Multimodal Excitation to Model the Quasibiennial Oscillation

The quasibiennial oscillation (QBO) of stratospheric winds is the most striking example of mean-flow generation and reversal by the nonlinear interactions of internal waves. Previous studies have used an idealized monochromatic forcing to investigate the QBO. Here we instead force a more realistic continuous wave spectrum. Unexpectedly, spreading the wave energy across a wide frequency range leads to more regular oscillations. We also find that different forcing spectra can yield the same QBO. Multimodal wave forcing is thus essential for understanding wave--mean-flow interactions in nature.