Referring to my first paragraph on the previous page relating to ‘away from coastal areas etc’. More often than not you may well get a general forecast saying essentially no wind and a passing reference to sea breezes. But very often you will find that there may be enough wind to fly. This is brought on by local conditions and you must appreciate general forecasts can not take these conditions into account otherwise the forecast would go on all day. Before I loosely explain about local conditions and what constitute them, let’s have a brief look at wind in simplistic terms (meteorologists please note).
In the meteorological world conditions occur where there can be a pressure difference between one spot on the earth’s surface and another, because there is a difference let’s call them a high pressure and a low pressure to distinguish them. In the natural world everything is trying to achieve a balance or state of rest, it is one of the many primary laws of physics. Applying this law to the above example means that there will be a movement between the two different pressure areas or systems, from the high to the low. If the earth was not spinning that would be the end of it, unfortunately or should I say fortunately for us, it is.
This introduces another factor, the air has already begun to move from the high to the low pressure but the earth is rotating and as a result the air is apparently deflected. To an observer this apparent deflection is to the right in the northern hemisphere and to the left in the southern hemisphere. The deflection is greater as the air speed increases and it is greater towards the poles. At the Equator it is null. It is known as the Coriolis Force. Both of these factors create the wind and how it initially behaves. These are the basic factors which cause lateral movement of air, we call it the wind. Of course air moves up and down too but we'll ignore that for the time being.
I have already referred to the wind systems as having different pressures. If we were to take pressure readings over a wide area we would be able to plot points of equal pressure and join them up using lines. These lines are known as isobars. They are just like contour lines on a map and the closer they are together the greater the gradient is between the lines and therefore the stronger the wind is going to be. If you then plot the wind direction as well you will see in the northern hemisphere the wind around a low pressure system flows anti-clockwise and is also known as a cyclone. The wind around a high pressure system flows clockwise and is known as an anticyclone.
You will have noticed, I hope, that I’ve lead you from calling wind systems just that, to being called pressure systems for that is what they are in meteorological terms. Apart from the properties above they also both exhibit similar features at their centres and where the systems meet on the edges, that of light variable winds, the effect may not even be noticed.
So that is is the bare structure of how wind is generated and how it initially behaves. But as they say if only life were that simple. Go to Wind Localised to find out about how geographical and local conditions can effect the wind.