# Changeset 988 for palm/trunk/DOC/tec/methods/cloud_physics/cloud_physics.tex

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Timestamp:
Sep 5, 2012 11:27:58 AM (10 years ago)
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Update of cloud_physics.pdf

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 r701 \linebreak 14.12.2009 \linebreak \linebreak last update \linebreak \today \end{center} \end{itemize} The dynamical processes are covered by advection and diffusion and they are described by the implemented methods. For the consideration of the thermodynamical processes modifications are necessary in the thermodynamics of PALM . In doing so evaporation and condensation are treated as thermodynamical processes modifications are necessary in the thermodynamics of PALM. In doing so evaporation and condensation are treated as adiabatic processes whereas precipitation and radiation are treated as diabatic processes. In the dry version of PALM the thermodynamic variable is the potential temperature $\theta$. The first law of thermodynamics provides the prognostic equation -\frac{\partial \left(\overline u_{j} \overline q\right)}{\partial x_{j}} -\frac{\partial\, \overline{u_{j}^{'} q^{'}}}{\partial x_{j}} +\left(\frac{\partial \overline q}{\partial t}\right)_{\mathrm{RAD}} +\left(\frac{\partial \overline q}{\partial t}\right)_{\mathrm{PREC}} \label{eq:total_water} \end{eqnarray} \left(\frac{\partial \overline q}{\partial t}\right)_{\mathrm{PREC}} & = & \begin{cases} \left(\overline q_{l}-\overline q_{l_{\mathrm{crit}}}\right)\cdot \tau & \left(\overline q_{l}-\overline q_{l_{\mathrm{crit}}}\right)/ \tau & \quad\overline q_{l} > \overline q_{l_{\mathrm{crit}}} \\ 0  & \quad\overline q_{l} \leq \overline q_{l_{\mathrm{crit}}} The precipitation leaves the grid volume immediately if the threshold of the liquid water content $\overline q_{l_{\mathrm{crit}}}=0.5\,\mathrm{g/kg}$ is exceeded. Hence, evaporation of the rain drops does not occur. $\tau$ is a time scale with a value of 0.001\,s. $\tau$ is a time scale with a value of 1000\,s. \newline The influence of the precipitation on the temperature is as follows: