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Blocking anti-cyclones

I am currently studying weather and climate for my main geography exam and we have just been covering the topic of 'anticyclones'.We know that anticyclones can last for days, weeks and months and are classed as blocking anticyclones.I was wondering if anybody knows the following information:
1) why do they last in an area (Britain for example in 2003) for a long time and then eventually clear and move away
2) If high pressure moves to low pressure, how do blocking anticyclones last.Any information on this would be really helpful for a presentation I'm doing!
Thanks!
-Brian
Met isn't my strongest subject, but I do know a little! I don't really know what level you're pitching at - for example have you covered general circulation/Hadley circulation?

Anyway some things to think about:
- anticyclones are not necessarily blocking anticyclones. An anticyclone is simply an area of high pressure, but a blocking anticyclone is one which lasts a long time and moves very slowly (some don't last long)
- air does move from high to low, but in an anticyclone that movement is generally slow as the pressure gradient is shallow. In addition, if more air is being brought in at upper level then that can replenish the low level outflow
- remember that an anticyclone is an area where air is descending, rotating clockwise (in the northern hemisphere) and flowing outwards
- this is a bit of guesswork from me, but I think it makes sense: think about what causes changes in pressure - differential heating. Areas of intense cold tend to be large (Siberia!) which gives a large air mass of relatively uniform characteristics, hence low pressure gradients. Without a pressure gradient there's nothing to make them move.
- you might also want to look at whether movement of the ITCZ and sub-polar low affect the formation of blocking anticyclones

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