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1 | 1 | CISM Changelog |
2 | 2 |
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| 3 | +Changes in CISM tag cism_main_2.01.014 |
| 4 | +====================================== |
| 5 | +Basal hydrology scheme, new basal friction and inversion options ESCOMP/CISM PR#61 |
| 6 | + |
| 7 | +This PR includes three main lines of effort: |
| 8 | +(1) updates to the slab test |
| 9 | +(2) a steady-state flux routing basal hydrology scheme |
| 10 | +(3) various basal friction and inversion options to support Antarctic ice sheet experiments |
| 11 | + |
| 12 | +The slab test is as described in Section 3.4 of Robinson et al. (TC, 2022). It was used in that paper |
| 13 | +to test the stability of various solvers (SIA, SSA, DIVA, L1L2) in the simple case of an infinite slab |
| 14 | +of ice flowing down an inclined plane. Various test parameters can be specified when launching |
| 15 | +the run script. See the README file for details. |
| 16 | + |
| 17 | +The hydrology scheme is based on the idea that all water input at the bed is conservatively routed down |
| 18 | +the hydraulic gradient until it reaches the ice margin. Steady state means that for each grid cell, the |
| 19 | +water output is equal to the input. Water can be routed to one downstream neighbor (D8), two neighbors |
| 20 | +(Dinf), or all downstream neighbors (FD8). The scheme uses the efficient algorithm of Planchon & Darboux |
| 21 | +(2001) to fill depressions. It is fully parallel, unlike the similar scheme in old Glimmer. The scheme |
| 22 | +has been tested for the Greenland and Antarctic ice sheets; more testing and tuning will follow. |
| 23 | + |
| 24 | +The basal friction and inversion changes include the following: |
| 25 | + |
| 26 | + - support for the Zoet-Iverson basal friction law |
| 27 | + - an option to invert for Cc (aka Coulomb_c) in basal friction laws that have a Cc term, including ZI and pseudo-plastic. Previous inversions were for Cp (aka powerlaw_c) only. |
| 28 | + - an option to apply an observation-based dH/dt field to floating ice during spin-up. This allows the ice to reach a spun-up steady-state and then to thin at observed rates during the subsequent forward run. This option was used for ISMIP6 Antarctica 2300 experiments. A similar option was used in the paper by van den Akker et al. (TC, 2024). |
| 29 | + - an option to include a relaxation term when inverting for Cp and Cc, in addition to the terms proportional to (H - Hobs) and dH/dt. This term reduces clumping of Cc and Cp around their max and min values. |
| 30 | + - new options for computing effective pressure, including an option to be used with the new hydrology scheme |
| 31 | + - an option to invert locally for deltaT_ocn |
| 32 | + - an option to invert for basin-scale flow factors |
| 33 | + - an optional velocity target for Cp and Cc inversion |
| 34 | + - an option to apply a time scale to mask-based calving |
| 35 | +Results from this branch were compared to main for several standard test cases. |
| 36 | +Using LIVVkit (with several dome, ISMIP-HOM, shelf, and stream tests), all tests pass. The stream test requires a config file change. |
| 37 | +MISMIP+ results are also BFB, with several config file changes. |
| 38 | +DIVA dome tests are not quite BFB, but agree within machine roundoff. I think this is acceptable, given the large number of changes on this branch. |
| 39 | + |
| 40 | + |
3 | 41 | Changes in CISM tag cism_main_2.01.013 |
4 | 42 | ====================================== |
5 | 43 |
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