QUOTE(Shauna_15 @ Aug 27 2009, 01:29 AM)
I'm 15, and just finished ground school, and there was one question I never got clearly answered.
Do commercial jets fly into the tropopause in the winter? If it gets to -30*C theoretically the tropopause is only 13 000' AGL, considering that it is a standard lapse rate that day.
===============4/feb/2011==========Theoretically, good bet. 13,000 is very low for a tropopause the lowest you are likely to get is about 26/28 at the Poles. My post below should have given the Equatorial Tropopauses a higher lift - but I forgot what they are.
-30*C you are allowing for +15* C on the ground (ISA)? Iif it is -30 on the ground, ah, I see where you are coming from . . . ok, 13 x -2= -26 -30 = -56 (oh boy)
Ok, very brainy question. You are bang on the lowest atmosopheric temps here. (-56.6)
Wow, you have actually, got me beat on this one. Well done!!
We were told in training that the lowest of them (tropopauses) was about FL260 at the poles.
I could try to wriggle out of it and mention Temp Dev (Temperature Deviation) this is when the temp is not what it should be so if it is 3*C warmer then then temp Dev is +2 we use this to accurately calculate our weight and fuel at high altitudes ((Temp Dev is often the case)). but this has no bearing on your theory - `fact` here.
So - yea, maybe you are right and you have taught me something. Give it -30*C on the ground and you may very well get a tropopause at FL130 - what an amazing point! Very good Shauna. [ I am in awe of the ability of today`s young.]
Shauna, Hi honey. Listen, the Tropopause is lower in the polar regions and higher in the equatorial regions. As the air is hotter around the equator the tropo get very high 36,000 and more. . . in the Polar regions it is typically 28,000 or less, because the colder air is a lot denser and heavier so the tropo is lower, ok? Also the heat in the Equatorial regions can cause massive uplift which can produce very high and very large CBs which if course go right up to the tropo.
You can fly in or above the tropopause as much as you want. the temperature is not a factor here. You can fly in -30 or +25 it does not matter. you may want to consider calculating the tropo by the OAT for an exercise if you like. Also, you may find that the lowest temp one gets is about -56.6 degrees C. hope this helps, keep studying, keep up the good work. Stay with it!! You sound like you are well on your way. Good luck.
Also, you may get a link or two on Tropopauses, from other members on this forum - also try a search on Google or somewhere, ok?
The only factor on the tropopause, I can think of, involving temperature is that when you are flying in a jetstream the core of the jetstream is towards the polar side of the jetstream and slightly higher, therefore, if you are in a jetstream you may want to work it out so that you avoid the core, as this is where the worst turbulence is - and you would not want to fly through that - also look up CAT Clear Air Turbulence which is also really lovely to avoid.. Also, there is usually no weather above the tropopause - a slight variation here is a troplical revolving storm, like those big hurricanes you get mid atlantic, on their way to the carib.
Also, in realation to your question; If you fly in the tropophere - thats here. Anything below the tropopause is the troposphere and down here, where we all are now is where all the weather is. In or on the tropopause you will get tops of CBs and Cirrus and maybe Cirrus above a bit, but I doubt it. Above the tropopause is invariably clear skies as there is no weather up there - up there you will find B.A. and all the rest of the airlines - typpically at FL410 enjoying the rarefied atmosphere and its here that your temp OAT will drop down to -56.6 and no lower. sometimes you will hear news reports of temps of -80 deg C, well, this is funny, you would only get that nearer the ground with the chill factor thingy, but forget that for your PPL. I had a mate, who admittedly had just done a Medical Degree and was a doctor, who came in at 5 PM, talked with me and the telly in the background and the sound of the R/T, he then went to the study room until about 9. He then had dinner, then revised until about 11:30 and went to bed. when he got up at 9 or something, he sat his Aerotechnical ground exam and got 82%. So he passed, with just that previoous evenings study. They don`t want you to be fantastically academic for the PPL but just enough to appreciate all the bits and pieces to be able to pre-flight a flight - taking everything into consideration - the things which will affect your flight. Tech, Met, Air Law and the Rules of the Air (most are international, so that if you are flying head on to an oncoming aircraft from the States then both pilots will do the required thing. . . . .which is what. . . ? Also: Loading and Balance, Nav/Flight Planning, the fuels, the oils, etc., etc., they want to know that you know what you are doing, rather than a First Class Honours Degree in Aernautical Science, ok? So don`t worry and don`t freak if you drop a subject (which you won`t) because you simply, revise and do it again. the same, more or less, applies if you are doing FAA or a JAR exams - its all the same stuff - in order to get you so that you can fly anywhere in the world. So, when you nip off for that impulsive trip to le touque` (UK/EUR) or down to Alliance (US) then you will have the flight well under your command, as a Captain, which , after you have passed everything, is precisely what you will be Student. Yes, with a PPL you are the Commander of the flight and indeed the Captain - whose word, by the way, on the flight, is final. It - whatever IT is, is ok or not, because the Captain says so.