A Non-hydrostatic Scheme for the NCEP's Global Forecast System (GFS)

    An effort is underway at the Environmental Modeling Centre of NCEP to extend the hydrostatic shallow-atmosphere dynamics of the current operational semi-Lagrangian GFS (Global Forecasting System) into a deep-atmosphere non-hydrostatic dynamics for future space weather applications. While the task is quite daunting with rather limited resources at our disposal, some incremental progress has been made towards extending the numerical scheme of the current hydrostatic shallow-atmosphere dynamics into a non-hydrostatic one. The non-hydrostatic extension introduces two additional prognostic variables, namely, w and p' ≡ p - π, where w, p, and π denote the height vertical-velocity, the true pressure, and the hydrostatic pressure, respectively. The vertical coordinate is terrain-following hybrid σ - π. By design, the vertical-difference scheme of the non-hydrostatic model conserves total energy and angular momentum, and transparently reverts back to the hydrostatic scheme when p' ≡ 0. The time-difference scheme of the non-hydrostatic model retains the semi-implicit scheme of the hydrostatic model, augmented by a novel explicit acoustic-wave damper. Yet another conventional option of the time-differencing includes a vertical time-implicit scheme for w and p'. Effectiveness of the non-hydrostatic scheme has been examined though a number of idealized 2D thermal convection and orographic mountain wave simulations. Details of the non-hydrostatic scheme along with some preliminary results will be presented at the conference.