BiogeophysicsLake

INTERFACE:

   subroutine BiogeophysicsLake (c)

DESCRIPTION:

   Calculates lake temperatures  and surface fluxes.
   Lake temperatures are determined from a one-dimensional thermal
   stratification model based on eddy diffusion concepts to 
   represent vertical mixing of heat.
   d ts    d            d ts     1 ds
   ---- = -- [(km + ke) ----] + -- --
    dt    dz             dz     cw dz   
   where: ts = temperature (kelvin)
           t = time (s)
           z = depth (m)
          km = molecular diffusion coefficient (m**2/s)
          ke = eddy diffusion coefficient (m**2/s)
          cw = heat capacity (j/m**3/kelvin)
           s = heat source term (w/m**2)
   There are two types of lakes: 
     Deep lakes are 50 m. 
     Shallow lakes are 10 m deep.
     For unfrozen deep lakes:    ke > 0 and    convective mixing
     For unfrozen shallow lakes: ke = 0 and no convective mixing
   Use the Crank-Nicholson method to set up tridiagonal system of equations to
   solve for ts at time n+1, where the temperature equation for layer i is
   r_i = a_i [ts_i-1] n+1 + b_i [ts_i] n+1 + c_i [ts_i+1] n+1
   The solution conserves energy as:
   cw*([ts(      1)] n+1 - [ts(      1)] n)*dz(      1)/dt + ... +
   cw*([ts(nlevlak)] n+1 - [ts(nlevlak)] n)*dz(nlevlak)/dt = fin
   where:
   [ts] n   = old temperature (kelvin)
   [ts] n+1 = new temperature (kelvin)
   fin      = heat flux into lake (w/m**2)
            = beta*sabg + forc_lwrad - eflx_lwrad_out - eflx_sh_tot - eflx_lh_tot 
              - hm + phi(1) + ... + phi(nlevlak)

USES:

     use shr_kind_mod, only: r8 => shr_kind_r8
     use clmtype
     use globals
     use clm_varpar, only : nlevlak
     use clm_varcon, only : hvap, hsub, hfus, cpair, cpliq, tkwat, tkice, &
          sb, vkc, grav, denh2o, tfrz, spval
     use SurfaceRadiationMod, only : SurfaceRadiation
     use QSatMod, only : QSat
     use FrictionVelocityMod, only : MoninObukIni, FrictionVelocity
     use TridiagonalMod, only : Tridiagonal

ARGUMENTS:

     implicit none
     type (column_type), target, intent(inout) :: c  !column derived type

CALLED FROM:

   subroutine driver

REVISION HISTORY:

   Author: Gordon Bonan
   15 September 1999: Yongjiu Dai; Initial code
   15 December 1999:  Paul Houser and Jon Radakovich; F90 Revision 
   Migrated to clm2.1 new data structures by Peter Thornton and M. Vertenstein

LOCAL VARIABLES:

   local pointers to implicit in scalars
     real(r8), pointer :: forc_t          !atmospheric temperature (Kelvin)
     real(r8), pointer :: forc_pbot       !atmospheric pressure (Pa)
     real(r8), pointer :: forc_hgt        !atmospheric reference height (m)
     real(r8), pointer :: forc_hgt_q      !observational height of humidity [m]
     real(r8), pointer :: forc_hgt_t      !observational height of temperature [m]
     real(r8), pointer :: forc_hgt_u      !observational height of wind [m]
     real(r8), pointer :: forc_th         !atmospheric potential temperature (Kelvin)
     real(r8), pointer :: forc_q          !atmospheric specific humidity (kg/kg)
     real(r8), pointer :: forc_u          !atmospheric wind speed in east direction (m/s)
     real(r8), pointer :: forc_v          !atmospheric wind speed in north direction (m/s)
     real(r8), pointer :: forc_lwrad      !downward infrared (longwave) radiation (W/m**2)
     real(r8), pointer :: forc_rho        !density (kg/m**3)
     real(r8), pointer :: forc_snow       !snow rate [mm/s]
     real(r8), pointer :: forc_rain       !rain rate [mm/s]
     real(r8), pointer :: t_grnd          !ground temperature (Kelvin)
     real(r8), pointer :: h2osno          !snow water (mm H2O)
     real(r8), pointer :: snowdp          !snow height (m)
     real(r8), pointer :: sabg            !solar radiation absorbed by ground (W/m**2)
     real(r8), pointer :: lat             !latitude (radians)
   local pointers to implicit out scalars
     real(r8), pointer :: begwb           !water mass begining of the time step
     real(r8), pointer :: qflx_prec_grnd  !water onto ground including canopy runoff [kg/(m2 s)]
     real(r8), pointer :: qflx_evap_soi   !soil evaporation (mm H2O/s) (+ = to atm)
     real(r8), pointer :: qflx_evap_tot   !qflx_evap_soi + qflx_evap_veg + qflx_tran_veg
     real(r8), pointer :: eflx_sh_grnd    !sensible heat flux from ground (W/m**2) [+ to atm]
     real(r8), pointer :: eflx_lwrad_out  !emitted infrared (longwave) radiation (W/m**2)
     real(r8), pointer :: eflx_lwrad_net  !net infrared (longwave) rad (W/m**2) [+ = to atm]
     real(r8), pointer :: eflx_soil_grnd  !soil heat flux (W/m**2) [+ = into soil]
     real(r8), pointer :: eflx_sh_tot     !total sensible heat flux (W/m**2) [+ to atm]
     real(r8), pointer :: eflx_lh_tot     !total latent heat flux (W/m8*2)  [+ to atm]
     real(r8), pointer :: eflx_lh_grnd    !ground evaporation heat flux (W/m**2) [+ to atm]
     real(r8), pointer :: t_rad_column    !radiative temperature (Kelvin)
     real(r8), pointer :: t_rad_pft       !radiative temperature (Kelvin)
     real(r8), pointer :: t_veg           !vegetation temperature (Kelvin)
     real(r8), pointer :: t_ref2m         !2 m height surface air temperature (Kelvin)
     real(r8), pointer :: taux            !wind (shear) stress: e-w (kg/m/s**2)
     real(r8), pointer :: tauy            !wind (shear) stress: n-s (kg/m/s**2)
     real(r8), pointer :: qmelt           !snow melt [mm/s]
     real(r8), pointer :: u10             !10-m wind (m/s) (for dust model)
     real(r8), pointer :: fv              !friction velocity (m/s) (for dust model)
     real(r8), pointer :: ram1            !aerodynamical resistance (s/m)
     real(r8), pointer :: errsoi          !soil/lake energy conservation error (W/m**2)
   local pointers to implicit in arrays
     real(r8), dimension(:), pointer :: dz !layer thickness (m)
     real(r8), dimension(:), pointer :: z  !layer depth (m)
   local pointers to implicit out arrays
     real(r8), dimension(:), pointer :: t_lake !lake temperature (Kelvin)