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Heat air near ground and clouds will form?


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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?

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An environmental lapse rate of 6.5c/km implies conditional instablilty (dry adiabatic > lapse rate (envir) > moist adiabatic), so the parcel will rise to the LCL (lifted condensation level) where T= Td. However due to latent heat of condensation the parcel can continue to rise (and remain warmer than) the surrounding environment provided the lapse rate in higher layers of the atmosphere is greater than moist adiabatic.

Yes, if the atmosphere is absolutely unstable (lapse rate ~ dry adiabatic) or conditionally unstable (lapse rate >= moist adiabatic), and provided there's sufficient moisture then surface warming alone can initiate convection.

The Pacific Northwest: Where storms go to die.

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  • 4 years later...

I think Swayseeker has a plausible idea. The good example might be the Salton Sea and the peak of the Oronocino? Mountain just east of the sea. Swayseekers tunnel might be a plastic covered greenhouse funnel/tunnel/chimney  that runs(10 miles ?) from the Sea surface to the peak (3500 ft?). With local heating of the sea, moisture laden air begins to rise and move through  the chimney delta that may cover several acres immediately above the surface of the sea and into the chimney stack at say 10:am and continues until near 5:pm on a summers day. The plastic framed stack winds along the ground up the mountain ridgebacks and at some point (elevation 2000' ?)the temperature of the plastic walls of the chimney stack fall below the dew point and water vapor condenses on the walls and runs back down hill to some collection point. The latent heat released keeps the chimney draft working to pull in more moisture laden air at the sea level. The pathway of the chimney will have to be maintain uphill always to keep the draft from stalling out. That covered pathway, with a cool and moist environment, could make an interesting hiking path. Didn't Swayseeker talk about this in another thread?

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