Microphysics NonEquilibrium
The MicrophysicsNonEq.jl module describes a bulk parameterization of diffusion of water vapour on cloud droplets and cloud ice crystals modeled as a relaxation to equilibrium.
The cloud microphysics variables are expressed as specific humidities:
q_tot- total water specific humidity,q_vap- water vapor specific humidity,q_liq- cloud water specific humidity,q_ice- cloud ice specific humidity,
Parameters used in the parameterization are defined in ClimaParams.jl package. They consist of:
| symbol | definition | units | default value | reference |
|---|---|---|---|---|
| $\tau_{cond\_evap}$ | cloud water condensation/evaporation timescale | $s$ | $10$ | |
| $\tau_{dep\_sub}$ | cloud ice deposition/sublimation timescale | $s$ | $10$ |
Cloud water condensation/evaporation
Condensation and evaporation of cloud liquid water is parameterized as a relaxation to equilibrium value at the current time step.
\[\begin{equation} \left. \frac{d \, q_{liq}}{dt} \right|_{cond, evap} = \frac{q^{eq}_{liq} - q_{liq}}{\tau_{cond\_evap}} \end{equation}\]
where:
- $q^{eq}_{liq}$ - liquid water specific humidity in equilibrium,
- $q_{liq}$ - liquid water specific humidity,
- $\tau_{cond\_evap}$ - relaxation timescale.
Cloud ice deposition/sublimation
Deposition and sublimation of cloud ice is parameterized as a relaxation to equilibrium value at the current time step.
\[\begin{equation} \left. \frac{d \, q_{ice}}{dt} \right|_{dep, sub} = \frac{q^{eq}_{ice} - q_{ice}}{\tau_{dep\_sub}} \end{equation}\]
where:
- $q^{eq}_{ice}$ - ice specific humidity in equilibrium,
- $q_{ice}$ - ice specific humidity,
- $\tau_{dep\_sub}$ - relaxation timescale.
Both $\tau_{cond\_evap}$ and $\tau_{dep\_sub}$ are assumed constant here. It would be great to make the relaxation time a function of available condensation nuclei, turbulence intensity, etc. See works by prof Raymond Shaw for hints. In particular, [28].