Hydrostatic vs Non-hydrostatic Models » Non-hydrostatic Equation

Most nonhydrostatic models use gridpoint formulations. They are generally applied to forecast problems requiring very high horizontal resolution (from tens of meters to a few kilometers) and cover relatively small domains.

The equation shows that in a nonhydrostatic model, changes in vertical motion may be caused by:

• Orographic uplift or descent (first term)
• Advection bringing in air with a different vertical velocity (first term)
• Pressure deviations from hydrostatic balance resulting from changes in horizontal divergence or phenomena with nonhydrostatic pressure perturbations, such as thunderstorms and mountain waves (second term)
• Buoyancy caused by temperature and or moisture anomalies compared to surrounding grid boxes (third term); g indicates gravity
• Downward drag caused by the weight of liquid or frozen cloud water and precipitation (fourth term)

Most models are hydrostatic, however the Rapid Update Cycle model, or RUC, is fully nonhydrostatic.