Informative article on development of cusped waveforms and Kelvin-Helmholtz instabilities

https://www.researchgate.net/publication/360620472_An_experimental_study_of_two-layer_liquid_sloshing_under_pitch_excitations?enrichId=rgreq-d22e582211b0f5030997e11c7a66a770-XXX&enrichSource=Y292ZXJQYWdlOzM2MDYyMDQ3MjtBUzoxMTU2MzEzMzAwMTE5NTU0QDE2NTI2OTc5ODI3OTA%3D&el=1_x_3&_esc=publicationCoverPdf

Amazing number of harmonics

A spectacular example of Kelvin-Helmholtz wave clouds over Mt Montara, south of Pacifica, California. These are formed, often over a barrier (i.e., hill/mountain), when there are different wind speeds with altitude. (Image by Peter Harrison, shared with permission) pic.twitter.com/0lWaB068o2

— Jan Null (@ggweather) July 5, 2022

The Kelvin–Helmholtz instability can occur when there is velocity shear in a single continuous fluid, or where there is a velocity difference across the interface between two fluids https://t.co/Uf4PfkS5dl pic.twitter.com/a0KLHjzEBr

— Massimo (@Rainmaker1973) June 28, 2022

https://www.sciencedirect.com/science/article/pii/B9780128215128000177

The most important mechanism for turbulence production in equatorial parallel shear flows is the inflectional instability, which operates at local maxima of the mean shear profile (Smyth and Carpenter, 2019). In the presence of stable stratification, inflectional instability is damped, but it may yet grow, provided that the minimum value of Ri is less than critical. In this case, the process is termed Kelvin–Helmholtz (KH) instability.