Atmospheric Circulation. The energy Flux from the Ocean and Atmosphere

The radiant energy of the sun reaches the world ocean by passing through the atmosphere. Figure 7-1 shows that 19 percent of the energy is retained in the atmosphere. Most of the energy retained in the atmosphere is absorbed directly by atmospheric dust, water vapor, and ozone; and a small amount of energy is absorbed by clouds.

Considerable energy is scattered back into space from clouds; small amounts are back-scattered from air, dust, haze in the atmosphere, and from the sea surface. The rest of the energy, about 52 percent, penetrates the earth's surface (of which 72 percent is ocean) and is absorbed as heat by the surface water.

Figure 7-1. Fate of incident, short-wave solar energy in traveling from the sun to the earth's surface

The energy absorbed by the atmosphere and surface layers of the ocean maintains the two media at temperatures that, on the whole, have changed little during recorded history. This long-term steady state exists because the ocean, land, and atmosphere release a total amount of thermal and radiant energy that just balances the solar energy incident on the planet. The energy leaving the earth is mostly long-wave radiation from clouds, water vapor, and C0₂. A small amount is radiated directly from the ocean to space (Fig. 7-2).

Figure 7-2. The energy flux from the ocean and atmosphere. Transfer of heat and emission of long-wave (thermal infrared and microwave) radiation

Most long-wave (infrared) energy radiated from the ocean is converted to heat in the lower atmosphere. It is added to heat carried from the ocean to the lower atmosphere by conduction and convection and to the latent heat involved in the evaporative transfer into the lower atmosphere of surface water from the ocean. The net effect is that while the ocean is heated from above and made stable, the atmosphere is heated from below and made unstable. The instability leads to atmospheric circulation which has a profound effect on the world ocean.

The physical interaction between the atmosphere and the ocean is critically important to many oceanic phenomena. Winds in the lower atmosphere are responsible for waves, surface currents, mixing of the surface layer of the ocean, and the exchange of energy in the form of heat and water vapor.

Particulate matter ranging from mineral grams, seeds, and spores to carbon and silica spherules that are the byproducts of industrial combustion are transported out to sea through atmospheric circulation. An understanding of this circulation, therefore, is a necessary part of the study of oceanography.

Figure 7-3. Surface winds over the world ocean (average for July). (After U.S. Navy Hydrographic Office Publication No. 9, 1958)

At first glance, the pattern of surface winds over the world ocean (Fig. 7-3) appears to be somewhat confused and difficult to interpret. This wind pattern can be understood, however, by first considering winds that might be found on a theoretically nonrotating, water-covered globe, and then considering winds on a rotating globe on which continents are present.