前程百利小编为考生带来讲解地球能源循环的托福阅读材料。在托福阅读地理类话题中曾经涉及到类似的话题，本材料中涉及很多相关的背景，所以希望本文会对大家有所帮助。
Earth’s energy budget
Earth’s climate is largely determined by the planet’s energy budget i.e. the balance of incoming and outgoing radiation. It is measured by satellites and shown in W/m2.
Earth’s energy budget or Earth’s radiation balance describes the net flow of energy into Earth in the form of shortwave radiation and the outgoing infrared radiation out to space.
The Earth’s equilibrium surface temperature is defined by radiative equilibrium the balance between the incident and outgoing radiation budget. Climate change is defined by changes in Earth’s energy budget.
Outgoing longwave flux radiation at the top-of-atmosphere (Jan 26-27 2012). Heat energy radiated from Earth (in watts per square meter) is shown in shades of yellow red blue and white. The brightest-yellow areas are the hottest and are emitting the most energy out to space while the dark blue areas and the bright white clouds are much colder emitting the least energy.
Received radiation is unevenly distributed over the planet because the Sun heats equatorial regions more than polar regions. Earth’s heat engine are the coupled processes of the atmosphere and hydrosphere to even out solar heating imbalances through evaporation of surface water convection rainfall winds and ocean circulation. The Earth’s energy balance will depend on many factors with the incident absorption varying with atmospheric and surface factors including cloud cover (albedo) snow cover atmospheric aerosols and vegetation and land use patterns and the outgoing radiation also varying with atmospheric and surface emissivity. These factors all vary with time.
Changes in surface temperature due to Earth’s energy budget changes do not occur instantaneously due to the inertia (slow response) of the oceans and cryosphere to react to the new energy budget. The net heat flux is buffered primarily in the ocean heat content until a new equilibrium state is established between incoming and outgoing radiative forcing and climate response.
When the amount of the solar energy reaching Earth equals the thermal energy amount being radiated out the radiative forcings are in a state of radiative equilibrium or balance.
Incoming radiant energy (shortwave)
The total amount of energy received by Earth’s atmosphere is normally measured in watts and determined by the solar constant. Earth incoming solar radiation depends on day-night cycles and the angle at which sun rays strike thus calculated by its cross section and distribution on the planets surface calculated with 4·π·RE2 in sum one-fourth the solar constant (approximately 340 W/m2 plus or minus 2 W/m2). Since the absorption varies with location as well as with diurnal seasonal and annual variations numbers quoted are long-term averages typically averaged from multiple satellite measurements.
Of the ~340 W/m2 of incident solar radiation intercepted by the Earth an average of ~77 W/m2 is reflected back to space by clouds and the atmosphere and ~23 W/m2 is reflected by the surface albedo leaving about 240 W/m2 of solar energy input to the Earth’s energy budget.
Earth’s internal heat and other small effects
The geothermal heat flux from the Earth’s interior is estimated to be 47 terawatts. This comes to 0.087 watt/square meter which represents only 0.027% of Earth’s total energy budget at the surface which is dominated by 173000 terawatts of incoming solar radiation.
There are other minor sources of energy that are usually ignored in these calculations: accretion of interplanetary dust and solar wind light from distant stars the thermal radiation of space. Although these are now known to be negligibly small this was not always obvious: Joseph Fourier initially thought radiation from deep space was significant when he discussed the Earth’s energy budget in a paper often cited as the first on the greenhouse effect.
Outgoing radiant energy (longwave)
Of the incident solar energy about 77 W/m2 is absorbed in the atmosphere and the remainder by the surface (both land and ocean). Heat energy is then transported between surface ocean and atmosphere by infrared radiated by the planet surface layers (land and ocean) to the atmosphere and from the atmosphere to the surface; and transported via evapotranspiration (84.4 W/m2 the latent heat) or conduction/convection (18.4 W/m2) processes. Ultimately the energy is then radiated in the form of thermal infrared radiation back into space.
Earth’s energy imbalance
If the incoming energy flux is not equal to the outgoing thermal (infrared) radiation the result is an energy imbalance resulting in net heat added to the planet (if the incoming flux is larger than the outgoing). Earth’s Energy Imbalance measurements provided by Argo floats detected accumulation of ocean heat content (OHC) in the recent decade. The estimated imbalance is 0.58± 0.15 W/m2.
Several satellites have been launched into Earth’s orbit that indirectly measure the energy absorbed and radiated by Earth and by inference the energy imbalance. The NASA Earth Radiation Budget Experiment (ERBE) project involves three such satellites: the Earth Radiation Budget Satellite (ERBS) launched October 1984; NOAA-9 launched December 1984; and NOAA-10 launched September 1986.
Today the NASA satellite instruments provided by CERES part of the NASA’s Earth Observing System (EOS) are especially designed to measure both solar-reflected and Earth-emitted radiation from the top of the atmosphere (TOA) to the Earth’s surface.
以上就是今天的托福阅读材料，大家可以在练习托福阅读材料的同时，积累一些相关词汇及句型，以便考试的时候更好地把握文意，夺得托福阅读的高分。前程百利小编预祝大家托福考试取得优异成绩!
