!! Ice-thickness-distribution (ITD) restore: adjust_ice_categories (PR 4a). module rdb_ice_itd !! Port of SIS2 `adjust_ice_categories` (`SIS_transport.F90:611-891`, !! Apache-2.0). SIS2's shipped algorithm is NOT the Lipscomb (2001) !! linear-profile remap — that is a `SIS_transport.F90:737` TODO !! comment, never code. What SIS2 actually runs (and what this module !! ports) is the *"for now move all of it"* WHOLE-CATEGORY shift: when !! a category's mean ice mass crosses a bin boundary, its ENTIRE !! area+mass moves to the adjacent category, merged into that !! category's existing area+mass via an area-weighted destination- !! thickness average (mass AND area conserving, SIS2:730-741) with !! upwind mass-weighted tracer mixing (equivalent in effect to SIS2's !! deferred `advect_tracers_thicker`, `SIS_tracer_advect.F90:1791-1850` !! — each category boundary is visited once per pass in a fixed order !! with running masses, so a single closed-form mass-weighted mix at !! the transfer site reproduces the same result; verified by the !! validated Python prototype, `tmp_local_artifacts/proto_itd_adjust.py`). !! !! Ported with `ice_cover_discard = -1` (off, SIS2 default), !! `ocean_part_min = 0`, `inconsistent_cover_bug = .false.` (i.e. DO !! the open-water resum). !! !! Algorithm per cell (all steps operate on the SAME category array — !! order matters, see the docstrings of each impl step below): !! 1. Massless cleanup (SIS2:664-685): any category with !! `m_ice <= 0` has its area returned to open water (flagged for !! the final resum, not applied immediately). !! 2. Upward pass, `c = 1..ncat-1` ascending (SIS2:714-767): a !! category whose ice mass exceeds ITS OWN upper bin edge !! (`mh_lim(c+1)`) moves ALL its area+mass into category `c+1`. !! 3. Downward pass, `c = ncat..2` descending (SIS2:786-839): mirror !! of step 2 — a category whose ice mass falls below its OWN !! lower bin edge (`mh_lim(c)`) moves ALL its area+mass into !! category `c-1`. !! 4. Cat-1 minimum-thickness compress (SIS2:850-864): category 1 has !! no category below it to demote into (`mh_lim(1) > 0` is the !! physical floor), so instead of a transfer it AREA-SHRINKS: !! `part(1) *= m_ice(1)/mh_lim(1)`, pinning `m_ice(1)` at the !! floor (mass- and per-remaining-area-tracer-conserving; the !! lost area returns to open water via the resum). !! 5. Open-water resum (SIS2:874-889): only if step 1 or step 4 !! fired (the up/down transfers of steps 2-3 preserve `Σ part` !! exactly, add/subtract the same `part_trans` on both sides, so !! they never need a resum) — `part(0) = max(1 - Σ_{c=1..ncat} !! part(c), 0)`. !! !! Deliberately NOT ported (SIS2 features orthogonal to the "for now !! move all of it" shift, or infra this branch does not have yet): !! melt ponds (no pond state on `ocean_sea_ice_t`), `t_surf` category !! remap (`tsurf_out` here is per-thermo-window scratch, recomputed !! from scratch every step — nothing to remap), `ice_cover_discard` !! (SIS2 default off), the FATAL input-consistency checks (a GPU !! `do concurrent` kernel cannot abort mid-loop — negative mass / !! snow-on-no-ice is treated as "massless", the same taxonomy as step !! 1), and SIS2's `do_j` per-row early-exit optimisation (the per-cell !! `if` gate below is the DC-kernel equivalent). Ridging is a SEPARATE, !! still-unported gap — NOT closed by `compress_ice` (PR 4b, !! `rdb_ice_transport`): `compress_ice` is SIS2's own !! `DO_RIDGING=.false.` fallback (area compaction, in-category, zero !! energetic cost), not the participation/redistribution ridging !! scheme SIS2 ships as an Icepack wrapper (`ice_ridge.F90`, default !! off). See `docs/CAPABILITIES_AND_LIMITATIONS.md` "Sea ice" for the !! physical consequence. !! !! **ncat==1 short-circuit (bit-identity contract, module docstring of !! `rdb_ice_state`)**: the outer shim returns immediately when !! `ice%ncat == 1` — the legacy lumped mode never runs any part of this !! module, by construction (not by an exactness argument). SIS2 itself !! would still run the cat-1 compress at nCat=1 (`mh_lim(1) = 1e-10 m` !! makes it physically unreachable in practice), but skipping it !! outright is the simplest statement of "ncat=1 is untouched" and is !! the explicit contract this branch commits to. use rdb_constants, only: wp use rdb_grid, only: hgrid_t use rdb_multilayer_state, only: multilayer_state_t use rdb_ice_state, only: ocean_sea_ice_t implicit none private public :: ice_adjust_categories contains pure subroutine ice_adjust_categories(grid, ms, ice) !! Outer shim (outer-shim + flat-impl pattern). No-op when the ice !! slot is not live (`is_init` gate) or when `ice%ncat == 1` (the !! legacy-mode bit-identity contract — see module docstring). No !! `dt`/`eos` needed: this is a pure area/mass reshuffle, no !! thermodynamics. type(hgrid_t), intent(in) :: grid type(multilayer_state_t), intent(in) :: ms !! READ-ONLY: only `wet_mask` is read (the gate). type(ocean_sea_ice_t), intent(inout) :: ice if (.not. ice%is_init) return if (ice%ncat == 1) return call ice_adjust_categories_impl(ms%wet_mask, ice%part_size, ice%m_ice, ice%m_snow, & ice%enth_ice, ice%enth_snow, ice%sal_ice, ice%mh_lim, & grid%nghost, ice%ncat, ice%nk_ice, & grid%nx_total, grid%ny_total) end subroutine ice_adjust_categories pure subroutine ice_adjust_categories_impl(wet_mask, part_size, m_ice, m_snow, & enth_ice, enth_snow, sal_ice, mh_lim, & nghost, ncat, nk, nx, ny) !! Device kernel: ONE `do concurrent(j, i)` over PHYSICAL cells !! (ghosts excluded), `wet_mask > 0.5` inner gate (never a masked DC !! header), serial `cat` loops inside — each cell touches only its !! own `(i, j, :)` slice, race-free. No per-cell gather into local !! category-sized arrays (avoids register pressure and any !! compile-time `ncat` cap, unlike the `ICE_NK_MAX`-capped !! PER-LAYER arrays elsewhere in the ice model) — scalar !! temporaries only, all declared in `local(...)`. !! !! Decl-order: all integer dims declared before the explicit-shape !! arrays that use them. No locals named after intrinsics. integer, intent(in) :: nghost, ncat, nk, nx, ny !! Grid + category + layer extents (declared first — decl-order). real(wp), intent(in) :: wet_mask(nx, ny) real(wp), intent(inout) :: part_size(nx, ny, 0:ncat) real(wp), intent(inout) :: m_ice(nx, ny, ncat) real(wp), intent(inout) :: m_snow(nx, ny, ncat) real(wp), intent(inout) :: enth_ice(nx, ny, ncat, nk) real(wp), intent(inout) :: enth_snow(nx, ny, ncat, 1) real(wp), intent(inout) :: sal_ice(nx, ny, ncat, nk) real(wp), intent(in) :: mh_lim(ncat + 1) integer :: i, j, i_lo, i_hi, j_lo, j_hi integer :: cat, lay logical :: resum real(wp) :: part_trans, part_sum real(wp) :: mca_ice_src, mca_ice_dst, mca_snow_src, mca_snow_dst, mnew, msnew i_lo = nghost + 1 i_hi = nx - nghost j_lo = nghost + 1 j_hi = ny - nghost do concurrent(j=j_lo:j_hi, i=i_lo:i_hi) local(cat, lay, resum, part_trans, part_sum, & mca_ice_src, mca_ice_dst, mca_snow_src, & mca_snow_dst, mnew, msnew) if (wet_mask(i, j) > 0.5_wp) then resum = .false. ! ---- 1. Massless cleanup (SIS2:664-685) ---- do cat = 1, ncat if (m_ice(i, j, cat) <= 0.0_wp) then if (part_size(i, j, cat) > 0.0_wp) resum = .true. part_size(i, j, cat) = 0.0_wp end if end do ! ---- 2. Upward pass, c = 1..ncat-1 ascending (SIS2:714-767) ---- do cat = 1, ncat - 1 if (part_size(i, j, cat)*m_ice(i, j, cat) > 0.0_wp .and. & m_ice(i, j, cat) > mh_lim(cat + 1)) then part_trans = part_size(i, j, cat) mca_snow_src = part_size(i, j, cat)*m_snow(i, j, cat) mca_snow_dst = part_size(i, j, cat + 1)*m_snow(i, j, cat + 1) mca_ice_src = part_trans*m_ice(i, j, cat) mca_ice_dst = part_size(i, j, cat + 1)*m_ice(i, j, cat + 1) m_ice(i, j, cat + 1) = (part_trans*m_ice(i, j, cat) & + part_size(i, j, cat + 1)*m_ice(i, j, cat + 1)) & /(part_trans + part_size(i, j, cat + 1)) m_ice(i, j, cat) = mh_lim(cat + 1) part_size(i, j, cat + 1) = part_size(i, j, cat + 1) + part_trans part_size(i, j, cat) = part_size(i, j, cat) - part_trans m_snow(i, j, cat) = 0.0_wp if (part_size(i, j, cat + 1) > 0.0_wp) then m_snow(i, j, cat + 1) = (mca_snow_src + mca_snow_dst)/part_size(i, j, cat + 1) else m_snow(i, j, cat + 1) = 0.0_wp end if mnew = mca_ice_src + mca_ice_dst if (mca_ice_src > 0.0_wp .and. mnew > 0.0_wp) then do lay = 1, nk enth_ice(i, j, cat + 1, lay) = (mca_ice_src*enth_ice(i, j, cat, lay) & + mca_ice_dst*enth_ice(i, j, cat + 1, lay)) & /mnew sal_ice(i, j, cat + 1, lay) = (mca_ice_src*sal_ice(i, j, cat, lay) & + mca_ice_dst*sal_ice(i, j, cat + 1, lay)) & /mnew end do end if msnew = mca_snow_src + mca_snow_dst if (mca_snow_src > 0.0_wp .and. msnew > 0.0_wp) then enth_snow(i, j, cat + 1, 1) = (mca_snow_src*enth_snow(i, j, cat, 1) & + mca_snow_dst*enth_snow(i, j, cat + 1, 1)) & /msnew end if end if end do ! ---- 3. Downward pass, c = ncat..2 descending (SIS2:786-839) ---- do cat = ncat, 2, -1 if (part_size(i, j, cat)*m_ice(i, j, cat) > 0.0_wp .and. & m_ice(i, j, cat) < mh_lim(cat)) then part_trans = part_size(i, j, cat) mca_snow_src = part_size(i, j, cat)*m_snow(i, j, cat) mca_snow_dst = part_size(i, j, cat - 1)*m_snow(i, j, cat - 1) mca_ice_src = part_trans*m_ice(i, j, cat) mca_ice_dst = part_size(i, j, cat - 1)*m_ice(i, j, cat - 1) m_ice(i, j, cat - 1) = (part_trans*m_ice(i, j, cat) & + part_size(i, j, cat - 1)*m_ice(i, j, cat - 1)) & /(part_trans + part_size(i, j, cat - 1)) m_ice(i, j, cat) = mh_lim(cat) part_size(i, j, cat - 1) = part_size(i, j, cat - 1) + part_trans part_size(i, j, cat) = part_size(i, j, cat) - part_trans m_snow(i, j, cat) = 0.0_wp if (part_size(i, j, cat - 1) > 0.0_wp) then m_snow(i, j, cat - 1) = (mca_snow_src + mca_snow_dst)/part_size(i, j, cat - 1) else m_snow(i, j, cat - 1) = 0.0_wp end if mnew = mca_ice_src + mca_ice_dst if (mca_ice_src > 0.0_wp .and. mnew > 0.0_wp) then do lay = 1, nk enth_ice(i, j, cat - 1, lay) = (mca_ice_src*enth_ice(i, j, cat, lay) & + mca_ice_dst*enth_ice(i, j, cat - 1, lay)) & /mnew sal_ice(i, j, cat - 1, lay) = (mca_ice_src*sal_ice(i, j, cat, lay) & + mca_ice_dst*sal_ice(i, j, cat - 1, lay)) & /mnew end do end if msnew = mca_snow_src + mca_snow_dst if (mca_snow_src > 0.0_wp .and. msnew > 0.0_wp) then enth_snow(i, j, cat - 1, 1) = (mca_snow_src*enth_snow(i, j, cat, 1) & + mca_snow_dst*enth_snow(i, j, cat - 1, 1)) & /msnew end if end if end do ! ---- 4. Cat-1 minimum-thickness compress (SIS2:850-864) ---- if (mh_lim(1) > 0.0_wp) then if (m_ice(i, j, 1)*part_size(i, j, 1) > 0.0_wp .and. m_ice(i, j, 1) < mh_lim(1)) then part_size(i, j, 1) = part_size(i, j, 1)*(m_ice(i, j, 1)/mh_lim(1)) if (m_ice(i, j, 1) > 0.0_wp) then m_snow(i, j, 1) = m_snow(i, j, 1)*(mh_lim(1)/m_ice(i, j, 1)) end if m_ice(i, j, 1) = mh_lim(1) resum = .true. end if end if ! ---- 5. Open-water resum (SIS2:874-889) ---- if (resum) then part_sum = 0.0_wp do cat = 1, ncat part_sum = part_sum + part_size(i, j, cat) end do part_size(i, j, 0) = max(1.0_wp - part_sum, 0.0_wp) end if end if end do end subroutine ice_adjust_categories_impl end module rdb_ice_itd