Environmental Engineering Reference
In-Depth Information
Plate 4.6
A well developed cyclone to the north-west of
Ireland associated with the characteristic spiral of cloud.
Discrete clouds over southern France indicate convectional
storms, in contrast to the widespread cloud sheets around the
cyclone. Image taken on 31 August 2000 at 15.10 GMT in the
visible waveband. The infra-red image for this time is shown
in
Plate 7.2.
Image: courtesy of the NERC Satellite Station, University of
Dundee.
There are a number of differences from convectional precipitation. The areal extent of
rising air associated with a depression is much larger, and the rate of upward movement
and the rate of condensation in the generally stratiform clouds are much less. Because of
this, the droplets grow more slowly and fall out of the cloud sooner. Being small, they
can be greatly affected by evaporation in the drier air beneath cloud base. For example, in
an atmosphere with a relative humidity of 90 per cent, a droplet of radius 10 µm will fall
