Equations of Radiative Balance

Due to the greenhouse effect, the Earth's surface gets the 102 Wm~2 of radiative heat additionally. An amount of 80 W m~2 of this heat is used in the process of evaporation and transpiration of water by plants, evapotranspiration, and 20Wm~2 are transported into the atmosphere by a turbulent (sensible) heat flow, Eturb, caused by a difference in the temperatures of the ground and the atmosphere. The first term is named a 'latent' flow; it is equal to L ■ Q, where L = 2453 J g is the specific enthalpy of evaporation (heat content) and Qis the flux of water, evaporated from the surface ofwater-bodies, soils, and plants, and also water, condensed on these surfaces. To close the balance, we add the value of Emech = 2W m~2 that is a dissipated mechanical energy (friction). The corresponding equation of radiative balance for the Earth's surface is rg = (E") g(1 - aG) - Eeff [4]

102 outgoing SWR

8 diffuse radiations

68 reflected by clouds

26 reflected by the ground

Incoming SWR 340

Incoming SWR 340

78 absorbed by the atmosphere

186 coming into the ground

238 outgoing LWR

Top of the atmosphere

1

r

1

180 LWR of the atmosphere

Internal energy of the atmosphere 8.6 x 1023 J (1.7 x 109 J m-2)

58 LWR of the ground

Turbulent heat flow 20

Friction 2

Evapotranspiration 80

160 absorbed by the ground

The Earth's surface

Figure 2 Energy flows in the system 'the Earth's surface + atmosphere'.

Since the radiative balance of the EAS is equal to zero, the radiative balance of the atmosphere

has to be negative. The negativeness is compensated by the latent and turbulent heat flows.

The main carriers of heat between the ground and the atmosphere are precipitation and water vapor. Then the radiative balance for the EAS can be represented as reas — F + L(Q - P)

where the term Fs is the sum of the heat inflows and outflows across the vertical walls of the EAS column with unit basement, the term L(Q— P) is a difference between the flows of latent heat L ? Qand heat brought by precipitation, L ? P, where P is the sum of all precipitations. Since for the globe and 1-year interval Q= P and Fs = 0, then the equation of energy (heat) balance for the EAS has a simple form:

The balance equations for the atmosphere and the Earth's surface are

Ra = - L?P - Eturb - Emech (atmosphere) Rg = L'Q, + Eturb + Emech(Earth's surface)

A generalized scheme of energy flows and their transformation is shown in Figure 2.

At least, we can estimate the internal energy of the atmosphere, which is equal to 8.6 X 1023J (1.7 X 109Jm"2), the storage of latent heat 3 X 1022J (6 X 107Jm"2 ), and the storage of mechanical energy 2.5 X 1015 (5 X 105Jm"2). About 40% of the total atmospheric internal energy constitutes a potential energy (0.7 X 109Jm_2), but only 4Wm~2 is necessary to maintain turbulent flows.

Parallel to the vertical redistribution of solar energy, there are powerful energy flows redistributing it over the Earth's surface. All of them form the complex system of atmospheric circulation and oceanic currents that provides to transport heat from the low latitudes to the high latitudes by 'softening' the Earth's climate.

Energetics of Photosynthesis and Vegetation

We described above the main processes of the transformation of solar energy, which are the principal components of the global energy balance, forming in essence the thermostat for the biosphere. However, there are other processes, which do not really influence the energy balance. Their heat flows are very small (mentioned above as the dissipation of mechanical energy, dew condensation, etc.). Some of them, nevertheless, play the principal role in the biosphere, for instance, photosynthesis.

Green plants (autotrophs) convert solar energy into the chemical energy of new living biomass in the process of photosynthesis. The process uses energy of visible light, which is absorbed by the chlorophyll molecules of plants to convert carbon dioxide and water into carbohydrates and oxygen. Note that the presence of oxygen in the Earth's atmosphere is a result of photosynthesis. Proteins, fats, nucleic acids, and other compounds are also synthesized during the process, as long as elements such as nitrogen, sulfur, and phosphorus are available.

Then the stored chemical energy flows into herbivores, carnivores (predators), parasites, decomposers, and all other forms of life. Photosynthesis produces the living biomass of vegetation, constituting more than 95% of the global biomass and being a main agent in the 'global biogeochemical cycle of carbon'.

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