What is or causes Wind?
The main cause of wind are pressure differences (High’s/Low’s) over large areas.
The term pressure difference relates to our changing weather systems worldwide.
We have big weather systems in the upper atmosphere, as well as comparably smaller ones in the lower atmosphere. The small weather systems are those we experience every day on earth.
How do the weather systems form?
Because sun rays strike the earth at different angles all over the world, our planet is heated unequally everywhere. Just take a look at the picture.
This results in different temperatures over big land areas (i.e.: ocean/land) and thus different radiation (radiation= air leaving the ground because it’s warmer and, therefore, lighter than it’s surrounding) into the atmosphere. This lifting of air is in turn responsible for the different pressure patterns (Highs/lows) that forms as a result.
How is wind actually measured?
Wind is measured at a height of about 10M over the surface by a so-called “anemometer”.
The air (or wind) turns the cups. Their rotation is directly proportional to the wind speed.