comment fix

Author: whannah1

components/eam/src/dynamics/se/gravity_waves_sources.F90

@@ -167,16 +167,16 @@ subroutine compute_frontogenesis( frontgf, frontga, tl, &
     ! using a mixture of Cartesian and spherical coordinates
     !
     ! This routine is a modified version of derivative_mod.F90:ugradv_sphere()
-    ! in that the grad(v) term is modified to compute grad_p(v) - the gradient
-    ! on p-surfaces expressed in terms of the gradient on model surfaces and a
-    ! vertical pressure gradient.
+    ! in that the grad(v) term is modified to compute grad_z(v) (or grad_p(v))
+    ! - the gradient on z-surfaces expressed in terms of the gradient on model
+    ! surfaces and a vertical geopotential gradient.
     !
     ! The old version only computed gradients on model surfaces, which creates
     ! issues around topograpy. This is address with use_fgf_pgrad_correction=.true.
     !
     ! First, v is represented in cartesian coordinates  v(c) for c=1,2,3
-    ! For each v(c), we compute its gradient on p-surfaces via:
-    !    grad(v(c)) - d(v(c))/dz grad(p)
+    ! For each v(c), we compute its gradient on z (or p) surfaces via:
+    !    grad(v(c)) - d(v(c))/dz grad(z)
     ! Each of these gradients is represented in *spherical* coordinates (i=1,2)
     !
     ! We then dot each of these vectors with grad(theta).  This dot product is