Albedo surface

When dark roofs are heated by the sun, they directly raise summertime building cooling demand. For highly absorptive (low-albedo) roofs, the surface/ambient air temperature difference may be 50°C (90°F), while for less absorptive (high-albedo) surfaces with similar insu-lative properties (e.g., white-coated roofs), the difference is only about 10°C (18 F), which means that cool surfaces can effectively reduce cooling-energy use. 

Clouds of Nonblack Particles The correction for nonblackness of the particles is complicated by multiple scatter of the radiation reflected by each particle. The emissivity . of a cloud of gray particles of individual surface emissivity 1 can be estimated by the use of Eq. (5-151), with its exponent multiplied by 1, if the optical thickness alv)L does not exceed about 2. Modified Eq. (5-151) would predict an approach of . to 1 as L 0°, an impossibihty in a scattering system the asymptotic value of . can be read from Fig. 5-14 as /, with albedo (0 given by particle-surface refleclance 1 — 1. Particles with a perimeter lying between 0.5 and 5 times the wavelength of interest can be handledwith difficulty by use of the Mie equations (see Hottel and Sarofim, op. cit., chaps. 12 and 13). 

The portion of the incoming radiation reflected and scattered back to space is the albedo. The albedo of clouds, snow, and ice-covered surfaces... 

In addition to the effect of albedo on the amount of radiation that reaches the earth s surface, the angle of incidence of the radiation compared to the perpendicular to the surface affects the amount of radiation flux on an area. The flux on a horizontal surface is as follows ... 

Percent of Incident Radiation Reflected by a Water Surface (Albedo of Water)"... 

On the average, the air over roughly half of the Earth s surface has an upward velocity and half has a downward velocity. This frontal activity (Section 7.5.3) and the interactions of marine air with the cold ocean surface result in about half of the Earth being covered by clouds and half being clear. As will be discussed in Chapter 17, this large fractional cloud cover is extremely important to the Earth s climate because it controls the planetary albedo (reflectivity). 

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

Another family of feedbacks involving biota arise via the process of evapotranspiration in which the rate of water vapor is transferred from the land surface to the atmosphere is mediated by plants. Several consequences have been proposed that include influences of biota on the greenhouse effect of water vapor as well as relative humidity and clouds. Lovelock (1988) suggested that tropical forests might be kept cool by increasing cloud cover in response to higher relative humidity released through enhanced evapotranspiration (via the clouds influences on albedo). Yet another connection arises because tree-covered land has different turbulence properties above it than bare soil, which also influences the cloud cover above. 

Barron, E.J., Solan, J.L. and Harrison, C.G.A. (1980) Potential significance of land-sea distribution and surface albedo variations as a climatic forcing factor 180 m.y. to the present. Paleoneogr. Paleoclimatol. PaleoecoL, 30, 17- 0. 

Increasing concentrations of gases, aerosols, and humidity into the atmosphere will increase the Earth s albedo. This would mean that less solar energy reaches the Earth s surface and thus less OLR to be emitted. Therefore, the Earth s effective temperature should decrease. 

The albedo of earth surface varies from about 0.1 for the oceans to 0.6-0.9 for ice and clouds which mean the clouds, snow and ice are good radiation reflectors while liquid water is not. In fact, snow and ice have the highest albedos of any parts of the earth s surface Some parts of Antarctic reflect up to 90% of incoming solar radiation. 

The fraction of the sun s energy which is reflected back into space (albedo) the non-reflected energy maintains the temperature of the atmosphere and the surface. 

Studies carried out on Earth, for example, by the NASA infrared telescope on Mauna Kea (Hawaii), showed albedo variations which indicated the presence of holes in the Titanian cloud formations (Griffith, 1993). It is, however, still unclear as to whether these inhomogeneities result from differences in the surface composition. Lorenz et al. (1997) reported large variations in Titan s atmosphere due to photochemical processes. The methane contained in the dense nitrogen atmosphere is decomposed by solar and thermal radiation, and its content may be replenished from methane lakes or from clathrates. 

High soil surface exposure and elevated albedo... 

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