INTRODUCTION - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 3

Figure 1-1. The main global atmospheric circulations. Source: NASA/JPL-Caltech.
the surface turns east, creating the westerlies. The westerlies are the reason wind
resources tend to be so good in the temperate and high latitudes (around 35 - 65 ◦ N)
of North America, Europe, and Asia, as well as the southern extremes of Africa, South
America, and Australia.
Superimposed on these global circulation patterns are many regional patterns. Large
land masses heat up and cool down more rapidly than the oceans, and even within land
masses, there are variations in surface heating, for instance, between a snow-covered
mountain top and a green valley below or between a desert and a cultivated plain.
The resulting temperature gradients set up what are called mesoscale atmospheric
circulations — mesoscale because they are in between the global scale and the local
scale, or microscale.
The most familiar mesoscale circulation is the sea breeze. During a typical summer
day, the land becomes warmer than the ocean, the pressure drops as the air above it
expands and rises, and relatively cool, dense air is pulled in from the ocean. At night,
the process reverses, resulting in a land breeze. Normally, sea breezes are weak, but
where the wind is concentrated by terrain, they can have a powerful effect. This is the
primary mechanism behind the very strong winds found in coastal mountain passes