Index: /NEMO/releases/release-4.0/src/ICE/icedyn_rhg_evp.F90
===================================================================
--- /NEMO/releases/release-4.0/src/ICE/icedyn_rhg_evp.F90	(revision 10889)
+++ /NEMO/releases/release-4.0/src/ICE/icedyn_rhg_evp.F90	(revision 10890)
@@ -112,5 +112,5 @@
       REAL(wp), DIMENSION(:,:), INTENT(  out) ::   pshear_i  , pdivu_i   , pdelta_i      !
       !!
-      LOGICAL, PARAMETER ::   ll_bdy_substep = .FALSE. ! temporary option to call bdy at each sub-time step (T)
+      LOGICAL, PARAMETER ::   ll_bdy_substep = .TRUE. ! temporary option to call bdy at each sub-time step (T)
       !                                                                              or only at the main time step (F)
       INTEGER ::   ji, jj       ! dummy loop indices
@@ -160,5 +160,6 @@
 
       REAL(wp), PARAMETER          ::   zepsi  = 1.0e-20_wp             ! tolerance parameter
-      REAL(wp), PARAMETER          ::   zmmin  = 1._wp                  ! ice mass (kg/m2) below which ice velocity equals ocean velocity
+      REAL(wp), PARAMETER          ::   zmmin  = 1._wp                  ! ice mass (kg/m2)  below which ice velocity becomes very small
+      REAL(wp), PARAMETER          ::   zamin  = 0.001_wp               ! ice concentration below which ice velocity becomes very small
       !! --- diags
       REAL(wp), DIMENSION(jpi,jpj) ::   zswi
@@ -319,6 +320,8 @@
 
             ! switches
-            zswitchU(ji,jj) = MAX( 0._wp, SIGN( 1._wp, zmassU - zmmin ) ) ! 0 if ice mass < zmmin
-            zswitchV(ji,jj) = MAX( 0._wp, SIGN( 1._wp, zmassV - zmmin ) ) ! 0 if ice mass < zmmin
+            IF( zmassU <= zmmin .AND. zaU(ji,jj) <= zamin ) THEN   ;   zswitchU(ji,jj) = 0._wp
+            ELSE                                                   ;   zswitchU(ji,jj) = 1._wp   ;   ENDIF
+            IF( zmassV <= zmmin .AND. zaV(ji,jj) <= zamin ) THEN   ;   zswitchV(ji,jj) = 0._wp
+            ELSE                                                   ;   zswitchV(ji,jj) = 1._wp   ;   ENDIF
 
          END DO
@@ -519,5 +522,5 @@
                      &                                  ) / MAX( zepsi, zmV_t(ji,jj) * ( zbeta(ji,jj) + 1._wp ) + zTauO - zTauB ) & ! m/dt + tau_io(only ice part) + landfast
                      &                 + ( 1._wp - rswitch ) * v_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )           & ! static friction => slow decrease to v=0
-                     &             ) * zswitchV(ji,jj) + v_oce(ji,jj) * ( 1._wp - zswitchV(ji,jj) )                               & ! v_ice = v_oce if mass < zmmin
+                     &             ) * zswitchV(ji,jj) + v_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchV(ji,jj) )                     & ! v_ice = v_oce/100 if mass < zmmin & conc < zamin
                      &           ) * zmaskV(ji,jj)
                   ELSE               !--- ice velocity using EVP implicit formulation (cf Madec doc & Bouillon 2009)
@@ -526,5 +529,5 @@
                      &                                     ) / MAX( zepsi, zmV_t(ji,jj) + zTauO - zTauB )             &  ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * v_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )  &  ! static friction => slow decrease to v=0
-                     &              ) * zswitchV(ji,jj) + v_oce(ji,jj) * ( 1._wp - zswitchV(ji,jj) )                  &  ! v_ice = v_oce if mass < zmmin
+                     &              ) * zswitchV(ji,jj) + v_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchV(ji,jj) )        &  ! v_ice = v_oce/100 if mass < zmmin & conc < zamin
                      &            ) * zmaskV(ji,jj)
                   ENDIF
@@ -567,5 +570,5 @@
                      &                                  ) / MAX( zepsi, zmU_t(ji,jj) * ( zbeta(ji,jj) + 1._wp ) + zTauO - zTauB ) & ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * u_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )              & ! static friction => slow decrease to v=0
-                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * ( 1._wp - zswitchU(ji,jj) )                              & ! v_ice = v_oce if mass < zmmin 
+                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchU(ji,jj) )                    & ! v_ice = v_oce/100 if mass < zmmin & conc < zamin 
                      &            ) * zmaskU(ji,jj)
                   ELSE               !--- ice velocity using EVP implicit formulation (cf Madec doc & Bouillon 2009)
@@ -574,5 +577,5 @@
                      &                                     ) / MAX( zepsi, zmU_t(ji,jj) + zTauO - zTauB )             &  ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * u_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )  &  ! static friction => slow decrease to v=0
-                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * ( 1._wp - zswitchU(ji,jj) )                  &  ! v_ice = v_oce if mass < zmmin 
+                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchU(ji,jj) )        &  ! v_ice = v_oce/100 if mass < zmmin & conc < zamin 
                      &            ) * zmaskU(ji,jj)
                   ENDIF
@@ -617,5 +620,5 @@
                      &                                  ) / MAX( zepsi, zmU_t(ji,jj) * ( zbeta(ji,jj) + 1._wp ) + zTauO - zTauB ) & ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * u_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )              & ! static friction => slow decrease to v=0
-                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * ( 1._wp - zswitchU(ji,jj) )                              & ! v_ice = v_oce if mass < zmmin 
+                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchU(ji,jj) )                    & ! v_ice = v_oce/100 if mass < zmmin & conc < zamin 
                      &            ) * zmaskU(ji,jj)
                   ELSE               !--- ice velocity using EVP implicit formulation (cf Madec doc & Bouillon 2009)
@@ -624,5 +627,5 @@
                      &                                     ) / MAX( zepsi, zmU_t(ji,jj) + zTauO - zTauB )             &  ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * u_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )  &  ! static friction => slow decrease to v=0
-                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * ( 1._wp - zswitchU(ji,jj) )                  &  ! v_ice = v_oce if mass < zmmin 
+                     &              ) * zswitchU(ji,jj) + u_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchU(ji,jj) )        &  ! v_ice = v_oce/100 if mass < zmmin & conc < zamin
                      &            ) * zmaskU(ji,jj)
                   ENDIF
@@ -665,5 +668,5 @@
                      &                                  ) / MAX( zepsi, zmV_t(ji,jj) * ( zbeta(ji,jj) + 1._wp ) + zTauO - zTauB ) & ! m/dt + tau_io(only ice part) + landfast
                      &                 + ( 1._wp - rswitch ) * v_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )           & ! static friction => slow decrease to v=0
-                     &             ) * zswitchV(ji,jj) + v_oce(ji,jj) * ( 1._wp - zswitchV(ji,jj) )                               & ! v_ice = v_oce if mass < zmmin
+                     &             ) * zswitchV(ji,jj) + v_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchV(ji,jj) )                     & ! v_ice = v_oce/100 if mass < zmmin & conc < zamin
                      &           ) * zmaskV(ji,jj)
                   ELSE               !--- ice velocity using EVP implicit formulation (cf Madec doc & Bouillon 2009)
@@ -672,5 +675,5 @@
                      &                                     ) / MAX( zepsi, zmV_t(ji,jj) + zTauO - zTauB )             &  ! m/dt + tau_io(only ice part) + landfast
                      &              + ( 1._wp - rswitch ) * v_ice(ji,jj) * MAX( 0._wp, 1._wp - zdtevp * rn_lfrelax )  &  ! static friction => slow decrease to v=0
-                     &              ) * zswitchV(ji,jj) + v_oce(ji,jj) * ( 1._wp - zswitchV(ji,jj) )                  &  ! v_ice = v_oce if mass < zmmin
+                     &              ) * zswitchV(ji,jj) + v_oce(ji,jj) * 0.01_wp * ( 1._wp - zswitchV(ji,jj) )        &  ! v_ice = v_oce/100 if mass < zmmin & conc < zamin
                      &            ) * zmaskV(ji,jj)
                   ENDIF
