Mirabelle,

Thanks for clarifying that this is specifically for the TF vertical coordinate system.

This does not seem like it will be too difficult.

The 3d dry pressure is defined as: p_dry(i,k,j) = eta(k) * mut(i,j) + ptop,

where eta(k) is the WRF vertical coordinate,

mut(i,j) is the dry column pressure,

ptop is the model lid.

If we are interested in the surface pressure, then the full level eta(k=1) is identically defined as 1.0.

So the DRY surface pressure simplifies to p_sfc_dry(i,j) = mut(i,j) + ptop

We know that mut(i,j) = mub(i,j) + mu(i,j),

where mub(i,j) is the reference column pressure (for eaqh (i,j), a time invariant for the simulation),

mu(i,j) is the perturbation column pressure (for each (i,j), mu is time varying)

The total surface pressure p_sfc_tot(i,j) = p_sfc_dry(i,j) + pressure due to the integrated moisture from the model lid all the way to the surface.

Once you compute your total surface pressure increments, then compute the surface pressure increments from the dry pressure by removing the integrated moisture through the column. Then the time difference of the p_sfc_dry(i,j) is defined as the time difference of the mu(i,j).