July 2014

Higher Clouds Retain Less Energy

ARM data shed light on how altitude affects cloud energy content.

Click to enlarge photo. Enlarge Photo

Image courtesy of Atmospheric Radiation Measurement (ARM) Climate Research Facility, Mike Alsop

ARM Mobile Facility instruments measure aerosol and cloud properties during a 2008 study in Shouxian, China. Data from this campaign are being used to better understand cloud effects on Earth’s energy budget.

The Science

Clouds reflect incoming energy from the sun but trap outgoing energy from Earth. The amount of energy clouds retain versus reflect determines their emissivity, or the ability to act as a source of energy themselves.

The Impact

These results significantly improve the ability to quantify how clouds forming at different altitudes affect Earth’s energy budget, or the total of all incoming energy and all losses of outgoing energy.


Satellite-based observations provide information about the top but not bottom of clouds. Thus, ground-based observations are still important to understand cloud effects on the atmosphere and surface radiation balance. Scientists used the Atmospheric Radiation Measurement (ARM) Climate Research Mobile Facility dataset collected from Shouxian, China, in 2008 to simulate the downwelling radiances on Earth’s surface. Results show that emissivity of clouds decreases as the height of cloud bases increases. That is, the higher the bases of the clouds, the less those clouds can act as energy sources.


Lü DaRen
Laboratory for Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China


Data were provided by the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement Climate Research Mobile Facility through a collaboration between DOE and the Chinese Academy of Sciences (CAS). The research was supported by CAS (grant no. XDA05040300) and the National Natural Science Foundation of China (grant no. 40710059003).


Pan, L.J., and Lü, D.R. “A new method for retrieving equivalent cloud base height and equivalent emissivity by using the ground-based Atmospheric Emitted Radiance Interferometer (AERI).” Science China: Earth Sciences 56, 43–53 (2013). [DOI: 10.1007/s11430-012-4398-z].

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Last modified: 8/1/2014 1:20:06 PM