From 3dcd065db832fd7952ebb5497560755cf2b1b541 Mon Sep 17 00:00:00 2001
From: Rusty Benson <Rusty.Benson@noaa.gov>
Date: Wed, 17 Mar 2021 15:18:16 -0400
Subject: [PATCH] correctly merge height monotonicity log in
 nh_utils::update_dz_*

---
 model/nh_utils.F90 | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/model/nh_utils.F90 b/model/nh_utils.F90
index baa4ec33c..a200c2932 100644
--- a/model/nh_utils.F90
+++ b/model/nh_utils.F90
@@ -196,14 +196,14 @@ subroutine update_dz_c(is, ie, js, je, km, ng, dt, dp0, zs, area, ut, vt, gz, ws
 ! Enforce monotonicity of height to prevent blowup
 !$OMP parallel do default(none) shared(is1,ie1,js1,je1,ws,zs,gz,rdt,km,dz_min)
   do j=js1, je1
-     do k=2, km+1
-        do i=is1, ie1
-           gz(i,j,k) = min( gz(i,j,k), gz(i,j,k-1) - dz_min )
-        enddo
-     enddo
      do i=is1, ie1
         ws(i,j) = ( zs(i,j) - gz(i,j,km+1) ) * rdt
      enddo
+     do k=km, 1, -1
+        do i=is1, ie1
+           gz(i,j,k) = max( gz(i,j,k), gz(i,j,k+1) + dz_min )
+        enddo
+     enddo
   enddo
 
   end subroutine update_dz_c
@@ -310,15 +310,15 @@ subroutine update_dz_d(ndif, damp, hord, is, ie, js, je, km, ng, npx, npy, area,
 
 !$OMP parallel do default(none) shared(is,ie,js,je,km,ws,zs,zh,rdt,dz_min)
   do j=js, je
-     do k=2, km+1
+     do i=is,ie
+        ws(i,j) = ( zs(i,j) - zh(i,j,km+1) ) * rdt
+     enddo
+     do k=km, 1, -1
         do i=is, ie
 ! Enforce monotonicity of height to prevent blowup
-           zh(i,j,k) = min( zh(i,j,k), zh(i,j,k-1) - dz_min )
+           zh(i,j,k) = max( zh(i,j,k), zh(i,j,k+1) + dz_min )
         enddo
      enddo
-     do i=is,ie
-        ws(i,j) = ( zs(i,j) - zh(i,j,km+1) ) * rdt
-     enddo
   enddo
 
   end subroutine update_dz_d