Working with Solar Power

The movements of the atmosphere and ocean are driven by the Sun through radiational heating and tide-generating force. In terms of the radiational heat input, if the Sun provides 100 units of radiation energy to the Earth, about 70 units are absorbed by the Earth, while the remaining 30 units are reflected by clouds and the Earth’s surface back into space (the reflection rate, called albedo, is 0.3 for the Earth). Of the 70 units absorbed by the Earth, about 50 units are absorbed by a very thin layer (on the order of centimeter) of the Earth’s surface, while the remaining 20 units are absorbed by the entire atmosphere, which has a thickness of tens of kilometers. In other words, most of the solar energy is absorbed by a thin layer of the Earth’s surface. The 20 units of solar energy heating the atmosphere are spread thin over tens of kilometers. This makes the Earth’s surface warmer than the atmosphere; the warmer surface then heats the atmosphere from the bottom up. As the air at the Earth’s surface is heated, it expands and becomes lighter, causing it to rise and carry moisture from the surface. The rising air may then form clouds if there is enough moisture above the lifting condensation level. The surrounding air moves in to compensate for the lost air at the surface, producing wind and other weather phenomena. The wind also drives ocean currents (in addition to tidal currents). Living things on Earth depend on the Sun's energy: photosynthesis provides energy for plants, which are then consumed and used by animals in the food chain.