Pressure vs Temperature
Thread Starter
Joined: Jul 2002
Posts: 524
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From: uk
Pressure vs Temperature
Hi all!
I am quite confused about the whole concept of pressure vs temperature. I am studying my ATPLs and have just hit a chapter about Anticyclones.
It says that you can get warm and cold anticyclones. It also says that Anticyclones are high pressure. How can you get a cold anticyclone? I always thought cold ment Low Pressure and warm ment High Pressure. I.e - Temp goes up, Pressure goes up, etc.
It says that cold anticyclones are formed when cold surface temperatures make the lower troposphere cold and dense. Yet it also says "Warm air mass - high pressure...Cool air mass - low pressure"...contradicting?
I too don't really get the Pressure/Density/Temperature realtionship as this is all screwed up in my head when thinking about anticyclones.
I would appreciate if someone could explain, use really basic english, and I mean go to extremeties...really BASIC!
I am quite confused about the whole concept of pressure vs temperature. I am studying my ATPLs and have just hit a chapter about Anticyclones.
It says that you can get warm and cold anticyclones. It also says that Anticyclones are high pressure. How can you get a cold anticyclone? I always thought cold ment Low Pressure and warm ment High Pressure. I.e - Temp goes up, Pressure goes up, etc.
It says that cold anticyclones are formed when cold surface temperatures make the lower troposphere cold and dense. Yet it also says "Warm air mass - high pressure...Cool air mass - low pressure"...contradicting?
I too don't really get the Pressure/Density/Temperature realtionship as this is all screwed up in my head when thinking about anticyclones.
I would appreciate if someone could explain, use really basic english, and I mean go to extremeties...really BASIC!
Joined: Dec 1999
Posts: 320
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From: S England
Lose the idea that highs are hot and lows are cold. This is definately not always the case. For example the air around the equator is "typically" hot, unstable and often moist. Hence deep low pressure systems develop and very active storms are produced. Conversely, the air over the poles is "typically" cold, dry and very stable in other words anticyclonic.
We in the UK sometimes assume that high means warm because in the summer we are often influenced by the Azores High. As its name would suggest it originates from the Azores and drags warm air up from the sub tropics. But you will also be familiar with those beautifully clear January days when this isn't a cloud in the sky, the sun is shining, but it is bitterly cold. Those conditions are also anticyclonic - High pressure.
Try and understand how the highs and lows originally develop (normally uneven surface heating over a large area) and forget the idea that highs must be hot.
Hope this helps.
We in the UK sometimes assume that high means warm because in the summer we are often influenced by the Azores High. As its name would suggest it originates from the Azores and drags warm air up from the sub tropics. But you will also be familiar with those beautifully clear January days when this isn't a cloud in the sky, the sun is shining, but it is bitterly cold. Those conditions are also anticyclonic - High pressure.
Try and understand how the highs and lows originally develop (normally uneven surface heating over a large area) and forget the idea that highs must be hot.
Hope this helps.
Joined: Aug 2000
Posts: 3,648
Likes: 2
From: UK
You've almost answered your own question. There are three variables involved:
Pressure - Density - Temperature
If you fix two you determine the third, but you do have two degrees of freedom. So you can have high temperature and high pressure, low temperature and high pressure, high temperature and low pressure, or low temperature and low pressure.
Pressure - Density - Temperature
If you fix two you determine the third, but you do have two degrees of freedom. So you can have high temperature and high pressure, low temperature and high pressure, high temperature and low pressure, or low temperature and low pressure.
Joined: Dec 2001
Posts: 546
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From: europe
I thought warm air rose causing a lower pressure at the surface, and cold air from a higher pressure region moved in to fill the low pressure region. Is it different when the expression 'air mass' is considered?
Joined: Dec 1999
Posts: 320
Likes: 0
From: S England
Bluskis
Yes, the airmass is very relevant. If you take my example of the Azores High. The air starts off in sub tropical latitudes and is dragged northwards by the anticyclonic flow. As the air moves northwards over an ever cooling ocean, the airmass also cools. Therfore becoming more stable. When the airmass reaches the UK, it is still warm relative to the airmass that is being replaced, but cooler and therefore more stable than when it started its journey.
On the flip side a cold, dry and stable airmass originating from the arctic increases its moisture content and increases in temperature as a typical low pressure sitting over Iceland drags the airmass south and southeastwards. As the air moves southward over an ever warming ocean it produces even more instability and therefore deepens the low.
As with anything in Meteorology you have to understand a number of basic theories before you can understand why we get any particular type of weather. In this case you need to understand, airmasses, stability/instability and as was eluded to in the original question, the relationship between pressure, temperature and density.
Yes, the airmass is very relevant. If you take my example of the Azores High. The air starts off in sub tropical latitudes and is dragged northwards by the anticyclonic flow. As the air moves northwards over an ever cooling ocean, the airmass also cools. Therfore becoming more stable. When the airmass reaches the UK, it is still warm relative to the airmass that is being replaced, but cooler and therefore more stable than when it started its journey.
On the flip side a cold, dry and stable airmass originating from the arctic increases its moisture content and increases in temperature as a typical low pressure sitting over Iceland drags the airmass south and southeastwards. As the air moves southward over an ever warming ocean it produces even more instability and therefore deepens the low.
As with anything in Meteorology you have to understand a number of basic theories before you can understand why we get any particular type of weather. In this case you need to understand, airmasses, stability/instability and as was eluded to in the original question, the relationship between pressure, temperature and density.
