Geoscience Reference
In-Depth Information
Fig. 3.8
Sketch of thunderstorm circulations associated with cold air outflow at the leading edge. Several
surges are shown. The darkened area consists of falling or suspended precipitation. The dashed line is
the upper boundary of the outflow at the rear in the wake of the storm. The insert shows the horizontal
wind coordinates relative to the front. (From Goff, 1976.)
Fig. 3.9
Sketch of the leading edge of the cold air outflow. The presence of cloud depends on the height of the
condensation level. The indicated flows are relative to the gust front. Plus and minus signs indicate
direct and indirect circulations, and the dotted line indicates separation due to local shear. (From Goff,
1976.)
Where they are combined with monsoon winds and orographic effects, as in Megha-
laya in the eastern parts of India, they have produced some of the largest long-term
rainfall amounts on record. Monsoons are large-scale quasi-steady wind regimes, often
resulting from specific geographic and topographic features of the regions where they
occur, and characterized by a seasonal reversal of wind direction. In response to the
differential heating by the surface, they blow from land to sea in winter, and from sea to
land in summer, producing a wet-dry season cycle.
3.2.4
Large-scale tropical convective systems
These are well-developed low-pressure systems, of tropical ocean origin, which can
travel long distances accompanied by strong winds and heavy rainfall. As they move
away from their origins, they can cause severe weather in the coastal regions. As long as
