Sun et al. (2012) proposed a modified non-hydrostatic model (MNH). in which the left-hand side of the continuity equation is multiplied by a parameter δ (4≤δ≤16 in the article) to suppress high-frequency acoustic waves. They showed that the MNH allows a longer time step than the original non-hydrostatic model (NH). https://www.roneverhart.com/Plastic-Jigger-with-Measuring-Lines-Box-of-12/