# Microphysics

We are using the Microphysics_1M.jl module from the CloudMicrophysics.jl package. See the documentation for further comments on the scheme derivation.

## Coupling to the state variables

### Warm Rain

The source of rain $\mathcal{S}_{q_{rai}}$ is a sum of the autoconversion, accretion, and rain evaporation processes. The sink of total water is equal to the source of rain: $\mathcal{S}_{q_{tot}}$ = -$\mathcal{S}_{q_{rai}}$. The sink of cloud liquid water is the sum of rain autoconversion and rain accretion processes. Following the conservation equations for mass, moisture, and precipitation the $\mathcal{S}_{q_{tot}}$ sink has to be multiplied by $\rho$ before adding it as one of the sink terms to both $\rho$ and $\rho q_{tot}$ state variables. The $\mathcal{S}_{q_{liq}}$, $\mathcal{S}_{q_{rai}}$ sources have to be multiplied by $\rho$ before adding them as one of the source terms to $\rho q_{liq}$ and $\rho q_{rai}$state variables. For the conservation equation for total energy, the sink due to removing $q_{tot}$ is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = \left. \sum_{j\in\{v,l,i\}}(I_j + \Phi) \rho C(q_j \rightarrow q_p) \right|_{precip} = (I_l + \Phi) \rho \, \mathcal{S}_{q_{tot}}$$$$$

where:

• $I_l = c_{vl} (T - T_0)$ is the internal energy of liquid water,
• $T$ is the temperature,
• $T_0$ is the thermodynamic reference temperature (which is unrelated to the reference temperature used in hydrostatic reference states used in the momentum equations),
• $c_{vl}$ is the isochoric specific heat of liquid water,
• $\Phi$ is the effective gravitational potential.

### Rain and Snow

The source of rain $\mathcal{S}_{q_{rai}}$ is a sum of the autoconversion, accretion, rain evaporation, and snow melt processes. Similarily, the source of snow $\mathcal{S}_{q_{sno}}$ is a sum of the autoconversion, accretion, snow deposition/sublimation, and snow melt processes. The sink of total water is equal to the sum of the rain and snow sources: $\mathcal{S}_{q_{tot}}$ = -$\mathcal{S}_{q_{rai}}$ - $\mathcal{S}_{q_{sno}}$. The sink of cloud liquid water $\mathcal{S}_{q_{liq}}$ is the sum of rain autoconversion, rain accretion with cloud liquid water, and snow accretion with cloud liquid water processes. The sink of cloud ice $\mathcal{S}_{q_{ice}}$ is the sum of snow autoconversion, snow accretion with cloud ice, and rain accretion with cloud ice processes. Following the conservation equations for mass, moisture, and precipitation the $\mathcal{S}_{q_{tot}}$ sink has to be multiplied by $\rho$ before adding it as one of the sink terms to both $\rho$ and $\rho q_{tot}$ state variables. The $\mathcal{S}_{q_{liq}}$, $\mathcal{S}_{q_{ice}}$, $\mathcal{S}_{q_{rai}}$, and $\mathcal{S}_{q_{sno}}$ sources have to be multiplied by $\rho$ before adding them as one of the source terms to $\rho q_{liq}$, $\rho q_{ice}$, $\rho q_{rai}$, and $\rho q_{sno}$state variables. For the conservation equation for total energy the source term due to microphysics processes is caused by either removing cloud condensate outside of the working fluid or by changing phase and releasing latent heat outside of the working fluid. Below, contributions from different microphysics processes are listed:\ The contribution from cloud liquid water to rain autoconversion, cloud liquid water accretion by rain, and rain evaporation is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = - (I_l + \Phi) \rho \, \mathcal{S}_{q_{rai}}$$$$$

where:

• $I_l = c_{vl} (T - T_0)$ is the internal energy of liquid water,
• $T$ is the temperature,
• $T_0$ is the thermodynamic reference temperature (which is unrelated to the reference temperature used in hydrostatic reference states used in the momentum equations),
• $c_{vl}$ is the isochoric specific heat of liquid water,
• $\Phi$ is the effective gravitational potential.
• $\mathcal{S}_{q_{rai}}$ is the source of rain from the above three processes.

The contribution from cloud ice to snow autoconversion, cloud ice accretion by snow, cloud liquid accretion by snow in temperatures below freezing, and snow deposition/sublimation is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = - (I_i + \Phi) \rho \, \mathcal{S}_{q_{sno}}$$$$$

where:

• $I_i = c_{vi} (T - T_0) - I_{i0}$ is the internal energy of ice,
• $c_{vi}$ is the isochoric specific heat of ice,
• $I_{i0}$ is the difference in specific internal energy between ice and liquid at $T_0$,
• $\mathcal{S}_{q_{sno}}$ is the source of snow from the above four processes.

The contribution from accretion of cloud liquid water by snow in temperatures above freezing is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = ((1 + \alpha) I_l - \alpha I_i + \Phi) \rho \, \mathcal{S}_{q_{liq}}$$$$$

where:

• $\alpha = \frac{c_{vl}}{L_f}(T - T_{freeze})$
• $\mathcal{S}_{q_{liq}}$ is the source of cloud liquid water from

accretion of cloud liquid water by snow in temperatures above freezing. The contribution from cloud ice accretion by rain (the result is snow) is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = (I_i + \Phi) \rho \, \mathcal{S}_{q_{ice}} - \rho L_f \mathcal{S}_{q_{rai}}$$$$$

where:

• $\mathcal{S}_{q_{ice}}$ and $\mathcal{S}_{q_{rai}}$

are the sinks of cloud ice and rain due to accretion.. Finally, the contribution from accretion between rain and snow as well as snow melting into rain is computed as:

$$$$$\left. \mathcal{S}_{\rho e} \right|_{precip} = \rho L_f \mathcal{S}_{q_{sno}}$$$$$

where:

• $\mathcal{S}_{q_{sno}}$ is the source of snow in those two processes.