Understanding 500Hpa Charts

[Avain]

I see these charts used frequently in the model discussion thread and although I have read the thread in this forum about the 500hpa charts I still was not able to grasp their significance, particularly in relation to the colour codes and what they mean, also in relation to the numbers on the key.

Also the value of the charts, what is is you can learn from them?

So if anyone has time to give a more detailed explanation I would be grateful.

Thanks in advance!

Edited January 2, 2010 by Avain

[Avain]

I should have titled this "trying to understand"

Anyway, I also read another thread in which this question was addressed by John Holmes Here

It has helped some but also raised further questions.

I am assuming that the colour coded numbers refer to the height of the 500mb line, and are abbreviated meters (i.e. 534 = 5340 meters)

this being the case I note that all the action on the colour section of these charts takes place in side 4000ft of upper air from 15700 ft to 19700ft (approx)

But what is puzzling is the way the colours seem to be the reverse of what \i would expect, in the instance I have seen, the lower temp are associated with the 500mb line being at a lower altitude and vis versa, also they seem to be more associated with low pressure systems, which by there nature are warm wet air rising, with High pressure being cold descending air columns, on top of that I would expect an increase in alt to give a lower temp reading, but the opposite seems the case with this, as the lowest alt of 480 is the coldest temp and 600 the warmest.

Obviously I don't have an accurate grasp of what the chart is intended to convey, so would still like further clarification if possible please.

[johnholmes]

hi

I'll come back to you(this) later this morning-glad some of the other info worked for you

[BrickFielder]

Here is a good starting point.

Understanding 500hpa charts

[Avain]

Hi BF, indeed yes, thanks for posting it. It is though the very page linked to in my second post, you must have missed it, but I do appreciate you taking time to help.

[johnholmes]

wow

good job I looked in again before starting to try and answer the question.

I would have been 'sick as a parrot' as they say if I had toiled all the way through trying to get a simple explanation out only to discover I'd already done it with help from others.

Anyway Av if you are still puzzling please ask, one of us will attempt to answer any questions.

[Avain]

Hi John, well, as I said, I had read your explanation on the page referred to by BF, but it still left the questions made in my second post regarding the hieghts and temps and the apparent reversal of logic, i.e. this bit:

I am assuming that the colour coded numbers refer to the height of the 500mb line, and are abbreviated meters (i.e. 534 = 5340 meters)

this being the case I note that all the action on the colour section of these charts takes place in side 4000ft of upper air from 15700 ft to 19700ft (approx)

But what is puzzling is the way the colours seem to be the reverse of what \i would expect, in the instance I have seen, the lower temp are associated with the 500mb line being at a lower altitude and vis versa, also they seem to be more associated with low pressure systems, which by there nature are warm wet air rising, with High pressure being cold descending air columns, on top of that I would expect an increase in alt to give a lower temp reading, but the opposite seems the case with this, as the lowest alt of 480 is the coldest temp and 600 the warmest.

Obviously I don't have an accurate grasp of what the chart is intended to convey, so would still like further clarification if possible please.

So yes, I am still wondering about that aspect.

[johnholmes]

okay I'll go away and put my thinking hat on and hopefully come back some time this evening with something I hope may help you.

[johnholmes]

hi

well here I am again with another attempt-hope this clears it up for you?

500mb charts-what they mean 3 jan 10.pdf

[BrickFielder]

I like to think that each surface system has its corresponding system above it.

The important thing about low pressure systems is that the air rises inside it because of the steep temperature difference between the surface and upper levels. As that air rises it will cool and what you need to think about is the temperature of the air at mid levels rather than at the surface. Yes moist warm air rises in a low pressure system but by mid levels it tends to be colder than the corresponding cold air decending in a high pressure system. This to me shows at mid levels the air is denser in a low pressure system than in a high pressure system. High density probably means a particular pressure is likely to be reached at a lower height.

Hence the strong correlation between 500hpa heights and 500hpa temperatures.

[Avain]

Many thanks to you both, the explanations in the pdf were very helpful and BF's explanation with the excellent diagrams have certainly made it a lot clearer, I realise that there is much more to learn as John says it gets a lot more complex afterwards, but I do now have a much better grasp of what the chart is showing.

It's great that you can get help like that.

Many thanks again!