In this study, we revise entropy budget estimated by earlier studies using satellite observations that have been taken since March 2000. The analysis of thermodynamics of the climate system is also used to understand how general circulation changes under a warming climate ( Kjellsson 2015 Laliberté et al. (2011) used climate models and estimated entropy production by nonradiative irreversible processes. (1991) and estimated entropy produced by irreversible processes within the Earth system. Goody (2000) extended work by Peixoto et al. Observational estimates of entropy production within the Earth system by absorption of shortwave radiation, however, have not been updated since the estimate by Peixoto et al. Stephens and O’Brien (1993) used satellites’ broadband radiance measurements to estimate entropy production by longwave radiation emitted to space. Their estimate was primarily based on in situ surface and upper-atmosphere data taken between 19 ( Peixoto and Oort 1992). Global entropy budget was first estimated by Peixoto et al. Earlier studies refer to entropy produced by irreversible processes within the Earth system as material entropy (e.g., Bannon 2015 Bannon and Lee 2017). Longwave radiation emitted to space then exports entropy. In addition to diabatic heating by irreversible processes occurring within the system, radiative cooling and heating by longwave radiation contribute to entropy production. Heating due to absorption of solar radiation and scattering ( Wu and Liu 2010) within the Earth system produce entropy. For the Earth system, entropy is imported by radiation emitted by the sun. Entropy produced by a blackbody is, therefore, the sum of entropy produced by radiative cooling and entropy carried by the blackbody radiation ( Planck 1913). In addition, entropy is carried by radiation. Energy transport is also associated with heating and cooling by radiation, dynamics, and water vapor phase change, which in turn alter entropy of the Earth system.Įntropy is produced by heating and cooling by irreversible processes. Water vapor enters the atmosphere and heats the atmosphere when it condenses. A part of shortwave irradiance absorbed by ocean and land is used to evaporate water vapor. While dynamics in the atmosphere and ocean distributes energy absorbed by Earth, energy is converted into different forms. Once averaged over a year and over the entire globe, about 71% of the solar irradiance is absorbed by Earth (e.g., Stephens et al. The hydrological cycle and dynamics in the Earth system are driven by energy received from the sun. Input and output temperatures derived by dividing the absorbed shortwave irradiance and emitted longwave irradiance to space by respective entropy production are, respectively, 282 and 259 K, which give the Carnot efficiency of the Earth system of 8.5%. The result implies that global annual mean entropy production by irreversible processes decreases with increasing shortwave absorption. The increase of entropy production by shortwave absorption is, however, larger than the increase of entropy production by longwave emission to space. Both global annual mean entropy productions by shortwave absorption and longwave emission to space increase with increasing shortwave absorption (i.e., with decreasing the planetary albedo). With a steady-state assumption, entropy production by irreversible processes within the Earth system is estimated to be 0.076 W m −2 K −1 and by nonradiative irreversible processes to be 0.049 W m −2 K −1. Global annual mean entropy production by shortwave absorption and longwave emission to space are, respectively, 0.852 and 0.928 W m −2 K −1. Similarly, entropy production by longwave radiation is computed by emitted irradiance to space from layers in the atmosphere and surface divided by their temperatures. Entropy production by shortwave radiation is computed by the absorbed irradiance within layers in the atmosphere and by the surface divided by their temperatures. Vertical profiles of shortwave and longwave irradiances computed with satellite-derived cloud properties and temperature and humidity profiles from reanalysis are used to estimate entropy production.
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