SUBROUTINE combin ( lb, snl, &                      z, dz, zi, wliq, wice, tss, scv, snowdp )!=======================================================================! Source file: combin.f90! Original version: Yongjiu Dai, September 15, 1999!! checks for elements which are below prescribed minimum for thickness or mass.! If snow element thickness or mass is less than a prescribed minimum,! it is combined with neighboring element to be best combine with,! and executes the combination of mass and energy in clm_combo.f90! !=======================================================================  USE PHYCON_MODULE ! physical constants  IMPLICIT NONE!!-------------------------- Dummy argument -----------------------------!  integer, INTENT(in) :: &        lb             ! lower bound of array! numbering from 1 (bottom) mss (surface)  real, INTENT(inout) :: &        wice(lb : 1), &! ice lens [kg/m2]        wliq(lb : 1), &! liquid water {kg/m2]        tss (lb : 1), &! nodel temperature [K]        dz  (lb : 1), &! layer thickness [m]        z   (lb : 1), &! node depth [m]        zi  (lb - 1 : 1), &! depth of layer interface [m]        snowdp,       &! snow depth [m]        scv            ! snow mass - water equivalent [kg/m2]  integer, INTENT(inout) :: &        snl           ! Number of snow!!----------------------- Local variables ------------------------------!  real drr,       &! thickness of the combined [m]       dzmin(5),  &! minimum of snow layer 1 (top) to msn0 (bottom)       zwice,     &! total ice mass in snow       zwliq       ! total liquid water in snow  integer         &!       i,         &! number of do looping       j,         &! node index       k,         &! number of do looping       l,         &! node index       msn_old,   &! number of snow layer 1 (top) to msn0 (bottom)       mssi,      &! node index       neibor      ! adjacent node selected for combination  data dzmin /0.010, 0.015, 0.025, 0.055, 0.115/!!-----------------------------------------------------------------------! check the mass of ice lens of snow, when the total less than a small value,! combine it with the underlying neighbor      msn_old = snl      do j = msn_old+1, 0         if(wice(j) <= .1)then            wliq(j+1) = wliq(j+1) + wliq(j)            wice(j+1) = wice(j+1) + wice(j)! shift all elements above this down one.            if(j > snl+1 .AND. snl < -1)then               do i =  j, snl+2, -1                  tss(i) = tss(i-1)                  wliq(i) = wliq(i-1)                  wice(i) = wice(i-1)                  dz(i) = dz(i-1)               enddo            endif            snl = snl + 1!*          write(6,*) 'one snow layer is gone'         endif      enddo      if(snl == 0)then         scv = 0.         snowdp = 0.!*       write(6,*) 'all snow has gone'         return      else         scv = 0.         snowdp = 0.         zwice = 0.         zwliq = 0.         do j = snl + 1, 0            scv = scv + wice(j) + wliq(j)            snowdp = snowdp + dz(j)            zwice = zwice + wice(j)            zwliq = zwliq + wliq(j)         enddo      endif!-----------------------------------------------------------------------! check the snow depth      if(snowdp < 0.01)then       !!! all snow gone                    snl = 0         scv = zwice         if(scv <= 0.) snowdp = 0.! the liquid water assumed ponding on soil surface         wliq(1) = wliq(1) + zwliq!*       write(6,'(17h all snow is gone)')         return      else                        !!! snow layers combined! two or more layers         if(snl < -1)then           msn_old = snl           mssi = 1           do i = msn_old+1, 0! If top node is removed, combine with bottom neighbor              if(dz(i) < dzmin(mssi))then                 if(i == snl+1)then                    neibor = i + 1! If the bottom neighbor is not snow, combine with the top neighbor                 else if(i == 0)then                    neibor = i - 1! If none of the above special cases apply, combine with the thinnest neighbor                 else                   neibor = i + 1                   if((dz(i-1)+dz(i)) < (dz(i+1)+dz(i))) neibor = i-1                 endif! Node l and j are combined and stored as node j.                 if(neibor > i)then                    j = neibor                    l = i                 else                    j = i                    l = neibor                 endif                 call combo ( dz(j), wliq(j), wice(j), tss(j),&                              dz(l), wliq(l), wice(l), tss(l) )! Now shift all elements above this down one.                 if(j-1 > snl+1) then                    do k = j-1, snl+2, -1                       tss(k) = tss(k-1)                       wice(k) = wice(k-1)                       wliq(k) = wliq(k-1)                       dz(k) = dz(k-1)                    enddo                 endif                 snl = snl + 1!*    write(6,'(7h Nodes ,i4,4h and,i4,14h combined into,i4)') l,j,j                 if(snl >= -1) EXIT! The layer thickness great than the prescibed minimum value              else                 mssi = mssi + 1               endif           enddo        end if! Reset the node depth and the depth of layer interface        do k = 0, snl+1, -1           z(k) = zi(k) - 0.5*dz(k)           zi(k-1) = zi(k) - dz(k)        enddo      endif                       !!! snow layers combined   END SUBROUTINE combin