precpd.f

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       subroutine precpd (im,ix,km,dt,del,prsl,q,cwm,t,rn,sr            &
     &,                   rainp,u00k,psautco,prautco,evpco,wminco       &
     &,                   lprnt,jpr)
!
!
!     ******************************************************************
!     *                                                                *
!     *           subroutine for precipitation processes               *
!     *           from suspended cloud water/ice                       *
!     *                                                                *
!     ******************************************************************
!     *                                                                *
!     *  originally created by  q. zhao                jan. 1995       *
!     *                         -------                                *    
!     *  modified and rewritten by shrinivas moorthi   oct. 1998       *
!     *                            -----------------                   *
!     *  and                       hua-lu pan                          *
!     *                            ----------                          *
!     *                                                                *
!     *  references:                                                   *
!     *                                                                *
!     *  zhao and carr (1997), monthly weather review (august)         *
!     *  sundqvist et al., (1989) monthly weather review. (august)     *
!     *  chuang 2013, modify sr to define frozen precipitation fraction*
!     ******************************************************************
!
!     in this code vertical indexing runs from surface to top of the
!     model
!
!     argument list:
!     --------------
!       im         : inner dimension over which calculation is made
!       ix         : maximum inner dimension
!       km         : number of vertical levels
!       dt         : time step in seconds
!       del(km)    : pressure layer thickness (bottom to top)
!       prsl(km)   : pressure values for model layers (bottom to top)
!       q(ix,km)   : specific humidity (updated in the code)
!       cwm(ix,km) : condensate mixing ratio (updated in the code)
!       t(ix,km)   : temperature       (updated in the code)
!       rn(im)     : precipitation over one time-step dt (m/dt)
!old    sr(im)     : index (=-1 snow, =0 rain/snow, =1 rain)
!new    sr(im)     : "snow ratio", ratio of snow to total precipitation
!       cll(ix,km) : cloud cover
!hchuang rn(im) unit in m per time step
!        precipitation rate conversion 1 mm/s = 1 kg/m2/s
!
      use machine , only : kind_phys
      use funcphys , only : fpvs
      use physcons, grav => con_g, hvap => con_hvap, hfus => con_hfus
     &,             ttp => con_ttp, cp => con_cp
     &,             eps => con_eps, epsm1 => con_epsm1
      implicit none
!     include 'constant.h'
!
      real (kind=kind_phys) g,      h1,    h1000
     &,                     d00
     &,                     elwv,   eliv,  row
     &,                     epsq,   eliw
     &,                     rcp,    rrow
       parameter(g=grav,         h1=1.e0,     h1000=1000.0
     &,           d00=0.e0
     &,           elwv=hvap,      eliv=hvap+hfus,   row=1.e3
     &,           epsq=2.e-12
     &,           eliw=eliv-elwv, rcp=h1/cp,   rrow=h1/row)
!
      real(kind=kind_phys), parameter :: cons_0=0.0,     cons_p01=0.01
     &,                                  cons_20=20.0
     &,                                  cons_m30=-30.0, cons_50=50.0
!
      integer im, ix, km, jpr
      real (kind=kind_phys) q(ix,km),   t(ix,km),    cwm(ix,km)         &
     &,                                 del(ix,km),  prsl(ix,km)        &
     &,                     rn(im),      sr(im)                         &
     &,                     dt                                          &
     &,                     rainp(im,km), rnp(im),                      &
     &                      psautco(im), prautco(im), evpco, wminco(2)
!
!
      real (kind=kind_phys) err(im),      ers(im),     precrl(im)       &
     &,                     precsl(im),   precrl1(im), precsl1(im)      &
     &,                     rq(im),       condt(im)                     &
     &,                     conde(im),    rconde(im),  tmt0(im)         &
     &,                     wmin(im,km),  wmink(im),   pres(im)         &
     &,                     wmini(im,km), ccr(im)                       &
     &,                     tt(im),       qq(im),      ww(im)           &
     &,                     u00k(im,km)                                 &
     &,                     zaodt
       real (kind=kind_phys) cclim(km)
!
      integer iw(im,km), ipr(im), iwl(im),     iwl1(im)
!
       logical comput(im)
       logical lprnt
!
      real (kind=kind_phys) ke,   rdt,  us, climit, cws, csm1
     &,                     crs1, crs2, cr, aa2,     dtcp,   c00, cmr
     &,                     tem,  c1,   c2, wwn
!    &,                     tem,  c1,   c2, u00b,    u00t,   wwn
     &,                     precrk, precsk, pres1,   qk,     qw,  qi
     &,                     qint, fiw, wws, cwmk, expf
     &,                     psaut, psaci, amaxcm, tem1, tem2
     &,                     tmt0k, psm1, psm2, ppr
     &,                     rprs,  erk,   pps, sid, rid, amaxps
     &,                     praut, fi, qc, amaxrq, rqkll
      integer i, k, ihpr, n
!
!-----------------------preliminaries ---------------------------------
!
!     do k=1,km
!       do i=1,im
!         cll(i,k) = 0.0
!       enddo
!     enddo
!
      rdt     = h1 / dt
!     ke      = 2.0e-5  ! commented on 09/10/99  -- opr value
!     ke      = 2.0e-6
!     ke      = 1.0e-5
!!!   ke      = 5.0e-5
!!    ke      = 7.0e-5
      ke      = evpco
!     ke      = 7.0e-5
      us      = h1
      climit  = 1.0e-20
      cws     = 0.025
!
      zaodt   = 800.0 * rdt
!
      csm1    = 5.0000e-8   * zaodt
      crs1    = 5.00000e-6  * zaodt
      crs2    = 6.66600e-10 * zaodt
      cr      = 5.0e-4      * zaodt
      aa2     = 1.25e-3     * zaodt
!
      ke      = ke * sqrt(rdt)
!     ke      = ke * sqrt(zaodt)
!
      dtcp    = dt * rcp
!
!     c00 = 1.5e-1 * dt
!     c00 = 10.0e-1 * dt
!     c00 = 3.0e-1 * dt          !05/09/2000
!     c00 = 1.0e-4 * dt          !05/09/2000
!     c00 = prautco * dt         !05/09/2000
      cmr = 1.0 / 3.0e-4
!     cmr = 1.0 / 5.0e-4
!     c1  = 100.0
      c1  = 300.0
      c2  = 0.5
!
!
!--------calculate c0 and cmr using lc at previous step-----------------
!
      do k=1,km
        do i=1,im
          tem   = (prsl(i,k)*0.00001)
!         tem   = sqrt(tem)
          iw(i,k)    = 0.0
!         wmin(i,k)  = 1.0e-5 * tem
!         wmini(i,k) = 1.0e-5 * tem       ! testing for ras
!

          wmin(i,k)  = wminco(1) * tem
          wmini(i,k) = wminco(2) * tem


          rainp(i,k) = 0.0

        enddo
      enddo
      do i=1,im
!       c0(i)  = 1.5e-1
!       cmr(i) = 3.0e-4
!
        iwl1(i)    = 0
        precrl1(i) = d00
        precsl1(i) = d00
        comput(i)  = .false.
        rn(i)      = d00
        sr(i)      = d00
        ccr(i)     = d00
!
        rnp(i)     = d00
      enddo

!------------select columns where rain can be produced--------------
      do k=1, km-1
        do i=1,im
          tem = min(wmin(i,k), wmini(i,k))
          if (cwm(i,k) > tem) comput(i) = .true.
        enddo
      enddo
      ihpr = 0
      do i=1,im
        if (comput(i)) then
           ihpr      = ihpr + 1
           ipr(ihpr) = i
        endif
      enddo
!***********************************************************************
!-----------------begining of precipitation calculation-----------------
!***********************************************************************
!     do k=km-1,2,-1
      do k=km,1,-1
        do n=1,ihpr
          precrl(n) = precrl1(n)
          precsl(n) = precsl1(n)
          err(n)  = d00
          ers(n)  = d00
          iwl(n)  = 0
!
          i         = ipr(n)
          tt(n)     = t(i,k)
          qq(n)     = q(i,k)
          ww(n)     = cwm(i,k)
          wmink(n)  = wmin(i,k)
          pres(n)   = prsl(i,k)
!
          precrk = max(cons_0,    precrl1(n))
          precsk = max(cons_0,    precsl1(n))
          wwn    = max(ww(n), climit)
!         if (wwn .gt. wmink(n) .or. (precrk+precsk) .gt. d00) then
          if (wwn > climit .or. (precrk+precsk) > d00) then
            comput(n) = .true.
          else
            comput(n) = .false.
          endif
        enddo
!
!       es(1:ihpr) = fpvs(tt(1:ihpr))
        do n=1,ihpr
          if (comput(n)) then
            i = ipr(n)
            conde(n)  = (dt/g) * del(i,k)
            condt(n)  = conde(n) * rdt
            rconde(n) = h1 / conde(n)
            qk        = max(epsq,  qq(n))
            tmt0(n)   = tt(n) - 273.16
            wwn       = max(ww(n), climit)
!
!           pl = pres(n) * 0.01
!           call qsatd(tt(n), pl, qc)
!           rq(n) = max(qq(n), epsq) / max(qc, 1.0e-10)
!           rq(n) = max(1.0e-10, rq(n))           ! -- relative humidity---
!
!  the global qsat computation is done in pa
            pres1   = pres(n) 
!           qw      = es(n)
            qw      = min(pres1, fpvs(tt(n)))
            qw      = eps * qw / (pres1 + epsm1 * qw)
            qw      = max(qw,epsq)
!
!           tmt15 = min(tmt0(n), cons_m15)
!           ai    = 0.008855
!           bi    = 1.0
!           if (tmt0(n) .lt. -20.0) then
!             ai = 0.007225
!             bi = 0.9674
!           endif
!           qi   = qw * (bi + ai*min(tmt0(n),cons_0))
!           qint = qw * (1.-0.00032*tmt15*(tmt15+15.))
!
            qi   = qw
            qint = qw
!           if (tmt0(n).le.-40.) qint = qi
!
!-------------------ice-water id number iw------------------------------
            if(tmt0(n) < -15.) then
               fi = qk - u00k(i,k)*qi
               if(fi > d00 .or. wwn > climit) then
                  iwl(n) = 1
               else
                  iwl(n) = 0
               endif
!           endif
            elseif (tmt0(n) >= 0.) then
               iwl(n) = 0
!
!           if(tmt0(n).lt.0.0.and.tmt0(n).ge.-15.0) then
            else
              iwl(n) = 0
              if(iwl1(n) == 1 .and. wwn > climit) iwl(n) = 1
            endif
!
!           if(tmt0(n).ge.0.) then
!              iwl(n) = 0
!           endif
!----------------the satuation specific humidity------------------------
            fiw   = float(iwl(n))
            qc    = (h1-fiw)*qint + fiw*qi
!----------------the relative humidity----------------------------------
            if(qc <= 1.0e-10) then
               rq(n) = d00
            else
               rq(n) = qk / qc
            endif
!----------------cloud cover ratio ccr----------------------------------
            if(rq(n) < u00k(i,k)) then
                   ccr(n) = d00
            elseif(rq(n) >= us) then
                   ccr(n) = us
            else
                 rqkll  = min(us,rq(n))
                 ccr(n) = h1-sqrt((us-rqkll)/(us-u00k(i,k)))
            endif
!
          endif
        enddo
!-------------------ice-water id number iwl------------------------------
!       do n=1,ihpr
!         if (comput(n) .and.  (ww(n) .gt. climit)) then
!           if (tmt0(n) .lt. -15.0
!    *         .or. (tmt0(n) .lt. 0.0 .and. iwl1(n) .eq. 1))
!    *                                      iwl(n) = 1
!             cll(ipr(n),k) = 1.0                           ! cloud cover!
!             cll(ipr(n),k) = min(1.0, ww(n)*cclim(k))      ! cloud cover!
!         endif
!       enddo
!
!---   precipitation production --  auto conversion and accretion
!
        do n=1,ihpr
          if (comput(n) .and. ccr(n) > 0.0) then
            wws    = ww(n)
            cwmk   = max(cons_0, wws)
            i      = ipr(n)
!           amaxcm = max(cons_0, cwmk - wmink(n))
            if (iwl(n) == 1) then                 !  ice phase
               amaxcm = max(cons_0, cwmk - wmini(i,k))
               expf      = dt * exp(0.025*tmt0(n))
               psaut     = min(cwmk, psautco(i)*expf*amaxcm)
               ww(n)     = ww(n) - psaut
               cwmk      = max(cons_0, ww(n))
!              cwmk      = max(cons_0, ww(n)-wmini(i,k))
               psaci     = min(cwmk, aa2*expf*precsl1(n)*cwmk)

               ww(n)     = ww(n) - psaci
               precsl(n) = precsl(n) + (wws - ww(n)) * condt(n)
            else                                    !  liquid water
!
!          for using sundqvist precip formulation of rain
!
               amaxcm    = max(cons_0, cwmk - wmink(n))
!!             amaxcm    = cwmk
               tem1      = precsl1(n) + precrl1(n)
               tem2      = min(max(cons_0, 268.0-tt(n)), cons_20)
               tem       = (1.0+c1*sqrt(tem1*rdt)) * (1+c2*sqrt(tem2))
!
               tem2      = amaxcm * cmr * tem / max(ccr(n),cons_p01)
               tem2      = min(cons_50, tem2*tem2)
!              praut     = c00  * tem * amaxcm * (1.0-exp(-tem2))
               praut     = (prautco(i)*dt) * tem * amaxcm
     &                                     * (1.0-exp(-tem2))
               praut     = min(praut, cwmk)
               ww(n)     = ww(n) - praut
!
!          below is for zhao's precip formulation (water)
!
!              amaxcm    = max(cons_0, cwmk - wmink(n))
!              praut     = min(cwmk, c00*amaxcm*amaxcm)
!              ww(n)     = ww(n) - praut
!
!              cwmk      = max(cons_0, ww(n))
!              tem1      = precsl1(n) + precrl1(n)
!              pracw     = min(cwmk, cr*dt*tem1*cwmk)
!              ww(n)     = ww(n) - pracw
!
               precrl(n) = precrl(n) + (wws - ww(n)) * condt(n)
!
!hchuang code change [+1l] : add record to record information in vertical
! turn rnp in unit of ww (cwm and q, kg/kg ???)
               rnp(n) = rnp(n) + (wws - ww(n))
            endif
          endif
        enddo
!
!-----evaporation of precipitation-------------------------
!**** err & ers positive--->evaporation-- negtive--->condensation
!
        do n=1,ihpr
          if (comput(n)) then
            i      = ipr(n)
            qk     = max(epsq,  qq(n))
            tmt0k  = max(cons_m30, tmt0(n))
            precrk = max(cons_0,    precrl(n))
            precsk = max(cons_0,    precsl(n))
            amaxrq = max(cons_0,    u00k(i,k)-rq(n)) * conde(n)
!----------------------------------------------------------------------
! increase the evaporation for strong/light prec
!----------------------------------------------------------------------
            ppr    = ke * amaxrq * sqrt(precrk)
!           ppr    = ke * amaxrq * sqrt(precrk*rdt)
            if (tmt0(n) .ge. 0.) then
              pps = 0.
            else
              pps = (crs1+crs2*tmt0k) * amaxrq * precsk / u00k(i,k)
            end if
!---------------correct if over-evapo./cond. occurs--------------------
            erk=precrk+precsk
            if(rq(n).ge.1.0e-10)  erk = amaxrq * qk * rdt / rq(n)
            if (ppr+pps .gt. abs(erk)) then
               rprs   = erk / (precrk+precsk)
               ppr    = precrk * rprs
               pps    = precsk * rprs
            endif
            ppr       = min(ppr, precrk)
            pps       = min(pps, precsk)
            err(n)    = ppr * rconde(n)
            ers(n)    = pps * rconde(n)
            precrl(n) = precrl(n) - ppr
!hchuang code change [+1l] : add record to record information in vertical
! use err for kg/kg/dt not the ppr (mm/dt=kg/m2/dt)
!
            rnp(n) = rnp(n) - err(n)
!
            precsl(n) = precsl(n) - pps
          endif
        enddo
!--------------------melting of the snow--------------------------------
        do n=1,ihpr
          if (comput(n)) then
            if (tmt0(n) .gt. 0.) then
               amaxps = max(cons_0,    precsl(n))
               psm1   = csm1 * tmt0(n) * tmt0(n) * amaxps
               psm2   = cws * cr * max(cons_0, ww(n)) * amaxps
               ppr    = (psm1 + psm2) * conde(n)
               if (ppr .gt. amaxps) then
                 ppr  = amaxps
                 psm1 = amaxps * rconde(n)
               endif
               precrl(n) = precrl(n) + ppr
!
!hchuang code change [+1l] : add record to record information in vertical
! turn ppr (mm/dt=kg/m2/dt) to kg/kg/dt -> ppr/air density (kg/m3)
               rnp(n) = rnp(n) + ppr * rconde(n)
!
               precsl(n) = precsl(n) - ppr
            else
               psm1 = d00
            endif
!
!---------------update t and q------------------------------------------

            tt(n) = tt(n) - dtcp * (elwv*err(n)+eliv*ers(n)+eliw*psm1)
            qq(n) = qq(n) + dt * (err(n)+ers(n))
          endif
        enddo
!
        do n=1,ihpr
          iwl1(n)    = iwl(n)
          precrl1(n) = max(cons_0, precrl(n))
          precsl1(n) = max(cons_0, precsl(n))
          i          = ipr(n)
          t(i,k)     = tt(n)
          q(i,k)     = qq(n)
          cwm(i,k)   = ww(n)
          iw(i,k)    = iwl(n)
!hchuang code change [+1l] : add record to record information in vertical
! rnp = precrl1*rconde(n) unit in kg/kg/dt
!
          rainp(i,k) = rnp(n)
        enddo
!
!  move water from vapor to liquid should the liquid amount be negative
!
        do i = 1, im
          if (cwm(i,k) < 0.) then
            tem      = q(i,k) + cwm(i,k)
            if (tem >= 0.0) then
              q(i,k)   = tem
              t(i,k)   = t(i,k) - elwv * rcp * cwm(i,k)
              cwm(i,k) = 0.
            elseif (q(i,k) > 0.0) then
              cwm(i,k) = tem
              t(i,k)   = t(i,k) + elwv * rcp * q(i,k)
              q(i,k)   = 0.0
            endif
          endif
        enddo
!
      enddo                               ! k loop ends here!
!**********************************************************************
!-----------------------end of precipitation processes-----------------
!**********************************************************************
!
      do n=1,ihpr
        i = ipr(n)
        rn(i) = (precrl1(n)  + precsl1(n)) * rrow  ! precip at surface
!
!----sr=1 if sfc prec is rain ; ----sr=-1 if sfc prec is snow
!----sr=0 for both of them or no sfc prec
!
!        rid = 0.
!        sid = 0.
!        if (precrl1(n) .ge. 1.e-13) rid = 1.
!        if (precsl1(n) .ge. 1.e-13) sid = -1.
!        sr(i) = rid + sid  ! sr=1 --> rain, sr=-1 -->snow, sr=0 -->both
! chuang, june 2013: change sr to define fraction of frozen precipitation instead
! because wpc uses it in their winter experiment

        rid = precrl1(n) + precsl1(n)
        if (rid < 1.e-13) then
           sr(i) = 0.
        else
           sr(i) = precsl1(n)/rid
        endif 
      enddo
!
      return
      end
!! @}