101 research outputs found
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Thermodynamics of climate change: generalized sensitivities
No full textUsing a recent theoretical approach, we study how global warming impacts the thermodynamics of the climate system by performing experiments with a simplified yet Earth-like climate model. The intensity of the Lorenz energy cycle, the Carnot efficiency, the material entropy production, and the degree of irreversibility of the system change monotonically with the CO2 concentration. Moreover, these quantities feature an approximately linear behaviour with respect to the logarithm of the CO2 concentration in a relatively wide range. These generalized sensitivities suggest that the climate becomes less efficient, more irreversible, and features higher entropy production as it becomes warmer, with changes in the latent heat fluxes playing a predominant role. These results may be of help for explaining recent findings obtained with state of the art climate models regarding how increases in CO2 concentration impact the vertical stratification of the tropical and extratropical atmosphere and the position of the storm tracks
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Thermodynamic analysis of snowball Earth hysteresis experiment: Efficiency, entropy production and irreversibility
No full textWe present an extensive thermodynamic analysis of a hysteresis experiment performed on a simplified yet Earth-like climate model. We slowly vary the solar constant by 20% around the present value and detect that for a large range of values of the solar constant the realization of snowball or of regular climate conditions depends on the history of the system. Using recent results on the global climate thermodynamics, we show that the two regimes feature radically different properties. The efficiency of the climate machine monotonically increases with decreasing solar constant in present climate conditions, whereas the opposite takes place in snowball conditions. Instead, entropy production is monotonically increasing with the solar constant in both branches of climate conditions, and its value is about four times larger in the warm branch than in the corresponding cold state. Finally, the degree of irreversibility of the system, measured as the fraction of excess entropy production due to irreversible heat transport processes, is much higher in the warm climate conditions, with an explosive growth in the upper range of the considered values of solar constants. Whereas in the cold climate regime a dominating role is played by changes in the meridional albedo contrast, in the warm climate regime changes in the intensity of latent heat fluxes are crucial for determining the observed properties. This substantiates the importance of addressing correctly the variations of the hydrological cycle in a changing climate. An interpretation of the climate transitions at the tipping points based upon macro-scale thermodynamic properties is also proposed. Our results support the adoption of a new generation of diagnostic tools based on the second law of thermodynamics for auditing climate models and outline a set of parametrizations to be used in conceptual and intermediate-complexity models or for the reconstruction of the past climate conditions. Copyright © 2010 Royal Meteorological Societ
On non-linear baroclinic adjustment with the stratosphere
No full textThe effect of the stratosphere on the baroclinic adjustment of a non-
linear Eady model is presented. The classical linear Eady model has been modified
by including an additional layer (the stratosphere), Ekman dissipation at the bottom
boundary and a Newtonian cooling at the surface and the tropopause, respectively;
non-linearity is introduced by wave-mean flow interaction for a single eddy mode.
Results for the rigid-lid case and for small troposphere/stratosphere stratification
ratio are compared with those for the linear Eady model with Ekman dissipation
at the surface. For these cases model solutions consist of a steady zonal correction
and an eddy field with a travelling constant amplitude wave. The equilibrated field,
as a function of small stratification ratio, shows that the minimum amplitude of
the eddy component raises to a height close to the tropopause (its steering level),
denoting that the wave solution becomes vertical evanescent. When realistic values
for the static stability in the stratosphere are considered, the zonal correction is
no more time independent and reveals a degree of chaotic behaviour, while the
eddy field is fully chaotic. Effects of changes in the zonal wind vertical shear and
a further decreasing static stability in the stratosphere are also analysed. Results
suggest that the minimum amplitude is, in average, higher than the one computed
for the classical rigid lid with Ekman dissipation at the surface. Thus, as in the
linear Eady model, the stratosphere induces a stabilising effect on the baroclinic
dynamics. Finally, the model solutions are compared with the time behaviour of a
simplified General Circulation Model
Transient chaotic mixing during a baroclinic life cycle
No full textWe discuss how atmospheric eddies affect transport and mixing of tracers
at midlatitudes. To this purpose, we study baroclinic life cycles in a
simple dynamical model of the atmosphere. We consider the trapping
properties of the developing eddies and the characteristics of
meridional transport, and we identify regions of increased mixing.
Although the flow is in principle three-dimensional, we illustrate how
some of the concepts developed in the study of two-dimensional chaotic
advection provide useful information on tracer dynamics in more
complicated flows. (C) 2000 American Institute of Physics.
{[}S1054-1500(00)02401-0]
Lagrangian tracer homogenization and dispersion in a simplified atmospheric GCM
No full textLagrangian transport in the atmosphere is numerically studied by using a simplified general circulation model (SGCM) with Newtonian cooling and Rayleigh friction.
Long-term Lagrangian behaviour is analyzed by determining
hemispheric and global homogenization times and by studying the time evolution of tracer distributions. At short times, the properties of absolute dispersion are considered. The tracer dynamics reveals the presence of transport barriers
associated with slow inter-hemispheric and
troposphere-stratosphere exchanges, and with a slow crossing of the boundary between the Ferrel and Hadley cells
Tropospheric double jets, meridional cells, and eddies: A case study and idealized simulations
No full textThe observed low-frequency variability of the zonally averaged atmospheric circulation in the winter hemisphere is found to be amenable to an interpretation where the subtropical jet is flanked by a secondary midlatitude one. Observations also suggest that the link between the stratosphere and the troposphere modulates the variability of the tropospheric double-jet structure. Moreover, the summer hemisphere is characterized by a strong midlatitude jet sided by an intermittent subtropical one and easterly winds in the stratosphere. This work addresses the question about the role of eddies in generating and maintaining these key features of the general circulation by means of a simplified general circulation model. Model solutions for different parameter settings and external radiative forcings in the stratosphere are studied with and without eddies active on the system. The following main findings are noted. 1) Eddy dynamics alone, through the baroclinic instability processes in an atmosphere subjected to radiative forcing and dissipation, may account for the observed meridional variance of the tropospheric jets. 2) The Hadley cell can extend to the pole overlying the Ferrel cell, a feature supported by observations in the summer hemisphere. 3) The meridional temperature gradient reversal in the summer stratosphere contributes to the observed low-frequency variability introducing an intermittent formation of a subtropical jet and the occurrence of easterlies in the tropical stratosphere. 4) Poleward propagation of the zonal wind anomaly is, when it occurs, related to the activity of synoptic eddies
Non-exponential return time distributions for vorticity extremes explained by fractional Poisson processes
No full textSerial correlation of extreme midlatitude cyclones observed at the storm track exits is explained by deviations from a Poisson process. To model these deviations, we apply fractional Poisson processes (FPPs) to extreme midlatitude cyclones, which are defined by the 850 hPa relative vorticity of the ERA interim reanalysis during boreal winter (DJF) and summer (JJA) seasons. Extremes are defined by a 99% quantile threshold in the grid-point time series. In general, FPPs are based on long-term memory and lead to non-exponential return time distributions. The return times are described by a Weibull distribution to approximate the Mittag–Leffler function in the FPPs. The Weibull shape parameter yields a dispersion parameter that agrees with results found for midlatitude cyclones. The memory of the FPP, which is determined by detrended fluctuation analysis, provides an independent estimate for the shape parameter. Thus, the analysis exhibits a concise framework of the deviation from Poisson statistics (by a dispersion parameter), non-exponential return times and memory (correlation) on the basis of a single parameter. The results have potential implications for the predictability of extreme cyclones
[CODE] maureenjcohen/ExoPlaSim: New haze optical data and tutorial
No full textThe PlaSim 3D general climate model, extended for terrestrial planets. This model contains the PlaSim GCM, as well as all necessary modifications to run tidally-locked planets, planets with substantially different surface pressures than Earth, planets orbiting stars with different effective temperatures, super-Earths, and more. This model also includes the ability to compute carbon-silicate weathering, dynamic orography through the glacier module (though only accumulation and ablation/evaporation/melting are included; glacial flow and spreading are not), and storm climatology. Future features will include support for multiple celestial light sources (e.g. for a habitable moon orbiting a Jovian planet, or circumbinary planets), coupling with N-body integrators such as REBOUND, and CO2 condensation. This release includes photochemical haze/dust transport and radiative transfer. Transport and radiative transfer schemes are described in "Haze optical depth in exoplanet atmospheres varies with rotation rate: Implications for observations," Cohen et al. (2024). Includes optical haze constants with corrected backscattering efficiencies, calculated based on data provided in He et al. 2023 and Corrales et al. 2023 for the stellar spectra of TRAPPIST-1 and Wolf 1061. A tutorial has been added demonstrating how to use the aerosol module, including references to the data sources.Cohen, M., Paradise, A., Borth, H., Lunkeit, F., & Kirk, E. (2023). maureenjcohen/ExoPlaSim: New haze optical data and tutorial (v3.2.3). Zenodo. https://doi.org/10.5281/zenodo.1027823
Stable Equatorial Ice Belts at High Obliquity in a Coupled Atmosphere-Ocean Model
No full textVarious climate states at high obliquity are realized for a range of stellar irradiance using a dynamical atmosphere-ocean-sea ice climate model in an Aquaplanet configuration. Three stable climate states are obtained that differ in the extent of the sea ice cover. For low values of irradiance the model simulates a Cryoplanet that has a perennial global sea ice cover. By increasing stellar irradiance, transitions occur to an Uncapped Cryoplanet with a perennial equatorial sea ice belt, and eventually to an Aquaplanet with no ice. Using an emulator model we find that the Uncapped Cryoplanet is a robust stable state for a range of irradiance and high obliquities and contrast earlier results that high-obliquity climate states with an equatorial ice belt may be unsustainable or unachievable. When the meridional ocean heat flux is strengthened, the parameter range permitting a stable Uncapped Cryoplanet decreases due to melting of equatorial sea ice. Beyond a critical threshold of meridional ocean heat flux, the perennial equatorial ice belt disappears. Therefore, a vigorous ocean circulation may render it unstable. Our results suggest that perennial equatorial ice cover is a viable climate state of a high-obliquity exoplanet. However, due to multiple equilibria, this state is only reached from more glaciated conditions, and not from less glaciated conditions. © 2018. The American Astronomical Society
Simulation der interannualen Variabilitaet mit einem globalen gekoppelten Atmosphaere-Ozean Modell
No full textAvailable from TIB Hannover: RR 1857(8) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
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