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116-651: Outgoing longwave radiation ( OLR ) is the longwave radiation emitted to space from the top of Earth's atmosphere. It may also be referred to as emitted terrestrial radiation . Outgoing longwave radiation plays an important role in planetary cooling. Longwave radiation generally spans wavelengths ranging from 3–100 micrometres (μm). A cutoff of 4 μm is sometimes used to differentiate sunlight from longwave radiation. Less than 1% of sunlight has wavelengths greater than 4 μm. Over 99% of outgoing longwave radiation has wavelengths between 4 μm and 100 μm. The flux of energy transported by outgoing longwave radiation

232-503: A critical component of Earth's energy budget . The principle of conservation of energy says that energy cannot appear or disappear. Thus, any energy that enters a system but does not leave must be retained within the system. So, the amount of energy retained on Earth (in Earth's climate system) is governed by an equation: Energy arrives in the form of absorbed solar radiation (ASR). Energy leaves as outgoing longwave radiation (OLR). Thus,

348-447: A greenhouse gas (such as carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), and water vapor (H 2 O) and is increased, this has a number of effects. At a given wavelength The size of the reduction in OLR will vary by wavelength. Even if OLR does not decrease at certain wavelengths (e.g., because 100% of surface emissions are absorbed and the emission altitude is in

464-418: A more ordered state to a less ordered state . In Fig. 7 , the melting of ice is shown within the lower left box heading from blue to green. At one specific thermodynamic point, the melting point (which is 0 °C across a wide pressure range in the case of water), all the atoms or molecules are, on average, at the maximum energy threshold their chemical bonds can withstand without breaking away from

580-461: A relative standard uncertainty of 0.37 ppm. Afterwards, by defining the Boltzmann constant as exactly 1.380 649 × 10  J/K , the 0.37 ppm uncertainty was transferred to the triple point of water, which became an experimentally determined value of 273.1600 ± 0.0001 K ( 0.0100 ± 0.0001 °C ). That the triple point of water ended up being exceedingly close to 273.16 K after

696-444: A theoretically perfect heat engine with such helium as one of its working fluids could never transfer any net kinetic energy ( heat energy ) to the other working fluid and no thermodynamic work could occur. Temperature is generally expressed in absolute terms when scientifically examining temperature's interrelationships with certain other physical properties of matter such as its volume or pressure (see Gay-Lussac's law ), or

812-407: A certain temperature. Nonetheless, all those degrees of freedom that are available to the molecules under a particular set of conditions contribute to the specific heat capacity of a substance; which is to say, they increase the amount of heat (kinetic energy) required to raise a given amount of the substance by one kelvin or one degree Celsius. The relationship of kinetic energy, mass, and velocity

928-569: A gas contributes to the pressure and volume of that gas is a proportional function of thermodynamic temperature as established by the Boltzmann constant (symbol:  k B ). The Boltzmann constant also relates the thermodynamic temperature of a gas to the mean kinetic energy of an individual particles' translational motion as follows: E ~ = 3 2 k B T {\displaystyle {\tilde {E}}={\frac {3}{2}}k_{\text{B}}T} where: While

1044-410: A good job of establishing—within the uncertainties due to isotopic variations between water samples—temperatures around the freezing and triple points of water, but required that intermediate values between the triple point and absolute zero, as well as extrapolated values from room temperature and beyond, to be experimentally determined via apparatus and procedures in individual labs. This shortcoming

1160-416: A high emissivity at some wavelengths, this does not necessarily correspond to a high rate of thermal radiation being emitted to space. This is because the atmosphere is generally much colder than the surface, and the rate at which longwave radiation is emitted scales as the fourth power of temperature. Thus, the higher the altitude at which longwave radiation is emitted, the lower its intensity. The atmosphere

1276-524: A kelvin) in 1994, they used optical lattice laser equipment to adiabatically cool cesium atoms. They then turned off the entrapment lasers and directly measured atom velocities of 7 mm per second to in order to calculate their temperature. Formulas for calculating the velocity and speed of translational motion are given in the following footnote. It is neither difficult to imagine atomic motions due to kinetic temperature, nor distinguish between such motions and those due to zero-point energy. Consider

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1392-413: A large amount of heat energy per mole with only a modest temperature change because each molecule comprises an average of 21 atoms and therefore has many internal degrees of freedom. Even larger, more complex molecules can have dozens of internal degrees of freedom. Heat conduction is the diffusion of thermal energy from hot parts of a system to cold parts. A system can be either a single bulk entity or

1508-423: A lower flux of long-wave radiation penetrating to higher altitudes. Clouds are effective at absorbing and scattering longwave radiation, and therefore reduce the amount of outgoing longwave radiation. Clouds have both cooling and warming effects. They have a cooling effect insofar as they reflect sunlight (as measured by cloud albedo ), and a warming effect, insofar as they absorb longwave radiation. For low clouds,

1624-529: A plurality of discrete bulk entities. The term bulk in this context means a statistically significant quantity of particles (which can be a microscopic amount). Whenever thermal energy diffuses within an isolated system, temperature differences within the system decrease (and entropy increases). One particular heat conduction mechanism occurs when translational motion, the particle motion underlying temperature, transfers momentum from particle to particle in collisions. In gases, these translational motions are of

1740-448: A rest mass only 1 ⁄ 1836 that of a proton . This is about the same ratio as a .22 Short bullet (29 grains or 1.88  g ) compared to the rifle that shoots it. As Isaac Newton wrote with his third law of motion , Law #3: All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction. However, a bullet accelerates faster than a rifle given an equal force. Since kinetic energy increases as

1856-413: A substance are as close as possible to complete rest and retain only ZPE (zero-point energy)-induced quantum mechanical motion, the substance is at the temperature of absolute zero ( T  = 0). Whereas absolute zero is the point of zero thermodynamic temperature and is also the point at which the particle constituents of matter have minimal motion, absolute zero is not necessarily the point at which

1972-521: A substance as the photons are absorbed by neighboring atoms, transferring momentum in the process. Black-body photons also easily escape from a substance and can be absorbed by the ambient environment; kinetic energy is lost in the process. As established by the Stefan–Boltzmann law , the intensity of black-body radiation increases as the fourth power of absolute temperature. Thus, a black-body at 824 K (just short of glowing dull red) emits 60 times

2088-669: A substance at equilibrium, black-body photons are emitted across a range of wavelengths in a spectrum that has a bell curve-like shape called a Planck curve (see graph in Fig. 5 at right). The top of a Planck curve ( the peak emittance wavelength ) is located in a particular part of the electromagnetic spectrum depending on the temperature of the black-body. Substances at extreme cryogenic temperatures emit at long radio wavelengths whereas extremely hot temperatures produce short gamma rays (see § Table of thermodynamic temperatures ). Black-body radiation diffuses thermal energy throughout

2204-454: A substance contains zero internal energy; one must be very precise with what one means by internal energy . Often, all the phase changes that can occur in a substance, will have occurred by the time it reaches absolute zero. However, this is not always the case. Notably, T  = 0 helium remains liquid at room pressure ( Fig. 9 at right) and must be under a pressure of at least 25  bar (2.5  MPa ) to crystallize. This

2320-425: A substance in equilibrium, the kinetic energy of particle motion is evenly distributed among all the active degrees of freedom available to the particles. Since the internal temperature of molecules are usually equal to their kinetic temperature, the distinction is usually of interest only in the detailed study of non- local thermodynamic equilibrium (LTE) phenomena such as combustion , the sublimation of solids, and

2436-491: A surface also provides a practical way of assessing surface temperatures on both local and global scales. This energy distribution is what drives atmospheric thermodynamics . Outgoing long-wave radiation (OLR) has been monitored and reported since 1970 by a progression of satellite missions and instruments. Longwave radiation at the surface (both outward and inward) is mainly measured by pyrgeometers . A most notable ground-based network for monitoring surface long-wave radiation

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2552-486: A virtual standstill (off the x –axis to the right). This graph uses inverse speed for its x -axis so the shape of the curve can easily be compared to the curves in Fig. 5 below. In both graphs, zero on the x -axis represents infinite temperature. Additionally, the x - and y -axes on both graphs are scaled proportionally. Although very specialized laboratory equipment is required to directly detect translational motions,

2668-444: Is a diatomic molecule, has five active degrees of freedom: the three comprising translational motion plus two rotational degrees of freedom internally. Not surprisingly, in accordance with the equipartition theorem, nitrogen has five-thirds the specific heat capacity per mole (a specific number of molecules) as do the monatomic gases. Another example is gasoline (see table showing its specific heat capacity). Gasoline can absorb

2784-467: Is a byproduct of the collisions arising from various vibrational motions of atoms. These collisions cause the electrons of the atoms to emit thermal photons (known as black-body radiation ). Photons are emitted anytime an electric charge is accelerated (as happens when electron clouds of two atoms collide). Even individual molecules with internal temperatures greater than absolute zero also emit black-body radiation from their atoms. In any bulk quantity of

2900-410: Is a function of the kinetic energy borne in the freely moving atoms' and molecules' three translational degrees of freedom. Fixing the Boltzmann constant at a specific value, along with other rule making, had the effect of precisely establishing the magnitude of the unit interval of SI temperature, the kelvin, in terms of the average kinetic behavior of the noble gases. Moreover, the starting point of

3016-412: Is a product of both downwelling infrared energy as well as emission by the underlying surface. The cooling associated with the divergence of longwave radiation is necessary for creating and sustaining lasting inversion layers close to the surface during polar night. Longwave radiation flux divergence also plays a role in the formation of fog. Absolute temperature Thermodynamic temperature

3132-419: Is a quantity defined in thermodynamics as distinct from kinetic theory or statistical mechanics . Historically, thermodynamic temperature was defined by Lord Kelvin in terms of a macroscopic relation between thermodynamic work and heat transfer as defined in thermodynamics, but the kelvin was redefined by international agreement in 2019 in terms of phenomena that are now understood as manifestations of

3248-413: Is a single levitated argon atom (argon comprises about 0.93% of air) that is illuminated and glowing against a dark backdrop. If this argon atom was at a beyond-record-setting one-trillionth of a kelvin above absolute zero, and was moving perpendicular to the field of view towards the right, it would require 13.9 seconds to move from the center of the image to the 200-micron tick mark; this travel distance

3364-475: Is a temperature of zero kelvins (0 K), precisely corresponds to −273.15 °C and −459.67 °F. Matter at absolute zero has no remaining transferable average kinetic energy and the only remaining particle motion is due to an ever-pervasive quantum mechanical phenomenon called ZPE ( zero-point energy ). Though the atoms in, for instance, a container of liquid helium that was precisely at absolute zero would still jostle slightly due to zero-point energy,

3480-445: Is about the same as the width of the period at the end of this sentence on modern computer monitors. As the argon atom slowly moved, the positional jitter due to zero-point energy would be much less than the 200-nanometer (0.0002 mm) resolution of an optical microscope. Importantly, the atom's translational velocity of 14.43 microns per second constitutes all its retained kinetic energy due to not being precisely at absolute zero. Were

3596-453: Is as likely that there will be less ZPE-induced particle motion after a given collision as more . This random nature of ZPE is why it has no net effect upon either the pressure or volume of any bulk quantity (a statistically significant quantity of particles) of gases. However, in temperature T = 0 condensed matter ; e.g., solids and liquids, ZPE causes inter-atomic jostling where atoms would otherwise be perfectly stationary. Inasmuch as

Outgoing longwave radiation - Misplaced Pages Continue

3712-418: Is because in solids, atoms and molecules are locked into place relative to their neighbors and are not free to roam. Metals however, are not restricted to only phonon-based heat conduction. Thermal energy conducts through metals extraordinarily quickly because instead of direct molecule-to-molecule collisions, the vast majority of thermal energy is mediated via very light, mobile conduction electrons . This

3828-426: Is dominated by longwave radiation during the night and in the polar regions. While there is no absorbed solar radiation during the night, terrestrial radiation continues to be emitted, primarily as a result of solar energy absorbed during the day. The reduction of the outgoing longwave radiation (OLR), relative to longwave radiation emitted by the surface, is at the heart of the greenhouse effect . More specifically,

3944-451: Is emitted by nearly all matter, in proportion to the fourth power of its absolute temperature. In particular, the emitted energy flux, M {\displaystyle M} (measured in W/m) is given by the Stefan–Boltzmann law for non- blackbody matter: where T {\displaystyle T} is the absolute temperature , σ {\displaystyle \sigma }

4060-422: Is given by the formula E k  =  ⁠ 1 / 2 ⁠ mv . Accordingly, particles with one unit of mass moving at one unit of velocity have precisely the same kinetic energy, and precisely the same temperature, as those with four times the mass but half the velocity. The extent to which the kinetic energy of translational motion in a statistically significant collection of atoms or molecules in

4176-417: Is just one contributor to the total thermal energy in a substance; another is phase transitions , which are the potential energy of molecular bonds that can form in a substance as it cools (such as during condensing and freezing ). The thermal energy required for a phase transition is called latent heat . This phenomenon may more easily be grasped by considering it in the reverse direction: latent heat

4292-408: Is liberated or absorbed during phase transitions, pure chemical elements , compounds , and eutectic alloys exhibit no temperature change whatsoever while they undergo them (see Fig. 7 , below right). Consider one particular type of phase transition: melting. When a solid is melting, crystal lattice chemical bonds are being broken apart; the substance is transitioning from what is known as

4408-455: Is more modest, ranging from 0.021 to 2.3 kJ per mole. Relatively speaking, phase transitions can be truly energetic events. To completely melt ice at 0 °C into water at 0 °C, one must add roughly 80 times the thermal energy as is required to increase the temperature of the same mass of liquid water by one degree Celsius. The metals' ratios are even greater, typically in the range of 400 to 1200 times. The phase transition of boiling

4524-429: Is much more energetic than freezing. For instance, the energy required to completely boil or vaporize water (what is known as enthalpy of vaporization ) is roughly 540 times that required for a one-degree increase. Water's sizable enthalpy of vaporization is why one's skin can be burned so quickly as steam condenses on it (heading from red to green in Fig. 7  above); water vapors (gas phase) are liquefied on

4640-448: Is of importance in thermodynamics because it is defined in purely thermodynamic terms. SI temperature is conceptually far different from thermodynamic temperature. Thermodynamic temperature was rigorously defined historically long before there was a fair knowledge of microscopic particles such as atoms, molecules, and electrons. The International System of Units (SI) specifies the international absolute scale for measuring temperature, and

4756-486: Is of particular importance for the third law of thermodynamics . By convention, it is reported on the Kelvin scale of temperature in which the unit of measurement is the kelvin (unit symbol: K). For comparison, a temperature of 295 K corresponds to 21.85 °C and 71.33 °F. Thermodynamic temperature, as distinct from SI temperature, is defined in terms of a macroscopic Carnot cycle . Thermodynamic temperature

Outgoing longwave radiation - Misplaced Pages Continue

4872-434: Is relatively transparent to solar radiation, but it is nearly opaque to longwave radiation. The atmosphere typically absorbs most of the longwave radiation emitted by the surface. Absorption of longwave radiation prevents that radiation from reaching space. At wavelengths where the atmosphere absorbs surface radiation, some portion of the radiation that was absorbed is replaced by a lesser amount of thermal radiation emitted by

4988-648: Is the Baseline Surface Radiation Network (BSRN) , which provides crucial well-calibrated measurements for studying global dimming and brightening. Data on surface longwave radiation and OLR is available from a number of sources including: Many applications call for calculation of long-wave radiation quantities. Local radiative cooling by outgoing longwave radiation, suppression of radiative cooling (by downwelling longwave radiation cancelling out energy transfer by upwelling longwave radiation), and radiative heating through incoming solar radiation drive

5104-422: Is the Stefan–Boltzmann constant , and ϵ {\displaystyle \epsilon } is the emissivity . The emissivity is a value between zero and one which indicates how much less radiation is emitted compared to what a perfect blackbody would emit. The emissivity of Earth's surface has been measured to be in the range 0.65 to 0.99 (based on observations in the 8-13 micron wavelength range) with

5220-452: Is the amount of power radiated through a given area, in the form of photons or other elementary particles, typically measured in W/m . It is used in astronomy to determine the magnitude and spectral class of a star and in meteorology to determine the intensity of the convection in the planetary boundary layer . Radiative flux also acts as a generalization of heat flux , which is equal to

5336-423: Is the energy required to break chemical bonds (such as during evaporation and melting ). Almost everyone is familiar with the effects of phase transitions; for instance, steam at 100 °C can cause severe burns much faster than the 100 °C air from a hair dryer . This occurs because a large amount of latent heat is liberated as steam condenses into liquid water on the skin. Even though thermal energy

5452-505: Is the same magnitude as the degree Fahrenheit (symbol: °F). A unit increment of one kelvin is exactly 1.8 times one degree Rankine; thus, to convert a specific temperature on the Kelvin scale to the Rankine scale, x K = 1.8 x °R , and to convert from a temperature on the Rankine scale to the Kelvin scale, x °R = x /1.8 K . Consequently, absolute zero is "0" for both scales, but

5568-408: Is typically measured in units of watts per metre squared (W⋅m). In the case of global energy flux, the W/m value is obtained by dividing the total energy flow over the surface of the globe (measured in watts) by the surface area of the Earth, 5.1 × 10 m (5.1 × 10 km; 2.0 × 10 sq mi). Emitting outgoing longwave radiation is the only way Earth loses energy to space, i.e., the only way

5684-420: Is what gives substances their temperature). The effect is rather like popcorn : at a certain temperature, additional thermal energy cannot make the kernels any hotter until the transition (popping) is complete. If the process is reversed (as in the freezing of a liquid), thermal energy must be removed from a substance. As stated above, the thermal energy required for a phase transition is called latent heat . In

5800-439: Is why there is a near-perfect correlation between metals' thermal conductivity and their electrical conductivity . Conduction electrons imbue metals with their extraordinary conductivity because they are delocalized (i.e., not tied to a specific atom) and behave rather like a sort of quantum gas due to the effects of zero-point energy (for more on ZPE, see Note 1 below). Furthermore, electrons are relatively light with

5916-472: Is zero, a planet is said to be in radiative equilibrium . Planets natural tend to a state of approximate radiative equilibrium. In recent decades, energy has been measured to be arriving on Earth at a higher rate than it leaves, corresponding to planetary warming. The energy imbalance has been increasing. It can take decades to centuries for oceans to warm and planetary temperature to shift sufficiently to compensate for an energy imbalance. Thermal radiation

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6032-524: The atmospheric window . The atmospheric window is a region of the electromagnetic wavelength spectrum between 8 and 11 μm where the atmosphere does not absorb longwave radiation (except for the ozone band between 9.6 and 9.8 μm). Greenhouse gases in the atmosphere are responsible for a majority of the absorption of longwave radiation in the atmosphere. The most important of these gases are water vapor , carbon dioxide , methane , and ozone . The absorption of longwave radiation by gases depends on

6148-464: The diffusion of hot gases in a partial vacuum. The kinetic energy stored internally in molecules causes substances to contain more heat energy at any given temperature and to absorb additional internal energy for a given temperature increase. This is because any kinetic energy that is, at a given instant, bound in internal motions, is not contributing to the molecules' translational motions at that same instant. This extra kinetic energy simply increases

6264-400: The noble gases helium and argon , which have only the three translational degrees of freedom (the X, Y, and Z axis). Kinetic energy is stored in molecules' internal degrees of freedom, which gives them an internal temperature . Even though these motions are called "internal", the external portions of molecules still move—rather like the jiggling of a stationary water balloon . This permits

6380-420: The 4.2221 K boiling point of helium." The Boltzmann constant and its related formulas describe the realm of particle kinetics and velocity vectors whereas ZPE ( zero-point energy ) is an energy field that jostles particles in ways described by the mathematics of quantum mechanics. In atomic and molecular collisions in gases, ZPE introduces a degree of chaos , i.e., unpredictability, to rebound kinetics; it

6496-435: The Boltzmann constant a precisely defined value had no practical effect on modern thermometry except for the most exquisitely precise measurements. Before the revision, the triple point of water was exactly 273.16 K and 0.01 °C and the Boltzmann constant was experimentally determined to be 1.380 649 03 (51) × 10  J/K , where the "(51)" denotes the uncertainty in the two least significant digits (the 03) and equals

6612-432: The Boltzmann constant is useful for finding the mean kinetic energy in a sample of particles, it is important to note that even when a substance is isolated and in thermodynamic equilibrium (all parts are at a uniform temperature and no heat is going into or out of it), the translational motions of individual atoms and molecules occurs across a wide range of speeds (see animation in Fig. 1 above). At any one instant,

6728-462: The Boltzmann constant, how heat energy causes precisely defined changes in the pressure and temperature of certain gases. This is because monatomic gases like helium and argon behave kinetically like freely moving perfectly elastic and spherical billiard balls that move only in a specific subset of the possible motions that can occur in matter: that comprising the three translational degrees of freedom . The translational degrees of freedom are

6844-485: The Rankine scale. Throughout the scientific world where modern measurements are nearly always made using the International System of Units, thermodynamic temperature is measured using the Kelvin scale. The Rankine scale is part of English engineering units and finds use in certain engineering fields, particularly in legacy reference works. The Rankine scale uses the degree Rankine (symbol: °R) as its unit, which

6960-463: The SI revision was no accident; the final value of the Boltzmann constant was determined, in part, through clever experiments with argon and helium that used the triple point of water for their key reference temperature. Notwithstanding the 2019 revision, water triple-point cells continue to serve in modern thermometry as exceedingly precise calibration references at 273.16 K and 0.01 °C. Moreover,

7076-497: The SI was primarily for the purpose of decoupling much of the SI system's definitional underpinnings from the kilogram , which was the last physical artifact defining an SI base unit (a platinum/iridium cylinder stored under three nested bell jars in a safe located in France) and which had highly questionable stability. The solution required that four physical constants, including the Boltzmann constant, be definitionally fixed. Assigning

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7192-694: The absolute zero of temperature. Examples are the International SI temperature scale, the Rankine temperature scale , and the thermodynamic temperature scale. Other temperature scales have their numerical zero far from the absolute zero of temperature. Examples are the Fahrenheit scale and the Celsius scale. At the zero point of thermodynamic temperature, absolute zero , the particle constituents of matter have minimal motion and can become no colder. Absolute zero, which

7308-420: The absorptivity of the gas is high and the gas is present in a high enough concentration, the absorption at certain wavelengths becomes saturated. This means there is enough gas present to completely absorb the radiated energy at that wavelength before the upper atmosphere is reached. It is sometimes incorrectly argued that this means an increase in the concentration of this gas will have no additional effect on

7424-504: The amount of internal energy that substance absorbs for a given temperature rise. This property is known as a substance's specific heat capacity . Different molecules absorb different amounts of internal energy for each incremental increase in temperature; that is, they have different specific heat capacities. High specific heat capacity arises, in part, because certain substances' molecules possess more internal degrees of freedom than others do. For instance, room-temperature nitrogen , which

7540-405: The atmosphere at a higher altitude. When absorbed, the energy transmitted by this radiation is transferred to the substance that absorbed it. However, overall, greenhouse gases in the troposphere emit more thermal radiation than they absorb, so longwave radiative heat transfer has a net cooling effect on air. Assuming no cloud cover, most of the surface emissions that reach space do so through

7656-438: The atmosphere result in greater absorption because of the cumulative absorption by many layers of gas. Lastly, the temperature and altitude of the absorbing gas also affect its absorption of longwave radiation. OLR is affected by Earth's surface skin temperature (i.e, the temperature of the top layer of the surface), skin surface emissivity, atmospheric temperature, water vapor profile, and cloud cover. The net all-wave radiation

7772-421: The atom precisely at absolute zero, imperceptible jostling due to zero-point energy would cause it to very slightly wander, but the atom would perpetually be located, on average, at the same spot within the field of view. This is analogous to a boat that has had its motor turned off and is now bobbing slightly in relatively calm and windless ocean waters; even though the boat randomly drifts to and fro, it stays in

7888-458: The distribution of energy changes). As temperatures increase, the amount of thermal radiation emitted also increases, leading to more outgoing longwave radiation (OLR), and a smaller energy imbalance (EEI). Similarly, if energy arrives at a lower rate than it leaves (i.e., ASR < OLR, so than EEI is negative), the amount of energy in Earth's climate decreases, and temperatures tend to decrease overall. As temperatures decrease, OLR decreases, making

8004-690: The effects of zero-point energy. Such are the consequences of statistical mechanics and the nature of thermodynamics. As mentioned above, there are other ways molecules can jiggle besides the three translational degrees of freedom that imbue substances with their kinetic temperature. As can be seen in the animation at right, molecules are complex objects; they are a population of atoms and thermal agitation can strain their internal chemical bonds in three different ways: via rotation, bond length, and bond angle movements; these are all types of internal degrees of freedom . This makes molecules distinct from monatomic substances (consisting of individual atoms) like

8120-466: The emissivity of matter is always equal to its absorptivity, at a given wavelength. At some wavelengths, greenhouse gases absorb 100% of the longwave radiation emitted by the surface. So, at those wavelengths, the emissivity of the atmosphere is 1 and the atmosphere emits thermal radiation much like an ideal blackbody would. However, this applies only at wavelengths where the atmosphere fully absorbs longwave radiation. Although greenhouse gases in air have

8236-475: The evaporation of just 20 mm of water from a 1.29-meter-deep pool chills its water 8.4 °C (15.1 °F). The total energy of all translational and internal particle motions, including that of conduction electrons, plus the potential energy of phase changes, plus zero-point energy of a substance comprise the internal energy of it. As a substance cools, different forms of internal energy and their related effects simultaneously decrease in magnitude:

8352-504: The familiar billiard ball-like movements along the X, Y, and Z axes of 3D space (see Fig. 1 , below). This is why the noble gases all have the same specific heat capacity per atom and why that value is lowest of all the gases. Molecules (two or more chemically bound atoms), however, have internal structure and therefore have additional internal degrees of freedom (see Fig. 3 , below), which makes molecules absorb more heat energy for any given amount of temperature rise than do

8468-413: The following hypothetical thought experiment, as illustrated in Fig. 2.5 at left, with an atom that is exceedingly close to absolute zero. Imagine peering through a common optical microscope set to 400 power, which is about the maximum practical magnification for optical microscopes. Such microscopes generally provide fields of view a bit over 0.4 mm in diameter. At the center of the field of view

8584-485: The form of phonons (see Fig. 4 at right). Phonons are constrained, quantized wave packets that travel at the speed of sound of a given substance. The manner in which phonons interact within a solid determines a variety of its properties, including its thermal conductivity. In electrically insulating solids, phonon-based heat conduction is usually inefficient and such solids are considered thermal insulators (such as glass, plastic, rubber, ceramic, and rock). This

8700-417: The greenhouse effect may be defined quantitatively as the amount of longwave radiation emitted by the surface that does not reach space. On Earth as of 2015, about 398 W/m of longwave radiation was emitted by the surface, while OLR, the amount reaching space, was 239 W/m. Thus, the greenhouse effect was 398−239 = 159 W/m , or 159/398 = 40% of surface emissions, not reaching space. When the concentration of

8816-417: The imbalance closer to zero. In this fashion, a planet naturally constantly adjusts its temperature so as to keep the energy imbalance small. If there is more solar radiation absorbed than OLR emitted, the planet will heat up. If there is more OLR than absorbed solar radiation the planet will cool. In both cases, the temperature change works to shift the energy imbalance towards zero. When the energy imbalance

8932-459: The increased concentration leads to the atmosphere emitting longwave radiation to space from a higher altitude. If the air at that higher altitude is colder (as is true throughout the troposphere), then thermal emissions to space will be reduced, decreasing OLR. False conclusions about the implications of absorption being "saturated" are examples of the surface budget fallacy , i.e., erroneous reasoning that results from focusing on energy exchange at

9048-425: The kelvin was redefined in 2019 in relation to the physical property underlying thermodynamic temperature: the kinetic energy of atomic free particle motion. The revision fixed the Boltzmann constant at exactly 1.380 649 × 10  joules per kelvin (J/K). The microscopic property that imbues material substances with a temperature can be readily understood by examining the ideal gas law , which relates, per

9164-442: The kinetic energy of free motion of microscopic particles such as atoms, molecules, and electrons. From the thermodynamic viewpoint, for historical reasons, because of how it is defined and measured, this microscopic kinetic definition is regarded as an "empirical" temperature. It was adopted because in practice it can generally be measured more precisely than can Kelvin's thermodynamic temperature. A thermodynamic temperature of zero

9280-541: The latent heat of available phase transitions is liberated as a substance changes from a less ordered state to a more ordered state; the translational motions of atoms and molecules diminish (their kinetic energy or temperature decreases); the internal motions of molecules diminish (their internal energy or temperature decreases); conduction electrons (if the substance is an electrical conductor) travel somewhat slower; and black-body radiation's peak emittance wavelength increases (the photons' energy decreases). When particles of

9396-407: The lattice. Chemical bonds are all-or-nothing forces: they either hold fast, or break; there is no in-between state. Consequently, when a substance is at its melting point, every joule of added thermal energy only breaks the bonds of a specific quantity of its atoms or molecules, converting them into a liquid of precisely the same temperature; no kinetic energy is added to translational motion (which

9512-512: The lowest values being for barren desert regions. The emissivity is mostly above 0.9, and the global average surface emissivity is estimated to be around 0.95. The most common gases in air (i.e., nitrogen, oxygen, and argon) have a negligible ability to absorb or emit longwave thermal radiation. Consequently, the ability of air to absorb and emit longwave radiation is determined by the concentration of trace gases like water vapor and carbon dioxide. According to Kirchhoff's law of thermal radiation ,

9628-467: The mean average kinetic energy of a specific kind of particle motion known as translational motion . These simple movements in the three X, Y, and Z–axis dimensions of space means the particles move in the three spatial degrees of freedom . This particular form of kinetic energy is sometimes referred to as kinetic temperature . Translational motion is but one form of heat energy and is what gives gases not only their temperature, but also their pressure and

9744-440: The melting point of water and that the triple point of water had long been experimentally determined to be indistinguishably close to 0.01 °C), the difference between the Celsius scale and Kelvin scale is accepted as 273.15 kelvins; which is to say, 0 °C corresponds to 273.15 kelvins. The net effect of this as well as later resolutions was twofold: 1) they defined absolute zero as precisely 0 K, and 2) they defined that

9860-418: The melting point of water ice (0 °C and 273.15 K) is 491.67 °R. To convert temperature intervals (a span or difference between two temperatures), the formulas from the preceding paragraph are applicable; for instance, an interval of 5 kelvin is precisely equal to an interval of 9 degrees Rankine. For 65 years, between 1954 and the 2019 revision of the SI , a temperature interval of one kelvin

9976-406: The monatomic gases. Heat energy is born in all available degrees of freedom; this is in accordance with the equipartition theorem , so all available internal degrees of freedom have the same temperature as their three external degrees of freedom. However, the property that gives all gases their pressure , which is the net force per unit area on a container arising from gas particles recoiling off it,

10092-496: The nature shown above in Fig. 1 . As can be seen in that animation, not only does momentum (heat) diffuse throughout the volume of the gas through serial collisions, but entire molecules or atoms can move forward into new territory, bringing their kinetic energy with them. Consequently, temperature differences equalize throughout gases very quickly—especially for light atoms or molecules; convection speeds this process even more. Translational motion in solids , however, takes

10208-414: The planet cools itself. Radiative heating from absorbed sunlight, and radiative cooling to space via OLR power the heat engine that drives atmospheric dynamics . The balance between OLR (energy lost) and incoming solar shortwave radiation (energy gained) determines whether the Earth is experiencing global heating or cooling (see Earth's energy budget ). Outgoing longwave radiation (OLR) constitutes

10324-431: The planet's energy budget. This argument neglects the fact that outgoing longwave radiation is determined not only by the amount of surface radiation that is absorbed , but also by the altitude (and temperature) at which longwave radiation is emitted to space. Even if 100% of surface emissions are absorbed at a given wavelength, the OLR at that wavelength can still be reduced by increased greenhouse gas concentration, since

10440-525: The proportion of particles moving at a given speed within this range is determined by probability as described by the Maxwell–Boltzmann distribution . The graph shown here in Fig. 2 shows the speed distribution of 5500 K helium atoms. They have a most probable speed of 4.780 km/s (0.2092 s/km). However, a certain proportion of atoms at any given instant are moving faster while others are moving relatively slowly; some are momentarily at

10556-456: The radiant power as it does at 296 K (room temperature). This is why one can so easily feel the radiant heat from hot objects at a distance. At higher temperatures, such as those found in an incandescent lamp , black-body radiation can be the principal mechanism by which thermal energy escapes a system. The table below shows various points on the thermodynamic scale, in order of increasing temperature. The kinetic energy of particle motion

10672-436: The radiative flux when restricted to the infrared spectrum . When radiative flux is incident on a surface, it is often called irradiance . Flux emitted from a surface may be called radiant exitance or radiant emittance . The ratio of irradiance reflected to the irradiance received by a surface is called albedo . In geophysics, shortwave flux is a result of specular and diffuse reflection of incident shortwave radiation by

10788-453: The rate of change in the energy in Earth's climate system is given by Earth's energy imbalance (EEI): When energy is arriving at a higher rate than it leaves (i.e., ASR > OLR, so that EEI is positive), the amount of energy in Earth's climate increases. Temperature is a measure of the amount of thermal energy in matter. So, under these circumstances, temperatures tend to increase overall (though temperatures might decrease in some places as

10904-546: The real-world effects that ZPE has on substances can vary as one alters a thermodynamic system (for example, due to ZPE, helium won't freeze unless under a pressure of at least 2.5  MPa (25  bar )), ZPE is very much a form of thermal energy and may properly be included when tallying a substance's internal energy. Though there have been many other temperature scales throughout history, there have been only two scales for measuring thermodynamic temperature which have absolute zero as their null point (0): The Kelvin scale and

11020-471: The reflection of solar radiation is the larger effect; so, these clouds cool the Earth. In contrast, for high thin clouds in cold air, the absorption of longwave radiation is the more significant effect; so these clouds warm the planet. The interaction between emitted longwave radiation and the atmosphere is complicated due to the factors that affect absorption. The path of the radiation in the atmosphere also determines radiative absorption: longer paths through

11136-474: The resultant collisions by atoms or molecules with small particles suspended in a fluid produces Brownian motion that can be seen with an ordinary microscope. The translational motions of elementary particles are very fast and temperatures close to absolute zero are required to directly observe them. For instance, when scientists at the NIST achieved a record-setting cold temperature of 700 nK (billionths of

11252-416: The same spot in the long term and makes no headway through the water. Accordingly, an atom that was precisely at absolute zero would not be "motionless", and yet, a statistically significant collection of such atoms would have zero net kinetic energy available to transfer to any other collection of atoms. This is because regardless of the kinetic temperature of the second collection of atoms, they too experience

11368-420: The skin with releasing a large amount of energy (enthalpy) to the environment including the skin, resulting in skin damage. In the opposite direction, this is why one's skin feels cool as liquid water on it evaporates (a process that occurs at a sub-ambient wet-bulb temperature that is dependent on relative humidity ); the water evaporation on the skin takes a large amount of energy from the environment including

11484-403: The skin, reducing the skin temperature. Water's highly energetic enthalpy of vaporization is also an important factor underlying why solar pool covers (floating, insulated blankets that cover swimming pools when the pools are not in use) are so effective at reducing heating costs: they prevent evaporation. (In other words, taking energy from water when it is evaporated is limited.) For instance,

11600-458: The specific absorption bands of the gases in the atmosphere. The specific absorption bands are determined by their molecular structure and energy levels. Each type of greenhouse gas has a unique group of absorption bands that correspond to particular wavelengths of radiation that the gas can absorb. The OLR balance is affected by clouds, dust, and aerosols in the atmosphere. Clouds tend to block penetration of upwelling longwave radiation, causing

11716-416: The specific cases of melting and freezing, it is called enthalpy of fusion or heat of fusion . If the molecular bonds in a crystal lattice are strong, the heat of fusion can be relatively great, typically in the range of 6 to 30 kJ per mole for water and most of the metallic elements. If the substance is one of the monatomic gases (which have little tendency to form molecular bonds) the heat of fusion

11832-513: The specific problem. Another common approach is to estimate values using surface temperature and emissivity , then compare to satellite top-of-atmosphere radiance or brightness temperature . There are online interactive tools that allow one to see the spectrum of outgoing longwave radiation that is predicted to reach space under various atmospheric conditions. Radiative flux Radiative flux, also known as radiative flux density or radiation flux (or sometimes power flux density ),

11948-472: The square of velocity, nearly all the kinetic energy goes into the bullet, not the rifle, even though both experience the same force from the expanding propellant gases. In the same manner, because they are much less massive, thermal energy is readily borne by mobile conduction electrons. Additionally, because they are delocalized and very fast, kinetic thermal energy conducts extremely quickly through metals with abundant conduction electrons. Thermal radiation

12064-449: The stratosphere), increased greenhouse gas concentration can still lead to significant reductions in OLR at other wavelengths where absorption is weaker. When OLR decreases, this leads to an energy imbalance, with energy received being greater than energy lost, causing a warming effect. Therefore, an increase in the concentrations of greenhouse gases causes energy to accumulate in Earth's climate system, contributing to global warming . If

12180-460: The surface, instead of focusing on the top-of-atmosphere (TOA) energy balance. Measurements of outgoing longwave radiation at the top of the atmosphere and of longwave radiation back towards the surface are important to understand how much energy is retained in Earth's climate system: for example, how thermal radiation cools and warms the surface, and how this energy is distributed to affect the development of clouds. Observing this radiative flux from

12296-445: The temperature and dynamics of different parts of the atmosphere. By using the radiance measured from a particular direction by an instrument, atmospheric properties (like temperature or humidity ) can be inversely inferred . Calculations of these quantities solve the radiative transfer equations that describe radiation in the atmosphere. Usually the solution is done numerically by atmospheric radiative transfer codes adapted to

12412-448: The thermodynamic temperature scale, absolute zero, was reaffirmed as the point at which zero average kinetic energy remains in a sample; the only remaining particle motion being that comprising random vibrations due to zero-point energy. Temperature scales are numerical. The numerical zero of a temperature scale is not bound to the absolute zero of temperature. Nevertheless, some temperature scales have their numerical zero coincident with

12528-402: The triple point of special isotopically controlled water called Vienna Standard Mean Ocean Water occurred at precisely 273.16 K and 0.01 °C. One effect of the aforementioned resolutions was that the melting point of water, while very close to 273.15 K and 0 °C, was not a defining value and was subject to refinement with more precise measurements. The 1954 BIPM standard did

12644-422: The triple point of water remains one of the 14 calibration points comprising ITS‑90, which spans from the triple point of hydrogen (13.8033 K) to the freezing point of copper (1,357.77 K), which is a nearly hundredfold range of thermodynamic temperature. The thermodynamic temperature of any bulk quantity of a substance (a statistically significant quantity of particles) is directly proportional to

12760-436: The two-way exchange of kinetic energy between internal motions and translational motions with each molecular collision. Accordingly, as internal energy is removed from molecules, both their kinetic temperature (the kinetic energy of translational motion) and their internal temperature simultaneously diminish in equal proportions. This phenomenon is described by the equipartition theorem , which states that for any bulk quantity of

12876-415: The underlying surface. This shortwave radiation, as solar radiation, can have a profound impact on certain biophysical processes of vegetation, such as canopy photosynthesis and land surface energy budgets, by being absorbed into the soil and canopies. As it is the main energy source of most weather phenomena, the solar shortwave radiation is used extensively in numerical weather prediction . Longwave flux

12992-434: The unit of measure kelvin (unit symbol: K) for specific values along the scale. The kelvin is also used for denoting temperature intervals (a span or difference between two temperatures) as per the following example usage: "A 60/40 tin/lead solder is non-eutectic and is plastic through a range of 5 kelvins as it solidifies." A temperature interval of one degree Celsius is the same magnitude as one kelvin. The magnitude of

13108-683: The vast majority of their volume. This relationship between the temperature, pressure, and volume of gases is established by the ideal gas law 's formula pV = nRT and is embodied in the gas laws . Though the kinetic energy borne exclusively in the three translational degrees of freedom comprise the thermodynamic temperature of a substance, molecules, as can be seen in Fig. 3 , can have other degrees of freedom, all of which fall under three categories: bond length, bond angle, and rotational. All three additional categories are not necessarily available to all molecules, and even for molecules that can experience all three, some can be "frozen out" below

13224-405: The wavelength of its emitted black-body radiation . Absolute temperature is also useful when calculating chemical reaction rates (see Arrhenius equation ). Furthermore, absolute temperature is typically used in cryogenics and related phenomena like superconductivity , as per the following example usage: "Conveniently, tantalum's transition temperature ( T c ) of 4.4924 kelvin is slightly above

13340-536: Was addressed by the International Temperature Scale of 1990 , or ITS‑90, which defined 13 additional points, from 13.8033 K, to 1,357.77 K. While definitional, ITS‑90 had—and still has—some challenges, partly because eight of its extrapolated values depend upon the melting or freezing points of metal samples, which must remain exceedingly pure lest their melting or freezing points be affected—usually depressed. The 2019 revision of

13456-597: Was defined as ⁠ 1 / 273.16 ⁠ the difference between the triple point of water and absolute zero. The 1954 resolution by the International Bureau of Weights and Measures (known by the French-language acronym BIPM), plus later resolutions and publications, defined the triple point of water as precisely 273.16 K and acknowledged that it was "common practice" to accept that due to previous conventions (namely, that 0 °C had long been defined as

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