Higher Clouds Retain Less Energy


Clouds reflect incoming energy from the sun but trap outgoing energy from the Earth. How much energy clouds retain versus reflect determines their
emissivity— their ability to act as a source of energy themselves. Satellite-based observations provide information about the top but not the bottom of clouds. Thus, ground-based observations are still important to understand the effect of clouds on the atmosphere and surface radiation balance. Scientists used the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) dataset collected from Shouxian, China, in 2008 to simulate the downwelling radiances on the surface. Results show that emissivity of clouds decreases as the height of their bases increases. That is, the higher the bases of the clouds, the less those clouds can act as sources of energy. These results significantly improve our ability to quantify the impact of clouds forming at different altitudes on Earth’s energy budget.


Pan, L. J., and D. R. Lu. 2013. “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(1), DOI: 10.1007/s11430-012-4398-z.