Power spectra of the horizontal velocity at selected values of the horizontal wavenumber for Pr = 1 (top) and Pr = 0.01 (bottom) at fixed height z₀ = 0.7H. The insets show the symmetrized power averaged over 150 ≤ kR ≤ 250 for Pr = 1 and averaged over 50 ≤ kR ≤ 150 for Pr = 0.01. The arrows in the inset of the bottom panel point to the characteristic frequency ν₀ = 2.4 μHz and to the first overtone at 2ν₀. The power is normalized with respect to the maximum power (away from the central peak).