chrisbell-nottheweatherman
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Posts posted by chrisbell-nottheweatherman
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flashes getting more frequent. just saw a lovely lightning strike - but cloud to cloud , rather than cloud to ground.
doing the "1.2.3.4..." counting between flash and sound , i got up to about 10. not sure how that translates into miles away.
About 2 miles.
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Don't worry John - that's why I said that I knew you were busy and that I was looking forward to your post over the weekend - I wasn't expecting an answer until then! Thanks though; it's nice to know that I've learnt something.
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Apparently, the reason that people don't think that we do get that many is because most are small and weak and therefore go unnoticed.
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making it a bit complicated, ignore the effects of gravity, but I will try and answer your P, V, T question over this weekend.
John, when I mentioned gravity, I meant purely on the basis of the air becoming thinner with altitude, which I understood to be due to gravitational pull. I'd read that this was the cause of air pressure also dropping as one ascends through the troposphere, therefore, as a parcel of air rises, it encounters steadily lowering air pressure around it, which encourages expansion of the parcel of air, thus cooling it. Eventually, as I've read, the temperature of the parcel of air drops toards the dew-point, eventually causing condensation and thus causing clouds to be formed.
I understand that you're busy, and I look forward eagerly to reading your post over the weekend - above all I want to make sure that I'm reading an accurate description of these processes: my philosophy is that it's better not to learn anything than to learn incorrect information.
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Ah, in my post of 12:42, I seem to have confused the reason why air temperature in the troposphere decreases with altitude, which I gather is due to warming of the Earth's surface radiating heat into the lower part of the troposphere to a greter degree than the upper part with the reason air cools as it rises: lowering atmospheric pressure due to reduced gravitational pull causes expansion of the volume of the parcel of air which requires an input of energy to do the work of increasing the distance between the molecules of the various gases, thus using-up heat energy in the parcel of air (hence the need for a hot-air baloon to use it's gas burners regularly to maintain altitude). Am I correct?
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hi Chris
I forgot that as a newcomer you have to do a certain number of posts before you are able to pm. That said I'll try and do my version of an asnwer to your original question as soon as I get the time. Hope you can be patient as I seem to have a lot of things to do away from Net Wx at the moment. Do keep reading the Guides it will help.
be in touch as soon as I can get the time.
regards
John
Thanks John.
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BrickFielder - thanks for the links.
Some already reinforce what I'd read in the Guides, but most are very helpful. I see exactly what you mean about the hypothetical baloon meeting the layer of warm air, and also the need to blast hot air into the canopy at regular intervals. Oddly enough, back when I were a lad (he says putting-on flat hat), I'd always wondered why the air got colder the higher you went; to my logic as a kid, the higher you went, the closer you were to the sun, so the hotter it should be. John - if I can work-out how to message you, I shall. I'm afraid I really am at a novice level here, so don't be afraid of patronising me.
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John should probably answer this but here is my take on the subject.
A Gas or air heated in a confined area will have its internal pressure rise. So the higher the temperature the higher the pressure. This is what the gas laws show (A steam engine is a good exaple of the principle)
The problem with the atmosphere is that it is not in a confined area as such. One result of low level heating of the atmosphere is that the air rises. The more you heat it the more it rises and this is how storms and clouds form. As the air rapidly rises then something has to try and fill the hole left by the rising air. If the air round about does not move quickly enough (wind) then there tends to be less air and so lower pressure at the surface. The end result is higher pressure at the tropopause and low pressure at the surface. This happens not just at the cloud or storm level ,but at weather system level and even gloabl levels with the Walker and Hadley cells. This is linked to the Gas laws just not in the same direct way as the confined area example. Look up Baroclinic and Barotropic for further information.
Weather is all about air moving either up and down or towards low pressure and away from high pressure and different levels in the atmosphere can have different air movements. These movements always relate to the temperatures of the air masses at various heights above sea level. This is why SkewT charts and soundings are usefull tools for weather prediction.
Thanks BrickFielder. I have to admit you lost me when you started saying words like "tropopause", "Walker and Hadley cells", and "Baroclinic and Barotropic" but I think I get the gist of what you were saying.
Would it be perhaps less potentially misleading to unknowing idiots like myself to think more in terms of air becoming less dense as it's heated and rises? Certainly, a molecular eye-view of this would show greater kinetic energy within a body of warming air, thus the already huge gaps between molecules of the constituent gases (of course oxygen and nitrogen are molecular as gases, not atomic) increase, which lowers the density and causes that body of warm air to rise, rather in the manner of a hot air baloon. All I'm saying is that, to my absolute beginner's logic, to speak of the body of air's pressure having an effect on whether it rises or not seems less than relevant as it's not being contained,as you pointed-out.
P.S, I've just looked-up "Baroclinic" and "Barotropic", and found the following explanation that I could understand (i.e. it didn't contain endless equations):
is this about right? I'm not, I'm afraid, going to be able to understand complex mathematical theories, I'm just interested in getting a qualitative, empirical understanding.
Thanks again.
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Sorry, I forgot to mention my name (seems a bit silly for people to call me w0033944
). I'm Chris Bell. -
Thanks Paul!
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Hello.
I'm new here, although I 'd spend some time posting on the now-defunct BBC weather boards during the winter of '05/'06, using (if memory serves) the screen name cpbell or cpbell0033944, only leaving when one of the Farkin/Allen alter-egos started being abusive. I read about NetWeather then, but was intimidated as it was full of experts and, as a dunce, I wasn't sure whether I'd be welcome or not
I'm not at all knowledgeable on things meterological, (I'm a biologist by training - my maths wasn't anywhere near good enough to get into this fascinating subject) and I'll soon be starting postgrad studies so I won't be able to post that often. However, I'm enthusiastic and would like to understand the weather better than I do now, and, to that end, I've started reading the guides. However, I'm now confused. In the guide entitled "The Mechanism Behind a Sea Breeze", johnholmes states
Just one little bit of physics here: temperature and pressure are related through the Gas Laws, so when the temperature increases, all other things being equal, then the pressure decreases.however, in the Learners Area, when Avain asks about how Lows and Highs Affect each other, Full Frontal Occlusion says
Temperature also affects pressure in that the individual atoms speed up with higher temperatures. This means that more collisions between atoms/molecules happen over the same time span than for a cooler gas. With greater numbers of collisions, the force exerted collectively has increased and hence the pressure within the gas is higher.and these two statements seem to me to contradict each other. With memories of GCSE Physics being baffling, I found a kid's revision guide, where it states that Charles' Law shows that pressure and temperature are proportionally-related, which suggests that FullFrontal Occlusion is right.
Can anyone please enlighten me?
). I'm Chris Bell.
Pressure, volume and temperature
in Spring Weather Discussion
Posted
Thanks BrickFielder - I now have a technical term to use in order to help describe this process.
Anyway, still staying on-topic, but moving the focus slightly, there's something else I want to clear-up if I may. Subject to John's weekend posting on the definitive link between P, V and T of a parcel of air, we seem to be broadly agreeing that thehotter a parcel of air is, the greater the pressure it has in terms of the pressure it applies to lower-pressure air around it. However, on reading the sections here and on the MetOffice's educational site regarding high and low pressure systems, it appears that high pressure areas tend to contain cooler air, whereas lows tend to carry warmth and moisture. :huh:
This baffled me until I spotted the mention of high pressure areas containing cool, heavy air. Does this literally mean that the barometric pressue that one might measure at ground level would be higher under a high pressure system beacause of a layer of cooler, and therefore "heavier" air sitting on top of what can (at least in summer) be warm air near the surface, thus acting like a saucepan lid, trapping the pressure? Would this then cause a high lapse rate, explaining why, if a parcel of air near the ground were to warm enough to escape the surface and to pass through the "lid" of cool air, it would be more likely to reach the tropopause before hitting its dew point?