Radiative Properties of Clouds SOEE3410 Ken Carslaw Lecture 3 of a series of 5 on clouds and climate • Properties and distribution of clouds • Cloud microphysics and precipitation • Clouds and radiation • Clouds and climate: forced changes to clouds • Clouds and climate: cloud response to climate change
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Radiative Properties of Clouds SOEE3410 Ken Carslaw Lecture 3 of a series of 5 on clouds and climate Properties and distribution of clouds Cloud microphysics.
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Radiative Properties of CloudsSOEE3410
Ken Carslaw
Lecture 3 of a series of 5 on clouds and climate• Properties and distribution of clouds• Cloud microphysics and precipitation• Clouds and radiation• Clouds and climate: forced changes to clouds• Clouds and climate: cloud response to climate
You should understand the role of clouds in the climate system, the different behaviour of long and shortwave radiation, and the different radiative effects of different cloud types
Scattering Versus Drop Size for Constant Water Content
• If Liquid Water Content (LWC [kg m-3]) is constant, then
• Total light scattered in a thin cloud depends on
• Therefore, scattering efficiency of a cloud depends on• Therefore, doubling N (r decreases) increases albedo by 25%• doubling r (N decreases) decreases albedo by 50%• But thickness is also important
Cloud Reflectivity in Solar Spectrum (Shortwave, SW)
• Visible light absorption negligible• Some weak absorption in near-IR part of solar spectrum• Cloud drop size and number are important in global energy balance
1. What are the approximate wavelengths of solar shortwave and terrestrial longwave radiation streams?
2. Which radiation stream (SW or LW) is absorbed more in the atmosphere?
3. Which radiation stream (SW or LW) is absorbed more in a cloud?
4. What is the main process that attenuates SW radiation as it passes through a cloud?
5. As you leave this lecture, what clouds can you see, what is their approximate droplet concentration, and what effect are they likely to be having on climate?
6. Why is the “atmospheric window” important for climate change?
7. Explain the reason why thin cirrus clouds can warm the climate.