Application of CERES Energy Budget Data to Improve Understanding of the Dynamic Role of Clouds in the Earth's Planetary Albedo

Cloud fraction has a large influence on the top of the atmosphere global energy balance through its control of the Earth's planetary albedo. Radiative-dynamic interaction of clouds occur at scales unresolved by GCMs so mechanistic models are needed for what controls the global response of cloud fraction to external forcings from changes in insolation. There is a periodic oscillation of globally averaged solar insolation due to the elliptical orbit of the earth of 11 Watts per meter squared or ~3.5% of its mean value of 340 Watts per meter squared. What is interesting is that analysis of CERES data shows that the northern hemisphere winter increase in global solar insolation is concurrent with an increase in the Earth's planetary albedo of ~0.01, which is also ~3.5% of the mean value of 0.29. However, the albedo declines from its maximum value approximately one month earlier than the solar maximum, concurrent with a decline in net energy deposition in the Earth's atmosphere, defined as the difference of the albedo-adjusted solar input and the outgoing longwave TOA flux. In prior work, we have shown that the radiative temperature difference between cloud base and the surface and below cloud air controls the potential energy that is available to be supplied to the cloud for driving dynamic motions and the extent of cloud cover spreading. We propose a speculative mechanism for the observed relationships between solar insolation and the Earth's planetary albedo. When there is net positive energy deposition in the Earth's atmosphere, this drives atmospheric convection and cloud spreading, which increases planetary albedo. A higher albedo acts as a negative feedback on increasing energy deposition from the Earth being closer to the sun, diminishing the solar input. This in turn acts as a negative feedback on cloud cover. Thus, the impact of solar eccentricity on net energy deposition is regulated by the response and control of cloud cover on planetary albedo. This interplay between cloud cover and solar eccentricity acts as a shortwave global-scale "iris".