02 January 2015

The Earth's Atmosphere

Being a complete aviation nerd, I have no shame in admitting that Meteorology was one of my favourite subjects in flight school. And whereas I'd like to jump into things like lapse rate and stability, I'll save those for later and start with the basics.  Our trusty Study and Reference Guide starts with these topics about the Earth's Atmosphere:

Properties - from ACWM Chapter 2

  • mobility
  • capacity for expansion
  • capacity for compression

Vertical Structure - in ascending order

  • troposhere
    • contains all the elements of the weather
    • temperature decreases with altitude
  • tropopause
    • height varies from about 8 km over the poles up to 17 km over the equator
    • there is an abrupt change in height over each frontal surface
    • higher in the summer than in the winter
    • In ISA conditions its height is 36 090 ft and temperature is -56.5 C
  • stratosphere
    • temperature remains steady and then increases with altitude
  • stratopause
    • temperature starts to decrease with altitude
  • mesosphere
    • temperature decreases with altitude to about 275 000 ft
  • mesopause
    • lowest temperature
  • thermosphere
    • where aurora are seen
    • temperature increases dramatically with altitude

ICAO Standard Atmosphere (ISA)

  • At sea level: 15 C and 1013.2 hPa / 29.92"Hg
  • Average lapse rate is 1.98 C / 1 000 ft


Some things you just have to memorize:

Pressure Level (mb) 

Altitude (ft)
700 10000
500 18000
400 24000
250 34000
200 39000
150 45000

And now... time for a POP QUIZ!

(1) What are lines drawn on weather charts joining places having the same temperature called?
(2) Does TAS increase or decrease with temperature?
(3) If the temperature at FL300 is -50, how would this be expressed in terms of an ISA deviation?




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