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Learning about isobars
Synoptic weather charts are covered in them. Isobars. So, get ready for a whistle-stop tour.
The air around is at different pressures in different places. A line joining those bits of air which (at a given height such as sea level) are at the same air pressure is an isobar (iso=same, bar=pressure).
On a map, contours join lines of equal height - the shape of the contours helps you 'read' the shape of the land. The same applies to isobars - they help you 'read' the weather. This is what a low pressure would look like on a synoptic chart.
This is what a high pressure looks like.
Yes, the only way to tell the difference is the 'L' for low and the 'H' for high. This is a bit like on a map where the top of a hill and the bowl of a valley can look similar from the contours
Low pressure air is warm, light air that wants to rise. High pressure air is cold, heavy air that wants to fall. Any particular lump of air will tend to be pushed away from high pressure air towards low pressure air.
This means that air tends to move away from the middle of a high pressure and towards the middle of a low pressure. The closer the isobars are to each other, the greater the pressure differential and the higher the winds (just as close contours = large height differential).
However, things aren't quite that simple. Because of the spinning of the earth wind always veers to the right. This is called the Coriolis effect. So, instead of air moving directly to the centre of a low pressure, it goes right a bit. This introduces an anti-clockwise spin to the air and is called a cyclone.
Similarly, instead of air moving directly away from a high pressure, it veers to the right, giving a clock-wise spin to the air (called an anti-cyclone).
So, when you look at a high pressure and a low pressure together, you can work out the likely wind patterns.
Finally we can see what this looks like on a real synoptic chart.
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