Clouds & Orographic Precipitation Practical

Overview

This page describes a practical exercise to aid in the understanding of the distribution of precipitation over a region with orographic uplift. Precipitation and the availability of water can have a strong impact on Ecology over such locations. The model used is a single column model (SCM), which models processes in a 1-dimensional column of air. At every level in the vertical the model calculates the evolution of cloud microphysical processes, such as:

condensation onto aerosol
collision-coalescence of drops
initiation of the ice phase
formation of precipitating particles (rain, snow)
and many more processes

It also calculates the transport of precipitation between vertical levels, which is a dominant transport mechanism here.

This column of air is lifted over a mountain and cools, allowing more condensation to take place (recall from the parcel modelling practical: lifting, leads to cooling). The extra condensation can be enough to initiate precipitation, which then falls to Earth. The model can be used to illustrate the following phenomena:

The effect of variations in cloud drop number concentrations on precipitation
The effect of varying temperatures on idealised clouds and precipitation
The effect of cloud depth on precipitation.
The distribution of precipitation in idealised clouds

Running the model

The idea for the practical is that you will run the model for different scenarios.

Examples

(a) shows the cloud droplet number concentration (CDNC); (b) shows the liquid water mixing ratio, \(q_c\); (c) shows the rain water mixing ratio, \(q_r\); (d) shows the ice crystal number concentration, \(N_{ice}\). The red patch shows the location of the mountain over which the air is lifted. Height of the mountain is around 1 km.

clouds_notes.pdf