deep conv: add timescale_grid_factor parameter

Jongil suggested we remove the grid dependence of the convective
timescale. The time scale is currently proportional to

(1 + 1 / 75 km dx)

Adjust the scaling to be (1 + timescale_grid_factor * dx) so we can use
different grid scalings for coarse resolution.

FV3/gfsphysics/GFS_layer/GFS_physics_driver.F90

@@ -3595,7 +3595,9 @@ subroutine GFS_physics_driver                                 &
                              Model%c1_deep,  Model%betal_deep, Model%betas_deep,   &
                              Model%evfact_deep, Model%evfactl_deep,                &
                              Model%pgcon_deep,  Model%asolfac_deep,&
-                             Model%cinpcrmx, Model%cinpcrmn, Model%cinacrmn)
+                             Model%cinpcrmx, Model%cinpcrmn, Model%cinacrmn,&
+                             Model%timescale_grid_factor,&
+                             )
 !           if (lprnt) print *,' rain1=',rain1(ipr)
           !elseif (Model%imfdeepcnv == 3) then
           !  if (Model%me==0) then

FV3/gfsphysics/GFS_layer/GFS_typedefs.F90

@@ -895,6 +895,7 @@ module GFS_typedefs
     real(kind=kind_phys) :: cinpcrmx
     real(kind=kind_phys) :: cinpcrmn
     real(kind=kind_phys) :: cinacrmn
+    real(kind=kind_phys) :: timescale_grid_factor
     real(kind=kind_phys) :: clam_deep       !< c_e for deep convection (Han and Pan, 2011, eq(6))
     real(kind=kind_phys) :: c0s_deep        !< convective rain conversion parameter
     real(kind=kind_phys) :: c1_deep         !< conversion parameter of detrainment from liquid water into grid-scale cloud water
@@ -3131,6 +3132,7 @@ subroutine control_initialize (Model, nlunit, fn_nml, me, master, &
     real(kind=kind_phys) :: cinpcrmx = 180.0
     real(kind=kind_phys) :: cinpcrmn = 120.0
     real(kind=kind_phys) :: cinacrmn = -120.0
+    real(kind=kind_phys) :: timescale_grid_factor = 1.33333e-05
 
 !--- aerosol scavenging factors
     character(len=20) :: fscav_aero(20) = 'default'
@@ -3230,7 +3232,7 @@ subroutine control_initialize (Model, nlunit, fn_nml, me, master, &
                                fscav_aero, &
                                sst_perturbation,                                            & 
                                override_surface_radiative_fluxes, use_climatological_sst, &
-                               cinpcrmx, cinpcrmn, cinacrmn
+                               cinpcrmx, cinpcrmn, cinacrmn, timescale_grid_factor
 
 
 !--- other parameters 
@@ -3614,6 +3616,7 @@ subroutine control_initialize (Model, nlunit, fn_nml, me, master, &
     Model%cinpcrmn = cinpcrmn
     Model%cinpcrmx = cinpcrmx
     Model%cinacrmn = cinacrmn
+    Model%timescale_grid_factor = timescale_grid_factor
     Model%clam_deep        = clam_deep
     Model%c0s_deep         = c0s_deep
     Model%c1_deep          = c1_deep

FV3/gfsphysics/physics/samfdeepcnv.f

@@ -87,7 +87,7 @@ subroutine samfdeepcnv(im,ix,km,delt,itc,ntc,ntk,ntr,delp,
 !    &     QLCN, QICN, w_upi, cf_upi, CNV_MFD, CNV_PRC3,
      &     CNV_DQLDT,CLCN,CNV_FICE,CNV_NDROP,CNV_NICE,mp_phys,
      &     clam,c0s,c1,betal,betas,evfact,evfactl,pgcon,asolfac,
-     &     cinpcrmx, cinpcrmn, cinacrmn)
+     &     cinpcrmx, cinpcrmn, cinacrmn, timescale_grid_factor)
 !
       use machine , only : kind_phys
       use funcphys , only : fpvs
@@ -114,6 +114,8 @@ subroutine samfdeepcnv(im,ix,km,delt,itc,ntc,ntk,ntr,delp,
      &   rn(im),      cnvw(ix,km),  cnvc(ix,km),
      &   ud_mf(im,km),dd_mf(im,km), dt_mf(im,km)
 
+
+      real(kind=kind_phys) timescale_grid_factor
       real(kind=kind_phys) clam,    c0s,     c1,
      &                     betal,   betas,   asolfac,
      &                     evfact,  evfactl, pgcon, cinpcrmn, cinpcrmx
@@ -2273,7 +2275,7 @@ subroutine samfdeepcnv(im,ix,km,delt,itc,ntc,ntk,ntr,delp,
         if(cnvflg(i)) then
           tem = zi(i,ktcon1(i)) - zi(i,kbcon1(i))
           dtconv(i) = tem / wc(i)
-          tfac = 1. + gdx(i) / 75000.
+          tfac = 1. + timescale_grid_factor * gdx(i)
           dtconv(i) = tfac * dtconv(i)
           dtconv(i) = max(dtconv(i),dtmin)
           dtconv(i) = min(dtconv(i),dtmax)