As the sun's radiation penetrates the earth's atmosphere. a series of selective depletions and diversions of energy take place. At an altitude of 95 mi (150 km), the radiation spectrum possesses almost 100 percent of its original energy, but in penetration to an altitude of 55 mi (88 km) absorption of X-rays is almost complete and some of the ultraviolet radiation has been absorbed as well.
As solar radiation penetrates into deeper and denser atmospheric layers, gas molecules cause the visible light rays to be turned aside in all possible directions, a process known as Rayleigh scattering. Where dust particles are encountered in the troposphere, further scattering occurs. The total process may be described as diffuse reflection. That the clear sky is blue in colour is explained by Rayleigh scattering of the shorter visible wavelengths. These predominantly blue light waves reach our eyes indirectly from all parts of the sky. The red wavelengths and infrared rays are less subject to scatter and largely continue in a straight-line path toward earth. The setting sun appears red because a part of the red rays escape deflection from the direct line of sight.
As a result of all forms of shortwave scattering, some solar energy is returned to space and forever lost, while at the same time some scattered shortwave energy also is directed earthward. The latter is referred to as diffuse sky radiation, or down scatter. An additional but minor cause of energy loss is that which occurs in the ozone layer as oxygen molecules are broken into atoms and reformed into ozone molecules.
Another form of energy loss takes place as the sun's rays penetrate the atmosphere. Both carbon dioxide and water vapour are capable of directly absorbing infrared radiation. Absorption results in a rise of sensible temperature of the air. Thus some direct heating of the lower atmosphere takes place during incoming solar radiation. Although carbon dioxide is a constant quantity in the air (0.033 percent by volume) the water vapour content varies greatly from place to place, being as low as 0.02 percent under desert conditions to as high as 1.8 percent in humid equatorial regions. Absorption correspondingly varies from one global environment to another.
All forms of direct absorption namely X-ray, gamma ray, and ultraviolet absorption in the ionosphere and ozone layer, combined with direct long-wave absorption by carbon dioxide, water vapour, and other gas molecules and dust particles, is estimated to average as little as 10 percent for conditions of clear, dry air, to as high as 30 percent when a cloud cover exists.
Yet another form of energy loss must be brought into the picture. The upper surfaces of clouds are extremely good reflectors of shortwave radiation. Air travelers are well aware of how painfully brilliant the sunlit upper surface of a cloud deck can be when seen from above. Cloud reflection can account for a direct turning back into space of from 30 to 60 percent of total incoming radiation. Thus we see that, under conditions of a heavy cloud layer, the combined reflection and absorption from clouds alone can account for a loss of from 35 to 80 percent of the incoming radiation and allow from 45 to 0 percent to reach the ground. A world average value for reflection from clouds to space is about 21 percent of the total insolation.
The surfaces of the land and ocean reflect some shortwave radiation directly back into the atmosphere. This small quantity, about 6% as a world average, may be combined with cloud reflection in evaluating total reflective losses. Altogether the losses to space by reflection total 32 percent of the total insolation.
The percentage of radiant energy reflected back by a surface is termed the albedo. This is an important property: of the earths surface because it determines the relative rate of heating of the surface when exposed to insolation. Albedo of a water surface is very low (2 percent) for nearly vertical rays, but high for low-angle rays. It is also extremely high for snow or ice (45 to 85 percent). For fields, forests, and bare ground the albedos are of intermediate value, ranging from as low as 3 percent to as high as 25 percent. For the earth as a planet, average albedo is on the order of 32 percent and is determined largely by the extent of cloud cover.
Locals hypothesize that the legacy of Italian blood and culture in Cologne, colonized by the Romans more than 1500 years ago, makes the people more jovial and lighthearted. Cologne is the largest city on the Rhine.
Kolsch is not only the dialect spoken here but, also the name of their own top-fermented beer. There are more than 4,000 pubs, restaurant's and brewery taverns in Cologne.
Unlike many of the world's large cities, Cologne, with a population of over a million, gets better every day, there are more things to do and see, more new and innovative buildings... more
Travel is an opportunity to learn, whether geography, languages, history or other subjects.
Cologne is situated on the beautiful Rhine River.