variations of QTDWs.…”