From eb301fe3976e48fbdbb0715a92404029e239fd2c Mon Sep 17 00:00:00 2001
From: alperaltuntas <alperaltuntas@gmail.com>
Date: Mon, 13 May 2019 18:21:45 -0600
Subject: [PATCH] skip first tstep and double second tstep

---
 config_src/nuopc_driver/mom_cap.F90 | 46 +++++++++++++++++++++++++++--
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/config_src/nuopc_driver/mom_cap.F90 b/config_src/nuopc_driver/mom_cap.F90
index 09af1d4cba..45c1b9df87 100644
--- a/config_src/nuopc_driver/mom_cap.F90
+++ b/config_src/nuopc_driver/mom_cap.F90
@@ -1764,6 +1764,7 @@ subroutine ModelAdvance(gcomp, rc)
   ! local variables
   integer                                :: userRc
   logical                                :: existflag, isPresent, isSet
+  logical                                :: do_advance = .true.
   type(ESMF_Clock)                       :: clock!< ESMF Clock class definition
   type(ESMF_Alarm)                       :: alarm
   type(ESMF_State)                       :: importState, exportState
@@ -1846,8 +1847,45 @@ subroutine ModelAdvance(gcomp, rc)
     file=__FILE__)) &
     return  ! bail out
 
-  Time = esmf2fms_time(currTime)
-  Time_step_coupled = esmf2fms_time(timeStep)
+  !---------------
+  ! Apply ocean lag at startup:
+  !---------------
+
+  if (trim(runtype) == "initial") then
+
+    ! Do not call MOM6 timestepping routine if the first cpl tstep of a startup run
+    if (currTime == startTime) then
+      call ESMF_LogWrite("MOM6 - Skipping the first coupling timestep", ESMF_LOGMSG_INFO, rc=rc)
+      if (ESMF_LogFoundError(rcToCheck=rc, msg=ESMF_LOGERR_PASSTHRU, &
+        line=__LINE__, &
+        file=__FILE__)) &
+        return  ! bail out
+      do_advance = .false.
+    else
+      do_advance = .true.
+    endif
+
+    ! If the second cpl tstep of a startup run, step back a cpl tstep and advance for two cpl tsteps
+    if (currTime == startTime + timeStep) then
+      call ESMF_LogWrite("MOM6 - Stepping back one coupling timestep", ESMF_LOGMSG_INFO, rc=rc)
+      if (ESMF_LogFoundError(rcToCheck=rc, msg=ESMF_LOGERR_PASSTHRU, &
+        line=__LINE__, &
+        file=__FILE__)) &
+        return  ! bail out
+      Time = esmf2fms_time(currTime-timeStep) ! i.e., startTime
+
+      call ESMF_LogWrite("MOM6 - doubling the coupling timestep", ESMF_LOGMSG_INFO, rc=rc)
+      if (ESMF_LogFoundError(rcToCheck=rc, msg=ESMF_LOGERR_PASSTHRU, &
+        line=__LINE__, &
+        file=__FILE__)) &
+        return  ! bail out
+      Time_step_coupled = 2 * esmf2fms_time(timeStep)
+    else
+      Time_step_coupled = esmf2fms_time(timeStep)
+      Time = esmf2fms_time(currTime)
+    endif
+  endif
+
 
   !---------------
   ! Write diagnostics for import
@@ -1890,7 +1928,9 @@ subroutine ModelAdvance(gcomp, rc)
   !---------------
 
   if(profile_memory) call ESMF_VMLogMemInfo("Entering MOM update_ocean_model: ")
-  call update_ocean_model(Ice_ocean_boundary, ocean_state, ocean_public, Time, Time_step_coupled)
+  if (do_advance) then
+    call update_ocean_model(Ice_ocean_boundary, ocean_state, ocean_public, Time, Time_step_coupled)
+  endif
   if(profile_memory) call ESMF_VMLogMemInfo("Leaving MOM update_ocean_model: ")
 
   !---------------