Environmental Engineering Reference
In-Depth Information
Figure 7.11
Simplified cross-sections through cold and warm
occluded fronts.
front. This may also explain why 'true' occluded fronts are relatively rare. Frequently one
or more of the frontal components of the Bergen model is missing. It also appears that
fronts which seem to have an occluded structure may have been formed by other
methods, such as growth northward from the junction of warm and cold fronts, or
'instant' occlusions whereby comma-shaped cloud features behind the cold front join
with open frontal waves to produce apparently mature occluded systems over a short
period of time. Much remains to be determined about the nature of occluded frontal
systems.
At one time it was believed that it was the air rising along the frontal surface that
caused the development of a depression. However, the role of divergence in the upper
atmosphere is now believed to be the most important factor, the fronts being the result of
the rotation of air around the low's centre. From being a cause of the
Plate 7.4
Typical trade-wind cumulus clouds. The clouds
provide visible evidence of the continuous evaporation from
the warm tropical seas.
Photo: Peter Smithson.
depression, the front has been relegated to a consequence. Nevertheless the weather
activity associated with fronts is still a very important aspect of the depression.
