An improved thermodynamic sea-ice model for WRF
Authors: Yao, Yao
Type: Model
Published: 2026-07-30

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<div># HIGHTSI — High-Resolution Thermodynamic Snow/Ice Model</div>
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<div>**HIGHTSI** (High-Resolution Thermodynamic Snow/Ice) is a 1-D column sea-ice thermodynamic model, here packaged as a WRF physics module (`module_hightsi.F90`) that plugs into the Noah-LSM sea-ice driver. It solves the surface energy balance and the vertical heat conduction equation through a coupled snow–ice column.</div>
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<div>## Key components</div>
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<div>**Surface energy balance** (`ts1` / `ts1_appr`)</div>
<div>Iteratively solves for skin temperature `T1` using a Newton scheme balancing net shortwave, longwave, sensible heat, latent heat, and conductive heat flux into the snow/ice. Turbulent fluxes use Businger–Dyer / Holtslag stability functions with a Launiainen (1995) roughness formulation (`coe`).</div>
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<div>**Solar radiation penetration** (`inice`, `insnow1`, `insnow2`, `qsall1`)</div>
<div>Distributes penetrated shortwave through snow and ice using several extinction schemes (Launiainen & Cheng 1998; Sahlberg 1988; Grenfell & Maykut 1979; Ebert & Curry 1993).</div>
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<div>**Heat conduction** (`nume1`, `nume2`, `tint`)</div>
<div>Solves the 1-D heat diffusion equation with a Crank–Nicolson-type implicit scheme (`st = 0.5`) via LU decomposition. `nume2` additionally supports snow density layering (e.g. fresh/old snow). Snow/ice interface temperature is diagnosed in `tint`.</div>
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<div>**Melting & growth** (`dhs`, and inline logic)</div>
<div>- **Surface melt**: when `T1` exceeds the melting point, excess energy thaws the surface layer of snow or ice.</div>
<div>- **Internal melt**: detects grid points reaching the melting point and converts absorbed radiation + conductive convergence into melt.</div>
<div>- **Basal growth/ablation**: driven by the ocean heat flux `fw` and the conductive flux at the ice bottom.</div>
<div>- Sea-ice melt point is depressed to −0.1355 °C (salinity effect).</div>
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<div>**Albedo** (inline in `HIGHTSI`)</div>
<div>A CCSM-style parameterization combining thickness-dependent and temperature-dependent bare-ice albedos with a snow-masked blending via `asnow = SNOWH/(SNOWH+0.02)`.</div>
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<div>**Snow metamorphism**</div>
<div>- `SNOW_NEW`: bulk density of fresh snow (now using the CLM/Slater 2017 + Liston 2007 wind-dependent scheme).</div>
<div>- `SNOWPACK`: overburden compaction (Anderson/Koren 1995).</div>
<div>- `WIND_DRIFT_COMPACTION`: wind-driven drift compaction (CLM scheme, newly added).</div>
<div>- `CSNOW`: snow thermal conductivity (Dyachkova 1960, doubled).</div>
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<div>## State variables</div>
<div>`SITHICK` (ice thickness), `SNOWH` / `SNEQV` (snow depth / water equivalent), `T1` (skin temp), `tice(nvi)` / `tsnow(nvs)` (internal layer temperatures), `rki` / `rks` (ice / snow conductivities), `SNDENS` (bulk snow density).</div>
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<div>## Typical use</div>
<div>Driven at each WRF time step by atmospheric forcing (wind, temperature, humidity, pressure, radiation, precipitation at height `ZLVL`) and a prescribed ocean heat flux; produces updated surface fluxes, skin temperature, and snow/ice evolution for coupled NWP. Originally developed for Arctic expeditions such as CHINARE.</div>
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