eXtension

Does heating air usually make clouds form (meteorology)?

Asked September 22, 2016, 9:28 AM EDT

Say I heat air that has a relative humidity of 60% near the ground. Let the initial temperature be 10 deg C and suppose I heat it to 25 deg C. Then the relative humidity is about 23.2%. If I use an environmental lapse rate of 6.5 deg C per km and an adiabatic lapse rate of 9.8 deg C then this air could rise (25-10)/(9.8-6.5)=4.5 km before it is at the same temperature as the surrounding air (it will then not rise or fall). The dew point for an RH of 23.2 and temperature of 25 deg C is 2.4. Espy's equation now tells me that the parcel only has to rise 125(25-2.4) = 2825 m before clouds form. It seems that generally one can just heat air near the ground and clouds will form. Is this correct?

Outside United States

1 Response

Answered by a physicist and climatologist:

The altitude at which the water condenses (reaches 100% RH) is called the Lifting Condensation Level (LCL). Heating the air is one way to raise an air parcel to the LCL. This is called convective lifting.


Frontal boundaries can also lift the air in front of them, so this is another way. This is called frontal lifting.

Pushing air up a mountainside is another way to do the lifting. This is a called orographic lifting.

Heating air near the ground will not always result in cloud formation. It’s often the case that there are circumstances that prevent the air parcel from reaching the LCL. For example, if there is a warm layer above the ground, it will prevent the air parcel from lifting very high (the air parcel reaches the warm layer, and it stops rising because it’s no longer warmer than the ambient air). Sinking air above, due to high pressure, is another way to suppress the lifting of air that has heated.