Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/CONFIG/SHARED/namelist_top_ref
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/CONFIG/SHARED/namelist_top_ref	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/CONFIG/SHARED/namelist_top_ref	(revision 6312)
@@ -62,4 +62,5 @@
    rn_ahtrc_0       =  2000.    !  horizontal eddy diffusivity for tracers [m2/s]
    rn_ahtrb_0       =     0.    !     background eddy diffusivity for ldf_iso [m2/s]
+   rn_fact_lap      =     1.    !     enhanced zonal eddy diffusivity
 /
 !-----------------------------------------------------------------------
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_oce.F90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_oce.F90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_oce.F90	(revision 6312)
@@ -41,4 +41,5 @@
 
    REAL(wp), PUBLIC ::   rldf                        !: multiplicative factor of diffusive coefficient
+   REAL(wp), PUBLIC, ALLOCATABLE, SAVE, DIMENSION(:,:,:) ::   r_fact_lap
                                                      !: Needed to define the ratio between passive and active tracer diffusion coef. 
 
@@ -92,5 +93,5 @@
       !!                 ***  FUNCTION ldftra_oce_alloc  ***
      !!----------------------------------------------------------------------
-     INTEGER, DIMENSION(3) :: ierr
+     INTEGER, DIMENSION(4) :: ierr
      !!----------------------------------------------------------------------
      ierr(:) = 0
@@ -116,4 +117,5 @@
 # endif
 #endif
+      ALLOCATE( r_fact_lap(jpi,jpj,jpk), STAT=ierr(4) )
       ldftra_oce_alloc = MAXVAL( ierr )
       IF( ldftra_oce_alloc /= 0 )   CALL ctl_warn('ldftra_oce_alloc: failed to allocate arrays')
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_substitute.h90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_substitute.h90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/LDF/ldftra_substitute.h90	(revision 6312)
@@ -13,5 +13,5 @@
 !   'key_traldf_c3d' :                 aht: 3D coefficient
 #       define   fsahtt(i,j,k)   rldf * ahtt(i,j,k)
-#       define   fsahtu(i,j,k)   rldf * ahtu(i,j,k)
+#       define   fsahtu(i,j,k)   rldf * ahtu(i,j,k) * r_fact_lap(i,j,k)
 #       define   fsahtv(i,j,k)   rldf * ahtv(i,j,k)
 #       define   fsahtw(i,j,k)   rldf * ahtw(i,j,k)
@@ -19,5 +19,5 @@
 !   'key_traldf_c2d' :                 aht: 2D coefficient
 #       define   fsahtt(i,j,k)   rldf * ahtt(i,j)
-#       define   fsahtu(i,j,k)   rldf * ahtu(i,j)
+#       define   fsahtu(i,j,k)   rldf * ahtu(i,j) * r_fact_lap(i,j,k)
 #       define   fsahtv(i,j,k)   rldf * ahtv(i,j)
 #       define   fsahtw(i,j,k)   rldf * ahtw(i,j)
@@ -25,5 +25,5 @@
 !   'key_traldf_c1d' :                aht: 1D coefficient
 #       define   fsahtt(i,j,k)   rldf * ahtt(k)
-#       define   fsahtu(i,j,k)   rldf * ahtu(k)
+#       define   fsahtu(i,j,k)   rldf * ahtu(k) * r_fact_lap(i,j,k)
 #       define   fsahtv(i,j,k)   rldf * ahtv(k)
 #       define   fsahtw(i,j,k)   rldf * ahtw(k)
@@ -31,5 +31,5 @@
 !   Default option :             aht: Constant coefficient
 #      define   fsahtt(i,j,k)   rldf * aht0
-#      define   fsahtu(i,j,k)   rldf * aht0
+#      define   fsahtu(i,j,k)   rldf * aht0 * r_fact_lap(i,j,k)
 #      define   fsahtv(i,j,k)   rldf * aht0
 #      define   fsahtw(i,j,k)   rldf * aht0
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/TRA/traldf.F90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/TRA/traldf.F90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/OPA_SRC/TRA/traldf.F90	(revision 6312)
@@ -68,4 +68,5 @@
       !
       rldf = 1     ! For active tracers the 
+      r_fact_lap(:,:,:) = 1.0
 
       IF( l_trdtra )   THEN                    !* Save ta and sa trends
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcldf.F90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcldf.F90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcldf.F90	(revision 6312)
@@ -56,5 +56,6 @@
       INTEGER, INTENT( in ) ::   kt   ! ocean time-step index
       !!
-      INTEGER            :: jn
+      INTEGER            :: ji, jj, jk, jn
+      REAL(wp)           :: zdep
       CHARACTER (len=22) :: charout
       REAL(wp), POINTER, DIMENSION(:,:,:,:) ::   ztrtrd
@@ -66,5 +67,17 @@
 
       rldf = rldf_rat
-
+      !
+      r_fact_lap(:,:,:) = 1.
+      DO jk= 1, jpk
+         DO jj = 1, jpj
+            DO ji = 1, jpi
+               IF( fsdept(ji,jj,jk) > 200. .AND. gphit(ji,jj) < 5. .AND. gphit(ji,jj) > -5. ) THEN
+                  zdep = MAX( fsdept(ji,jj,jk) - 1000., 0. ) / 1000.
+                  r_fact_lap(ji,jj,jk) = MAX( 1., rn_fact_lap * EXP( -zdep ) )
+               ENDIF
+            END DO
+         END DO
+      END DO
+      !
       IF( l_trdtrc )  THEN
          CALL wrk_alloc( jpi, jpj, jpk, jptra, ztrtrd )
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcnam_trp.F90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcnam_trp.F90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/TRP/trcnam_trp.F90	(revision 6312)
@@ -40,4 +40,5 @@
    REAL(wp), PUBLIC ::   rn_ahtrc_0          !: diffusivity coefficient for passive tracer (m2/s)
    REAL(wp), PUBLIC ::   rn_ahtrb_0          !: background diffusivity coefficient for passive tracer (m2/s)
+   REAL(wp), PUBLIC ::   rn_fact_lap         !: Enhanced zonal diffusivity coefficent in the equatorial domain
 
    !                                        !!: ** Treatment of Negative concentrations ( nam_trcrad )
@@ -74,5 +75,7 @@
       NAMELIST/namtrc_ldf/ ln_trcldf_lap  ,     &
          &                 ln_trcldf_bilap, ln_trcldf_level,     &
-         &                 ln_trcldf_hor  , ln_trcldf_iso  , rn_ahtrc_0, rn_ahtrb_0
+         &                 ln_trcldf_hor  , ln_trcldf_iso  , rn_ahtrc_0, rn_ahtrb_0,   &
+         &                 rn_fact_lap
+
       NAMELIST/namtrc_zdf/ ln_trczdf_exp  , nn_trczdf_exp
       NAMELIST/namtrc_rad/ ln_trcrad
@@ -127,4 +130,5 @@
          WRITE(numout,*) '      diffusivity coefficient                                 rn_ahtrc_0 = ', rn_ahtrc_0
          WRITE(numout,*) '      background hor. diffusivity                             rn_ahtrb_0 = ', rn_ahtrb_0
+         WRITE(numout,*) '      enhanced zonal diffusivity                             rn_fact_lap = ', rn_fact_lap
       ENDIF
 
Index: /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/oce_trc.F90
===================================================================
--- /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/oce_trc.F90	(revision 6311)
+++ /branches/2015/nemo_v3_6_STABLE/NEMOGCM/NEMO/TOP_SRC/oce_trc.F90	(revision 6312)
@@ -116,4 +116,5 @@
    USE ldftra_oce , ONLY :  aeiw     =>   aeiw        !: eddy induced velocity coef. at w-points (m2/s) 
    USE ldftra_oce , ONLY :  lk_traldf_eiv  =>  lk_traldf_eiv     !: eddy induced velocity flag
+   USE ldftra_oce , ONLY :  r_fact_lap     =>  r_fact_lap        !: enhanced zonal diffusivity coefficient
 
    !* vertical diffusion *
