! source file: /sfs/fs6/home-geomar/smomw258/UVic_ESCM/2.9/source/mom/convect.F
      subroutine convct (ts, ncon, joff, js, je, istrt, iend, kmt)

      implicit none

      integer is, ie, nn, ncon, ks, js, je, j, jrow, joff, i, k, n
      integer iend, istrt

      real dense

      include "size.h"
      include "param.h"
      include "pconst.h"
      include "stdunits.h"
      include "accel.h"

      integer kmt(imt,jmt)
      parameter (is=2, ie=imt-1)

      real ts(imt,km,1:jmw,nt), temp(imt,km,jsmw:jmw)

!-----------------------------------------------------------------------
!     standard explicit convection scheme
!     convectively adjust water column if gravitationally unstable

!     inputs:

!     ncon  = number of passes through convection routine
!     joff  = offset between "j" in MW and "jrow" latitude on disk
!     js    = starting row in MW
!     je    = ending row in MW
!     is    = starting longitude index
!     ie    = ending longitude index

!     Note: istrt,iend are currently bypassed. instead, is and ie are
!           set as parameters to optimize performance
!     kmt   = number of ocean "t" boxes in the vertical
!     ts    = temperature and salinity before convection

!     outputs:

!     ts    = tracers after convection

!-----------------------------------------------------------------------

!     ks=1: compare lev. 1 to 2; 3 to 4; etc.
!     ks=2: compare lev. 2 to 3; 4 to 5; etc.

      do nn=1,ncon
        do ks=1,2

!         find density for rows

          call statec (ts(1,1,1,1), ts(1,1,1,2), temp(1,1,jsmw)
     &,                max(js,jsmw), je, is, ie, ks)

!         set "heavy water" in land to stop convection

          dense = 1.e15
          do j=js,je
            jrow = j + joff
            do i=is,ie
              k = kmt(i,jrow) + 1
              if (k .le. km) then
                temp(i,k,j) = dense
              endif
            enddo
          enddo

!         if unstable,  mix tracers on adjoining levels

          do n=1,nt
            do j=js,je
              do k=ks,kmm1,2
                do i=is,ie
                  if (temp(i,k,j) .gt. temp(i,k+1,j)) then
                    ts(i,k,j,n)   = (dztxcl(k)*ts(i,k,j,n) +
     &                          dztxcl(k+1)*ts(i,k+1,j,n))*dzwxcl(k)
                    ts(i,k+1,j,n) = ts(i,k,j,n)
                  endif
                enddo
              enddo
            enddo
          enddo
        enddo
      enddo

      do n=1,nt
        do j=js,je
          call setbcx (ts(1,1,j,n), imt, km)
        enddo
      enddo

      return
      end

      subroutine convct2 (ts, joff, js, je, is, ie, kmt)

!=======================================================================
!     The following convection scheme is an alternative to the standard
!     scheme. In contrast to the standard scheme, it totally removes
!     all gravitational instability in the water column. It does that
!     in one pass, so the parameter ncon becomes irrelevant if this
!     option is selected. Since most convection propagates downward the
!     scheme looks downward first and follows any instability (upward or
!     downward) before checking the other direction. The routine mixes
!     passive tracers only after the entire instability is found. The
!     scheme is similar to that used by Rahmstorf (jgr 96,6951-6963) and
!     by Marotzke (jpo 21,903-907). It is discussed in a note to Ocean
!     Modelling (101). It uses as much cpu time as 1-3 passes of the
!     standard scheme, depending on the amount of static instability
!     found in the model, and is much faster than using "implicitvmix".

!     inputs:

!     joff   = offset between "j" in MW and "jrow" latitude on disk
!     js     = starting row in MW
!     je     = ending row in MW
!     is     = starting longitude index
!     ie     = ending longitude index
!     kmt    = number of ocean "t" boxes in the vertical
!     ts     = tracers before convection

!     outputs:

!     ts     = tracers after convection

!     other previously undefined variables:

!     chk_la = logical flag to check level above kt
!     chk_lb = logical flag to check level below kb
!     kb     = bottom level of (potential) instability
!     kbo    = bottom level of ocean
!     kt     = top level of (potential) instability
!     ktot   = total number of levels convecting in the column
!     kven   = number of levels that ventilated in the column
!     la     = test level above kt
!     lb     = test level below kb
!     rl     = lower level density referenced to lower level
!     ru     = upper level density referenced to lower level
!     tmx    = mixed tracer (1=temp, 2=salt, 3=other)
!     tsm    = sum of tracers (weighted by thickness) in the instability
!     zsm    = total thickness of the instability
!=======================================================================

      implicit none

      integer i, ie, is, j, je, joff, jrow, js, k, kb, kbo
      integer kt, ktot, kven, la, lb, n

      logical chk_la, chk_lb

      real rl, ru, tmx(3), tsm(3), zsm, dens, tq, sq, drodt, drods
      real drhodt, drhods, ddensdtdt, ddensdtds, ddensdsds

      include "size.h"
      include "param.h"
      include "pconst.h"
      include "stdunits.h"
      include "accel.h"

      include "coord.h"
      include "scalar.h"
      include "switch.h"
      include "diaga.h"

      include "state.h"
      include "dens.h"

      integer kmt(imt,jmt)

      real ts(imt,km,1:jmw,nt)

      do j=js,je
        jrow = j + joff
        do i=is,ie
!         ktot = 0
          kbo = kmt(i,jrow)

          if (timavgperts) then
            totalk(i,j) = 0.0
            vdepth(i,j) = 0.0
            pe(i,j) = 0.0
            do k=1,km
              ru = dens (ts(i,k,j,1)-to(k), ts(i,k,j,2)-so(k), k)
              pe(i,j) = pe(i,j) + grav*zt(k)*ru*dztxcl(k)
            enddo
          endif

!         search for unstable regions starting from the top
          kt = 1
          kb = 2
          do while (kt .lt. kbo)
            ru = dens (ts(i,kt,j,1)-to(kb), ts(i,kt,j,2)-so(kb), kb)
            rl = dens (ts(i,kb,j,1)-to(kb), ts(i,kb,j,2)-so(kb), kb)

!           sum the first pair found in an unstable region
            if (ru .gt. rl) then
              chk_la = .true.
              chk_lb = .true.
              zsm = dztxcl(kt) + dztxcl(kb)
              tsm(1) = ts(i,kt,j,1)*dztxcl(kt) + ts(i,kb,j,1)*dztxcl(kb)
              tmx(1) = tsm(1)/zsm
              tsm(2) = ts(i,kt,j,2)*dztxcl(kt) + ts(i,kb,j,2)*dztxcl(kb)
              tmx(2) = tsm(2)/zsm

              do while (chk_lb .or. chk_la)

!               check for an unstable level (lb) below kb
                if (kb .ge. kbo) chk_lb = .false.
                do while (chk_lb)
                  chk_lb = .false.
                  lb = kb + 1
                  ru = dens (tmx(1)-to(lb),      tmx(2)-so(lb),      lb)
                  rl = dens (ts(i,lb,j,1)-to(lb),ts(i,lb,j,2)-so(lb),lb)
                  if (ru .gt. rl) then
!                   add new level to sums
                    kb = lb
                   zsm = zsm + dztxcl(kb)
                    tsm(1) = tsm(1) + ts(i,kb,j,1)*dztxcl(kb)
                    tmx(1) = tsm(1)/zsm
                    tsm(2) = tsm(2) + ts(i,kb,j,2)*dztxcl(kb)
                    tmx(2) = tsm(2)/zsm
                    chk_la = .true.
                    if (kb .lt. kbo) chk_lb = .true.
                  endif
                enddo

!               check for an unstable level (la) above kt
! to get the equivalent of Rahmstorf's scheme uncomment the next line
                chk_la = .true.
                if (kt .le. 1) chk_la = .false.
                do while (chk_la)
                  chk_la = .false.
                  la = kt - 1
                  ru = dens (ts(i,la,j,1)-to(kt),ts(i,la,j,2)-so(kt),kt)
                  rl = dens (tmx(1)-to(kt),      tmx(2)-so(kt),      kt)
                  if (ru .gt. rl) then
!                   add new level to sums
                    kt = la
                    zsm = zsm + dztxcl(kt)
                    tsm(1) = tsm(1) + ts(i,kt,j,1)*dztxcl(kt)
                    tmx(1) = tsm(1)/zsm
                    tsm(2) = tsm(2) + ts(i,kt,j,2)*dztxcl(kt)
                    tmx(2) = tsm(2)/zsm
                    chk_lb = .true.
! to get the equivalent of Rahmstorf's scheme comment out the next line
!                    if (kt .gt. 1) chk_la = .true.
                  endif
                enddo
              enddo

!             mix all tracers from kt to kb
              do k=kt,kb
                ts(i,k,j,1) = tmx(1)
                ts(i,k,j,2) = tmx(2)
              enddo
              do n=3,nt
                tsm(3) = c0
                do k=kt,kb
                  tsm(3) = tsm(3) + ts(i,k,j,n)*dztxcl(k)
                enddo
                tmx(3) = tsm(3)/zsm
                do k=kt,kb
                  ts(i,k,j,n) = tmx(3)
                enddo
              enddo

!             some possible diagnostics
!              ktot = ktot + kb - kt + 1
!              if (kt .eq. 1) kven = kb

!             finished this region, save convection diagnostics
              if (timavgperts) then
                totalk(i,j) = totalk(i,j) + float(kb - kt + 1)
                if (kt .eq. 1) vdepth(i,j) = zw(kb)
              endif

              kt = kb + 1
            else
              kt = kb
            endif

!           continue the search for other unstable regions
            kb = kt + 1
          enddo

          if (timavgperts) then
            do k=1,km
              ru = dens (ts(i,k,j,1)-to(k), ts(i,k,j,2)-so(k), k)
              pe(i,j) = pe(i,j) - grav*zt(k)*ru*dztxcl(k)
            enddo
            pe(i,j) = pe(i,j)/c2dtts
          endif

        enddo

      enddo

      return
      end