Lifted condensation level
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The Lifted condensation level (LCL), represent the height at which an air parcel being lifted will become saturated because of adiabatic cooling (caused by expansion).
One may find the LCL doing:
- Start at the initial temperature T of the parcel and follow upward the dry adiabatic lapse rate if the air is not saturated. Otherwise, the parcel is already at LCL.
- From the dew point temperature of the parcel, follow upward the mixing ratio line at that point.
- At the intersection of the two lines, one reach the LCL.
Here is the explanation. While the potential temperature of the parcel remain the same, as it is done adiabatically (no exchange of heat with the environment), the volume expand due to a lower outside pressure. This leads to a lowering of the parcel temperature to compensate (ideal gas law). Since the air parcel does not lose matter either, the mixing ratio of water vapor to dry air remain the same until the temperature has reached the saturation. Then condensation occur and, if the lift continue, the parcel will form cloud.
[edit] Bibliography
- M K Yau and R.R. Rogers, Short Course in Cloud Physics, Third Edition, published by Butterworth-Heinemann, January 1, 1989, 304 pages. EAN 9780750632157 ISBN 0-7506-3215-1
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