Environmental Engineering Reference
In-Depth Information
much less. This is one reason why some of the world's most severe storms are found in
warm climates.
Let us illustrate the effect of condensation by considering a specific example. Figure
4.3 shows the path curve for the bubble. Its initial temperature as a result of surface
heating is at 21° C. As it is warmer than its environment, it will cool at 9·8° C/1000 m
until saturation point is reached. It is at this level that we first see the visible evidence of
our bubble - a small cloud will be seen forming. Above condensation level the rate of
cooling slows down to the saturated lapse rate as long as the bubble's temperature is still
higher than that of the environment. If it is, we get large convectional clouds building up
which will probably bring rain (Plate 4.2).
Whether the atmosphere is still stable or not will depend upon the relative rates of
cooling of the dry bubbles, the saturated bubbles and the environment. We can
summarize this in Figure 4.4. If the environmental lapse rate is cooling more rapidly than
the dry adiabatic lapse rate we have absolute instability, as bubbles of air,
Figure 4.4
The stability relationship between the
environmental lapse rate (ELR), the dry adiabatic lapse rate
(DALR) and the saturated adiabatic lapse rate (SALR).
