try using the initial pressure profile in the exner function

src/modstartup.f90

@@ -741,8 +741,8 @@ subroutine readinitfiles
       svm  = sv0
       e12m = e120
       call calc_halflev
-      exnf = (presf/pref0)**(rd/cp)
-      exnh = (presh/pref0)**(rd/cp)
+      exnf = (initial_presf/pref0)**(rd/cp)
+      exnh = (initial_presh/pref0)**(rd/cp)
 
       do  j=2,j1
       do  i=2,i1

src/modthermodynamics.f90

@@ -223,9 +223,10 @@ end subroutine calthv
 !! \author      Pier Siebesma   K.N.M.I.     06/01/1995
   subroutine diagfld
 
-  use modglobal, only : i1,ih,j1,jh,k1,nsv,zh,zf,cu,cv,ijtot,grav,rlv,cp,rd,rv,pref0
+  use modglobal, only : i1,ih,j1,jh,k1,nsv,zh,zf,cu,cv,ijtot,grav,rlv,cp,rd,rv,pref0,timee
   use modfields, only : u0,v0,thl0,qt0,ql0,sv0,u0av,v0av,thl0av,qt0av,ql0av,sv0av, &
-                        presf,presh,exnf,exnh,rhof,thvf
+                        presf,presh,exnf,exnh,rhof,thvf, &
+                        initial_presf,initial_presh
   use modsurfdata,only : thls,ps
   use modmpi,    only : slabsum
   implicit none
@@ -258,8 +259,11 @@ subroutine diagfld
    thl0av = thl0av/ijtot
    qt0av = qt0av /ijtot
    ql0av = ql0av /ijtot
-   exnf   = 1-grav*zf/(cp*thls)
-   exnh  = 1-grav*zh/(cp*thls)
+   if (timee < 0.01) then
+      exnf   = 1-grav*zf/(cp*thls)  ! What's this?
+      exnh  = 1-grav*zh/(cp*thls)   !
+   endif
+
    th0av  = thl0av + (rlv/cp)*ql0av/exnf
    do n=1,nsv
       call slabsum(sv0av(1,n),1,k1,sv0(1,1,1,n),2-ih,i1+ih,2-jh,j1+jh,1,k1,2,i1,2,j1,1,k1)
@@ -272,7 +276,9 @@ subroutine diagfld
 
 !    2.1 Use first guess of theta, then recalculate theta
    call fromztop
-   exnf = (presf/pref0)**(rd/cp)
+   if (timee < 0.01) then
+      exnf = (presf/pref0)**(rd/cp)
+   endif
    th0av = thl0av + (rlv/cp)*ql0av/exnf
 
 !    2.2 Use new updated value of theta for determination of pressure
@@ -286,13 +292,14 @@ subroutine diagfld
 !***********************************************************
 
 !    3.1 determine exner
-
-   exnh(1) = (ps/pref0)**(rd/cp)
-   exnf(1) = (presf(1)/pref0)**(rd/cp)
-   do k=2,k1
-     exnf(k) = (presf(k)/pref0)**(rd/cp)
-     exnh(k) = (presh(k)/pref0)**(rd/cp)
-   end do
+   if (timee < 0.01) then
+      exnh(1) = (ps/pref0)**(rd/cp)
+      exnf(1) = (presf(1)/pref0)**(rd/cp)
+      do k=2,k1
+         exnf(k) = (presf(k)/pref0)**(rd/cp)
+         exnh(k) = (presh(k)/pref0)**(rd/cp)
+      end do
+   endif
    thvf(1) = th0av(1)*exnf(1)*(1+(rv/rd-1)*qt0av(1)-rv/rd*ql0av(1))
    rhof(1) = presf(1)/(rd*thvf(1))