Geoscience Reference
In-Depth Information
Table 11.1
Saturated vapor pressure over water and ice as a function of temperature.
Saturated vapor pressure
over water (kPa)
Saturated vapor
pressure over ice (kPa)
Temperature (°C)
0
0.611
0.611
-2
0.527
0.517
-4
0.454
0.437
-6
0.390
0.369
-8
0.334
0.310
-10
0.286
0.260
-12
0.244
0.218
-14
0.207
0.182
-16
0.175
0.151
-18
0.148
0.125
-20
0.124
0.104
vapor is frozen out of the air and directly deposited on to the ice particles. Because
there is no physical movement of cloud particles involved, the transfer of vapor
and resulting ice particle growth can be rapid.
Which clouds produce rain?
Most clouds do not produce rain. This can be seen easily by comparing satellite
derived maps of cloud cover with simultaneous maps of precipitation intensity
derived from rainfall radar, both of which are now readily available on the Internet.
Clouds do not produce rain if they are:
too short lived
, or have not yet been in existence long enough for drops of
sufficient size to escape from the cloud and fall to the ground;
●
too shallow to allow vertical motion
that encourages particle growth;
●
too high
, which implies that they have low moisture content because they are
cold, they have limited internal vertical motion, and any precipitation gener-
ated has abundant opportunity to evaporate before reaching the ground.
●
Clouds that are more likely to produce precipitation have the opposite characteristics
to those given above, specifically they:
have existed for some time
, so they more likely have greater dynamical activ-
ity which includes differential vertical motion, and there has been more time
for multiple collisions to have occurred between component cloud particles;
●
