INTRODUCTION
Life pivots completely on energy. We cannot talk about living beings without considering the interchanges of energy that they make with their environment. If these interchanges did not take place or if a source of energy like our Sun did not exist, the living beings on Earth would not exist either. Consequently, the biologists must thoroughly understand the ways by which our planet acquires energy, the amount of energy that it receives, the anual balance of that energy in the different Earth subsystems and how the living beings can take advantage of that energy.
The following article is a summary of the amount of energy that receives our planet from the Sun, its magnitudes and of how it is distributed in the terrestrial system.
I have included the amount of incident solar energy upon each planet and the planetoid Pluto so that you have an idea of the privileged situation of our planet in the neighborhood of the Solar System.
AMOUNT OF INCIDENT SOLAR RADIATION UPON EACH PLANET
Formula:
GPL = QSUN / 4π (POR)^2
Where,
GPL is the amount of incident solar radiation upon the planet.
QSUN is the total amount of energy emitted by the Sun expressed in Watts (3.94832e+26 W).
4π = 12.56637061
POR is the Planet Orbital Radius, expressed in meters.
VALUES OF THE TOTAL INCIDENT ENERGY UPON EACH PLANET:
Mercury = 9.449.43 W/m^2
Venus = 2687.6 W/m^2
Earth = 1402.8 W/m^2
Mars = 612.55 W/m^2
Jupiter = 52.34 W/m^2
Saturn = 17.2 W/m^2
Uranus = 3.89 W/m^2
Neptune = 1.55 W/m^2
Pluto (Planetoid) = 0.8998 W/m^2
Average of incident solar energy upon Earth during Aphelion = 1359.02 W/m^2
Average of incident solar energy upon Earth during Perihelion = 1452.77 W/m^2
BALANCE OF THE INCIDENT SOLAR ENERGY UPON EARTH:
1359.02 W/m^2 - 1452.77 W/m^2 is the net incident Solar Radiation upon Earth.
50.01% of the received energy is Infrared Radiation. From this percentage:
51% is absorbed by the Earth surface.
24% is reflected in the troposphere by clouds.
14% is absorbed by the air, specifically by the water vapor and dew. Carbon Dioxide is almost “transparent” to the short wave infrared radiation incoming from the Sun.
7% is reflected by the upper atmosphere.
4% is reflected by ground and oceans.
CALCULUS OF THE NET ENERGY:
1396.44 W/m^2 is the current total amount of electromagnetic solar radiation that incides on Earth.
698.36 W/m^2 are infrared radiation.
356.16 W/m^2 incide upon the top of the Earth's atmosphere.
181.64 W/m^2 are absorbed by the surface of Earth (Land and Oceans).
85.48 W/m^2 are reflected by clouds towards the deep space.
49.861 W/m^2 are absorbed by the atmospheric steam and water dew. This heat is known as latent heat.
24.9305 W/m^2 are reflected by the atmosphere (oxygen and aerosols).
14.246 W/m^2 are reflected by sand, snow and oceans.
BALANCE:
Total absorbed by the surface: 181.64 W/m^2
Emitted by the surface to space (Sensible Heat Flux, i.e. without evaporation): 36.33 W/m^2
Stored energy by the surface: 145.27 W/m^2
Emitted by the surface to the atmosphere: 70.51 W/m^2
Absorbed by the dry air from the surface: 16.3 W/m^2 33.22
Absorbed by water vapor from the surface: 16.92 W/m^2
Transferred by conduction to land and oceans: 26.79 W/m^2
Generation of kinetic energy: 14.75 W/m^2
What happens in the air:
Total absorbed by the dry air: 26.79 W/m^2
Absorbed by dry air from the surface: 17.95 W/m^2
Absorbed by dry air from clouds and water vapor: 0.71 W/m^2
Stored by the dry air ((stirring): 6.25 W/m^2
Emitted directly from the air to the space: 2.35 W/m^2
Transferred to water vapor: 15.67 W/m^2
Transferred to colder systems on the surface (averaged absorptivity = 0.1206): 2.52 W/m^2
What happens in water vapor:
Total absorbed by water vapor: 82.451 W/m^2
Absorbed radiation incoming from the Sun: 49.861 W/m^2
Absorbed from the surface: 16.92 W/m^2
Absorbed from the dry air: 15.67 W/m^2
Emitted to space from water vapor: 41.131 W/m^2
Stored by water vapor (stirring): 20.61 W/m^2
Transferred to colder systems on the surface: 20.1 W/m^2
Transferred to air: 0.61 W/m^2
STORED ENERGY BY OCEANS
The oceans are the main deposits of energy. Oceans maintain the nights lukewarm and they avoid that the Earth is freeze. An enormous part of the heat absorbed by the ground is transferred by conduction to the oceanic waters. The oceans store the energy more time than the air and ground because the water thermal capacity is higher than the air and ground thermal capacity. We must take into account that the absorbency-emissivity of the air are almost equal, whereas the partial conductivity of the gases that form the atmosphere is too low; for example, the thermal conductivity of CO2 is hardly 0.016572, thus, CO2 is considered to be a poor conductor of heat. On the other hand, the water steam, which mass in the atmosphere is unpredictable (from 2 to 7%), is a better absorbent, emitter and conductor of heat. Put 1.384 x 10^21 kg of water on Venus or Mars and you will have the benign and comfortable climate we have here on Earth.
The radiant energy may take three ways when it is incident upon a thermodynamic body: A fraction of that energy is reflected (reflectivity); part of that energy may be transmitted (transmissivity) and a fraction of that incident energy may be absorbed (absorptivity).
For gases, the relation is α + τ = 1, which means that the gases reflect a very small fraction of the radiant energy incident upon them. However, the emissivity and the absorptivity of a known gas have almost the same numerical value.
If the absorptivity of 690 mg/m^3 of carbon dioxide is 0.001 at 300.15 K and 1 atm, then its transmissivity would be:
τ = 1 - α
τ = 1 - 0.001 = 0.99
This means that the carbon dioxide let the 99% of the heat pass through its volume.
The dissertation on the previous paragraphs has the objective to state that the CO2, or the dry air as a whole, does not store heat. CO2 does not store heat because its heat capacity is low; besides, the transmissivity of CO2 is high and it emits the same amount of heat than it absorbs. All the thermodynamic systems emit the same amount of heat that they absorb, but some of them do it hastily, while others do it slowly. Air does it hastily; water (in its three phases) does it slowly.
The atmosphere cannot store heat for ever, but throughout some seconds due to its thermal capacity. If there is more heat in the lower tropospheric layer than in the middle and upper layers it is because the surface is absorbing-radiating more heat to the atmospheric layer in contact with it, not because the air stored heat. As long as the surface is absorbing heat, the atmosphere above it will be warm. But the heat always is transferred from the warmer system to the colder system. If the lower tropospheric layer warms and the middle and upper layers are colder, the heat radiated by the lower layer will be TRANSMITTED through the higher layers. As the absorptivity of gases decreases with altitude, then the middle and upper layers of the troposphere are colder than the lower layer and the surface. But almost all the heat goes through the higher layers and to the troposphere, where it is transferred by conduction. Hence the upper stratosphere is warmer than the lower stratosphere.
May 10, 2007
