2 x ATPL MET QUESTIONS

[Greg2041]

Grateful for your advice on these questions and on how I can calculate these answers.

At a certain position, the temperature on the 300 hPa chart is -48 degrees celcius; according to the tropopause chart, the tropopause is at FL 330. What is the most likely temperature at FL350?

A) -54C

The average height of the tropopause at 50°N is about:

A) 11 km

HELP!!!!!!!!!!!!!

[wbryce]

300hpa = 30,000ft.

at FL300 its -48, apply the 1.98 lapse rate per 1000ft to give -54 at FL330, temperture stops decreasing after the tropopause in the standard atmosphere model, so at FL350 it remains at -54.

for the 11km, convert that into feet for ease (11,000 x 3.28), roughly, 36,000ft, its one of those numbers you need to learn, just remember the height of the tropopause at the poles and the equator, then you can easily make a 'interpolated' guess for anything inbetween.

[Greg2041]

Wow! You are clearly gifted in the art of making it simple. Many thanks!

... and finally why is it that...

... if the tropopause is at FL330 at a temperature of -54 °C the most likely temperature at FL350 is also -54 °C and not the expected ISA value of -56.5 °C?

[wbryce]

the tempertures given are not based on an ISA day...with the figures given in your question, it would be +12 on the ground.

Maybe I confused you a little by saying 'standard atmosphere', i was trying to draw a line on FL300 being related to 300hpa! hopefully that should help you understand, if not then don't be afraid to ask or say your not sure!

[Greg2041]

Great stuff. Many thanks!
Greg