Snow parameterizations helping permafrost#1766
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…ttom-temp Follow-up to #1766. Addresses review findings on the snow thermal-conductivity and snow-bottom-temperature work: - Fix LandModel possible-diagnostics name mismatch "snow_tbot" -> "snowtbot" (the snow-bottom-temp diagnostic was unreachable and output_vars=:long errored). - Make the ghf and snow-conductivity diagnostics reachable; rename the non-ASCII short name snowκ -> snowk (and compute_snow_κ! -> compute_snow_k!). - Add units/comments to the new snow diagnostics (K, W m^-1 K^-1, W m^-2). - Fix the duplicated "F_g = F_g =" in update_soil_snow_ground_heat_flux! and restore the Δz_snow 10 cm cap rationale. - Remove the vestigial, unused κ_ice kwarg from SnowParameters(toml_dict, Δt). - Expand the snow_T_bottom docstring and add it to the API docs. - Add tests: Sturm conductivity branches, snow_T_bottom limits/cap, and a diagnostics reachability regression test. - Add NEWS.md entries (feature, breaking κ_ice->κ_snow, behavioral GHF change). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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See suggestions in #1769 which is mostly some cleanup suggestions - feel free to add or not! (edit it as needed!)
kmdeck
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…ttom-temp Follow-up to #1766. Addresses review findings on the snow thermal-conductivity and snow-bottom-temperature work: - Fix LandModel possible-diagnostics name mismatch "snow_tbot" -> "snowtbot" (the snow-bottom-temp diagnostic was unreachable and output_vars=:long errored). - Make the ghf and snow-conductivity diagnostics reachable; rename the non-ASCII short name snowκ -> snowk (and compute_snow_κ! -> compute_snow_k!). - Add units/comments to the new snow diagnostics (K, W m^-1 K^-1, W m^-2). - Fix the duplicated "F_g = F_g =" in update_soil_snow_ground_heat_flux! and restore the Δz_snow 10 cm cap rationale. - Remove the vestigial, unused κ_ice kwarg from SnowParameters(toml_dict, Δt). - Expand the snow_T_bottom docstring and add it to the API docs. - Add tests: Sturm conductivity branches, snow_T_bottom limits/cap, and a diagnostics reachability regression test. - Add NEWS.md entries (feature, breaking κ_ice->κ_snow, behavioral GHF change). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Purpose
Adds a simple parameterization for the bottom temperature of the snow (not optional), modularizes the thermal conductivity model of the snow, and adds a second parameterization option for this (Sturm).
This typically makes the bottom temperature warmer than the bulk temperature, which improves snow insulation over the soil, and has a big effect on permafrost locations. The Sturm conductivity model is also lower than the Jordan parameterization in general, and this helps with permafrost.
To-do
Impact
Main:
Bottom alone:
Sturm + Tbottom:
Content
Adds bottom snow temp as a cache variable to integrated models with soil and snow, and computes it during the ground heat flux computation
Adds another parameterization for thermal conductivity