TABLE OF CONTENTS Apart from the obvious influence of topography in producing shelter or the enhanced exposure to wind (discussed later), the influence of large topographic features can be sufficient to generate small-scale weather systems which are capable of producing significant winds. Three types of wind are associated with topography:
Diurnal winds
Gravity winds
Lee waves
Under clear skies in daytime the slopes of hills and mountains facing the sun will receive greater solar heating than the flat ground in valley bottoms. Convection then causes an upslope flow, called anabatic wind, which is generally light and variable but which can often initiate thunderstorms. At night, the upper slopes lose heat by radiation faster than the lower slopes and the reverse effect happens, producing downslope katabatic winds. However, the denser cold air falling into the warmer valley can produce strong winds in a layer near the ground. The higher the mountains, the stronger is the effect. As the mountains in the UK are not very high, it is not surprising that the speeds of katabatic winds do not approach those of large depressions.
The effect of katabatic winds can be much enhanced if greater differences in air temperature can be obtained from external sources. A continuous range of...
