Hoi Marcus,
Deze tekst komt van de BBC site. Aangezien UKMO "UK MetOffice" betekent, is je veronderstelling waarschijnlijk juist.
Met vriendelijke groet,
Alwin
The wind arrows on the graphics used by the BBC's Weather Forecasters and on this website provide two pieces of weather data, wind direction and wind strength. The former is shown by the direction of the arrow head, as to the strength, the larger an arrow the stronger the wind flow, but we do not tie particular sizes of arrow to either the Beaufort scale or to a specific speed. The smallest wind arrows are an indication of a gentle breeze; large wind arrows forecast gales.
The data files as supplied by the Met Office contain a number of fields of each arrow. Apart from direction and a value of size, each arrow is given a temperature value and is also tagged with a unique number. We can use the temperature to colour arrows so that cold air (when it blows from the north, for example) will be seen as blue arrows and warmer air, typically from the south, in yellows and oranges.
The temperature colours are similar to those used in the temperature charts seen in our broadcasts and on this website. The unique number can be used to track the progress of a specific arrow across a given area enabling us to create a moving sequence, as seen on TV broadcasts. In these sequences it is intriguing to see how individual arrows change in size and direction, especially when they cross from the sea onto the land, where there is always a marked decrease in wind strength due to features in the landscape.
The wind arrow graphics are closely related to the pressure charts, in that as the isobars on the latter become more tightly packed, so then the wind will strengthen - this being depicted by the larger arrows!
It is worth noting that the wind direction is approximately in line with isobars (if you stand with your back to the wind, you will have low pressure on your left hand side and high pressure on your right hand side).
It would be an interesting exercise to overlay a wind chart for a particular area over a pressure chart for the same time and area, to see the relationship between the two weather tools.
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