MET question
Hello,
I was wondering if someone could oblige and clear up a MET question I keep getting on PPLquiz, I have still not worked out how they get the answer. "Given a surface temperature of 21C and a dew point of 7C what height would you expect the cloudbase to be?" The way I have tried to work it out as follows. DALR 3C/1000' To cool to 7C from 21C will take 4600' the answer they are giving is 5500', where am I going wrong? Many thanks if you reply. |
For each degree (C) spread, the cloud base rises approx. 400' in the ISA atmosphere.
21-7 = 14 degrees spread. Times 400 is 5600'. The explanation I forgot, but it had to do with the intersection of the Temperature/DALR and Dewpoint/WALR line. It's in my PPL book somewhere. |
Backpacker,
Thank you for the reply, I have not seen that statement in my Met book yet, will have to go back for a thorough re-read, must have missed it. Handy to know thank you. |
A quick search for DALR gave me a link to this thread:
http://www.pprune.org/private-flying...-question.html Contains a good explanation. |
dew point changes with height. Reduces by 0.5 degree/1000. this gives a cloud base of 5600.
|
Become a caver. It gets warmer the deeper you go - although I don't think the ISA rule of 2C per 1000' applies.
Any you get warm climbing out too. |
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