Skip to content
Snippets Groups Projects
icedyn_adv_pra.F90 72.2 KiB
Newer Older
Guillaume Samson's avatar
Guillaume Samson committed
MODULE icedyn_adv_pra
   !!======================================================================
   !!                       ***  MODULE icedyn_adv_pra   ***
   !!   sea-ice : advection => Prather scheme
   !!======================================================================
   !! History :       !  2008-03  (M. Vancoppenolle) original code
   !!            4.0  !  2018     (many people)      SI3 [aka Sea Ice cube]
   !!--------------------------------------------------------------------
#if defined key_si3
   !!----------------------------------------------------------------------
   !!   'key_si3'                                       SI3 sea-ice model
   !!----------------------------------------------------------------------
   !!   ice_dyn_adv_pra : advection of sea ice using Prather scheme
   !!   adv_x, adv_y    : Prather scheme applied in i- and j-direction, resp.
   !!   adv_pra_init    : initialisation of the Prather scheme
   !!   adv_pra_rst     : read/write Prather field in ice restart file, or initialized to zero
   !!----------------------------------------------------------------------
   USE phycst         ! physical constant
   USE dom_oce        ! ocean domain
   USE ice            ! sea-ice variables
   USE sbc_oce , ONLY : nn_fsbc   ! frequency of sea-ice call
   USE icevar         ! sea-ice: operations
   !
   USE in_out_manager ! I/O manager
   USE iom            ! I/O manager library
   USE lib_mpp        ! MPP library
   USE lib_fortran    ! fortran utilities (glob_sum + no signed zero)
   USE lbclnk         ! lateral boundary conditions (or mpp links)

   IMPLICIT NONE
   PRIVATE

   PUBLIC   ice_dyn_adv_pra   ! called by icedyn_adv
   PUBLIC   adv_pra_init      ! called by icedyn_adv

   ! Moments for advection
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxice, syice, sxxice, syyice, sxyice   ! ice thickness
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxsn , sysn , sxxsn , syysn , sxysn    ! snow thickness
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxa  , sya  , sxxa  , syya  , sxya     ! ice concentration
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxsal, sysal, sxxsal, syysal, sxysal   ! ice salinity
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxage, syage, sxxage, syyage, sxyage   ! ice age
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:,:) ::   sxc0 , syc0 , sxxc0 , syyc0 , sxyc0    ! snow layers heat content
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:,:) ::   sxe  , sye  , sxxe  , syye  , sxye     ! ice layers heat content
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxap , syap , sxxap , syyap , sxyap    ! melt pond fraction
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxvp , syvp , sxxvp , syyvp , sxyvp    ! melt pond volume
   REAL(wp), ALLOCATABLE, SAVE, DIMENSION(:,:,:)   ::   sxvl , syvl , sxxvl , syyvl , sxyvl    ! melt pond lid volume

   !! * Substitutions
#  include "do_loop_substitute.h90"
   !!----------------------------------------------------------------------
   !! NEMO/ICE 4.0 , NEMO Consortium (2018)
   !! $Id: icedyn_adv_pra.F90 15049 2021-06-23 16:17:30Z clem $
   !! Software governed by the CeCILL license (see ./LICENSE)
   !!----------------------------------------------------------------------
CONTAINS

   SUBROUTINE ice_dyn_adv_pra(         kt, pu_ice, pv_ice, ph_i, ph_s, ph_ip,  &
      &                        pato_i, pv_i, pv_s, psv_i, poa_i, pa_i, pa_ip, pv_ip, pv_il, pe_s, pe_i )
      !!----------------------------------------------------------------------
      !!                **  routine ice_dyn_adv_pra  **
      !!
      !! ** purpose :   Computes and adds the advection trend to sea-ice
      !!
      !! ** method  :   Uses Prather second order scheme that advects tracers
      !!                but also their quadratic forms. The method preserves
      !!                tracer structures by conserving second order moments.
      !!
      !! Reference:  Prather, 1986, JGR, 91, D6. 6671-6681.
      !!----------------------------------------------------------------------
      INTEGER                     , INTENT(in   ) ::   kt         ! time step
      REAL(wp), DIMENSION(:,:)    , INTENT(in   ) ::   pu_ice     ! ice i-velocity
      REAL(wp), DIMENSION(:,:)    , INTENT(in   ) ::   pv_ice     ! ice j-velocity
      REAL(wp), DIMENSION(:,:,:)  , INTENT(in   ) ::   ph_i       ! ice thickness
      REAL(wp), DIMENSION(:,:,:)  , INTENT(in   ) ::   ph_s       ! snw thickness
      REAL(wp), DIMENSION(:,:,:)  , INTENT(in   ) ::   ph_ip      ! ice pond thickness
      REAL(wp), DIMENSION(:,:)    , INTENT(inout) ::   pato_i     ! open water area
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_i       ! ice volume
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_s       ! snw volume
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   psv_i      ! salt content
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   poa_i      ! age content
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pa_i       ! ice concentration
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pa_ip      ! melt pond fraction
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_ip      ! melt pond volume
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_il      ! melt pond lid thickness
      REAL(wp), DIMENSION(:,:,:,:), INTENT(inout) ::   pe_s       ! snw heat content
      REAL(wp), DIMENSION(:,:,:,:), INTENT(inout) ::   pe_i       ! ice heat content
      !
      INTEGER  ::   ji, jj, jk, jl, jt      ! dummy loop indices
      INTEGER  ::   icycle                  ! number of sub-timestep for the advection
      REAL(wp) ::   zdt, z1_dt              !   -      -
      REAL(wp), DIMENSION(1)                  ::   zcflprv, zcflnow   ! for global communication
      REAL(wp), DIMENSION(jpi,jpj)            ::   zati1, zati2
      REAL(wp), DIMENSION(jpi,jpj)            ::   zudy, zvdx
      REAL(wp), DIMENSION(jpi,jpj,jpl)        ::   zhi_max, zhs_max, zhip_max, zs_i, zsi_max
      REAL(wp), DIMENSION(jpi,jpj,nlay_i,jpl) ::   ze_i, zei_max
      REAL(wp), DIMENSION(jpi,jpj,nlay_s,jpl) ::   ze_s, zes_max
      REAL(wp), DIMENSION(jpi,jpj,jpl)        ::   zarea
      REAL(wp), DIMENSION(jpi,jpj,jpl)        ::   z0ice, z0snw, z0ai, z0smi, z0oi
      REAL(wp), DIMENSION(jpi,jpj,jpl)        ::   z0ap , z0vp, z0vl
      REAL(wp), DIMENSION(jpi,jpj,nlay_s,jpl) ::   z0es
      REAL(wp), DIMENSION(jpi,jpj,nlay_i,jpl) ::   z0ei
      !! diagnostics
      REAL(wp), DIMENSION(jpi,jpj)            ::   zdiag_adv_mass, zdiag_adv_salt, zdiag_adv_heat
      !!----------------------------------------------------------------------
      !
      IF( kt == nit000 .AND. lwp )   WRITE(numout,*) '-- ice_dyn_adv_pra: Prather advection scheme'
      !
      ! --- Record max of the surrounding 9-pts (for call Hbig) --- !
      ! thickness and salinity
      WHERE( pv_i(:,:,:) >= epsi10 ) ; zs_i(:,:,:) = psv_i(:,:,:) / pv_i(:,:,:)
      ELSEWHERE                      ; zs_i(:,:,:) = 0._wp
      END WHERE
      CALL icemax3D( ph_i , zhi_max )
      CALL icemax3D( ph_s , zhs_max )
      CALL icemax3D( ph_ip, zhip_max)
      CALL icemax3D( zs_i , zsi_max )
      CALL lbc_lnk( 'icedyn_adv_pra', zhi_max, 'T', 1._wp, zhs_max, 'T', 1._wp, zhip_max, 'T', 1._wp, zsi_max, 'T', 1._wp )
      !
      ! enthalpies
      DO jk = 1, nlay_i
         WHERE( pv_i(:,:,:) >= epsi10 ) ; ze_i(:,:,jk,:) = pe_i(:,:,jk,:) / pv_i(:,:,:)
         ELSEWHERE                      ; ze_i(:,:,jk,:) = 0._wp
         END WHERE
      END DO
      DO jk = 1, nlay_s
         WHERE( pv_s(:,:,:) >= epsi10 ) ; ze_s(:,:,jk,:) = pe_s(:,:,jk,:) / pv_s(:,:,:)
         ELSEWHERE                      ; ze_s(:,:,jk,:) = 0._wp
         END WHERE
      END DO
      CALL icemax4D( ze_i , zei_max )
      CALL icemax4D( ze_s , zes_max )
      CALL lbc_lnk( 'icedyn_adv_pra', zei_max, 'T', 1._wp )
      CALL lbc_lnk( 'icedyn_adv_pra', zes_max, 'T', 1._wp )
      !
      !
      ! --- If ice drift is too fast, use  subtime steps for advection (CFL test for stability) --- !
      !        Note: the advection split is applied at the next time-step in order to avoid blocking global comm.
      !              this should not affect too much the stability
      zcflnow(1) =                  MAXVAL( ABS( pu_ice(:,:) ) * rDt_ice * r1_e1u(:,:) )
      zcflnow(1) = MAX( zcflnow(1), MAXVAL( ABS( pv_ice(:,:) ) * rDt_ice * r1_e2v(:,:) ) )

      ! non-blocking global communication send zcflnow and receive zcflprv
      CALL mpp_delay_max( 'icedyn_adv_pra', 'cflice', zcflnow(:), zcflprv(:), kt == nitend - nn_fsbc + 1 )

      IF( zcflprv(1) > .5 ) THEN   ;   icycle = 2
      ELSE                         ;   icycle = 1
      ENDIF
      zdt = rDt_ice / REAL(icycle)
      z1_dt = 1._wp / zdt

      ! --- transport --- !
      zudy(:,:) = pu_ice(:,:) * e2u(:,:)
      zvdx(:,:) = pv_ice(:,:) * e1v(:,:)

      DO jt = 1, icycle

         ! diagnostics
         zdiag_adv_mass(:,:) =   SUM( pv_i (:,:,:) , dim=3 ) * rhoi + SUM( pv_s (:,:,:) , dim=3 ) * rhos &
            &                  + SUM( pv_ip(:,:,:) , dim=3 ) * rhow + SUM( pv_il(:,:,:) , dim=3 ) * rhow
         zdiag_adv_salt(:,:) =   SUM( psv_i(:,:,:) , dim=3 ) * rhoi
         zdiag_adv_heat(:,:) = - SUM(SUM( pe_i(:,:,1:nlay_i,:) , dim=4 ), dim=3 ) &
            &                  - SUM(SUM( pe_s(:,:,1:nlay_s,:) , dim=4 ), dim=3 )

         ! record at_i before advection (for open water)
         zati1(:,:) = SUM( pa_i(:,:,:), dim=3 )

         ! --- transported fields --- !
         DO jl = 1, jpl
            zarea(:,:,jl) = e1e2t(:,:)
            z0snw(:,:,jl) = pv_s (:,:,jl) * e1e2t(:,:)        ! Snow volume
            z0ice(:,:,jl) = pv_i (:,:,jl) * e1e2t(:,:)        ! Ice  volume
            z0ai (:,:,jl) = pa_i (:,:,jl) * e1e2t(:,:)        ! Ice area
            z0smi(:,:,jl) = psv_i(:,:,jl) * e1e2t(:,:)        ! Salt content
            z0oi (:,:,jl) = poa_i(:,:,jl) * e1e2t(:,:)        ! Age content
            DO jk = 1, nlay_s
               z0es(:,:,jk,jl) = pe_s(:,:,jk,jl) * e1e2t(:,:) ! Snow heat content
            END DO
            DO jk = 1, nlay_i
               z0ei(:,:,jk,jl) = pe_i(:,:,jk,jl) * e1e2t(:,:) ! Ice  heat content
            END DO
            IF ( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
               z0ap(:,:,jl) = pa_ip(:,:,jl) * e1e2t(:,:)      ! Melt pond fraction
               z0vp(:,:,jl) = pv_ip(:,:,jl) * e1e2t(:,:)      ! Melt pond volume
               IF ( ln_pnd_lids ) THEN
                  z0vl(:,:,jl) = pv_il(:,:,jl) * e1e2t(:,:)   ! Melt pond lid volume
               ENDIF
            ENDIF
         END DO
         !
         !                                                                  !--------------------------------------------!
         IF( MOD( (kt - 1) / nn_fsbc , 2 ) ==  MOD( (jt - 1) , 2 ) ) THEN   !==  odd ice time step:  adv_x then adv_y  ==!
            !                                                               !--------------------------------------------!
            CALL adv_x( zdt , zudy , 1._wp , zarea , z0ice , sxice , sxxice , syice , syyice , sxyice ) !--- ice volume
            CALL adv_y( zdt , zvdx , 0._wp , zarea , z0ice , sxice , sxxice , syice , syyice , sxyice )
            CALL adv_x( zdt , zudy , 1._wp , zarea , z0snw , sxsn  , sxxsn  , sysn  , syysn  , sxysn  ) !--- snow volume
            CALL adv_y( zdt , zvdx , 0._wp , zarea , z0snw , sxsn  , sxxsn  , sysn  , syysn  , sxysn  )
            CALL adv_x( zdt , zudy , 1._wp , zarea , z0smi , sxsal , sxxsal , sysal , syysal , sxysal ) !--- ice salinity
            CALL adv_y( zdt , zvdx , 0._wp , zarea , z0smi , sxsal , sxxsal , sysal , syysal , sxysal )
            CALL adv_x( zdt , zudy , 1._wp , zarea , z0ai  , sxa   , sxxa   , sya   , syya   , sxya   ) !--- ice concentration
            CALL adv_y( zdt , zvdx , 0._wp , zarea , z0ai  , sxa   , sxxa   , sya   , syya   , sxya   )
Guillaume Samson's avatar
Guillaume Samson committed
201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252
            CALL adv_x( zdt , zudy , 1._wp , zarea , z0oi  , sxage , sxxage , syage , syyage , sxyage ) !--- ice age
            CALL adv_y( zdt , zvdx , 0._wp , zarea , z0oi  , sxage , sxxage , syage , syyage , sxyage )
            !
            DO jk = 1, nlay_s                                                                           !--- snow heat content
               CALL adv_x( zdt, zudy, 1._wp, zarea, z0es (:,:,jk,:), sxc0(:,:,jk,:),   &
                  &                                 sxxc0(:,:,jk,:), syc0(:,:,jk,:), syyc0(:,:,jk,:), sxyc0(:,:,jk,:) )
               CALL adv_y( zdt, zvdx, 0._wp, zarea, z0es (:,:,jk,:), sxc0(:,:,jk,:),   &
                  &                                 sxxc0(:,:,jk,:), syc0(:,:,jk,:), syyc0(:,:,jk,:), sxyc0(:,:,jk,:) )
            END DO
            DO jk = 1, nlay_i                                                                           !--- ice heat content
               CALL adv_x( zdt, zudy, 1._wp, zarea, z0ei(:,:,jk,:), sxe(:,:,jk,:),   &
                  &                                 sxxe(:,:,jk,:), sye(:,:,jk,:), syye(:,:,jk,:), sxye(:,:,jk,:) )
               CALL adv_y( zdt, zvdx, 0._wp, zarea, z0ei(:,:,jk,:), sxe(:,:,jk,:),   &
                  &                                 sxxe(:,:,jk,:), sye(:,:,jk,:), syye(:,:,jk,:), sxye(:,:,jk,:) )
            END DO
            !
            IF ( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
               CALL adv_x( zdt , zudy , 1._wp , zarea , z0ap , sxap , sxxap , syap , syyap , sxyap )    !--- melt pond fraction
               CALL adv_y( zdt , zvdx , 0._wp , zarea , z0ap , sxap , sxxap , syap , syyap , sxyap )
               CALL adv_x( zdt , zudy , 1._wp , zarea , z0vp , sxvp , sxxvp , syvp , syyvp , sxyvp )    !--- melt pond volume
               CALL adv_y( zdt , zvdx , 0._wp , zarea , z0vp , sxvp , sxxvp , syvp , syyvp , sxyvp )
               IF ( ln_pnd_lids ) THEN
                  CALL adv_x( zdt , zudy , 1._wp , zarea , z0vl , sxvl , sxxvl , syvl , syyvl , sxyvl ) !--- melt pond lid volume
                  CALL adv_y( zdt , zvdx , 0._wp , zarea , z0vl , sxvl , sxxvl , syvl , syyvl , sxyvl )
               ENDIF
            ENDIF
            !                                                               !--------------------------------------------!
         ELSE                                                               !== even ice time step:  adv_y then adv_x  ==!
            !                                                               !--------------------------------------------!
            CALL adv_y( zdt , zvdx , 1._wp , zarea , z0ice , sxice , sxxice , syice , syyice , sxyice ) !--- ice volume
            CALL adv_x( zdt , zudy , 0._wp , zarea , z0ice , sxice , sxxice , syice , syyice , sxyice )
            CALL adv_y( zdt , zvdx , 1._wp , zarea , z0snw , sxsn  , sxxsn  , sysn  , syysn  , sxysn  ) !--- snow volume
            CALL adv_x( zdt , zudy , 0._wp , zarea , z0snw , sxsn  , sxxsn  , sysn  , syysn  , sxysn  )
            CALL adv_y( zdt , zvdx , 1._wp , zarea , z0smi , sxsal , sxxsal , sysal , syysal , sxysal ) !--- ice salinity
            CALL adv_x( zdt , zudy , 0._wp , zarea , z0smi , sxsal , sxxsal , sysal , syysal , sxysal )
            CALL adv_y( zdt , zvdx , 1._wp , zarea , z0ai  , sxa   , sxxa   , sya   , syya   , sxya   ) !--- ice concentration
            CALL adv_x( zdt , zudy , 0._wp , zarea , z0ai  , sxa   , sxxa   , sya   , syya   , sxya   )
            CALL adv_y( zdt , zvdx , 1._wp , zarea , z0oi  , sxage , sxxage , syage , syyage , sxyage ) !--- ice age
            CALL adv_x( zdt , zudy , 0._wp , zarea , z0oi  , sxage , sxxage , syage , syyage , sxyage )
            DO jk = 1, nlay_s                                                                           !--- snow heat content
               CALL adv_y( zdt, zvdx, 1._wp, zarea, z0es (:,:,jk,:), sxc0(:,:,jk,:),   &
                  &                                 sxxc0(:,:,jk,:), syc0(:,:,jk,:), syyc0(:,:,jk,:), sxyc0(:,:,jk,:) )
               CALL adv_x( zdt, zudy, 0._wp, zarea, z0es (:,:,jk,:), sxc0(:,:,jk,:),   &
                  &                                 sxxc0(:,:,jk,:), syc0(:,:,jk,:), syyc0(:,:,jk,:), sxyc0(:,:,jk,:) )
            END DO
            DO jk = 1, nlay_i                                                                           !--- ice heat content
               CALL adv_y( zdt, zvdx, 1._wp, zarea, z0ei(:,:,jk,:), sxe(:,:,jk,:),   &
                  &                                 sxxe(:,:,jk,:), sye(:,:,jk,:), syye(:,:,jk,:), sxye(:,:,jk,:) )
               CALL adv_x( zdt, zudy, 0._wp, zarea, z0ei(:,:,jk,:), sxe(:,:,jk,:),   &
                  &                                 sxxe(:,:,jk,:), sye(:,:,jk,:), syye(:,:,jk,:), sxye(:,:,jk,:) )
            END DO
            IF ( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
               CALL adv_y( zdt , zvdx , 1._wp , zarea , z0ap , sxap , sxxap , syap , syyap , sxyap )    !--- melt pond fraction
               CALL adv_x( zdt , zudy , 0._wp , zarea , z0ap , sxap , sxxap , syap , syyap , sxyap )
               CALL adv_y( zdt , zvdx , 1._wp , zarea , z0vp , sxvp , sxxvp , syvp , syyvp , sxyvp )    !--- melt pond volume
               CALL adv_x( zdt , zudy , 0._wp , zarea , z0vp , sxvp , sxxvp , syvp , syyvp , sxyvp )
               IF ( ln_pnd_lids ) THEN
                  CALL adv_y( zdt , zvdx , 1._wp , zarea , z0vl , sxvl , sxxvl , syvl , syyvl , sxyvl ) !--- melt pond lid volume
                  CALL adv_x( zdt , zudy , 0._wp , zarea , z0vl , sxvl , sxxvl , syvl , syyvl , sxyvl )
               ENDIF
            ENDIF
            !
         ENDIF

         ! --- Lateral boundary conditions --- !
         !     caution: for gradients (sx and sy) the sign changes
         CALL lbc_lnk( 'icedyn_adv_pra', z0ice , 'T', 1._wp, sxice , 'T', -1._wp, syice , 'T', -1._wp  & ! ice volume
            &                          , sxxice, 'T', 1._wp, syyice, 'T',  1._wp, sxyice, 'T',  1._wp  &
            &                          , z0snw , 'T', 1._wp, sxsn  , 'T', -1._wp, sysn  , 'T', -1._wp  & ! snw volume
            &                          , sxxsn , 'T', 1._wp, syysn , 'T',  1._wp, sxysn , 'T',  1._wp  &
            &                          , z0smi , 'T', 1._wp, sxsal , 'T', -1._wp, sysal , 'T', -1._wp  & ! ice salinity
            &                          , sxxsal, 'T', 1._wp, syysal, 'T',  1._wp, sxysal, 'T',  1._wp  &
            &                          , z0ai  , 'T', 1._wp, sxa   , 'T', -1._wp, sya   , 'T', -1._wp  & ! ice concentration
            &                          , sxxa  , 'T', 1._wp, syya  , 'T',  1._wp, sxya  , 'T',  1._wp  &
            &                          , z0oi  , 'T', 1._wp, sxage , 'T', -1._wp, syage , 'T', -1._wp  & ! ice age
            &                          , sxxage, 'T', 1._wp, syyage, 'T',  1._wp, sxyage, 'T',  1._wp  )
         CALL lbc_lnk( 'icedyn_adv_pra', z0es  , 'T', 1._wp, sxc0  , 'T', -1._wp, syc0  , 'T', -1._wp  & ! snw enthalpy
            &                          , sxxc0 , 'T', 1._wp, syyc0 , 'T',  1._wp, sxyc0 , 'T',  1._wp  )
         CALL lbc_lnk( 'icedyn_adv_pra', z0ei  , 'T', 1._wp, sxe   , 'T', -1._wp, sye   , 'T', -1._wp  & ! ice enthalpy
            &                          , sxxe  , 'T', 1._wp, syye  , 'T',  1._wp, sxye  , 'T',  1._wp  )
         IF ( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
            IF( ln_pnd_lids ) THEN
               CALL lbc_lnk( 'icedyn_adv_pra', z0ap , 'T', 1._wp, sxap , 'T', -1._wp, syap , 'T', -1._wp  & ! melt pond fraction
                  &                          , sxxap, 'T', 1._wp, syyap, 'T',  1._wp, sxyap, 'T',  1._wp  &
                  &                          , z0vp , 'T', 1._wp, sxvp , 'T', -1._wp, syvp , 'T', -1._wp  & ! melt pond volume
                  &                          , sxxvp, 'T', 1._wp, syyvp, 'T',  1._wp, sxyvp, 'T',  1._wp  &
                  &                          , z0vl , 'T', 1._wp, sxvl , 'T', -1._wp, syvl , 'T', -1._wp  & ! melt pond lid volume
                  &                          , sxxvl, 'T', 1._wp, syyvl, 'T',  1._wp, sxyvl, 'T',  1._wp  )
            ELSE
               CALL lbc_lnk( 'icedyn_adv_pra', z0ap , 'T', 1._wp, sxap , 'T', -1._wp, syap , 'T', -1._wp  & ! melt pond fraction
                  &                          , sxxap, 'T', 1._wp, syyap, 'T',  1._wp, sxyap, 'T',  1._wp  &
                  &                          , z0vp , 'T', 1._wp, sxvp , 'T', -1._wp, syvp , 'T', -1._wp  & ! melt pond volume
                  &                          , sxxvp, 'T', 1._wp, syyvp, 'T',  1._wp, sxyvp, 'T',  1._wp  )
            ENDIF
         ENDIF

         ! --- Recover the properties from their contents --- !
         DO jl = 1, jpl
            pv_i (:,:,jl) = z0ice(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            pv_s (:,:,jl) = z0snw(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            psv_i(:,:,jl) = z0smi(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            poa_i(:,:,jl) = z0oi (:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            pa_i (:,:,jl) = z0ai (:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            DO jk = 1, nlay_s
               pe_s(:,:,jk,jl) = z0es(:,:,jk,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            END DO
            DO jk = 1, nlay_i
               pe_i(:,:,jk,jl) = z0ei(:,:,jk,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
            END DO
            IF ( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
               pa_ip(:,:,jl) = z0ap(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
               pv_ip(:,:,jl) = z0vp(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
               IF ( ln_pnd_lids ) THEN
                  pv_il(:,:,jl) = z0vl(:,:,jl) * r1_e1e2t(:,:) * tmask(:,:,1)
               ENDIF
            ENDIF
         END DO
         !
         ! derive open water from ice concentration
         zati2(:,:) = SUM( pa_i(:,:,:), dim=3 )
         DO_2D( 0, 0, 0, 0 )
            pato_i(ji,jj) = pato_i(ji,jj) - ( zati2(ji,jj) - zati1(ji,jj) ) &                        !--- open water
               &                          - ( zudy(ji,jj) - zudy(ji-1,jj) + zvdx(ji,jj) - zvdx(ji,jj-1) ) * r1_e1e2t(ji,jj) * zdt
         END_2D
         CALL lbc_lnk( 'icedyn_adv_pra', pato_i, 'T',  1.0_wp )
         !
         ! --- diagnostics --- !
         diag_adv_mass(:,:) = diag_adv_mass(:,:) + (   SUM( pv_i (:,:,:) , dim=3 ) * rhoi + SUM( pv_s (:,:,:) , dim=3 ) * rhos &
            &                                        + SUM( pv_ip(:,:,:) , dim=3 ) * rhow + SUM( pv_il(:,:,:) , dim=3 ) * rhow &
            &                                        - zdiag_adv_mass(:,:) ) * z1_dt
         diag_adv_salt(:,:) = diag_adv_salt(:,:) + (   SUM( psv_i(:,:,:) , dim=3 ) * rhoi &
            &                                        - zdiag_adv_salt(:,:) ) * z1_dt
         diag_adv_heat(:,:) = diag_adv_heat(:,:) + ( - SUM(SUM( pe_i(:,:,1:nlay_i,:) , dim=4 ), dim=3 ) &
            &                                        - SUM(SUM( pe_s(:,:,1:nlay_s,:) , dim=4 ), dim=3 ) &
            &                                        - zdiag_adv_heat(:,:) ) * z1_dt
         !
         ! --- Ensure non-negative fields --- !
         !     Remove negative values (conservation is ensured)
         !     (because advected fields are not perfectly bounded and tiny negative values can occur, e.g. -1.e-20)
         CALL ice_var_zapneg( zdt, pato_i, pv_i, pv_s, psv_i, poa_i, pa_i, pa_ip, pv_ip, pv_il, pe_s, pe_i )
         !
         ! --- Make sure ice thickness is not too big --- !
         !     (because ice thickness can be too large where ice concentration is very small)
         CALL Hbig( zdt, zhi_max, zhs_max, zhip_max, zsi_max, zes_max, zei_max, &
            &            pv_i, pv_s, pa_i, pa_ip, pv_ip, psv_i, pe_s, pe_i )
         !
         ! --- Ensure snow load is not too big --- !
         CALL Hsnow( zdt, pv_i, pv_s, pa_i, pa_ip, pe_s )
         !
      END DO
      !
      IF( lrst_ice )   CALL adv_pra_rst( 'WRITE', kt )   !* write Prather fields in the restart file
      !
   END SUBROUTINE ice_dyn_adv_pra


   SUBROUTINE adv_x( pdt, put , pcrh, psm , ps0 ,   &
      &              psx, psxx, psy , psyy, psxy )
      !!----------------------------------------------------------------------
      !!                **  routine adv_x  **
      !!
      !! ** purpose :   Computes and adds the advection trend to sea-ice
      !!                variable on x axis
      !!----------------------------------------------------------------------
      REAL(wp)                  , INTENT(in   ) ::   pdt                ! the time step
      REAL(wp)                  , INTENT(in   ) ::   pcrh               ! call adv_x then adv_y (=1) or the opposite (=0)
      REAL(wp), DIMENSION(:,:)  , INTENT(in   ) ::   put                ! i-direction ice velocity at U-point [m/s]
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psm                ! area
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   ps0                ! field to be advected
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psx , psy          ! 1st moments
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psxx, psyy, psxy   ! 2nd moments
      !!
      INTEGER  ::   ji, jj, jl, jcat                     ! dummy loop indices
      INTEGER  ::   jj0                                  ! dummy loop indices
      REAL(wp) ::   zs1max, zslpmax, ztemp               ! local scalars
      REAL(wp) ::   zs1new, zalf , zalfq , zbt           !   -      -
      REAL(wp) ::   zs2new, zalf1, zalf1q, zbt1          !   -      -
      REAL(wp) ::   zpsm, zps0
      REAL(wp) ::   zpsx, zpsy, zpsxx, zpsyy, zpsxy
      REAL(wp), DIMENSION(jpi,jpj) ::   zf0 , zfx  , zfy   , zbet   ! 2D workspace
      REAL(wp), DIMENSION(jpi,jpj) ::   zfm , zfxx , zfyy  , zfxy   !  -      -
      REAL(wp), DIMENSION(jpi,jpj) ::   zalg, zalg1, zalg1q         !  -      -
      !-----------------------------------------------------------------------
      ! in order to avoid lbc_lnk (communications):
      !    jj loop must be 1:jpj   if adv_x is called first
      !                and 2:jpj-1 if adv_x is called second
      jj0 = NINT(pcrh)
      !
      jcat = SIZE( ps0 , 3 )   ! size of input arrays
      !
      DO jl = 1, jcat   ! loop on categories
         !
         ! Limitation of moments.
         DO jj = Njs0 - jj0, Nje0 + jj0

            DO ji = Nis0 - 1, Nie0 + 1

               zpsm  = psm (ji,jj,jl) ! optimization
               zps0  = ps0 (ji,jj,jl)
               zpsx  = psx (ji,jj,jl)
               zpsxx = psxx(ji,jj,jl)
               zpsy  = psy (ji,jj,jl)
               zpsyy = psyy(ji,jj,jl)
               zpsxy = psxy(ji,jj,jl)

               !  Initialize volumes of boxes  (=area if adv_x first called, =psm otherwise)
               zpsm = MAX( pcrh * e1e2t(ji,jj) + ( 1.0 - pcrh ) * zpsm , epsi20 )
               !
               zslpmax = MAX( 0._wp, zps0 )
               zs1max  = 1.5 * zslpmax
               zs1new  = MIN( zs1max, MAX( -zs1max, zpsx ) )
               zs2new  = MIN( 2.0 * zslpmax - 0.3334 * ABS( zs1new ), MAX( ABS( zs1new ) - zslpmax, zpsxx ) )
               rswitch = ( 1.0 - MAX( 0._wp, SIGN( 1._wp, -zslpmax) ) ) * tmask(ji,jj,1)   ! Case of empty boxes & Apply mask

               zps0  = zslpmax
               zpsx  = zs1new  * rswitch
               zpsxx = zs2new  * rswitch
               zpsy  = zpsy    * rswitch
               zpsyy = zpsyy   * rswitch
               zpsxy = MIN( zslpmax, MAX( -zslpmax, zpsxy ) ) * rswitch

               !  Calculate fluxes and moments between boxes i<-->i+1
               !                                !  Flux from i to i+1 WHEN u GT 0
               zbet(ji,jj)  =  MAX( 0._wp, SIGN( 1._wp, put(ji,jj) ) )
               zalf         =  MAX( 0._wp, put(ji,jj) ) * pdt / zpsm
               zalfq        =  zalf * zalf
               zalf1        =  1.0 - zalf
               zalf1q       =  zalf1 * zalf1
               !
               zfm (ji,jj)  =  zalf  *   zpsm
               zf0 (ji,jj)  =  zalf  * ( zps0  + zalf1 * ( zpsx + (zalf1 - zalf) * zpsxx ) )
               zfx (ji,jj)  =  zalfq * ( zpsx  + 3.0 * zalf1 * zpsxx )
               zfxx(ji,jj)  =  zalf  *   zpsxx * zalfq
               zfy (ji,jj)  =  zalf  * ( zpsy  + zalf1 * zpsxy )
               zfxy(ji,jj)  =  zalfq *   zpsxy
               zfyy(ji,jj)  =  zalf  *   zpsyy

               !                                !  Readjust moments remaining in the box.
               zpsm  =  zpsm  - zfm(ji,jj)
               zps0  =  zps0  - zf0(ji,jj)
               zpsx  =  zalf1q * ( zpsx - 3.0 * zalf * zpsxx )
               zpsxx =  zalf1  * zalf1q * zpsxx
               zpsy  =  zpsy  - zfy (ji,jj)
               zpsyy =  zpsyy - zfyy(ji,jj)
               zpsxy =  zalf1q * zpsxy
               !
               psm (ji,jj,jl) = zpsm ! optimization
               ps0 (ji,jj,jl) = zps0
               psx (ji,jj,jl) = zpsx
               psxx(ji,jj,jl) = zpsxx
               psy (ji,jj,jl) = zpsy
               psyy(ji,jj,jl) = zpsyy
               psxy(ji,jj,jl) = zpsxy
               !
            END DO

            DO ji = Nis0 - 1, Nie0
               !                                !  Flux from i+1 to i when u LT 0.
               zalf          = MAX( 0._wp, -put(ji,jj) ) * pdt / psm(ji+1,jj,jl)
               zalg  (ji,jj) = zalf
               zalfq         = zalf * zalf
               zalf1         = 1.0 - zalf
               zalg1 (ji,jj) = zalf1
               zalf1q        = zalf1 * zalf1
               zalg1q(ji,jj) = zalf1q
               !
               zfm   (ji,jj) = zfm (ji,jj) + zalf  *    psm (ji+1,jj,jl)
               zf0   (ji,jj) = zf0 (ji,jj) + zalf  * (  ps0 (ji+1,jj,jl) &
                  &                                   - zalf1 * ( psx(ji+1,jj,jl) - (zalf1 - zalf ) * psxx(ji+1,jj,jl) ) )
               zfx   (ji,jj) = zfx (ji,jj) + zalfq * (  psx (ji+1,jj,jl) - 3.0 * zalf1 * psxx(ji+1,jj,jl) )
               zfxx  (ji,jj) = zfxx(ji,jj) + zalf  *    psxx(ji+1,jj,jl) * zalfq
               zfy   (ji,jj) = zfy (ji,jj) + zalf  * (  psy (ji+1,jj,jl) - zalf1 * psxy(ji+1,jj,jl) )
               zfxy  (ji,jj) = zfxy(ji,jj) + zalfq *    psxy(ji+1,jj,jl)
               zfyy  (ji,jj) = zfyy(ji,jj) + zalf  *    psyy(ji+1,jj,jl)
            END DO

            DO ji = Nis0, Nie0
               !
               zpsm  = psm (ji,jj,jl) ! optimization
               zps0  = ps0 (ji,jj,jl)
               zpsx  = psx (ji,jj,jl)
               zpsxx = psxx(ji,jj,jl)
               zpsy  = psy (ji,jj,jl)
               zpsyy = psyy(ji,jj,jl)
               zpsxy = psxy(ji,jj,jl)
               !                                !  Readjust moments remaining in the box.
               zbt  =       zbet(ji-1,jj)
               zbt1 = 1.0 - zbet(ji-1,jj)
               !
               zpsm  = zbt * zpsm + zbt1 * ( zpsm - zfm(ji-1,jj) )
               zps0  = zbt * zps0 + zbt1 * ( zps0 - zf0(ji-1,jj) )
               zpsx  = zalg1q(ji-1,jj) * ( zpsx + 3.0 * zalg(ji-1,jj) * zpsxx )
               zpsxx = zalg1 (ji-1,jj) * zalg1q(ji-1,jj) * zpsxx
               zpsy  = zbt * zpsy  + zbt1 * ( zpsy  - zfy (ji-1,jj) )
               zpsyy = zbt * zpsyy + zbt1 * ( zpsyy - zfyy(ji-1,jj) )
               zpsxy = zalg1q(ji-1,jj) * zpsxy

               !   Put the temporary moments into appropriate neighboring boxes.
               !                                !   Flux from i to i+1 IF u GT 0.
               zbt   =       zbet(ji-1,jj)
               zbt1  = 1.0 - zbet(ji-1,jj)
               zpsm  = zbt * ( zpsm + zfm(ji-1,jj) ) + zbt1 * zpsm
               zalf  = zbt * zfm(ji-1,jj) / zpsm
               zalf1 = 1.0 - zalf
               ztemp = zalf * zps0 - zalf1 * zf0(ji-1,jj)
               !
               zps0  =  zbt  * ( zps0 + zf0(ji-1,jj) ) + zbt1 * zps0
               zpsx  =  zbt  * ( zalf * zfx(ji-1,jj) + zalf1 * zpsx + 3.0 * ztemp ) + zbt1 * zpsx
               zpsxx =  zbt  * ( zalf * zalf * zfxx(ji-1,jj) + zalf1 * zalf1 * zpsxx                            &
                  &            + 5.0 * ( zalf * zalf1 * ( zpsx  - zfx(ji-1,jj) ) - ( zalf1 - zalf ) * ztemp ) ) &
                  &            + zbt1 * zpsxx
               zpsxy =  zbt  * ( zalf * zfxy(ji-1,jj) + zalf1 * zpsxy            &
                  &            + 3.0 * (- zalf1*zfy(ji-1,jj)  + zalf * zpsy ) )  &
                  &            + zbt1 * zpsxy
               zpsy  =  zbt  * ( zpsy  + zfy (ji-1,jj) ) + zbt1 * zpsy
               zpsyy =  zbt  * ( zpsyy + zfyy(ji-1,jj) ) + zbt1 * zpsyy

               !                                !  Flux from i+1 to i IF u LT 0.
               zbt   =       zbet(ji,jj)
               zbt1  = 1.0 - zbet(ji,jj)
               zpsm  = zbt * zpsm + zbt1 * ( zpsm + zfm(ji,jj) )
               zalf  = zbt1 * zfm(ji,jj) / zpsm
               zalf1 = 1.0 - zalf
               ztemp = - zalf * zps0 + zalf1 * zf0(ji,jj)
               !
               zps0  = zbt * zps0  + zbt1 * ( zps0 + zf0(ji,jj) )
               zpsx  = zbt * zpsx  + zbt1 * ( zalf * zfx(ji,jj) + zalf1 * zpsx + 3.0 * ztemp )
               zpsxx = zbt * zpsxx + zbt1 * ( zalf * zalf * zfxx(ji,jj) + zalf1 * zalf1 * zpsxx &
                  &                         + 5.0 * ( zalf * zalf1 * ( - zpsx + zfx(ji,jj) )    &
                  &                         + ( zalf1 - zalf ) * ztemp ) )
               zpsxy = zbt * zpsxy + zbt1 * ( zalf * zfxy(ji,jj) + zalf1 * zpsxy  &
                  &                         + 3.0 * ( zalf1 * zfy(ji,jj) - zalf * zpsy ) )
               zpsy  = zbt * zpsy  + zbt1 * ( zpsy  + zfy (ji,jj) )
               zpsyy = zbt * zpsyy + zbt1 * ( zpsyy + zfyy(ji,jj) )
               !
               psm (ji,jj,jl) = zpsm  ! optimization
               ps0 (ji,jj,jl) = zps0
               psx (ji,jj,jl) = zpsx
               psxx(ji,jj,jl) = zpsxx
               psy (ji,jj,jl) = zpsy
               psyy(ji,jj,jl) = zpsyy
               psxy(ji,jj,jl) = zpsxy
            END DO
            !
         END DO
         !
      END DO
      !
   END SUBROUTINE adv_x


   SUBROUTINE adv_y( pdt, pvt , pcrh, psm , ps0 ,   &
      &              psx, psxx, psy , psyy, psxy )
      !!---------------------------------------------------------------------
      !!                **  routine adv_y  **
      !!
      !! ** purpose :   Computes and adds the advection trend to sea-ice
      !!                variable on y axis
      !!---------------------------------------------------------------------
      REAL(wp)                  , INTENT(in   ) ::   pdt                ! time step
      REAL(wp)                  , INTENT(in   ) ::   pcrh               ! call adv_x then adv_y (=1) or the opposite (=0)
      REAL(wp), DIMENSION(:,:)  , INTENT(in   ) ::   pvt                ! j-direction ice velocity at V-point [m/s]
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psm                ! area
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   ps0                ! field to be advected
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psx , psy          ! 1st moments
      REAL(wp), DIMENSION(:,:,:), INTENT(inout) ::   psxx, psyy, psxy   ! 2nd moments
      !!
      INTEGER  ::   ji, jj, jl, jcat                     ! dummy loop indices
      INTEGER  ::   ji0                                  ! dummy loop indices
      REAL(wp) ::   zs1max, zslpmax, ztemp               ! temporary scalars
      REAL(wp) ::   zs1new, zalf , zalfq , zbt           !    -         -
      REAL(wp) ::   zs2new, zalf1, zalf1q, zbt1          !    -         -
      REAL(wp) ::   zpsm, zps0
      REAL(wp) ::   zpsx, zpsy, zpsxx, zpsyy, zpsxy
      REAL(wp), DIMENSION(jpi,jpj) ::   zf0, zfx , zfy , zbet   ! 2D workspace
      REAL(wp), DIMENSION(jpi,jpj) ::   zfm, zfxx, zfyy, zfxy   !  -      -
      REAL(wp), DIMENSION(jpi,jpj) ::   zalg, zalg1, zalg1q     !  -      -
      !---------------------------------------------------------------------
      ! in order to avoid lbc_lnk (communications):
      !    ji loop must be 1:jpi   if adv_y is called first
      !                and 2:jpi-1 if adv_y is called second
      ji0 = NINT(pcrh)
      !
      jcat = SIZE( ps0 , 3 )   ! size of input arrays
      !
      DO jl = 1, jcat   ! loop on categories
         !
         ! Limitation of moments.
         DO_2D( ji0, ji0, 1, 1 )
            !
            zpsm  = psm (ji,jj,jl) ! optimization
            zps0  = ps0 (ji,jj,jl)
            zpsx  = psx (ji,jj,jl)
            zpsxx = psxx(ji,jj,jl)
            zpsy  = psy (ji,jj,jl)
            zpsyy = psyy(ji,jj,jl)
            zpsxy = psxy(ji,jj,jl)
            !
            !  Initialize volumes of boxes (=area if adv_y first called, =psm otherwise)
            zpsm = MAX(  pcrh * e1e2t(ji,jj) + ( 1.0 - pcrh ) * zpsm , epsi20  )
            !
            zslpmax = MAX( 0._wp, zps0 )
            zs1max  = 1.5 * zslpmax
            zs1new  = MIN( zs1max, MAX( -zs1max, zpsy ) )
            zs2new  = MIN( ( 2.0 * zslpmax - 0.3334 * ABS( zs1new ) ), MAX( ABS( zs1new )-zslpmax, zpsyy ) )
            rswitch = ( 1.0 - MAX( 0._wp, SIGN( 1._wp, -zslpmax) ) ) * tmask(ji,jj,1)   ! Case of empty boxes & Apply mask
            !
            zps0  = zslpmax
            zpsx  = zpsx  * rswitch
            zpsxx = zpsxx * rswitch
            zpsy  = zs1new         * rswitch
            zpsyy = zs2new         * rswitch
            zpsxy = MIN( zslpmax, MAX( -zslpmax, zpsxy ) ) * rswitch

            !  Calculate fluxes and moments between boxes j<-->j+1
            !                                !  Flux from j to j+1 WHEN v GT 0
            zbet(ji,jj)  =  MAX( 0._wp, SIGN( 1._wp, pvt(ji,jj) ) )
            zalf         =  MAX( 0._wp, pvt(ji,jj) ) * pdt / zpsm
            zalfq        =  zalf * zalf
            zalf1        =  1.0 - zalf
            zalf1q       =  zalf1 * zalf1
            !
            zfm (ji,jj)  =  zalf  * zpsm
            zf0 (ji,jj)  =  zalf  * ( zps0 + zalf1 * ( zpsy  + (zalf1-zalf) * zpsyy ) )
            zfy (ji,jj)  =  zalfq *( zpsy + 3.0*zalf1*zpsyy )
            zfyy(ji,jj)  =  zalf  * zalfq * zpsyy
            zfx (ji,jj)  =  zalf  * ( zpsx + zalf1 * zpsxy )
            zfxy(ji,jj)  =  zalfq * zpsxy
            zfxx(ji,jj)  =  zalf  * zpsxx
            !
            !                                !  Readjust moments remaining in the box.
            zpsm   =  zpsm  - zfm(ji,jj)
            zps0   =  zps0  - zf0(ji,jj)
            zpsy   =  zalf1q * ( zpsy -3.0 * zalf * zpsyy )
            zpsyy  =  zalf1 * zalf1q * zpsyy
            zpsx   =  zpsx  - zfx(ji,jj)
            zpsxx  =  zpsxx - zfxx(ji,jj)
            zpsxy  =  zalf1q * zpsxy
            !
            psm (ji,jj,jl) = zpsm ! optimization
            ps0 (ji,jj,jl) = zps0
            psx (ji,jj,jl) = zpsx
            psxx(ji,jj,jl) = zpsxx
            psy (ji,jj,jl) = zpsy
            psyy(ji,jj,jl) = zpsyy
            psxy(ji,jj,jl) = zpsxy
         END_2D
         !
         DO_2D( ji0, ji0, 1, 0 )
            !                                !  Flux from j+1 to j when v LT 0.
            zalf          = MAX( 0._wp, -pvt(ji,jj) ) * pdt / psm(ji,jj+1,jl)
            zalg  (ji,jj) = zalf
            zalfq         = zalf * zalf
            zalf1         = 1.0 - zalf
            zalg1 (ji,jj) = zalf1
            zalf1q        = zalf1 * zalf1
            zalg1q(ji,jj) = zalf1q
            !
            zfm   (ji,jj) = zfm (ji,jj) + zalf  *    psm (ji,jj+1,jl)
            zf0   (ji,jj) = zf0 (ji,jj) + zalf  * (  ps0 (ji,jj+1,jl) &
               &                                   - zalf1 * (psy(ji,jj+1,jl) - (zalf1 - zalf ) * psyy(ji,jj+1,jl) ) )
            zfy   (ji,jj) = zfy (ji,jj) + zalfq * (  psy (ji,jj+1,jl) - 3.0 * zalf1 * psyy(ji,jj+1,jl) )
            zfyy  (ji,jj) = zfyy(ji,jj) + zalf  *    psyy(ji,jj+1,jl) * zalfq
            zfx   (ji,jj) = zfx (ji,jj) + zalf  * (  psx (ji,jj+1,jl) - zalf1 * psxy(ji,jj+1,jl) )
            zfxy  (ji,jj) = zfxy(ji,jj) + zalfq *    psxy(ji,jj+1,jl)
            zfxx  (ji,jj) = zfxx(ji,jj) + zalf  *    psxx(ji,jj+1,jl)
         END_2D

         DO_2D( ji0, ji0, 0, 0 )
            !                                !  Readjust moments remaining in the box.
            zbt  =         zbet(ji,jj-1)
            zbt1 = ( 1.0 - zbet(ji,jj-1) )
            !
            zpsm  = psm (ji,jj,jl) ! optimization
            zps0  = ps0 (ji,jj,jl)
            zpsx  = psx (ji,jj,jl)
            zpsxx = psxx(ji,jj,jl)
            zpsy  = psy (ji,jj,jl)
            zpsyy = psyy(ji,jj,jl)
            zpsxy = psxy(ji,jj,jl)
            !
            zpsm  = zbt * zpsm + zbt1 * ( zpsm - zfm(ji,jj-1) )
            zps0  = zbt * zps0 + zbt1 * ( zps0 - zf0(ji,jj-1) )
            zpsy  = zalg1q(ji,jj-1) * ( zpsy + 3.0 * zalg(ji,jj-1) * zpsyy )
            zpsyy = zalg1 (ji,jj-1) * zalg1q(ji,jj-1) * zpsyy
            zpsx  = zbt * zpsx  + zbt1 * ( zpsx  - zfx (ji,jj-1) )
            zpsxx = zbt * zpsxx + zbt1 * ( zpsxx - zfxx(ji,jj-1) )
            zpsxy = zalg1q(ji,jj-1) * zpsxy

            !   Put the temporary moments into appropriate neighboring boxes.
            !                                !   Flux from j to j+1 IF v GT 0.
            zbt   =       zbet(ji,jj-1)
            zbt1  = 1.0 - zbet(ji,jj-1)
            zpsm  = zbt * ( zpsm + zfm(ji,jj-1) ) + zbt1 * zpsm
            zalf  = zbt * zfm(ji,jj-1) / zpsm
            zalf1 = 1.0 - zalf
            ztemp = zalf * zps0 - zalf1 * zf0(ji,jj-1)
            !
            zps0  =   zbt  * ( zps0 + zf0(ji,jj-1) ) + zbt1 * zps0
            zpsy  =   zbt  * ( zalf * zfy(ji,jj-1) + zalf1 * zpsy + 3.0 * ztemp )  &
               &             + zbt1 * zpsy
            zpsyy =   zbt  * ( zalf * zalf * zfyy(ji,jj-1) + zalf1 * zalf1 * zpsyy                           &
               &             + 5.0 * ( zalf * zalf1 * ( zpsy - zfy(ji,jj-1) ) - ( zalf1 - zalf ) * ztemp ) ) &
               &             + zbt1 * zpsyy
            zpsxy =   zbt  * ( zalf * zfxy(ji,jj-1) + zalf1 * zpsxy             &
               &             + 3.0 * (- zalf1 * zfx(ji,jj-1) + zalf * zpsx ) )  &
               &             + zbt1 * zpsxy
            zpsx  =   zbt * ( zpsx  + zfx (ji,jj-1) ) + zbt1 * zpsx
            zpsxx =   zbt * ( zpsxx + zfxx(ji,jj-1) ) + zbt1 * zpsxx

            !                                !  Flux from j+1 to j IF v LT 0.
            zbt   =       zbet(ji,jj)
            zbt1  = 1.0 - zbet(ji,jj)
            zpsm  = zbt * zpsm + zbt1 * ( zpsm + zfm(ji,jj) )
            zalf  = zbt1 * zfm(ji,jj) / zpsm
            zalf1 = 1.0 - zalf
            ztemp = - zalf * zps0 + zalf1 * zf0(ji,jj)
            !
            zps0  = zbt * zps0  + zbt1 * (  zps0 + zf0(ji,jj) )
            zpsy  = zbt * zpsy  + zbt1 * (  zalf * zfy(ji,jj) + zalf1 * zpsy + 3.0 * ztemp )
            zpsyy = zbt * zpsyy + zbt1 * (  zalf * zalf * zfyy(ji,jj) + zalf1 * zalf1 * zpsyy &
               &                         + 5.0 * ( zalf * zalf1 * ( - zpsy + zfy(ji,jj) )     &
               &                         + ( zalf1 - zalf ) * ztemp ) )
            zpsxy = zbt * zpsxy + zbt1 * (  zalf * zfxy(ji,jj) + zalf1 * zpsxy  &
               &                         + 3.0 * ( zalf1 * zfx(ji,jj) - zalf * zpsx ) )
            zpsx  = zbt * zpsx  + zbt1 * ( zpsx  + zfx (ji,jj) )
            zpsxx = zbt * zpsxx + zbt1 * ( zpsxx + zfxx(ji,jj) )
            !
            psm (ji,jj,jl) = zpsm ! optimization
            ps0 (ji,jj,jl) = zps0
            psx (ji,jj,jl) = zpsx
            psxx(ji,jj,jl) = zpsxx
            psy (ji,jj,jl) = zpsy
            psyy(ji,jj,jl) = zpsyy
            psxy(ji,jj,jl) = zpsxy
         END_2D
         !
      END DO
      !
   END SUBROUTINE adv_y


   SUBROUTINE Hbig( pdt, phi_max, phs_max, phip_max, psi_max, pes_max, pei_max, &
      &                  pv_i, pv_s, pa_i, pa_ip, pv_ip, psv_i, pe_s, pe_i )
      !!-------------------------------------------------------------------
      !!                  ***  ROUTINE Hbig  ***
      !!
      !! ** Purpose : Thickness correction in case advection scheme creates
      !!              abnormally tick ice or snow
      !!
      !! ** Method  : 1- check whether ice thickness is larger than the surrounding 9-points
      !!                 (before advection) and reduce it by adapting ice concentration
      !!              2- check whether snow thickness is larger than the surrounding 9-points
      !!                 (before advection) and reduce it by sending the excess in the ocean
      !!
      !! ** input   : Max thickness of the surrounding 9-points
      !!-------------------------------------------------------------------
      REAL(wp)                    , INTENT(in   ) ::   pdt                                   ! tracer time-step
      REAL(wp), DIMENSION(:,:,:)  , INTENT(in   ) ::   phi_max, phs_max, phip_max, psi_max   ! max ice thick from surrounding 9-pts
      REAL(wp), DIMENSION(:,:,:,:), INTENT(in   ) ::   pes_max
      REAL(wp), DIMENSION(:,:,:,:), INTENT(in   ) ::   pei_max
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_i, pv_s, pa_i, pa_ip, pv_ip, psv_i
      REAL(wp), DIMENSION(:,:,:,:), INTENT(inout) ::   pe_s
      REAL(wp), DIMENSION(:,:,:,:), INTENT(inout) ::   pe_i
      !
      INTEGER  ::   ji, jj, jk, jl         ! dummy loop indices
      REAL(wp) ::   z1_dt, zhip, zhi, zhs, zsi, zes, zei, zfra
      !!-------------------------------------------------------------------
      !
      z1_dt = 1._wp / pdt
      !
      DO jl = 1, jpl
         DO_2D( nn_hls, nn_hls, nn_hls, nn_hls )
            IF ( pv_i(ji,jj,jl) > 0._wp ) THEN
               !
               !                               ! -- check h_ip -- !
               ! if h_ip is larger than the surrounding 9 pts => reduce h_ip and increase a_ip
               IF( ln_pnd_LEV .OR. ln_pnd_TOPO .AND. pv_ip(ji,jj,jl) > 0._wp ) THEN
                  zhip = pv_ip(ji,jj,jl) / MAX( epsi20, pa_ip(ji,jj,jl) )
                  IF( zhip > phip_max(ji,jj,jl) .AND. pa_ip(ji,jj,jl) < 0.15 ) THEN
                     pa_ip(ji,jj,jl) = pv_ip(ji,jj,jl) / phip_max(ji,jj,jl)
                  ENDIF
               ENDIF
               !
               !                               ! -- check h_i -- !
               ! if h_i is larger than the surrounding 9 pts => reduce h_i and increase a_i
               zhi = pv_i(ji,jj,jl) / pa_i(ji,jj,jl)
               IF( zhi > phi_max(ji,jj,jl) .AND. pa_i(ji,jj,jl) < 0.15 ) THEN
                  pa_i(ji,jj,jl) = pv_i(ji,jj,jl) / MIN( phi_max(ji,jj,jl), hi_max(jpl) )   !-- bound h_i to hi_max (99 m)
               ENDIF
               !
               !                               ! -- check h_s -- !
               ! if h_s is larger than the surrounding 9 pts => put the snow excess in the ocean
               zhs = pv_s(ji,jj,jl) / pa_i(ji,jj,jl)
               IF( pv_s(ji,jj,jl) > 0._wp .AND. zhs > phs_max(ji,jj,jl) .AND. pa_i(ji,jj,jl) < 0.15 ) THEN
                  zfra = phs_max(ji,jj,jl) / MAX( zhs, epsi20 )
                  !
                  wfx_res(ji,jj) = wfx_res(ji,jj) + ( pv_s(ji,jj,jl) - pa_i(ji,jj,jl) * phs_max(ji,jj,jl) ) * rhos * z1_dt
                  hfx_res(ji,jj) = hfx_res(ji,jj) - SUM( pe_s(ji,jj,1:nlay_s,jl) ) * ( 1._wp - zfra ) * z1_dt ! W.m-2 <0
                  !
                  pe_s(ji,jj,1:nlay_s,jl) = pe_s(ji,jj,1:nlay_s,jl) * zfra
                  pv_s(ji,jj,jl)          = pa_i(ji,jj,jl) * phs_max(ji,jj,jl)
               ENDIF
               !
               !                               ! -- check s_i -- !
               ! if s_i is larger than the surrounding 9 pts => put salt excess in the ocean
               zsi = psv_i(ji,jj,jl) / pv_i(ji,jj,jl)
               IF( zsi > psi_max(ji,jj,jl) .AND. pa_i(ji,jj,jl) < 0.15 ) THEN
                  zfra = psi_max(ji,jj,jl) / zsi
                  sfx_res(ji,jj) = sfx_res(ji,jj) + psv_i(ji,jj,jl) * ( 1._wp - zfra ) * rhoi * z1_dt
                  psv_i(ji,jj,jl) = psv_i(ji,jj,jl) * zfra
               ENDIF
               !
            ENDIF
         END_2D
      END DO
      !
      !                                           ! -- check e_i/v_i -- !
      DO jl = 1, jpl
         DO_3D( nn_hls, nn_hls, nn_hls, nn_hls, 1, nlay_i )
            IF ( pv_i(ji,jj,jl) > 0._wp ) THEN
               ! if e_i/v_i is larger than the surrounding 9 pts => put the heat excess in the ocean
               zei = pe_i(ji,jj,jk,jl) / pv_i(ji,jj,jl)
               IF( zei > pei_max(ji,jj,jk,jl) .AND. pa_i(ji,jj,jl) < 0.15 ) THEN
                  zfra = pei_max(ji,jj,jk,jl) / zei
                  hfx_res(ji,jj) = hfx_res(ji,jj) - pe_i(ji,jj,jk,jl) * ( 1._wp - zfra ) * z1_dt ! W.m-2 <0
                  pe_i(ji,jj,jk,jl) = pe_i(ji,jj,jk,jl) * zfra
               ENDIF
            ENDIF
         END_3D
      END DO
      !                                           ! -- check e_s/v_s -- !
      DO jl = 1, jpl
         DO_3D( nn_hls, nn_hls, nn_hls, nn_hls, 1, nlay_s )
            IF ( pv_s(ji,jj,jl) > 0._wp ) THEN
               ! if e_s/v_s is larger than the surrounding 9 pts => put the heat excess in the ocean
               zes = pe_s(ji,jj,jk,jl) / pv_s(ji,jj,jl)
               IF( zes > pes_max(ji,jj,jk,jl) .AND. pa_i(ji,jj,jl) < 0.15 ) THEN
                  zfra = pes_max(ji,jj,jk,jl) / zes
                  hfx_res(ji,jj) = hfx_res(ji,jj) - pe_s(ji,jj,jk,jl) * ( 1._wp - zfra ) * z1_dt ! W.m-2 <0
                  pe_s(ji,jj,jk,jl) = pe_s(ji,jj,jk,jl) * zfra
               ENDIF
            ENDIF
         END_3D
      END DO
      !
   END SUBROUTINE Hbig


   SUBROUTINE Hsnow( pdt, pv_i, pv_s, pa_i, pa_ip, pe_s )
      !!-------------------------------------------------------------------
      !!                  ***  ROUTINE Hsnow  ***
      !!
      !! ** Purpose : 1- Check snow load after advection
      !!              2- Correct pond concentration to avoid a_ip > a_i
      !!
      !! ** Method :  If snow load makes snow-ice interface to deplet below the ocean surface
      !!              then put the snow excess in the ocean
      !!
      !! ** Notes :   This correction is crucial because of the call to routine icecor afterwards
      !!              which imposes a mini of ice thick. (rn_himin). This imposed mini can artificially
      !!              make the snow very thick (if concentration decreases drastically)
      !!              This behavior has been seen in Ultimate-Macho and supposedly it can also be true for Prather
      !!-------------------------------------------------------------------
      REAL(wp)                    , INTENT(in   ) ::   pdt   ! tracer time-step
      REAL(wp), DIMENSION(:,:,:)  , INTENT(inout) ::   pv_i, pv_s, pa_i, pa_ip
      REAL(wp), DIMENSION(:,:,:,:), INTENT(inout) ::   pe_s
      !
      INTEGER  ::   ji, jj, jl   ! dummy loop indices
      REAL(wp) ::   z1_dt, zvs_excess, zfra
      !!-------------------------------------------------------------------
      !
      z1_dt = 1._wp / pdt
      !
      ! -- check snow load -- !
      DO jl = 1, jpl
         DO_2D( nn_hls, nn_hls, nn_hls, nn_hls )
            IF ( pv_i(ji,jj,jl) > 0._wp ) THEN
               !
               zvs_excess = MAX( 0._wp, pv_s(ji,jj,jl) - pv_i(ji,jj,jl) * (rho0-rhoi) * r1_rhos )
               !
               IF( zvs_excess > 0._wp ) THEN   ! snow-ice interface deplets below the ocean surface
                  ! put snow excess in the ocean
                  zfra = ( pv_s(ji,jj,jl) - zvs_excess ) / MAX( pv_s(ji,jj,jl), epsi20 )
                  wfx_res(ji,jj) = wfx_res(ji,jj) + zvs_excess * rhos * z1_dt
                  hfx_res(ji,jj) = hfx_res(ji,jj) - SUM( pe_s(ji,jj,1:nlay_s,jl) ) * ( 1._wp - zfra ) * z1_dt ! W.m-2 <0
                  ! correct snow volume and heat content
                  pe_s(ji,jj,1:nlay_s,jl) = pe_s(ji,jj,1:nlay_s,jl) * zfra
                  pv_s(ji,jj,jl)          = pv_s(ji,jj,jl) - zvs_excess
               ENDIF
               !
            ENDIF
         END_2D
      END DO
      !
      !-- correct pond concentration to avoid a_ip > a_i -- !
      WHERE( pa_ip(:,:,:) > pa_i(:,:,:) )   pa_ip(:,:,:) = pa_i(:,:,:)
      !
   END SUBROUTINE Hsnow


   SUBROUTINE adv_pra_init
      !!-------------------------------------------------------------------
      !!                  ***  ROUTINE adv_pra_init  ***
      !!
      !! ** Purpose :   allocate and initialize arrays for Prather advection
      !!-------------------------------------------------------------------
      INTEGER ::   ierr
      !!-------------------------------------------------------------------
      !
      !                             !* allocate prather fields
      ALLOCATE( sxice(jpi,jpj,jpl) , syice(jpi,jpj,jpl) , sxxice(jpi,jpj,jpl) , syyice(jpi,jpj,jpl) , sxyice(jpi,jpj,jpl) ,   &
         &      sxsn (jpi,jpj,jpl) , sysn (jpi,jpj,jpl) , sxxsn (jpi,jpj,jpl) , syysn (jpi,jpj,jpl) , sxysn (jpi,jpj,jpl) ,   &
         &      sxa  (jpi,jpj,jpl) , sya  (jpi,jpj,jpl) , sxxa  (jpi,jpj,jpl) , syya  (jpi,jpj,jpl) , sxya  (jpi,jpj,jpl) ,   &
         &      sxsal(jpi,jpj,jpl) , sysal(jpi,jpj,jpl) , sxxsal(jpi,jpj,jpl) , syysal(jpi,jpj,jpl) , sxysal(jpi,jpj,jpl) ,   &
         &      sxage(jpi,jpj,jpl) , syage(jpi,jpj,jpl) , sxxage(jpi,jpj,jpl) , syyage(jpi,jpj,jpl) , sxyage(jpi,jpj,jpl) ,   &
         &      sxap (jpi,jpj,jpl) , syap (jpi,jpj,jpl) , sxxap (jpi,jpj,jpl) , syyap (jpi,jpj,jpl) , sxyap (jpi,jpj,jpl) ,   &
         &      sxvp (jpi,jpj,jpl) , syvp (jpi,jpj,jpl) , sxxvp (jpi,jpj,jpl) , syyvp (jpi,jpj,jpl) , sxyvp (jpi,jpj,jpl) ,   &
         &      sxvl (jpi,jpj,jpl) , syvl (jpi,jpj,jpl) , sxxvl (jpi,jpj,jpl) , syyvl (jpi,jpj,jpl) , sxyvl (jpi,jpj,jpl) ,   &
         !
         &      sxc0 (jpi,jpj,nlay_s,jpl) , syc0 (jpi,jpj,nlay_s,jpl) , sxxc0(jpi,jpj,nlay_s,jpl) , &
         &      syyc0(jpi,jpj,nlay_s,jpl) , sxyc0(jpi,jpj,nlay_s,jpl)                             , &
         !
         &      sxe  (jpi,jpj,nlay_i,jpl) , sye  (jpi,jpj,nlay_i,jpl) , sxxe (jpi,jpj,nlay_i,jpl) , &
         &      syye (jpi,jpj,nlay_i,jpl) , sxye (jpi,jpj,nlay_i,jpl)                             , &
         &      STAT = ierr )
      !
      CALL mpp_sum( 'icedyn_adv_pra', ierr )
      IF( ierr /= 0 )   CALL ctl_stop('STOP', 'adv_pra_init : unable to allocate ice arrays for Prather advection scheme')
      !
      CALL adv_pra_rst( 'READ' )    !* read or initialize all required files
      !
   END SUBROUTINE adv_pra_init


   SUBROUTINE adv_pra_rst( cdrw, kt )
      !!---------------------------------------------------------------------
      !!                   ***  ROUTINE adv_pra_rst  ***
      !!
      !! ** Purpose :   Read or write file in restart file
      !!
      !! ** Method  :   use of IOM library
      !!----------------------------------------------------------------------
      CHARACTER(len=*) , INTENT(in) ::   cdrw   ! "READ"/"WRITE" flag
      INTEGER, OPTIONAL, INTENT(in) ::   kt     ! ice time-step
      !
      INTEGER ::   jk, jl   ! dummy loop indices
      INTEGER ::   iter     ! local integer
      INTEGER ::   id1      ! local integer
      CHARACTER(len=25) ::   znam
      CHARACTER(len=2)  ::   zchar, zchar1
      REAL(wp), DIMENSION(jpi,jpj,jpl) ::   z3d   ! 3D workspace
      !!----------------------------------------------------------------------
      !
      !                                      !==========================!
      IF( TRIM(cdrw) == 'READ' ) THEN        !==  Read or initialize  ==!
         !                                   !==========================!
         !
         IF( ln_rstart ) THEN   ;   id1 = iom_varid( numrir, 'sxice' , ldstop = .FALSE. )    ! file exist: id1>0
         ELSE                   ;   id1 = 0                                                  ! no restart: id1=0
         ENDIF
         !
         IF( id1 > 0 ) THEN                     !**  Read the restart file  **!
            !
            !                                                        ! ice thickness
            CALL iom_get( numrir, jpdom_auto, 'sxice' , sxice , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'syice' , syice , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sxxice', sxxice )
            CALL iom_get( numrir, jpdom_auto, 'syyice', syyice )
            CALL iom_get( numrir, jpdom_auto, 'sxyice', sxyice )
            !                                                        ! snow thickness
            CALL iom_get( numrir, jpdom_auto, 'sxsn'  , sxsn  , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sysn'  , sysn  , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sxxsn' , sxxsn  )
            CALL iom_get( numrir, jpdom_auto, 'syysn' , syysn  )
            CALL iom_get( numrir, jpdom_auto, 'sxysn' , sxysn  )
            !                                                        ! ice concentration
            CALL iom_get( numrir, jpdom_auto, 'sxa'   , sxa   , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sya'   , sya   , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sxxa'  , sxxa   )
            CALL iom_get( numrir, jpdom_auto, 'syya'  , syya   )
            CALL iom_get( numrir, jpdom_auto, 'sxya'  , sxya   )
            !                                                        ! ice salinity
            CALL iom_get( numrir, jpdom_auto, 'sxsal' , sxsal , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sysal' , sysal , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sxxsal', sxxsal )
            CALL iom_get( numrir, jpdom_auto, 'syysal', syysal )
            CALL iom_get( numrir, jpdom_auto, 'sxysal', sxysal )
            !                                                        ! ice age
            CALL iom_get( numrir, jpdom_auto, 'sxage' , sxage , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'syage' , syage , psgn = -1._wp )
            CALL iom_get( numrir, jpdom_auto, 'sxxage', sxxage )
            CALL iom_get( numrir, jpdom_auto, 'syyage', syyage )
            CALL iom_get( numrir, jpdom_auto, 'sxyage', sxyage )
            !                                                        ! snow layers heat content
            DO jk = 1, nlay_s
               WRITE(zchar1,'(I2.2)') jk
               znam = 'sxc0'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d, psgn = -1._wp )   ;   sxc0 (:,:,jk,:) = z3d(:,:,:)
               znam = 'syc0'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d, psgn = -1._wp )   ;   syc0 (:,:,jk,:) = z3d(:,:,:)
               znam = 'sxxc0'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   sxxc0(:,:,jk,:) = z3d(:,:,:)
               znam = 'syyc0'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   syyc0(:,:,jk,:) = z3d(:,:,:)
               znam = 'sxyc0'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   sxyc0(:,:,jk,:) = z3d(:,:,:)
            END DO
            !                                                        ! ice layers heat content
            DO jk = 1, nlay_i
               WRITE(zchar1,'(I2.2)') jk
               znam = 'sxe'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d, psgn = -1._wp )   ;   sxe (:,:,jk,:) = z3d(:,:,:)
               znam = 'sye'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d, psgn = -1._wp )   ;   sye (:,:,jk,:) = z3d(:,:,:)
               znam = 'sxxe'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   sxxe(:,:,jk,:) = z3d(:,:,:)
               znam = 'syye'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   syye(:,:,jk,:) = z3d(:,:,:)
               znam = 'sxye'//'_l'//zchar1
               CALL iom_get( numrir, jpdom_auto, znam , z3d )   ;   sxye(:,:,jk,:) = z3d(:,:,:)
            END DO
            !
            IF( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN                                    ! melt pond fraction
               IF( iom_varid( numrir, 'sxap', ldstop = .FALSE. ) > 0 ) THEN
                  CALL iom_get( numrir, jpdom_auto, 'sxap' , sxap , psgn = -1._wp )
                  CALL iom_get( numrir, jpdom_auto, 'syap' , syap , psgn = -1._wp )
                  CALL iom_get( numrir, jpdom_auto, 'sxxap', sxxap )
                  CALL iom_get( numrir, jpdom_auto, 'syyap', syyap )
                  CALL iom_get( numrir, jpdom_auto, 'sxyap', sxyap )
                  !                                                     ! melt pond volume
                  CALL iom_get( numrir, jpdom_auto, 'sxvp' , sxvp , psgn = -1._wp )
                  CALL iom_get( numrir, jpdom_auto, 'syvp' , syvp , psgn = -1._wp )
                  CALL iom_get( numrir, jpdom_auto, 'sxxvp', sxxvp )
                  CALL iom_get( numrir, jpdom_auto, 'syyvp', syyvp )
                  CALL iom_get( numrir, jpdom_auto, 'sxyvp', sxyvp )
               ELSE
                  sxap = 0._wp ;   syap = 0._wp    ;   sxxap = 0._wp    ;   syyap = 0._wp    ;   sxyap = 0._wp   ! melt pond fraction
                  sxvp = 0._wp ;   syvp = 0._wp    ;   sxxvp = 0._wp    ;   syyvp = 0._wp    ;   sxyvp = 0._wp   ! melt pond volume
               ENDIF
                  !
               IF ( ln_pnd_lids ) THEN                               ! melt pond lid volume
                  IF( iom_varid( numrir, 'sxvl', ldstop = .FALSE. ) > 0 ) THEN
                     CALL iom_get( numrir, jpdom_auto, 'sxvl' , sxvl , psgn = -1._wp )
                     CALL iom_get( numrir, jpdom_auto, 'syvl' , syvl , psgn = -1._wp )
                     CALL iom_get( numrir, jpdom_auto, 'sxxvl', sxxvl )
                     CALL iom_get( numrir, jpdom_auto, 'syyvl', syyvl )
                     CALL iom_get( numrir, jpdom_auto, 'sxyvl', sxyvl )
                  ELSE
                     sxvl = 0._wp; syvl = 0._wp    ;   sxxvl = 0._wp    ;   syyvl = 0._wp    ;   sxyvl = 0._wp   ! melt pond lid volume
                  ENDIF
               ENDIF
            ENDIF
            !
         ELSE                                   !**  start rheology from rest  **!
            !
            IF(lwp) WRITE(numout,*) '   ==>>   start from rest OR previous run without Prather, set moments to 0'
            !
            sxice = 0._wp   ;   syice = 0._wp   ;   sxxice = 0._wp   ;   syyice = 0._wp   ;   sxyice = 0._wp      ! ice thickness
            sxsn  = 0._wp   ;   sysn  = 0._wp   ;   sxxsn  = 0._wp   ;   syysn  = 0._wp   ;   sxysn  = 0._wp      ! snow thickness
            sxa   = 0._wp   ;   sya   = 0._wp   ;   sxxa   = 0._wp   ;   syya   = 0._wp   ;   sxya   = 0._wp      ! ice concentration
            sxsal = 0._wp   ;   sysal = 0._wp   ;   sxxsal = 0._wp   ;   syysal = 0._wp   ;   sxysal = 0._wp      ! ice salinity
            sxage = 0._wp   ;   syage = 0._wp   ;   sxxage = 0._wp   ;   syyage = 0._wp   ;   sxyage = 0._wp      ! ice age
            sxc0  = 0._wp   ;   syc0  = 0._wp   ;   sxxc0  = 0._wp   ;   syyc0  = 0._wp   ;   sxyc0  = 0._wp      ! snow layers heat content
            sxe   = 0._wp   ;   sye   = 0._wp   ;   sxxe   = 0._wp   ;   syye   = 0._wp   ;   sxye   = 0._wp      ! ice layers heat content
            IF( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN
               sxap = 0._wp ;   syap = 0._wp    ;   sxxap = 0._wp    ;   syyap = 0._wp    ;   sxyap = 0._wp       ! melt pond fraction
               sxvp = 0._wp ;   syvp = 0._wp    ;   sxxvp = 0._wp    ;   syyvp = 0._wp    ;   sxyvp = 0._wp       ! melt pond volume
               IF ( ln_pnd_lids ) THEN
                  sxvl = 0._wp; syvl = 0._wp    ;   sxxvl = 0._wp    ;   syyvl = 0._wp    ;   sxyvl = 0._wp       ! melt pond lid volume
               ENDIF
            ENDIF
         ENDIF
         !
         !                                   !=====================================!
      ELSEIF( TRIM(cdrw) == 'WRITE' ) THEN   !==  write in the ice restart file  ==!
         !                                   !=====================================!
         IF(lwp) WRITE(numout,*) '----  ice-adv-rst  ----'
         iter = kt + nn_fsbc - 1             ! ice restarts are written at kt == nitrst - nn_fsbc + 1
         !
         !
         ! In case Prather scheme is used for advection, write second order moments
         ! ------------------------------------------------------------------------
         !
         !                                                           ! ice thickness
         CALL iom_rstput( iter, nitrst, numriw, 'sxice' , sxice  )
         CALL iom_rstput( iter, nitrst, numriw, 'syice' , syice  )
         CALL iom_rstput( iter, nitrst, numriw, 'sxxice', sxxice )
         CALL iom_rstput( iter, nitrst, numriw, 'syyice', syyice )
         CALL iom_rstput( iter, nitrst, numriw, 'sxyice', sxyice )
         !                                                           ! snow thickness
         CALL iom_rstput( iter, nitrst, numriw, 'sxsn'  , sxsn   )
         CALL iom_rstput( iter, nitrst, numriw, 'sysn'  , sysn   )
         CALL iom_rstput( iter, nitrst, numriw, 'sxxsn' , sxxsn  )
         CALL iom_rstput( iter, nitrst, numriw, 'syysn' , syysn  )
         CALL iom_rstput( iter, nitrst, numriw, 'sxysn' , sxysn  )
         !                                                           ! ice concentration
         CALL iom_rstput( iter, nitrst, numriw, 'sxa'   , sxa    )
         CALL iom_rstput( iter, nitrst, numriw, 'sya'   , sya    )
         CALL iom_rstput( iter, nitrst, numriw, 'sxxa'  , sxxa   )
         CALL iom_rstput( iter, nitrst, numriw, 'syya'  , syya   )
         CALL iom_rstput( iter, nitrst, numriw, 'sxya'  , sxya   )
         !                                                           ! ice salinity
         CALL iom_rstput( iter, nitrst, numriw, 'sxsal' , sxsal  )
         CALL iom_rstput( iter, nitrst, numriw, 'sysal' , sysal  )
         CALL iom_rstput( iter, nitrst, numriw, 'sxxsal', sxxsal )
         CALL iom_rstput( iter, nitrst, numriw, 'syysal', syysal )
         CALL iom_rstput( iter, nitrst, numriw, 'sxysal', sxysal )
         !                                                           ! ice age
         CALL iom_rstput( iter, nitrst, numriw, 'sxage' , sxage  )
         CALL iom_rstput( iter, nitrst, numriw, 'syage' , syage  )
         CALL iom_rstput( iter, nitrst, numriw, 'sxxage', sxxage )
         CALL iom_rstput( iter, nitrst, numriw, 'syyage', syyage )
         CALL iom_rstput( iter, nitrst, numriw, 'sxyage', sxyage )
         !                                                           ! snow layers heat content
         DO jk = 1, nlay_s
            WRITE(zchar1,'(I2.2)') jk
            znam = 'sxc0'//'_l'//zchar1  ;   z3d(:,:,:) = sxc0 (:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'syc0'//'_l'//zchar1  ;   z3d(:,:,:) = syc0 (:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'sxxc0'//'_l'//zchar1 ;   z3d(:,:,:) = sxxc0(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'syyc0'//'_l'//zchar1 ;   z3d(:,:,:) = syyc0(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'sxyc0'//'_l'//zchar1 ;   z3d(:,:,:) = sxyc0(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
         END DO
         !                                                           ! ice layers heat content
         DO jk = 1, nlay_i
            WRITE(zchar1,'(I2.2)') jk
            znam = 'sxe'//'_l'//zchar1   ;   z3d(:,:,:) = sxe (:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'sye'//'_l'//zchar1   ;   z3d(:,:,:) = sye (:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'sxxe'//'_l'//zchar1  ;   z3d(:,:,:) = sxxe(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'syye'//'_l'//zchar1  ;   z3d(:,:,:) = syye(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
            znam = 'sxye'//'_l'//zchar1  ;   z3d(:,:,:) = sxye(:,:,jk,:)
            CALL iom_rstput( iter, nitrst, numriw, znam , z3d )
         END DO
         !
         IF( ln_pnd_LEV .OR. ln_pnd_TOPO ) THEN                                       ! melt pond fraction
            CALL iom_rstput( iter, nitrst, numriw, 'sxap' , sxap  )
            CALL iom_rstput( iter, nitrst, numriw, 'syap' , syap  )
            CALL iom_rstput( iter, nitrst, numriw, 'sxxap', sxxap )
            CALL iom_rstput( iter, nitrst, numriw, 'syyap', syyap )
            CALL iom_rstput( iter, nitrst, numriw, 'sxyap', sxyap )
            !                                                        ! melt pond volume
            CALL iom_rstput( iter, nitrst, numriw, 'sxvp' , sxvp  )
            CALL iom_rstput( iter, nitrst, numriw, 'syvp' , syvp  )
            CALL iom_rstput( iter, nitrst, numriw, 'sxxvp', sxxvp )
            CALL iom_rstput( iter, nitrst, numriw, 'syyvp', syyvp )
            CALL iom_rstput( iter, nitrst, numriw, 'sxyvp', sxyvp )
            !
            IF ( ln_pnd_lids ) THEN                                  ! melt pond lid volume
               CALL iom_rstput( iter, nitrst, numriw, 'sxvl' , sxvl  )
               CALL iom_rstput( iter, nitrst, numriw, 'syvl' , syvl  )
               CALL iom_rstput( iter, nitrst, numriw, 'sxxvl', sxxvl )
               CALL iom_rstput( iter, nitrst, numriw, 'syyvl', syyvl )
               CALL iom_rstput( iter, nitrst, numriw, 'sxyvl', sxyvl )
            ENDIF
         ENDIF
         !
      ENDIF
      !
   END SUBROUTINE adv_pra_rst

   SUBROUTINE icemax3D( pice , pmax )
      !!---------------------------------------------------------------------
      !!                   ***  ROUTINE icemax3D ***
      !! ** Purpose :  compute the max of the 9 points around
      !!----------------------------------------------------------------------
      REAL(wp), DIMENSION(:,:,:), INTENT(in ) ::   pice   ! input
      REAL(wp), DIMENSION(:,:,:), INTENT(out) ::   pmax   ! output
      !
      REAL(wp), DIMENSION(Nis0:Nie0) ::   zmax1, zmax2
      REAL(wp)                       ::   zmax3
      INTEGER  ::   ji, jj, jl   ! dummy loop indices
      !!----------------------------------------------------------------------
      ! basic version: get the max of epsi20 + 9 neighbours
!!$      DO jl = 1, jpl
!!$         DO_2D( 0, 0, 0, 0 )
!!$            pmax(ji,jj,jl) = MAX( epsi20, pice(ji-1,jj-1,jl), pice(ji,jj-1,jl), pice(ji+1,jj-1,jl),   &
!!$               &                          pice(ji-1,jj  ,jl), pice(ji,jj  ,jl), pice(ji+1,jj  ,jl),   &
!!$               &                          pice(ji-1,jj+1,jl), pice(ji,jj+1,jl), pice(ji+1,jj+1,jl) )
!!$         END_2D
!!$      END DO
      ! optimized version : does a little bit more than 2 max of epsi20 + 3 neighbours
      DO jl = 1, jpl
         DO ji = Nis0, Nie0
            zmax1(ji) = MAX( epsi20, pice(ji,Njs0-1,jl), pice(ji-1,Njs0-1,jl), pice(ji+1,Njs0-1,jl) )
            zmax2(ji) = MAX( epsi20, pice(ji,Njs0  ,jl), pice(ji-1,Njs0  ,jl), pice(ji+1,Njs0  ,jl) )
         END DO
         DO_2D( 0, 0, 0, 0 )
            zmax3 = MAX( epsi20, pice(ji,jj+1,jl), pice(ji-1,jj+1,jl), pice(ji+1,jj+1,jl) )
            pmax(ji,jj,jl) = MAX( epsi20, zmax1(ji), zmax2(ji), zmax3 )
            zmax1(ji) = zmax2(ji)
            zmax2(ji) = zmax3
         END_2D
      END DO
   END SUBROUTINE icemax3D

   SUBROUTINE icemax4D( pice , pmax )
      !!---------------------------------------------------------------------
      !!                   ***  ROUTINE icemax4D ***
      !! ** Purpose :  compute the max of the 9 points around
      !!----------------------------------------------------------------------
      REAL(wp), DIMENSION(:,:,:,:), INTENT(in ) ::   pice   ! input
      REAL(wp), DIMENSION(:,:,:,:), INTENT(out) ::   pmax   ! output
      !
      REAL(wp), DIMENSION(Nis0:Nie0) ::   zmax1, zmax2
      REAL(wp)                       ::   zmax3
      INTEGER  ::   jlay, ji, jj, jk, jl   ! dummy loop indices
      !!----------------------------------------------------------------------
      jlay = SIZE( pice , 3 )   ! size of input arrays
      ! basic version: get the max of epsi20 + 9 neighbours
!!$      DO jl = 1, jpl
!!$         DO jk = 1, jlay
!!$            DO_2D( 0, 0, 0, 0 )
!!$               pmax(ji,jj,jk,jl) = MAX( epsi20, pice(ji-1,jj-1,jk,jl), pice(ji,jj-1,jk,jl), pice(ji+1,jj-1,jk,jl),   &
!!$                  &                             pice(ji-1,jj  ,jk,jl), pice(ji,jj  ,jk,jl), pice(ji+1,jj  ,jk,jl),   &
!!$                  &                             pice(ji-1,jj+1,jk,jl), pice(ji,jj+1,jk,jl), pice(ji+1,jj+1,jk,jl) )
!!$            END_2D
!!$         END DO
!!$      END DO
      ! optimized version : does a little bit more than 2 max of epsi20 + 3 neighbours
      DO jl = 1, jpl
         DO jk = 1, jlay
            DO ji = Nis0, Nie0
               zmax1(ji) = MAX( epsi20, pice(ji,Njs0-1,jk,jl), pice(ji-1,Njs0-1,jk,jl), pice(ji+1,Njs0-1,jk,jl) )
               zmax2(ji) = MAX( epsi20, pice(ji,Njs0  ,jk,jl), pice(ji-1,Njs0  ,jk,jl), pice(ji+1,Njs0  ,jk,jl) )
            END DO
            DO_2D( 0, 0, 0, 0 )
               zmax3 = MAX( epsi20, pice(ji,jj+1,jk,jl), pice(ji-1,jj+1,jk,jl), pice(ji+1,jj+1,jk,jl) )
               pmax(ji,jj,jk,jl) = MAX( epsi20, zmax1(ji), zmax2(ji), zmax3 )
               zmax1(ji) = zmax2(ji)
               zmax2(ji) = zmax3
            END_2D
         END DO
      END DO
   END SUBROUTINE icemax4D

#else
   !!----------------------------------------------------------------------
   !!   Default option            Dummy module        NO SI3 sea-ice model
   !!----------------------------------------------------------------------
#endif

   !!======================================================================
END MODULE icedyn_adv_pra