Highs and lows

[Duffer]

As we are all fed up with this weather, with no settled weather in sight, I wonder if anyone can explain to me WHY depressions/low pressure are associated with cloud/rain while areas of high pressure are associated with sunny/dry weather (at least in the UK in "summer")?

Is it some intrinsic property of air pressure? Does rain collect in areas of low pressure like puddles on the partially inflated cover of a Wimbledon tennis court? Or is it more to do with humidity in the areas where the weather systems originate?

This might help to cheer you up. I was rafted alongside a Spanish yacht at Dittisham (above Dartmouth). The fluent skipper said he came to the UK every summer. I asked why given the weather. He said because in the UK the air conditioning is free! /forums/images/graemlins/smile.gif

 

[Vara]

http://www.metoffice.gov.uk/education/primary/students/the_rain.html

Is a good place to start,If you're feeling confident scroll onto secondary/higher school resources. /forums/images/graemlins/smile.gif

 

[ChrisE]

Here's an explanation

Basically, highs are 'sucking' clear air in their centre from the stratosphere, lows are pulling damp air from ground level and compressing it into clouds.

 

[jamesjermain]

Shall I be the first to dip a toe into this?

Depressions are formed at the boundry between warm air to the south and cold air to the north. Turbulent whirlpools of air form in which two areas of cold air form a pincer movement on a wedge of warm air. The latter is forced to rise over the denser, heavier cold air and, being warm and wet, the moisture in it soon condenses to form rain. Becasue the air in the middle is warmer, lighter and rising the pressure drops, air is pulled in towards the centre of low pressure and this causes the often very strong winds associated with a low.

A high pressure system, on the otherhand, is formed in areas where cold high altitude air sinks back down to the surface. Being cold and sinking it is heavier and pressure is higher. Because there are no dynamics within a high pressure system - no fronts - the air is stable. Because it is warming up, there is no condensation. The air tends to flow out from the centre of the high quite gently and gathers a slight clockwize spin (in the northern hemisphere) due to the coriolis effect.

I think!

OK, so not the first

 

[Duffer]

Thanks for the replies - an interesting subject which I have never had the opportunity to study.