The UK is set for some stormy weather over the next few days. As one low pressure system moves away we will be afforded a day or so of relatively calm weather before a deep depression hits bringing with it high wind speeds and heavy rain.
Wind is all around us but what is it and what actually causes it? Here we examine one of the simplest aspects of weather and some of the terminology that surrounds it.
Wind simply is the movement of air. And the air moves because of differences in temperature and pressure around the globe.
This difference in temperature and pressure is because at the equator (the hottest area on earth) the hot air rises before cooling and sinking as it moves towards the poles. This leads to the basic concept of atmospheric circulation… the three-cell model (see right).
As the air cools it shrinks and as it heats it expands. This is the basis of air pressure, with high pressure essentially pushing down harder on the Earth’s surface because there is more air present it is just more dense.