Temp and Height change per Millibar
Thread Starter
Joined: Apr 2000
Posts: 294
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From: West Midlands, UK.
Temp and Height change per Millibar
I have seen mention of a '4% rule' in meteorology notes relating to the relationship between temp and height change per millibar:
eg 1mb = 27' at sea level, 73' at 30,000.
I would be grateful for some explanation of this. Thanks in advance.
eg 1mb = 27' at sea level, 73' at 30,000.
I would be grateful for some explanation of this. Thanks in advance.
Joined: Jan 2001
Posts: 609
Likes: 1
From: Around the world.
To find the value of 1mb pressure change at a specific alt in feet
96 x T
-------------
Pressure
Where T is temperature in Kelvin, Pressure is in millibars.
so at MSL (ISA):
96x288K
---------- = 27ft/mb
1013mb
At 20,000ft
96x 248K
--------- = 51ft/mb
466mb
At 30,000ft
96x 228K
---------- = 73ft/mb
300mb
Remember pressure does not lapse in a linear fashion with height.
All the best,
Tom.
96 x T
-------------
Pressure
Where T is temperature in Kelvin, Pressure is in millibars.
so at MSL (ISA):
96x288K
---------- = 27ft/mb
1013mb
At 20,000ft
96x 248K
--------- = 51ft/mb
466mb
At 30,000ft
96x 228K
---------- = 73ft/mb
300mb
Remember pressure does not lapse in a linear fashion with height.
All the best,
Tom.
