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Guest giln

Tropo or tropopause in mcdu, what is it?????

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Guest giln

Well, what is tropo or tropopause? What is it used for???

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Hello thereTropopause is a meteorological term. Weatherwise it is the top of the atmosphere. From ground level upto the tropopause the atmosphere cools down to about minus 60 to 70 dgs Celsius. There are some exceptions; like an inversion, where the temperature rises for a few hundred or thousand feet. Inversions mainly occur near ground level.The tropopause is a layer where the temperature remains almost unchanged for some thousand feet. It has the same effect as an inversion. It stops clouds from developing.Warm air rises in a colder surrounding atmosphere. This air cools down while rising and when it has cooled far enough condensation will take place, which we see as clouds.As long as the rising air remains warmer than the surrounding atmosphere, clouds will rise. The moment the surrounding atmosphere gets warmer or remains unchanged the rising air will also get the same temperature and stops rising. Therefore, above the tropopause there are no clouds, as we all know when we go on a long haul flight. Nearly all gas, watervapor meteorologically being the most important, is to be found in the Troposphere. The Troposphere is the lower layer of the atmosphere, and the tropopause is the top of this layer. The next layer is the stratosphere. The hight of the tropopause differs. Over the poles it is about 6 kms and over the equator about 15 kms. It also changes along with the seasons, being higher during summer and lower during winter. That is because it expands when it gets warmer and shrinks when it gets cooler.I suppose an airline captain would like to know the hight of the tropopause. Flying above the tropopause is much smoother. There is simply no weather. I am afraid this is a rather simple explanation, but i hope it is enough. Otherwise this would become a very long story.Peter

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Guest Sjaako

Tropopause,Very well explained by peter.What it is used for in the aircraft is that the FMGS calculates no more reduction in outside temperature when planning above the entered tropopause altitude. This is important since the aircraft performance and mainly fuel efficiency will be adversly affected when flying above the tropopause altitude.Regards Sjaako.

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