MET question
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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.
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.
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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.
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.
Last edited by BackPacker; 9th Dec 2010 at 14:04. Reason: Must learn to do multiplications properly.
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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.
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.
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A quick search for DALR gave me a link to this thread:
http://www.pprune.org/private-flying...-question.html
Contains a good explanation.
http://www.pprune.org/private-flying...-question.html
Contains a good explanation.