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Joseph E Borovsky - One of the best experts on this subject based on the ideXlab platform.
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no evidence for the localized heating of solar wind protons at intense velocity shear zones
Journal of Geophysical Research, 2014Co-Authors: Joseph E Borovsky, J T SteinbergAbstract:Using measurements from the Wind spacecraft at 1 AU, the heating of protons in the solar wind at locations of intense velocity shear is examined. The 4321 sites of intense shear in fast coronal hole origin plasma are analyzed. The proton temperature, the proton Specific Entropy, and the proton number density at the locations of the shears are compared with the same quantities in the plasmas adjacent to the shears. A very slight but statistically significant enhancement of the proton temperature is seen at the sites of the shears, but it is accompanied by a larger enhancement of the proton number density at the sites of the shears. Consequently, there is no enhancement of the proton Specific Entropy at the shear sites, indicating no production of Entropy; hence, no evidence for plasma heating is found at the sites of the velocity shears. Since the shearing velocities have appreciable Mach numbers, the authors suggest that there can be a slight adiabatic compression of the plasma at the shear zones.
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the velocity and magnetic field fluctuations of the solar wind at 1 au statistical analysis of fourier spectra and correlations with plasma properties
Journal of Geophysical Research, 2012Co-Authors: Joseph E BorovskyAbstract:[1] Ten years of ACE plasma and magnetic field measurements are divided into 20,076 subintervals that are 4.55 h long. Each subinterval is Fourier analyzed resulting in a statistical ensemble of 20,076 realizations of the solar wind and its “turbulence.” Oxygen charge-state ratios are used to categorize each subinterval as coronal-hole-origin plasma, non-coronal-hole-origin plasma, or ejecta. A number of known properties of the solar wind v and B fluctuations are statistically confirmed and new informatin as functions of the type of plasma is obtained. For the fluctuations it is found that the coronal-hole-origin versus non-coronal-hole-origin classification is more fundamental than a fast-wind versus slow-wind classification. In the frequency range 4.3 × 10−4–1.9 × 10−3 Hz, the ensemble the mean spectral indices of the magnetic field, velocity, and total energy are −1.62, −1.41, and −1.52, however the spectral indices vary with changes in the type of plasma. The number of strong current sheets in each subinterval is recorded. The fluctuation amplitudes, Alfven ratios, and outward-inward Elsasser ratios are all strongly correlated with the properties of the plasma and the density of current sheets. Regions wherein the fluctuation spectra are shallowest correspond to coronal-hole plasma; regions wherein the spectra are steepest correspond to non-coronal-hole plasma and ejecta. The autocorrelation times for the spectral indices and amplitudes are 20–30 h, similar to the autocorrelation times for the proton Specific Entropy, the carbon charge-state ratio, the density of strong current sheets, and the classification of plasma. Analysis is performed to interpret ensembles of spectra with variance error.
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Entropy mapping of the outer electron radiation belt between the magnetotail and geosynchronous orbit
Journal of Geophysical Research, 2011Co-Authors: Joseph E Borovsky, T E CaytonAbstract:[1] The Specific Entropy (Entropy density) S is examined for the outer electron radiation belt at geosynchronous orbit and for the energetic electron population in the Earth's magnetotail. The outer electron radiation belt is measured with the SOPA detectors on board six geosynchronous satellites and the energetic electrons of the magnetotail are measured with instrumentation on board 12 Global Positioning Satellites (GPS) with a magnetic field model used to map the GPS orbit to the magnetotail. Density n and temperature T values are determined from relativistic Maxwellian fits to the electron measurements, enabling the Specific Entropy S to be calculated. For low temperatures the nonrelativstic Specific Entropy is S = T/n2/3; for a relativistic Maxwellian distribution a relativistically correct expression for S = S(T,n) is derived and used. The outer electron radiation belt at geosynchronous orbit local midnight (n ∼ 3 × 10−4 cm−3 and T ∼ 140 keV) and the energetic-electron population in the magnetotail (n ∼ 1 × 10−4 cm−3 and T ∼ 50 keV) statistically have the same Specific Entropy. Hence the two populations are probably the same. This implies adiabatic transport (1) from the magnetotail to the dipole (where the magnetotail electrons are the source of the outer electron radiation belt) or (2) from the dipole to the magnetotail (where the magnetotail electrons are leakage from the radiation belt).
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on the heating of the outer radiation belt to produce high fluxes of relativistic electrons measured heating rates at geosynchronous orbit for high speed stream driven storms
Journal of Geophysical Research, 2010Co-Authors: Joseph E Borovsky, M H DentonAbstract:[1] The heating rate of the outer electron radiation belt at geosynchronous orbit is determined for the interval from 36 to 72 h after the onset of high-speed stream-driven storms. Multisatellite measurements of the radiation belt temperature are used for 93 high-speed stream-driven storms. During the storms, the outer electron radiation belt temperature changes from ∼120 keV to ∼190 keV. The average heating rate of 32 keV d−1 is obtained. The heating rate during the storms is found to be positively correlated with the solar wind velocity and with the Kp index of geomagnetic activity and to be negatively correlated with the solar wind number density. When the solar wind velocity is held fixed, the correlation of the heating rate with Kp vanishes. Expressions for the change in the heating rate as function of the solar wind speed, the solar wind density, and the Kp index are fit to the data. The heating rate is uncorrelated with the amplitude of magnetic field fluctuations in the magnetosphere. Correlations between the heating rate and the level of velocity, density, and magnetic field fluctuations in the magnetosphere and in the solar wind are weaker than the correlations of the heating rate with the solar wind velocity and density. The heating rates correspond to a kinetic energy density change of 3.6 × 10−11 erg cm−3 d−1 at geosynchronous orbit, to a Specific Entropy change of 4.1 × 106 eV cm2 d−1 at geosynchronous orbit, and to a total heating rate of the geosynchronous orbit region of 5.3 × 106 Watts.
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electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere the calm before the storm
Journal of Geophysical Research, 2009Co-Authors: Joseph E Borovsky, M H DentonAbstract:Measurements from seven spacecraft in geosynchronous orbit are analyzed to determine the decay rate of the number density of the outer electron radiation belt prior to the onset of high-speed-stream-driven geomagnetic storms. Superposed-data analysis is used with a collection of 124 storms. When there is a calm before the storm, the electron number density decays exponentially before the storm with a 3.4-day e-folding time: beginning about 4 days before storm onset, the density decreases from ∼4 × 10−4 cm−3 to ∼1 × 10−4 cm−3. When there is not a calm before the storm, the number density decay is very small. The decay in the number density of radiation belt electrons is believed to be caused by pitch angle scattering of electrons into the atmospheric loss cone as the outer plasmasphere fills during the calms. This is confirmed by separately measuring the density decay rate for times when the outer plasmasphere is present or absent. While the radiation belt electron density decreases, the temperature of the electron radiation belt holds approximately constant, indicating that the electron precipitation occurs equally at all energies. Along with the number density decay, the pressure of the outer electron radiation belt decays, and the Specific Entropy increases. From the measured decay rates, the electron flux to the atmosphere is calculated, and that flux is 3 orders of magnitude less than thermal fluxes in the magnetosphere, indicating that the radiation belt pitch angle scattering is 3 orders weaker than strong diffusion. Energy fluxes into the atmosphere are calculated and found to be insufficient to produce visible airglow.
M H Denton - One of the best experts on this subject based on the ideXlab platform.
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on the heating of the outer radiation belt to produce high fluxes of relativistic electrons measured heating rates at geosynchronous orbit for high speed stream driven storms
Journal of Geophysical Research, 2010Co-Authors: Joseph E Borovsky, M H DentonAbstract:[1] The heating rate of the outer electron radiation belt at geosynchronous orbit is determined for the interval from 36 to 72 h after the onset of high-speed stream-driven storms. Multisatellite measurements of the radiation belt temperature are used for 93 high-speed stream-driven storms. During the storms, the outer electron radiation belt temperature changes from ∼120 keV to ∼190 keV. The average heating rate of 32 keV d−1 is obtained. The heating rate during the storms is found to be positively correlated with the solar wind velocity and with the Kp index of geomagnetic activity and to be negatively correlated with the solar wind number density. When the solar wind velocity is held fixed, the correlation of the heating rate with Kp vanishes. Expressions for the change in the heating rate as function of the solar wind speed, the solar wind density, and the Kp index are fit to the data. The heating rate is uncorrelated with the amplitude of magnetic field fluctuations in the magnetosphere. Correlations between the heating rate and the level of velocity, density, and magnetic field fluctuations in the magnetosphere and in the solar wind are weaker than the correlations of the heating rate with the solar wind velocity and density. The heating rates correspond to a kinetic energy density change of 3.6 × 10−11 erg cm−3 d−1 at geosynchronous orbit, to a Specific Entropy change of 4.1 × 106 eV cm2 d−1 at geosynchronous orbit, and to a total heating rate of the geosynchronous orbit region of 5.3 × 106 Watts.
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electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere the calm before the storm
Journal of Geophysical Research, 2009Co-Authors: Joseph E Borovsky, M H DentonAbstract:Measurements from seven spacecraft in geosynchronous orbit are analyzed to determine the decay rate of the number density of the outer electron radiation belt prior to the onset of high-speed-stream-driven geomagnetic storms. Superposed-data analysis is used with a collection of 124 storms. When there is a calm before the storm, the electron number density decays exponentially before the storm with a 3.4-day e-folding time: beginning about 4 days before storm onset, the density decreases from ∼4 × 10−4 cm−3 to ∼1 × 10−4 cm−3. When there is not a calm before the storm, the number density decay is very small. The decay in the number density of radiation belt electrons is believed to be caused by pitch angle scattering of electrons into the atmospheric loss cone as the outer plasmasphere fills during the calms. This is confirmed by separately measuring the density decay rate for times when the outer plasmasphere is present or absent. While the radiation belt electron density decreases, the temperature of the electron radiation belt holds approximately constant, indicating that the electron precipitation occurs equally at all energies. Along with the number density decay, the pressure of the outer electron radiation belt decays, and the Specific Entropy increases. From the measured decay rates, the electron flux to the atmosphere is calculated, and that flux is 3 orders of magnitude less than thermal fluxes in the magnetosphere, indicating that the radiation belt pitch angle scattering is 3 orders weaker than strong diffusion. Energy fluxes into the atmosphere are calculated and found to be insufficient to produce visible airglow.
Pascal Marquet - One of the best experts on this subject based on the ideXlab platform.
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on the definition of a moist air potential vorticity
arXiv: Atmospheric and Oceanic Physics, 2014Co-Authors: Pascal MarquetAbstract:A new potential vorticity is derived by using a Specific Entropy formulation expressed in terms of a moist-air Entropy potential temperature. The new formulation is compared with Ertel's version and with others based on virtual and equivalent potential temperatures. The new potential vorticity is subject to conservative properties ensured by the Second Law applied to the moist-air material derivatives. It is shown that the upper tropospheric and stratospheric (dry) structures are nearly the same as those obtained with Ertel's component. Moreover, new structures are observed in the low troposphere, with negative values associated with moist frontal regions. The negative values are observed in the frontal regions where slantwise convection instabilities may take place, but they are smaller than those observed with the equivalent potential vorticity. The main purpose of the article is to diagnose the behaviour of the new potential vorticity from numerical output generated by the ARPEGE NWP model, with the help of isobaric charts and vertical cross-sections. Two inversion methods are suggested. The first method could be based on the invertibility principle verified by the virtual potential vorticity, with a possibility to control and modify separately potential vorticity components in the (dry) upper and (moist) lower atmospheric levels. The other method may consist of an inversion process directly applied to the new moist-air Entropy potential vorticity, because the negative values and the solenoidal term are smaller than those observed with equivalent potential vorticity, as shown by numerical evaluations.
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on the definition of a moist air potential vorticity
arXiv: Atmospheric and Oceanic Physics, 2014Co-Authors: Pascal MarquetAbstract:A new potential vorticity is derived by using a Specific Entropy formulation expressed in terms of a moist-air Entropy potential temperature. The new formulation is compared with Ertel's version and with others based on virtual and equivalent potential temperatures. The new potential vorticity is subject to conservative properties ensured by the Second Law applied to the moist-air material derivatives. It is shown that the upper tropospheric and stratospheric (dry) structures are nearly the same as those obtained with Ertel's component. Moreover, new structures are observed in the low troposphere, with negative values associated with moist frontal regions. The negative values are observed in the frontal regions where slantwise convection instabilities may take place, but they are smaller than those observed with the equivalent potential vorticity. The main purpose of the article is to diagnose the behaviour of the new potential vorticity from numerical output generated by the ARPEGE NWP model, with the help of isobaric charts and vertical cross-sections. Two inversion methods are suggested. The first method could be based on the invertibility principle verified by the virtual potential vorticity, with a possibility to control and modify separately potential vorticity components in the (dry) upper and (moist) lower atmospheric levels. The other method may consist of an inversion process directly applied to the new moist-air Entropy potential vorticity, because the negative values and the solenoidal term are smaller than those observed with equivalent potential vorticity, as shown by numerical evaluations.
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definition of a moist Entropy potential temperature application to fire i data flights
Quarterly Journal of the Royal Meteorological Society, 2011Co-Authors: Pascal MarquetAbstract:A moist Entropy potential temperature–denoted by θs–is defined analytically in terms of the Specific Entropy for moist air. The expression for θs is valid for a general mixing of dry air, water vapour and possible condensed water species. It displays the same conservative properties as the moist Entropy, even for varying dry air or total water content. The moist formulation for θs is equal to the dry formulation θ if dry air is considered, and it displays new properties valid for the moist air cases, both saturated or unsaturated ones. Exact and approximate versions of θs are evaluated for several stratocumulus cases, in particular by using the aircraft observation datasets from the FIRE-I experiment. It appears that there is no (or only a small) jump in θs at the top of the planetary boundary layer (PBL). The mixing in moist Entropy is almost complete in the PBL, with the same values observed in the clear air and the cloudy regions, including the very top of the entrainment region. The Randall–Deardorff Cloud-Top Entrainment Instability analysis may be interpreted as a mixing in moist Entropy criterion. The iso-θs lines are plotted on skew T–log p and conserved variable diagrams. All these properties could suggest some hints on the use of moist Entropy (or θs) in cloud modelling or in mixing processes, with the marine stratocumulus considered as a paradigm of moist turbulence. Copyright © 2011 Royal Meteorological Society
D Gerbal - One of the best experts on this subject based on the ideXlab platform.
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energy Entropy and mass scaling relations for elliptical galaxies towards a physical understanding of their photometric properties
Astronomy and Astrophysics, 2001Co-Authors: I Marquez, G Lima B Neto, D Gerbal, H V Capelato, F Durret, B LanzoniAbstract:In the present paper, we show that elliptical galaxies (Es) obey a scaling relation between potential energy and mass. Since they are relaxed systems in a post violent-relaxation stage, they are quasi-equilibrium gravitational systems and therefore they also have a quasi-constant Specific Entropy. Assuming that light traces mass, these two laws imply that in the space defined by the three S\\ersic law parameters (intensity Sigma_0, scale a and shape nu), elliptical galaxies are distributed on two intersecting 2-manifolds: the Entropic Surface and the Energy-Mass Surface. Using a sample of 132 galaxies belonging to three nearby clusters, we have verified that ellipticals indeed follow these laws. This also implies that they are distributed along the intersection line (the Energy-Entropy line), thus they constitute a one-parameter family. These two physical laws (separately or combined), allow to find the theoretical origin of several observed photometrical relations, such as the correlation between absolute magnitude and effective surface brightness, and the fact that ellipticals are located on a surface in the [log R_eff, -2.5 log Sigma_0, log nu] space. The fact that elliptical galaxies are a one-parameter family has important implications for cosmology and galaxy formation and evolution models. Moreover, the Energy-Entropy line could be used as a distance indicator.
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the Specific Entropy of elliptical galaxies an explanation for profile shape distance indicators
Monthly Notices of the Royal Astronomical Society, 1999Co-Authors: G Lima B Neto, D Gerbal, I MarquezAbstract:Dynamical systems in equilibrium have a stationary Entropy; we suggest that ellipti- cal galaxies, as stellar systems in a stage of quasi-equilibrium, may have in principle a unique Specific Entropy. This uniqueness, a priori unknown, should be reflected in correlations between the fundamental parameters describing the mass (light) distribu- tion in galaxies. Following recent photometrical work on elliptical galaxies (Caon et al. 1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to describe the light profile and an analytical approximation to its three dimensional de- projection. The Specific Entropy is then calculated supposing that the galaxy behaves as a spherical, isotropic, one-component system in hydrostatic equilibrium, obeying the ideal gas state equations. We predict a relation between the 3 parameters of the Sersic law linked to the Specific Entropy, defining a surface in the parameter space, an 'Entropic Plane', by analogy with the well-known Fundamental Plane. We have analysed elliptical galaxies in two rich clusters of galaxies (Coma and ABCG 85) and a group of galaxies (associated with NGC 4839, near Coma). We show that, for a given cluster, the galaxies follow closely a relation predicted by the constant Specific Entropy hypothesis with a typical dispersion (one standard deviation) of 9.5% around the mean value of the Specific Entropy. Moreover, assuming that the Specific Entropy is also the same for galaxies of different clusters, we are able to derive relative distances between Coma, ABGC 85, and the group of NGC 4839. If the errors are only due to the determination of the Specific Entropy (about 10%), then the error in the relative distance determination should be less than 20% for rich clusters. We suggest that the unique Specific Entropy may provide a physical explanation for the distance indicators based on the Sersic profile put forward by Young & Currie (1994, 1995) and recently discussed by Binggeli & Jerjen (1998).
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the Specific Entropy of elliptical galaxies an explanation for profile shape distance indicators
arXiv: Astrophysics, 1999Co-Authors: Gastao Lima B Neto, D Gerbal, I MarquezAbstract:Dynamical systems in equilibrium have a stationary Entropy; we suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a unique Specific Entropy. This uniqueness, a priori unknown, should be reflected in correlations between the parameters describing the mass (light) distribution in galaxies. Following recent photometrical work (Caon et al. 1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to describe the light profile of elliptical galaxies and an analytical approximation to its three dimensional deprojection. The Specific Entropy is calculated supposing that the galaxy behaves as a spherical, isotropic, one-component system in hydrostatic equilibrium, obeying the ideal gas state equations. We predict a relation between the 3 parameters of the Sersic, defining a surface in the parameter space, an `Entropic Plane', by analogy with the well-known Fundamental Plane. We have analysed elliptical galaxies in Coma and ABCG 85 clusters and a group of galaxies (associated with NGC 4839). We show that the galaxies in clusters follow closely a relation predicted by the constant Specific Entropy hypothesis with a one-sigma dispersion of 9.5% around the mean value of the Specific Entropy. Assuming that the Specific Entropy is also the same for galaxies of different clusters, we are able to derive relative distances between the studied clusters. If the errors are only due to the determination of the Specific Entropy (about 10%), then the error in the relative distance determination should be less than 20% for rich clusters. We suggest that the unique Specific Entropy may provide a physical explanation for the distance indicators based on the Sersic profile put forward by Young & Currie (1994, 1995) and discussed by Binggeli & Jerjen (1998).
Pierre Demarque - One of the best experts on this subject based on the ideXlab platform.
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stellar evolution models with Entropy calibrated mixing length parameter application to red giants
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: F Spada, Pierre Demarque, F KupkaAbstract:We present evolutionary models for solar-like stars with an improved treatment of convection that results in a more accurate estimate of the radius and effective temperature. This is achieved by improving the calibration of the mixing-length parameter, which sets the length scale in the 1D convection model implemented in the stellar evolution code. Our calibration relies on the results of 2D and 3D radiation hydrodynamics simulations of convection to specify the value of the adiabatic Specific Entropy at the bottom of the convective envelope in stars as a function of their effective temperature, surface gravity and metallicity. For the first time, this calibration is fully integrated within the flow of a stellar evolution code, with the mixing-length parameter being continuously updated at run-time. This approach replaces the more common, but questionable, procedure of calibrating the length scale parameter on the Sun, and then applying the solar-calibrated value in modeling other stars, regardless of their mass, composition and evolutionary status. The internal consistency of our current implementation makes it suitable for application to evolved stars, in particular to red giants. We show that the Entropy calibrated models yield a revised position of the red giant branch that is in better agreement with observational constraints than that of standard models.
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testing the Entropy calibration of the radii of cool stars models of α centauri a and b
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: F Spada, Pierre DemarqueAbstract:We present models of alpha Centauri A and B implementing an Entropy calibration of the mixing-length parameter alpha_MLT, recently developed and successfully applied to the Sun (Spada et al. 2018, ApJ, 869, 135). In this technique the value of alpha_MLT in the 1D stellar evolution code is calibrated to match the adiabatic Specific Entropy derived from 3D radiation-hydrodynamics simulations of stellar convective envelopes, whose effective temperature, surface gravity, and metallicity are selected consistently along the evolutionary track. The customary treatment of convection in stellar evolution models relies on a constant, solar-calibrated alpha_MLT. There is, however, mounting evidence that this procedure does not reproduce the observed radii of cool stars satisfactorily. For instance, modelling alpha Cen A and B requires an ad-hoc tuning of alpha_MLT to distinct, non-solar values. The Entropy-calibrated models of alpha Cen A and B reproduce their observed radii within 1% (or better) without externally adjusted parameters. The fit is of comparable quality to that of models with freely adjusted alpha_MLT for alpha Cen B (within 1 sigma), while it is less satisfactory for alpha Cen A (within ~ 2.5 sigma). This level of accuracy is consistent with the intrinsic uncertainties of the method. Our results demonstrate the capability of the Entropy calibration method to produce stellar models with radii accurate within 1%. This is especially relevant in characterising exoplanet-host stars and their planetary systems accurately.
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improved calibration of the radii of cool stars based on 3d simulations of convection implications for the solar model
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: F Spada, Pierre Demarque, Sarbani Basu, Joel D TannerAbstract:Main sequence, solar-like stars (M < 1.5 Msun) have outer convective envelopes that are sufficiently thick to affect significantly their overall structure. The radii of these stars, in particular, are sensitive to the details of inefficient, super-adiabatic convection occurring in their outermost layers. The standard treatment of convection in stellar evolution models, based on the Mixing-Length Theory (MLT), provides only a very approximate description of convection in the super-adiabatic regime. Moreover, it contains a free parameter, alpha_MLT, whose standard calibration is based on the Sun, and is routinely applied to other stars ignoring the differences in their global parameters (e.g., effective temperature, gravity, chemical composition) and previous evolutionary history. In this paper, we present a calibration of alpha_MLT based on three-dimensional radiation-hydrodynamics (3D RHD) simulations of convection. The value of alpha_MLT is adjusted to match the Specific Entropy in the deep, adiabatic layers of the convective envelope to the corresponding value obtained from the 3D RHD simulations, as a function of the position of the star in the (log g, log T_eff) plane and its chemical composition. We have constructed a model of the present-day Sun using such Entropy-based calibration. We find that its past luminosity evolution is not affected by the Entropy calibration. The predicted solar radius, however, exceeds that of the standard model during the past several billion years, resulting in a lower surface temperature. This illustrative calculation also demonstrates the viability of the Entropy approach for calibrating the radii of other late-type stars.
