# question about the nbq_grav option

Hello,

Here is a question about the 'nbq_grav' cpp option. I see that in 'step3d_fast.F', that flag seems to control the 'gravity' term in the vertical momentum equation. My question is, if 'nbq_grav' is undefined, does it mean the nbq gravity term is not included in the w-equation? I tend to think that gravity term is important for driving non-hydrostatic dynamics. Can someone tell me the rationale for not including gravity in w-equation?

Thanks! Guangyu