Talk:Lapse rate

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1 Units
2 Dry adiabatic lapse rate cannot be a constant
3 Rename the article
4 Low importance?
5 Merge
6 Disambiguation
7 What matters? Altitude change or pressure change?
8 External Links
9 Inline references
10 Mechanism
11 mathematical definition

[edit] Units

Conversions should be provided for non-metric users. Aviation users in particular need to know feet/F rather than km/C for the dry adiabatic lapse rate.

The article has been changed, but I actually find the change less satisfactory. American aviation uses F/1000ft, and european aviation uses C/m (I think). In Canada, we use C/1000ft — do we just get screwed? (I actually can't see a reasonable way to prevent Canadian pilots from getting screwed, especially as I do not support the numbers being expressed in three different units). -Lommer | ^talk 23:24, 26 July 2005 (UTC)

How about a little table with three columns? -- hike395 03:33, July 27, 2005 (UTC)

Actually, that's not a bad suggestion... -Lommer | ^talk 04:31, 27 July 2005 (UTC)

The US FAA converted from Fahrenheit to Celsius in 1996. American aviators have been using Celsius for the last ten years. Bobblewik 03:37, 23 September 2005 (UTC)

As an American aviator who made the initial comment, temperature is reported in C but all vertical distances are, and will for a very long time, be in feet. In aviation publications, the formula for lapse rate is almost -always- given as degF/ft or degC (degF) / ft. However, the important part here (And perhaps it wasn't strongly enough emphasized)is that we need the 'feet' part, not so much that we need the temperature part in F.Kysh 22:14, 20 October 2005 (UTC)

What you say is reasonable. Just add the feet equivalents. Bobblewik 20:08, 8 October 2005 (UTC)

P.S. please use the autosignature function by adding 4 tildes ~~~~ .

Didn't have an account at the time, but I now do. Thanks. Kysh 22:14, 20 October 2005 (UTC)

UPDATE FOR PILOTS. In Europe we use the JAA as the aviation authority, and they state and test that the SALR is 0.6C/100m for the purpose of the ATPL exams. Very seldom do instructors and very seldom in the exams now will you see the SALR as c/ft. (1.8C/1000ft).--Pugzi 08:29, 15 May 2006 (UTC) (Steve Francis)

[edit] Dry adiabatic lapse rate cannot be a constant

The relationship between temperature and pressure is nearly fixed (it'll vary as the composition of the atmosphere changes, but presumably not by much). However, the relationship between pressure and altitude is not so nearly fixed, since it depends on the density profile over altitude, which depends on temperature over altitude (and also on humidity over altitude, to some extent).

The relationship of temperature and pressure is

${T_2 \over T_1} = \left({P_2 \over P_1}\right)^{{\gamma-1} \over \gamma}$

This is only true if T1,P1 and T2,P2 have the same entropy, i.e. if state 2 can be reached from state 1 by an adiabatic process.

The $γ$ here is not the same as the gamma used in the article body to denote lapse rate. The usage in the article is unfortunate, since $γ$ is usually used to denote the specific heat ratio, see adiabatic. Is the article's usage standard?

Actually, the

γ

in the adiabatic equation is precisely the specific heat ratio. Same letter, same meaning.

The pressure in the atmosphere drops off approximately exponentially with altitude. This means a 1000m increase in elevation typically produces a 12.6% drop in pressure. That drop in pressure would cause a 3.45% drop in temperature, which is about 10 C.

In any case, my point is that pressure at altitude varies, and varies with some independence from the pressure at sea level directly below, and as a result the dry adiabatic lapse rate is not a constant.

Iain McClatchie 18:34, 1 October 2005 (UTC)

Ok, it's not strictly constant, but it does turn out to be vary remarkably little if you do the numerical integration.

The dependence of pressure on altitude is only exponential if the temperature is constant. The dry adiabatic lapse rate is how the temperature varies with altitude if the atmosphere is adiabatic, i.e., if the entropy is constant. It turns out that in this case, dT/dz is in fact exactly constant. Of course, the atmosphere is neither precisely isothermal nor adiabatic; the troposphere is approximately adiabatic, and the stratosphere is approximately isothermal. 67.186.28.212 11:44, 2 September 2007 (UTC)

[edit] Rename the article

Why isn't this article called Lapse rate? The adiabatic is just one of the lapse rates that the article describes. The environmental lapse rate in particular is not adiabatic. It is the actual change in temperature with height. JMcC 14:42, 13 September 2006 (UTC)

The simplest course was to copy this article to Lapse rate and to modify it so that it starts with lapse rates in general before getting specific. I suggest this article is now reduced to cover adiabatic lapse rates. I would also suggest that the off-putting equation is moved to the end of the article. If there is no change in th next few days I will do this myself JMcC 11:38, 15 September 2006 (UTC)

Only Adiabatic lapse rate should be treated in this article, dry and moist, I agree. I just wonder why there is an article on Lapse rate in the first place as this should be a part of an article the atmosphere or the standard atmosphere. Lapse rate is just a term while Adiabatic Lapse Rate is a concept that needs to be explained? Pierre cb 11:56, 15 September 2006 (UTC)

Almost the other way round I think. The two adiabatic lapse rates are constants and are not as interesting as the environmental lapse rate. They are just one of the physical properties of dry and moist air. It is the variation in the environmental lapse rate that produces the weather. This leads on the tephigrams and SkewTlogP (or is that Harry Potter? :-) ) and so needs separate explanation. JMcC 17:53, 18 September 2006 (UTC)

Well you have a point but one may think the other way around that all depends on the relation to the adiabatic lapse rates to be stable, neutral, or unstable. Thus explaining why it is so, is the important part for me. There is a proposition to merge the two articles. I was not for it but this could solve the problem with the proper redirections. Pierre cb 17:36, 19 September 2006 (UTC)

[edit] Low importance?

To quote from the article itself "The varying environmental lapse rates across the earth surface are of critical importance in meteorology." Why does the Met Project rate is as low? JMcC 14:56, 13 September 2006 (UTC)

[edit] Merge

It seems to me that adiabatic lapse rate and lapse rate now strongly overlap. Should we merge them, or at least refactor them into 2 distinct articles? hike395 22:00, 16 September 2006 (UTC)

Yes they overlap but I don't think a merge is needed. Lapse rate should be trimmed to the minimum. It should ONLY mention that it is a change of temperature with altitude and refer to Adiabatic lapse rate for the rest. Pierre cb 01:32, 17 September 2006 (UTC)

I changed my mind on the subject and think that the merge might be the solution. Why not rename one of the articles Atmospheric Lapse Rates which is more accurate, put all the information from both articles and then make the redirect from the other to this new article. Pierre cb 17:32, 19 September 2006 (UTC)

I think the simplest title is the best --- I made Atmospheric lapse rate redirect to here. Completed the merge. hike395 11:15, 20 September 2006 (UTC)

[edit] Disambiguation

A lapse rate is also an important metric in various fields of insurance. Presently I'm not seeing anything about lapse rates on any of the insurance pages either, but maybe a link to the insurance category would be a good idea.

I would suggest starting an article on Lapse rate (insurance), and make that part of the insurance category, rather than having this non-insurance article be miscategorized. hike395 05:39, 20 October 2006 (UTC)

[edit] What matters? Altitude change or pressure change?

The lapse rates are always presented as some temperature change per altitude change. For example, 9.78 degrees per 1000 metres. Is this really constant? It would seem to me that it is the change of temperature with pressure change that would be constant and that since the pressure drop over a 1000 metre altitude change decreases with altitude, that the lapse rate with respect to altitude change would not be constant. Sancho McCann 05:15, 1 December 2006 (UTC)

Disregard... I see the discussion above. Sancho McCann 05:18, 1 December 2006 (UTC)

Actually, for completeness, would it be worth mentioning dry lapse rate as a function of pressure?? It isn't necessary for understanding of the term and a 9.78 per km is a really close approximation as mentioned above. There's a good description on a lecture slide here: http://www.sparc.sunysb.edu/atm205/fall2001/lecture7/sld004.htm. What do you think? Sancho McCann 19:40, 1 December 2006 (UTC)

Here is an alternative simpler way, the same as the German page uses, to calculate the lapse rate for rock in the earth interior. [1] and it only depends on specific heat capacity which is almost the same for air and rock. Davidjonsson Davidjonsson 23:30, 1 December 2007 (UTC)

[edit] External Links

I cannot open the External Links. Do they work? --Natasha2006 14:16, 16 April 2007 (UTC)

[edit] Inline references

I will give you all until June 20 to add inline references per the Wikipedia Guide of Style, at least one per paragraph. If not, I will downgrade the article to Start. Thegreatdr 20:45, 18 May 2007 (UTC)

Per a comment left on my talk page, I've decided to leave this article completely alone. If you all are happy with the current state of the article, that is definitely your call. Just keep in mind that if a certain type of citation (like inline references) is needed for an article to become GA or FA class, why not do it early on in an article's life cycle to save a lot of work later in the article's life? I can tell you that a lack on inline citations will generally keep me from updating an article because of all the extra work it would entail to upgrade its class. The citations used in the article should all be of a similar type, however, which they currently are not. Thegreatdr 03:26, 19 May 2007 (UTC)

Inline references are great --- we should definitely have them. I was just objecting to the multiple warning templates: it makes it seem that the article is dubious.

Your user page states that you are an expert in meteorology --- are there specific dubious facts in this article? Anything you're uncertain about? Please feel free to mark them with {{fact}}. Thanks! hike395 04:45, 19 May 2007 (UTC)

Not offhand. Actually, considering the lack on inline references, I don't see any fact problems. I've seen other articles with tags in each section without inline references before (October 2006 form of the tornado article, for instance). It didn't appear right in this case to just tag the top, because it would imply there were no inline references at all in the article, when there are a couple in the last section. Thegreatdr 12:15, 19 May 2007 (UTC)

I found a more appropriate tag for the top: {{Refimprove}}. It still encourages people to improve the references, but doesn't imply that there are none. hike395 12:45, 19 May 2007 (UTC)

Good find. =) Thegreatdr 13:36, 19 May 2007 (UTC)

[edit] Mechanism

Can anyone comment on why the lapse rate has the value it does? The atmosphere is a complicated and dynamic system: There's convection, radiation, heating by the ground, etc. But it is universally true that higher altitudes are colder. My hunch is that gravity is the fundamental mechanism. I'm interested to know how an ideal gas behaves at equilibrium in a gravitational field. My guess is that it would end up with a temperature gradient equal to the adiabatic lapse rate 9.78 °C/km, otherwise parcels of air would generate energy by trading altitudes. I'll leave with the comment that 9.78°C/km is on the order of Mg/k_B (34°C/km), where M is the mass of an air molecule (29 u). That is the lapse rate you'd get by making the naive assumption that k_BT increases by the amount of energy gained as a molecule "falls" to lower altitude. I think the article would benefit from a statement about the fundamental reason it is colder up there. Spiel496 03:01, 20 July 2007 (UTC)

IIRC from my atmospheric physics lectures, then you're pretty much right - we ought to put something about the derivation of the adiabatic value on the page - this website offers quite a useful derivation of the constant, and shows how it would vary between different bodies. --Neo 10:18, 20 July 2007 (UTC)

[edit] mathematical definition

Is the lapse rate truly defined by professionals as the slope, -(T2-T1)/(z2-z1), rather than the derivative -dT/dz? 76.120.154.6 14:44, 30 September 2007 (UTC)