Fig. 2: Altitude-averaged (80–96 km) cross-wavelet spectrum of horizontal wind between Mohe (122^∘E, 54^∘N) and Juliusruh (13^∘E, 55^∘N).

Averaged here is the sum of the spectrum of zonal wind u and that of the meridional wind v. The darkness and color hue in each panel denote the modulus and argument of the spectrum, namely,\(\parallel\! \tilde{C} \!\parallel\) and \(\arg \{\tilde{C}\}\), respectively. The phase is a function of zonal wavenumber m as specified in the color code. The six numbers following the symbol # index the most substantial peaks in descending order of their amplitudes, as specified in Table 1. The solid black isolines denote amplitudes at 6 ms⁻¹ and the vertical dashed line indicates the central day of the 2019 new year stratospheric sudden warming event. Readers with colour vision deficiencies are referred to Supplementary Fig. 1 for color-filtered versions of the current figure.