By Philip Mulholland
The next picture exhibits the Earth’s outgoing longwave radiation recorded by the CERES (Clouds and the Earth’s Radiant Power System) Instrument onboard the NASA Aqua Satellite tv for pc (Damadeo and Hanson, 2017). This picture is compiled from measurements made on March 18 2011, close to the time of the Vernal Equinox.
Picture credit score: NASA
The color desk legend information the vitality flux of the outgoing radiation. This flux ranges from a minimal worth of 150 W/m2 displayed as white, to a most flux of 350 W/m2, displayed as yellow. Utilizing the Stefan-Boltzmann regulation of radiative emission these vitality flux values might be transformed to emission temperatures utilizing the next equation: –
Equation 1: T = (j*/σ)zero.25
The place T is the thermodynamic temperature in Kelvin.
j* is the black physique radiant emittance in Watts per sq. metre.
σ is the Stefan-Boltzmann fixed of proportionality.
(Sigma has a price of 5.670373 * 10-Eight W m-2 Okay-Four)
Utilizing equation 1 we will decide that the emission temperatures recorded by the Ceres instrument vary from a minimal worth of 226.Eight Kelvin (-46.2oC) for the 150 W/m2 low-end flux, to a most worth of 280.three Kelvin (7.3oC) for the 350 W/m2 high-end flux.
2. Calibrating the CERES picture
The CERES picture is a single snapshot of the Earth’s thermal radiant emission to area. This picture incorporates a big quantity of knowledge, nonetheless to grasp this in its world context we should first calibrate the picture towards identified measurements of the most important elements of the Earth’s atmospheric system.
The Earth’s environment is a dynamic system composed of three separate forms of interlocking cells, symmetrically distributed in every hemisphere. These cells include two thermal cells and one mechanical cell, they’re: –
1. The tropical thermal Hadley cell positioned between the equator and latitude 30 levels.
2. The temperate mechanical Ferrel cell positioned between latitude 30 levels and latitude 66.56 levels.
three. The frigid thermal Polar cell positioned round every pole and outlined by the Arctic and Antarctic circles.
The worldwide areal distribution of every cell is as follows: –
1. The Hadley cells occupy 50% of the floor space of the globe, and in complete intercept 60.9% of the solar’s insolation.
2. The Ferrel cells occupy 41.75% of the floor space of the globe, and in complete intercept 36.29% of the solar’s insolation.
three. The Polar cells occupy Eight.25% of the floor space of the globe, and in complete intercept solely 2.81% of the solar’s insolation.
The excessive focus of insolation intercepted by the tropical Hadley cells, in comparison with the low insolation intercepted by the Polar cells, is the elemental purpose for the low floor temperatures discovered within the polar areas of our planet.
Visible inspection of the CERES picture exhibits the presence of cloud tops related to the convective storms of the equatorial intertropical convergence zone (ITCZ) or doldrums. These storms are radiating at 150 W/m2 and have an emission temperature of 227 Kelvin (-46.2oC). In an effort to decide the elevation of this emission, we have to set up three atmospheric parameters for the Hadley, Ferrel and Polar cells, that are: –
1. The peak of the tropopause.
2. The temperature of the tropopause.
three. The environmental lapse charge of the atmospheric cell.
Utilizing these three metrics we will then calculate the temperature elevation profile that pertains to the given emission charge for every of the three atmospheric circulation cells. Revealed data for the temperature of the tropopause will not be simple to determine, nonetheless utilizing numerous sources the values used on this evaluation have been obtained and are recorded in Desk 1.
Tropopause Top (km)
Tropopause Temperature (Celsius)
Environmental Lapse Charge (Okay/km)
Environmental Lapse Charge
Desk 1: Atmospheric Cell Parameters.
Utilizing the values established in Desk 1 we will now decide the highest down temperature profile for every of the three atmospheric cells. The calculations for the Hadley cell present that to take care of a 17 km tropopause with a temperature of 190 Kelvin (-83oC) and a lapse charge of -6.5 Okay/km, then the common floor temperature of the tropical zone should be 301 Kelvin (27.9oC).
Desk 2: Hadley Cell – CERES Picture Emissions Calibration Desk.
Changing this common floor temperature of ~28oC right into a radiant vitality emission flux, by utilizing the Stefan-Boltzmann equation, we will set up that the tropical floor vitality flux is 465 W/m2. This worth is 115 W/m2 increased than the utmost noticed flux of 350 W/m2 within the Ceres picture, and so we have now established that this picture doesn’t report direct sea degree floor radiant emission. Somewhat, with this picture we’re observing the atmospheric temperatures at elevations of three,160 m (10,370 ft) and above. Consequently, all excessive elevation land surfaces within the latitude zone of 30oS to 30oN, such because the Tibetan plateau at Four,500m (14,750 ft), will probably be able to instantly emitting thermal radiant vitality to area by the overlying environment.
The calculations for the Ferrel cell present that to take care of a 13 km tropopause with a temperature of 195 Kelvin (-78oC) and a lapse charge of -6.5 Okay/km, then the common annual floor temperature of the temperate zone will probably be 280 Kelvin (6.5oC).
Desk three: Ferrel Cell – CERES Picture Emissions Calibration Desk.
Changing this common floor temperature of 6.5oC right into a radiant vitality emission flux, by utilizing the Stefan-Boltzmann equation, we will now set up that the temperate zone floor vitality flux is 346 W/m2. This worth is 46 W/m2 increased than the utmost noticed flux within the Ceres picture of 300 W/m2 for the temperate zone as seen from area. As soon as once more, though this picture doesn’t report direct sea degree floor radiant emission, all land surfaces with an elevation above 1,500 m (Four,920 ft) will probably be able to instantly emitting thermal radiant vitality to area by the overlying environment.
The calculations for the Polar cell present that to take care of an 9 km tropopause with a temperature of 194.5 Kelvin (-78.5oC) and a lapse charge of -6.5 Okay/km, then the common annual floor temperature of the polar zone will probably be 253 Kelvin (-20oC).
Desk Four: Polar Cell – CERES Picture Emissions Calibration Desk.
Changing this common floor temperature of -20oC right into a radiant vitality emission flux, by utilizing the Stefan-Boltzmann equation, we will now set up that the polar zone floor vitality flux is 232 W/m2. This worth is simply 7 W/m2 increased than the utmost noticed flux within the Ceres picture of 225 W/m2 for the area of the Southern Ocean, south of the Antarctic circle. This calculation demonstrates that every one elements of the polar areas above 310 m (1,zero20 ft) elevation, and particularly the excessive elevation ice domes, will probably be able to instantly emitting thermal radiant vitality to area by the overlying environment.
Utilizing the common floor temperature values calculated for every cell (Tables 2, three & Four), mixed with the proportion of the worldwide areal distribution of every cell (Desk 5)
Desk 5: Calculating the International Areal Distribution of the Atmospheric Cells.
we will now compute the common annual floor temperature of the Earth (Desk 6).
Desk 6: Calculating the International Common Temperature of the Earth.
The typical temperature of the Earth decided by this calculation technique is 288 Kelvin, which is the at the moment accepted worth of 15oC utilized by local weather science.
The method of building the common temperature of the floor of the Earth offered right here, depends on the next atmospheric measurements and elementary planetary parameters.
These are: –
1. The peak of the tropopause for every atmospheric cell.
2. The temperature of its tropopause.
three. The environmental lapse charge of every atmospheric cell.
Four. The relative proportion of the Earth’s floor occupied by every cell.
With these measurements established, the worldwide common temperature of the Earth is just the arithmetical sum of the relative proportion floor temperatures for the three atmospheric cells.
Maybe probably the most fascinating a part of this evaluation is the obvious coincidence between the utmost floor elevation of the Antarctic Icecap at Dome A (4093m) and the utmost elevation of supercooled water (Moore and Molinero, 2011) within the atmospheric profile of the Polar Cell (Rubin, 1953). It might seem that the vertical elevation of continental ice caps is proscribed by atmospheric processes, nonetheless it’s equally clear that no such vertical constraint happens with stable rock land floor elevation. As a result of mountain ranges can attain vertical elevations that lie inside the radiant transmission zone to area for every atmospheric cell, it seems that these topographic options can type leak zones that emit radiant vitality to area independently of the transmission properties of the overlying environment.
Beal, A. 2011. The Floor Space of a Sphere Between Parallel Planes. On-line Weblog
Damadeo, Okay. and Hanson, H. 2017. CERES Clouds and the Earth’s Radiant Power System. NASA 9pp.
Moore, E.B. and Molinero, V. 2011. Structural transformation in supercooled water controls the crystallization charge of ice. Nature, 479, 506-508.
Rubin, M.J., 1953. Differences due to the season of the Antarctic tropopause. Journal of Meteorology, 10(2), pp.127-134.
Excel unfold sheet containing the supply tables for the essay.