This is for the issue "R21B to IC4 subroutine"

I have ported my changes from COAMPS/WW3 (which is v6.07) to my fork, branch "1167-R21B-in-IC4" (which is version 7.14+).
Changes are made to 4 of the WW3 fortran files.'
I needed to do the merge manually, since there are a lot of formatting changes (etc.) going from 6.07 to 7.14.

model/src/w3gdatmd.F90

@@ -199,10 +199,14 @@ MODULE W3GDATMD
   !                               Default is 1.0, meaning that 100% ice
   !                               concentration result in zero source term
   !                               If set to 0.0, then ice has no direct impact on Sln / Sin / Snl / Sds
-  !      IC3PARS   R.A.  Public   various parameters for use in IC4, handled as
+  !      IC3PARS   R.A.  Public   various parameters for use in IC3, handled as
   !                               an array for simplicity
-  !      IC4_KI    R.A.  Public   KI (dissipation rate) values for use in IC4
-  !      IC4_FC    R.A.  Public   FC (frequency bin separators) for use in IC4
+  !      IC4_KI    R.A.  Public   KI (dissipation rate) values for use in IC4M6
+  !      IC4_FC    R.A.  Public   FC (frequency bin separators) for use in IC4M6
+  !      IC4_CN    R.A.  Public   Coefficients for use in IC4M2
+  !      IC4_FMIN  Real  Public   Minimum frequency below which ki is set to 
+  !                               some background level dissipation (for S_ice)
+  !      IC4_KIBK  Real  Public   Low, background level dissipation (for S_ice)
   !      PFMOVE    Real  Public   Tunable parameter in GSE correction
   !                               for moving grids.
   !      GRIDSHIFT Real  Public   Grid offset for multi-grid w/SCRIP
@@ -615,7 +619,7 @@ MODULE W3GDATMD
        IPARS = -1, NAUXGR
   !
 #ifdef W3_IC4
-  INTEGER, PARAMETER      :: NIC4=10
+  INTEGER, PARAMETER      :: NIC4=16 ,  NIC42=5
 #endif
   INTEGER, PARAMETER      :: RLGTYPE = 1
   INTEGER, PARAMETER      :: CLGTYPE = 2
@@ -732,6 +736,8 @@ MODULE W3GDATMD
     INTEGER, POINTER      :: IC4PARS(:)
     REAL, POINTER         :: IC4_KI(:)
     REAL, POINTER         :: IC4_FC(:)
+    REAL, POINTER         :: IC4_CN(:)
+    REAL                  :: IC4_FMIN, IC4_KIBK
 #endif
 #ifdef W3_IC5
     REAL,    POINTER      :: IC5PARS(:)
@@ -1144,6 +1150,8 @@ MODULE W3GDATMD
   INTEGER, POINTER        :: IC4PARS(:)
   REAL, POINTER           :: IC4_KI(:)
   REAL, POINTER           :: IC4_FC(:)
+  REAL, POINTER           :: IC4_CN(:)
+  REAL, POINTER           :: IC4_FMIN, IC4_KIBK
 #endif
 #ifdef W3_IC5
   REAL,    POINTER        :: IC5PARS(:)
@@ -1840,6 +1848,8 @@ SUBROUTINE W3DIMX  ( IMOD, MX, MY, MSEA, NDSE, NDST   &
     CHECK_ALLOC_STATUS ( ISTAT )
     ALLOCATE ( GRIDS(IMOD)%IC4_FC(NIC4), STAT=ISTAT )
     CHECK_ALLOC_STATUS ( ISTAT )
+    ALLOCATE ( GRIDS(IMOD)%IC4_CN(NIC42), STAT=ISTAT )
+    CHECK_ALLOC_STATUS ( ISTAT )
 #endif
 #ifdef W3_IC5
     ALLOCATE ( GRIDS(IMOD)%IC5PARS(9), STAT=ISTAT )
@@ -2308,6 +2318,9 @@ SUBROUTINE W3SETG ( IMOD, NDSE, NDST )
     IC4PARS => GRIDS(IMOD)%IC4PARS
     IC4_KI => GRIDS(IMOD)%IC4_KI
     IC4_FC => GRIDS(IMOD)%IC4_FC
+    IC4_CN => GRIDS(IMOD)%IC4_CN
+    IC4_FMIN => GRIDS(IMOD)%IC4_FMIN
+    IC4_KIBK => GRIDS(IMOD)%IC4_KIBK
 #endif
 #ifdef W3_IC5
     IC5PARS => GRIDS(IMOD)%IC5PARS

model/src/w3gridmd.F90

@@ -114,6 +114,7 @@ MODULE W3GRIDMD
   !/    07-Jun-2021 : S_{nl} GKE NL5 (Q. Liu)             ( version 7.13 )
   !/    19-Jul-2021 : Momentum and air density support    ( version 7.14 )
   !/    28-Feb-2023 : GQM as an alternative for NL1       ( version 7.15 )
+  !/    11-Jan-2024 : New namelist parameters for IC4     ( version 7.15 )
   !/
   !/    Copyright 2009-2013 National Weather Service (NWS),
   !/       National Oceanic and Atmospheric Administration.  All rights
@@ -764,9 +765,10 @@ MODULE W3GRIDMD
 
 #ifdef W3_IC4
   INTEGER                 :: IC4METHOD
-  REAL                    :: IC4KI(NIC4), IC4FC(NIC4)
+  REAL                    :: IC4KI(NIC4), IC4FC(NIC4),            &
+                             IC4CN(NIC42), IC4FMIN, IC4KIBK
 #endif
-  !
+
 #ifdef W3_IC5
   REAL                    :: IC5MINIG, IC5MINWT,                  &
        IC5MAXKRATIO, IC5MAXKI, IC5MINHW,    &
@@ -968,7 +970,8 @@ MODULE W3GRIDMD
        IC3VISC, IC3ELAS, IC3DENS, IC3HICE
 #endif
 #ifdef W3_IC4
-  NAMELIST /SIC4/  IC4METHOD, IC4KI, IC4FC
+  NAMELIST /SIC4/  IC4METHOD, IC4KI, IC4FC, IC4CN, IC4FMIN,  &
+                   IC4KIBK
 #endif
 #ifdef W3_IC5
   NAMELIST /SIC5/  IC5MINIG, IC5MINWT, IC5MAXKRATIO,        &
@@ -2877,6 +2880,9 @@ SUBROUTINE W3GRID()
     IC4METHOD = 1 !switch for methods within IC4
     IC4KI=0.0
     IC4FC=0.0
+    IC4CN=0.0
+    IC4FMIN=0.0
+    IC4KIBK=0.0
 #endif
     !
 #ifdef W3_IC5
@@ -5298,6 +5304,9 @@ SUBROUTINE W3GRID()
     IC4PARS(1)=IC4METHOD
     IC4_KI=IC4KI
     IC4_FC=IC4FC
+    IC4_CN=IC4CN
+    IC4_FMIN=IC4FMIN
+    IC4_KIBK=IC4KIBK
 #endif
     !
 #ifdef W3_IC5

model/src/w3iogrmd.F90

@@ -1292,11 +1292,11 @@ SUBROUTINE W3IOGR ( INXOUT, NDSM, IMOD, FEXT &
 #endif
 #ifdef W3_IC4
       WRITE   (NDSM)                                             &
-           IC4PARS,IC4_KI,IC4_FC
+           IC4PARS,IC4_KI,IC4_FC,IC4_CN,IC4_FMIN,IC4_KIBK
 #ifdef W3_ASCII
       WRITE   (NDSA,*)                                           &
-           'IC4PARS,IC4_KI,IC4_FC:',                             &
-           IC4PARS,IC4_KI,IC4_FC
+           'IC4PARS,IC4_KI,IC4_FC,IC4_CN,IC4_FMIN,IC4_KIBK:',    &
+           IC4PARS,IC4_KI,IC4_FC,IC4_CN,IC4_FMIN,IC4_KIBK
 #endif
 #endif
 #ifdef W3_IC5
@@ -1338,7 +1338,7 @@ SUBROUTINE W3IOGR ( INXOUT, NDSM, IMOD, FEXT &
 #endif
 #ifdef W3_IC4
       READ   (NDSM)                                              &
-           IC4PARS,IC4_KI,IC4_FC
+           IC4PARS,IC4_KI,IC4_FC,IC4_CN,IC4_FMIN,IC4_KIBK
 #endif
 #ifdef W3_IC5
       READ   (NDSM)                                              &