Environmental Engineering Reference
In-Depth Information
an area of high pressure to one of lower pressure. This gives rise to the phenomenon we
call wind. We can see this principle in action in our own living rooms; when we open the
window on a winter's day, the cool air from outside rushes into the warm room, creating a
current of air or a draught. This cool air falls, which explains why some people like to have
a blanket over their legs and feet, and why it is not unusual to enter the living room in the
morning and find the dog on the couch.
From Draughts to Hurricanes
The greater the difference in pressure between two air masses, the faster will be the speed
of the wind. A draught is perhaps the least powerful and most localized of all wind types.
Another localized, but more powerful movement of air is a breeze (see
Figure 4.7
). Breezes
typically move from land to sea during the day (when the land is cooler than the sea) and
fromseatolandatnight(whentheseaiscoolerthantheland).Thereasonforthedifference
in temperature between land and sea is that soil temperatures can vary greatly over the
course of a day whereas seawater maintains a more constant temperature. You will never
burn your feet paddling in the sea, but you may on a beach in summer.
