Impose max limit on in-cloud water-content in pc2_checks

CONTRIBUTORS.md

@@ -34,4 +34,5 @@
 | thomasmelvin        | Thomas Melvin      | Met Office                       | 2026-01-15 |
 | tinyendian          | Wolfgang Hayek     | Earth Sciences New Zealand       | 2026-02-02 |
 | DanStoneMO          | Daniel Stone       | Met Office                       | 2026-02-26 |
-| ericaneininger      | Erica Neininger    | Met Office                       | 2026-03-02 |
+| ericaneininger      | Erica Neininger    | Met Office                       | 2026-03-02 |
+| MichaelWhitall      | Michael Whitall    | Met Office                       | 2026-03-26 |

interfaces/physics_schemes_interface/rose-meta/um-cloud/HEAD/rose-meta.conf

@@ -399,6 +399,22 @@ ns=namelist/Science/UM Cloud
 sort-key=Panel-A10
 type=logical
 
+[namelist:cloud=l_ensure_max_in_cloud_pc2]
+compulsory=true
+description=Impose a max limit on in-cloud water contents (liquid and ice)
+help=The max allowed in-cloud water content qc/cf is calculated interactively;
+    =it scales with the mean total-water q+qcl+qcf in the column below
+    =the current level.  It also scales with the cloud-fraction, so that
+    =the limit is lower at points with very tiny cloud-amounts
+    =(these points are the ones most likely to have ill-constrained
+    = in-cloud water content, since the transport scheme applied
+    = independently to condensate mass and cloud-fraction can create tiny
+    = inconsistent values of the two near the edges of advected clouds).
+!kind=default
+ns=namelist/Science/UM Cloud
+sort-key=Panel-A09b
+type=logical
+
 [namelist:cloud=max_sigmas]
 compulsory=true
 description=Max width of bimodal cloud-scheme Gaussian PDFs
@@ -569,6 +585,7 @@ trigger=namelist:cloud=mphys_erosion: 'pc2' ;
        =namelist:cloud=i_bm_ez_opt: 'pc2', 'bimodal' ;
        =namelist:cloud=l_bm_sigma_s_grad: 'pc2', 'bimodal' ;
        =namelist:cloud=l_bm_tweaks: 'pc2', 'bimodal' ;
+       =namelist:cloud=l_ensure_max_in_cloud_pc2: 'pc2' ;
        =namelist:cloud=max_sigmas: 'pc2', 'bimodal' ;
        =namelist:cloud=min_sigx_ft: 'pc2', 'bimodal' ;
        =namelist:cloud=turb_var_fac_bm: 'pc2', 'bimodal' ;

interfaces/physics_schemes_interface/rose-meta/um-cloud/versions.py

@@ -31,3 +31,17 @@ def upgrade(self, config, meta_config=None):
         # Add settings
         return config, self.reports
 """
+
+class vn31_t243(MacroUpgrade):
+    # Upgrade macro for Issue #243 by Mike Whitall
+
+    BEFORE_TAG = "vn3.1"
+    AFTER_TAG = "vn3.1_t243"
+
+    def upgrade(self, config, meta_config=None):
+        # Add settings
+
+        nml = "namelist:cloud"
+        self.add_setting(config, [nml,"l_ensure_max_in_cloud_pc2"], ".false.")
+
+        return config, self.reports

interfaces/physics_schemes_interface/rose-meta/um-microphysics/HEAD/rose-meta.conf

@@ -211,6 +211,19 @@ value-titles=Assumed homogenous sub-grid areas,
             =Assumed sub-grid spatial correlations
 values='homog','correl'
 
+[namelist:microphysics=l_improve_precfrac_checks]
+compulsory=true
+description=Improved safety-checks on the prognostic precip fraction
+help=a) Variable max limit on the in-rainshaft precip-mass better-targets small
+    =   noise values generated by the advection scheme.
+    =b) Avoid wrong application of the check where precip-mass is negative
+    =c) Reset precip-fraction to zero where precip-mass is zero.
+    =d) Extra call to the checking routine before convection if needed
+!kind=default
+ns=namelist/Science/UM Microphysics
+sort-key=Panel-A01g
+type=logical
+
 [namelist:microphysics=l_mcr_precfrac]
 compulsory=true
 description=Include prognostic rain/graupel fraction
@@ -237,6 +250,7 @@ help=Switch to include a prognostic field for the fraction of the
 ns=namelist/Science/UM Microphysics
 sort-key=Panel-A01e
 trigger=namelist:microphysics=i_update_precfrac: .true. ;
+       =namelist:microphysics=l_improve_precfrac_checks: .true. ;
 type=logical
 
 [namelist:microphysics=l_proc_fluxes]

interfaces/physics_schemes_interface/rose-meta/um-microphysics/versions.py

@@ -31,3 +31,17 @@ def upgrade(self, config, meta_config=None):
         # Add settings
         return config, self.reports
 """
+
+class vn31_t243(MacroUpgrade):
+    # Upgrade macro for Issue #243 by Mike Whitall
+
+    BEFORE_TAG = "vn3.1"
+    AFTER_TAG = "vn3.1_t243"
+
+    def upgrade(self, config, meta_config=None):
+        # Add settings
+
+        nml = "namelist:microphysics"
+        self.add_setting(config, [nml,"l_improve_precfrac_checks"], ".false.")
+
+        return config, self.reports

interfaces/physics_schemes_interface/source/algorithm/iau/iau_pc2_assimilation_alg_mod.X90

@@ -33,6 +33,7 @@ module iau_pc2_assimilation_alg_mod
   !>@param[in,out]  cloud_fields       Fields for cloud scheme
   !>@param[in]      theta              Potential temperature
   !>@param[in]      theta_earlier      Copy of potential temperature before incrementing
+  !>@param[in]      exner              Exner pressure on w3 space
   !>@param[in]      exner_wth          Exner pressure on wtheta space
   !>@param[in]      exner_earlier_wth  Copy of exner pressure on wtheta before incrementing
   !>@param[in]      m_v                Vapour mass mixing ratio
@@ -44,7 +45,7 @@ module iau_pc2_assimilation_alg_mod
   !>@param[in]      m_g                Graupel mixing ratio
   !>@param[in]      mg_earlier         Copy of graupel mixing ratio before incrementing
   !>@param[in]      dt                 Timestep length (s)
-  subroutine iau_pc2_assimilation( exner_wth,exner_earlier_wth,             &
+  subroutine iau_pc2_assimilation( exner, exner_wth,exner_earlier_wth,      &
                                    theta, theta_earlier,                    &
                                    m_v, mv_earlier ,                        &
                                    m_cl, mcl_earlier,                       &
@@ -60,6 +61,7 @@ module iau_pc2_assimilation_alg_mod
     type( field_collection_type ), intent(inout) :: cloud_fields
     type( field_type ),            intent(inout) :: theta
     type( field_type ),            intent(in)    :: theta_earlier
+    type( field_type ),            intent(in)    :: exner
     type( field_type ),            intent(in)    :: exner_wth
     type( field_type ),            intent(in)    :: exner_earlier_wth
     type( field_type ),            intent(inout) :: m_v
@@ -167,6 +169,7 @@ module iau_pc2_assimilation_alg_mod
                                          bcf,                   &
                                          theta,                 &
                                          exner_wth,             &
+                                         exner,                 &
                                          ! Responses
                                          theta_inc_wth,         &
                                          mv_inc_wth,            &

interfaces/physics_schemes_interface/source/algorithm/iau/update_iau_inc_alg_mod.X90

@@ -264,7 +264,7 @@ module update_iau_inc_alg_mod
     ! PC2 cloud and humidity adjustments
     if ( iau_pc2 ) then
 
-      call iau_pc2_assimilation( exner_wth, exner_earlier_wth,     &
+      call iau_pc2_assimilation( exner, exner_wth, exner_earlier_wth,          &
                                  theta, theta_earlier,             &
                                  m_v, mv_earlier ,                 &
                                  m_cl, mcl_earlier,                &

interfaces/physics_schemes_interface/source/algorithm/pc2_checks_alg_mod.x90

@@ -29,6 +29,7 @@ contains
   !>         See UMDP30 for full scheme details.
   !>@param[in]     mr               Start of timestep mixing ratios
   !>@param[in]     theta            Potential temperature (theta) in wth space
+  !>@param[in]     exner            Exner pressure on w3 space
   !>@param[in]     derived_fields   Group of derived fields
   !>@param[in]     cloud_fields     Group of cloud fields
   !>@param[out]    dtheta_pc2_inc   Potential temperature response in wth space
@@ -41,6 +42,7 @@ contains
 
   subroutine pc2_checks_alg( mr,             &
                              theta,          &
+                             exner,          &
                              derived_fields, &
                              cloud_fields,   &
                              dtheta_pc2_inc, &
@@ -59,8 +61,7 @@ contains
     implicit none
 
     type( field_type ), intent( in ) :: mr ( nummr )
-    type( field_type ), intent( in ) :: theta
-
+    type( field_type ), intent( in ) :: theta, exner
     type( field_collection_type ), intent(in) :: derived_fields, cloud_fields
 
     type( field_type ), intent(out) :: dtheta_pc2_inc
@@ -108,6 +109,7 @@ contains
                                            bulk_fraction,       &
                                            theta,               &
                                            exner_in_wth,        &
+                                           exner,               &
                                                       ! Responses
                                            dtheta_pc2_inc,      &
                                            dmv_pc2_inc,         &

interfaces/physics_schemes_interface/source/kernel/conv_comorph_kernel_mod.F90

@@ -774,8 +774,8 @@ subroutine conv_comorph_code(nlayers, seg_len,             &
                                 fldname_n_cor_ins,                             &
                                 fldname_cor_ins_du
 
-    use aerosol_config_mod,        only: glomap_mode,               &
-                                         glomap_mode_dust_and_clim, &
+    use aerosol_config_mod,        only: glomap_mode,                          &
+                                         glomap_mode_dust_and_clim,            &
                                          glomap_mode_ukca
 
     use log_mod, only : log_event, log_scratch_space, LOG_LEVEL_ERROR
@@ -785,13 +785,15 @@ subroutine conv_comorph_code(nlayers, seg_len,             &
     ! UM modules containing switches or global constants
     !---------------------------------------
     use bl_option_mod, only: max_tke
-    use cloud_inputs_mod, only: l_pc2_homog_conv_pressure
-    use cv_run_mod, only: l_mom,                                          &
-                          l_conv_prog_dtheta, l_conv_prog_dq,             &
+    use cloud_inputs_mod, only: l_pc2_homog_conv_pressure,                     &
+                                l_cloud_call_b4_conv,                          &
+                                l_ensure_max_in_cloud_pc2
+    use cv_run_mod, only: l_mom,                                               &
+                          l_conv_prog_dtheta, l_conv_prog_dq,                  &
                           tau_conv_prog_dtheta, tau_conv_prog_dq
     use jules_surface_mod, only: srf_ex_cnv_gust, IP_SrfExWithCnv
-    use mphys_inputs_mod, only: l_mcr_qgraup, l_mcr_qrain, l_mcr_precfrac, &
-         l_mcr_qcf2
+    use mphys_inputs_mod, only: l_mcr_qgraup, l_mcr_qrain, l_mcr_qcf2,         &
+                                l_mcr_precfrac, l_improve_precfrac_checks
     use nlsizes_namelist_mod, only: row_length, rows, bl_levels
     use planet_constants_mod, only: p_zero, kappa, planet_radius, g
     use timestep_mod, only: timestep
@@ -2008,28 +2010,28 @@ subroutine conv_comorph_code(nlayers, seg_len,             &
       end do
     end do
 
+    do i = 1, row_length
+      do k = 1, nlayers
+        precfrac_star(i,1,k) = precfrac(map_wth(1,i)+k)
+      end do
+    end do
+
     ! The "latest" (_star) fields used by convection are values
     ! interpolated to departure points by SL advection.
     ! The interpolation is not guaranteed to preserve consistency
     ! between the cloud fraction and cloud water fields.
     ! However, various things can go wrong within CoMorph if they
-    ! are inconsistent; especially the routine calc_env_partitions,
-    ! which attempts to calculate the internal properties of
-    ! the in-cloud and clear sub-regions of the grid-box.
-    ! E.g. a common problem is if qcf is large but CFF is small,
-    ! the in-cloud qcf can get implausibly large, which can
-    ! cause the phase-change calculations to yield nonsense.
+    ! are inconsistent.
     ! Therefore, apply safety checks to the cloud-fractions
     ! before passing them into convection...
-    do i = 1, row_length
-      do k = 1, nlayers
-        precfrac_star(i,1,k) = precfrac(map_wth(1,i)+k)
-      end do
-    end do
-    CALL fracs_consistency  ( qcl_conv, qcf_conv, qcf2_conv,                   &
+    if ( ( .not. (l_cloud_call_b4_conv .and. l_ensure_max_in_cloud_pc2) ) .or. &
+         ( l_mcr_precfrac .and. ( .not. l_improve_precfrac_checks ) ) ) then
+      ! Don't need to do this if similar checks already switched on elsewhere
+      CALL fracs_consistency( qcl_conv, qcf_conv, qcf2_conv,                   &
                               qrain_conv, qgraup_conv,                         &
                               cf_liquid_conv, cf_frozen_conv, bulk_cf_conv,    &
                               precfrac_star )
+    end if
 
     ! Note: if not using PC2, the cloud-fraction _star fields do exist
     ! but are just set to values after slow_physics