A non-hydrostatic version of the NMC's regional Eta model

Abstract

A non-hydrostatic version of the regional Eta model used operationally at the National Meteorological Center (NMC) has been developed by implementing the ideas of Juang (1992) and Laprise (1992), who independently recommended a hydrostatically based, vertical coordinate for a fully compressible set of equations. The grid-point model dynamics is based on perturbation equations in the η-vertical coordinate; the base state may be taken from the operational NMC model, and thus updated with time. The non-hydrostatic model uses a stepwise treatment of terrain present in the operational version, eliminating the pressure-gradient-term error associated with sigma-coordinate models over steep topography. The compressible equations are written in a form that allows conservation of energy in a horizontally closed domain with appropriate advective schemes. A two-dimensional version of the model, without parametrizations of physical processes, has been used successfully to simulate ascending warm bubbles and collapsing cold bubbles at high resolutions.