The Experts below are selected from a list of 97395 Experts worldwide ranked by ideXlab platform
M Lopezpuertas - One of the best experts on this subject based on the ideXlab platform.
-
radiation transfer in the atmosphere non local Thermodynamic Equilibrium
Reference Module in Earth Systems and Environmental Sciences#R##N#Encyclopedia of Atmospheric Sciences (Second Edition), 2015Co-Authors: M Lopezpuertas, B FunkeAbstract:This article introduces the concept of non-local Thermodynamic Equilibrium (non-LTE) in planetary atmospheres and provides a basic theoretical framework of non-LTE radiative transfer and statistical Equilibrium of molecular states. Accurate and approximate solutions of the non-LTE problem are discussed. A climatology of non-LTE populations of the most important vibrational levels of the atmospheric species is provided. Examples of non-LTE applications in general circulation models and the remote sensing of the Earth's and other planetary atmospheres are given.
-
evidence for n2o ν3 4 5 μm non local Thermodynamic Equilibrium emission in the atmosphere
Geophysical Research Letters, 2007Co-Authors: M Lopezpuertas, T. Von Clarmann, B Funke, Udo Grabowski, G. P. Stiller, D Bermejopantaleon, M HopfnerAbstract:[1] We present a clear evidence for N2O 4.5 μm non-local Thermodynamic Equilibrium (non-LTE) emissions in the daylight stratosphere and mesosphere from measurements by the MIPAS experiment on board Envisat. We have used non-LTE radiative transfer models in order to quantify the magnitude and extent of the non-LTE deviation of N2O(001) in the Earth's atmosphere. The departure from LTE in N2O during daytime commences at altitudes around 40–50 km, but have significant effects (10%) on daytime limb radiance down to tangent heights of 20 km. The enhancement increases rapidly with altitude, being 20–80% at 50 km, and reaching factors of 2–8 in the lower mesosphere. This study shows that the enhancement is mainly produced by absorption of solar radiation by N2O at 4.5 μm and by V-V collisions with N2(1). Non-LTE effects are also significant at nighttime, where LTE calculations overpredict N2O radiances by 10–20% at 40–55 km tangent heights.
-
evidence for ch4 7 6 μm non local Thermodynamic Equilibrium emission in the mesosphere
Geophysical Research Letters, 2005Co-Authors: M Lopezpuertas, T. Von Clarmann, B Funke, Maria-elissavet Koukouli, Norbert Glatthor, Udo Grabowski, Sergio Gillopez, G. P. StillerAbstract:[1] We present unequivocal evidence for CH4 7.6 μm non-local Thermodynamic Equilibrium (non-LTE) mesospheric emissions as measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) experiment on board the ESA Envisat satellite. We have employed non-LTE radiative transfer models, already used and validated in studies of other atmospheric gases, in order to quantify the magnitude and extent of the CH4 non-LTE deviation in the Earth's atmosphere. The observed daytime enhancement signatures apparent in the measured radiances cannot be attributed to enhanced daytime temperatures and/or CH4 abundance variations and are reproduced successfully with a dedicated CH4 non-LTE radiative transfer model. We conclude that, depending on the upper stratospheric/mesospheric temperature structure, the departure from LTE might commence at an altitude as low as 45 km, reaching limb radiance deviations of 20% at 60 km and quickly rising up to 60% at 70 km, for the 7.6 μm CH4 lines.
-
nonlocal Thermodynamic Equilibrium vibrational rotational and spin state distribution of no ν 0 1 2 under quiescent atmospheric conditions
Journal of Geophysical Research, 2000Co-Authors: B Funke, M LopezpuertasAbstract:A nonlocal Thermodynamic Equilibrium (non-LTE) model for the NO(ν ≤ 2, J, S) state distributions for altitudes from ground to 200 km for nonauroral conditions is presented. The model includes (1) vibrational excitation due to collisions of NO with O and O2, (2) excitation due to photolysis of NO2 and due to NO2 + O→ NO + O2 in the stratosphere, and (3) excitation due to N(4S,2 D) +O2 → NO + O in the thermosphere. Spontaneous emission, induced emission, and absorption of tropospheric and solar radiation are included. Intravibrational spin and rotational relaxations are included by means of an exponential power gap law approach. This model improves upon previous work mainly through its completeness. It provides non-LTE distributions of the three spin, rotational, and vibrational degrees of freedom covering the whole atmosphere up to the upper thermosphere. All previous knowledge of non-LTE excitation processes of NO has been incorporated. The most important results of the model are (1) the stratospheric daytime vibrational distribution departs from local Thermodynamic Equilibrium (LTE) due to NO(ν≥1) production by NO2 photolysis; (2) the rotational and spin distributions of the NO(ν = 1, 2) are in non-LTE above ∼110 km; (3) a 90% propensity to conserve the spin orbit state in intravibrational NO+O collisional relaxation was determined by comparison of the model results to cryogenic infrared radiance for shuttle (CIRRIS-1A) data. The implications of the non-LTE model results to remote sensing of stratospheric NO abundances from spectrally resolved 5.3 μm limb radiances are discussed. The neglect of thermospheric rotational/spin non-LTE as well as the neglect of NO(ν>1) production by NO2 photolysis map into errors in the modeled spectra of 20–25%.
-
non local Thermodynamic Equilibrium in general circulation models of the martian atmosphere 1 effects of the local Thermodynamic Equilibrium approximation on thermal cooling and solar heating
Journal of Geophysical Research, 1998Co-Authors: M A Lopezvalverde, M Lopezpuertas, D P Edwards, Cristina RoldánAbstract:Calculations of CO2 thermal cooling and near-IR solar heating rates under non-local Thermodynamic Equilibrium (non-LTE) situations have been performed to understand and evaluate the effects of non-LTE on the energy balance of the upper atmosphere of Mars. We find that the 15-μm cooling rates can be in error if LTE is assumed above 80 km. In general, the correct non-LTE values are significantly smaller than the LTE values above about 85 km, but the magnitude and sign of the error depend on the temperature structure and the top altitude of the model and, to a lesser extent, on the collisions with atomic oxygen. A detailed analysis of the relevance of the upper boundary layer and a suggested buffer region are presented for both LTE and non-LTE. Based on general considerations of the thermal profile in the mesosphere and lower thermosphere, recommendations for general circulation models (GCM) are presented as a first guide for minimizing the LTE cooling rates inaccuracies. The error of assuming LTE on the CO2 near-IR solar heating rates is found to be about 20% at 85 km and increases strongly above this altitude. The dependences of this LTE-non-LTE difference on rate coefficients, thermal structure, surface pressure, and solar zenith angle (SZA) are studied. In contrast to the large effect of the SZA on the solar heating rate, we find it is not important for the LTE-non-LTE relative difference, which permits a simple tabulation of the non-LTE effect as a function of pressure only. A table of LTE correction factors for the solar heating rate is included for its potential use as a fast yet accurate operative scheme within GCMs.
E Caffau - One of the best experts on this subject based on the ideXlab platform.
-
barium abundance in red giants of ngc 6752 non local Thermodynamic Equilibrium and three dimensional effects
Astronomy and Astrophysics, 2012Co-Authors: V Dobrovolskas, A Kucinskas, S M Andrievsky, S A Korotin, T V Mishenina, P Bonifacio, H G Ludwig, E CaffauAbstract:Aims. We study the effects related to departures from non-local Thermodynamic Equilibrium (NLTE) and homogeneity in the atmospheres of red giant stars, to assess their influence on the fo rmation of Ba II lines. We estimate the impact of these effects on the barium abundance determinations for 20 red giants in Galactic globular cluster NGC 6752. Methods. One-dimensional (1D) local Thermodynamic Equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1DATLAS9 stellar model atmospheres. The three-dimensional (3D) LTE abundances were obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE abundances using 3D‐1D abundance corrections, i.e., the differences between the abundances obtained from the same spectral line using the 3D hydrodynamical and classical 1D stellar model atmospheres. The 3D‐1D abundance corrections were obtained in a strictly differential way using the 3D hydrodynamical and classical 1D codesCO 5 BOLD andLHD. Both codes utilized identical stellar atmospheric parameters, opacities, and equation of state. Results. The mean 1D barium-to-iron abundance ratios derived for 20 giants areh [Ba/Fe]i 1D LTE = 0.24± 0.05(stat.)± 0.08(sys.) and h [Ba/Fe]i 1D NLTE = 0.05± 0.06(stat.)± 0.08(sys.). The 3D‐1D abundance correction obtained for 8 giants is small (∼ +0.05 dex), thus leads to only minor adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for the 20 giants, h [Ba/Fe]i 3D+NLTE = 0.10± 0.06(stat.)± 0.10(sys.). The intrinsic abundance spread between the individual cluster stars is small and can be explained in terms of uncertainties in the abundance determinations. Conclusions. Deviations from LTE play an important role in the formation of barium lines in the atmospheres of red giants studied here. The role of 3D hydrodynamical effects should not be dismissed either, even if the obtained 3D‐1D abundance corrections are small. This result is a consequence of subtle fine-tuning of i ndividual contributions from horizontal temperature fluct uations and differences between the average temperature profiles in the 3D a nd 1D model atmospheres: owing to the comparable size and opposite sign, their contributions nearly cancel each other. This fin e-tuning is characteristic of the particular set of atmosph eric parameters and the element investigated, hence should not necessarily be a general property of spectral line formation in the atmosphe res of red giant stars.
-
barium abundance in red giants of ngc 6752 non local Thermodynamic Equilibrium and three dimensional effects
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: V Dobrovolskas, A Kucinskas, S M Andrievsky, S A Korotin, T V Mishenina, P Bonifacio, H G Ludwig, E CaffauAbstract:(Abridged) Aims: We study the effects related to departures from non-local Thermodynamic Equilibrium (NLTE) and homogeneity in the atmospheres of red giant stars in Galactic globular cluster NGC 6752, to assess their influence on the formation of Ba II lines. Methods: One-dimensional (1D) local Thermodynamic Equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D ATLAS stellar model atmospheres. The three-dimensional (3D) LTE abundances were obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE abundances using 3D-1D abundance corrections, i.e., the differences between the abundances obtained from the same spectral line using the 3D hydrodynamical (CO5BOLD) and classical 1D (LHD) stellar model atmospheres. Results: The mean 1D barium-to-iron abundance ratios derived for 20 giants are _{1D NLTE} = 0.05 \pm0.06 (stat.) \pm0.08 (sys.). The 3D-1D abundance correction obtained for 8 giants is small (~+0.05 dex), thus leads to only minor adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for the 20 giants, _{3D+NLTE} = 0.10 \pm0.06(stat.) \pm0.10(sys.). The intrinsic abundance spread between the individual cluster stars is small and can be explained in terms of uncertainties in the abundance determinations. Conclusions: Deviations from LTE play an important role in the formation of barium lines in the atmospheres of red giants studied here. The role of 3D hydrodynamical effects should not be dismissed either, even if the obtained 3D-1D abundance corrections are small. This result is a consequence of subtle fine-tuning of individual contributions from horizontal temperature fluctuations and differences between the average temperature profiles in the 3D and 1D model atmospheres: owing to the comparable size and opposite sign, their contributions nearly cancel each other.
F. Becattini - One of the best experts on this subject based on the ideXlab platform.
-
General Thermodynamic Equilibrium with axial chemical potential for the free Dirac field
Journal of High Energy Physics, 2018Co-Authors: M. Buzzegoli, F. BecattiniAbstract:We calculate the constitutive equations of the stress-energy tensor and the currents of the free massless Dirac field at Thermodynamic Equilibrium with acceleration and rotation and a conserved axial charge by using the density operator approach. We carry out an expansion in thermal vorticity to the second order with finite axial chemical potential μ _ A . The obtained coefficients of the expansion are expressed as correlators of angular momenta and boost operators with the currents. We confirm previous observations that the axial chemical potential induces non-vanishing components of the stress-energy tensor at first order in thermal vorticity due to breaking of parity invariance of the density operator with μ _ A ≠ 0. The appearance of these components might play an important role in chiral hydrodynamics.
-
general Thermodynamic Equilibrium with axial chemical potential for the free dirac field
arXiv: High Energy Physics - Theory, 2018Co-Authors: M. Buzzegoli, F. BecattiniAbstract:We calculate the constitutive equations of the stress-energy tensor and the currents of the free massless Dirac field at Thermodynamic Equilibrium with acceleration and rotation and a conserved axial charge by using the density operator approach. We carry out an expansion in thermal vorticity to the second order with finite axial chemical potential $\mu_A$. The obtained coefficients of the expansion are expressed as correlators of angular momenta and boost operators with the currents. We confirm previous observations that the axial chemical potential induces non-vanishing components of the stress-energy tensor at first order in thermal vorticity due to breaking of parity invariance of the density operator with $\mu_A \ne 0$. The appearance of these components might play an important role in chiral hydrodynamics.
-
quantum corrections to the stress energy tensor in Thermodynamic Equilibrium with acceleration
Physical Review D, 2015Co-Authors: F. Becattini, Eduardo GrossiAbstract:We show that the stress-energy tensor has additional terms with respect to the ideal form in states of global Thermodynamic Equilibrium in flat spacetime with non-vanishing acceleration and vorticity. These corrections are of quantum origin and their leading terms are second order in the gradients of the Thermodynamic fields. Their relevant coefficients can be expressed in terms of correlators of the stress-energy tensor operator and the generators of the Lorentz group. With respect to previous assessments, we find that there are more second order coefficients and that all Thermodynamic functions including energy density receive acceleration and vorticity dependent corrections. Notably, also the relation between \rho and p, that is the equation of state, is affected by acceleration and vorticity. We have calculated the corrections for a free real scalar field -- both massive and massless -- and we have found that they increase, particularly for a massive field, at very high acceleration and vorticity and very low temperature. Finally, these non-ideal terms depend on the explicit form of the stress-energy operator, implying that different stress-energy tensor of the scalar field -- canonical or improved -- are Thermodynamically inequivalent.
Gilles Ledoux - One of the best experts on this subject based on the ideXlab platform.
-
investigation of local Thermodynamic Equilibrium in laser induced plasmas measurements of rotational and excitation temperatures at long time scales
Spectrochimica Acta Part B: Atomic Spectroscopy, 2014Co-Authors: Julien Lam, Vincent Mottoros, Dimitri Misiak, C Dujardin, Gilles LedouxAbstract:article i nfo We studied the rotational temperature of diatomic molecules in the context of laser induced plasma from a solid target. In particular, its temporal evolution is investigated at long time scales (≥30 μs). The measured values are compared to ionic and atomic excitation temperatures and the issue of local Thermodynamic Equilibrium is discussed. The investigation was carried out using an aluminium oxide (Al2O3) target doped with titanium (Ti) and iron (Fe). The ionic and the atomic excitation temperatures are deduced from the Ti II lines and the Fe I lines respectively. For the molecular temperature, a temporally resolved study of the aluminium monoxide (AlO) blue-green spectrum was carried out. We show that underthese experimental conditions, a complete Thermodynamic Equilibrium is not reached for up to 50 μs after the laser pulse. The plasma is identified as cold plasma, with two different temperatures: the electron kinetic temperature and the heavy species kinetic temperature.
M D Calzada - One of the best experts on this subject based on the ideXlab platform.
-
influence of gas flow on the axial distribution of densities temperatures and Thermodynamic Equilibrium degree in surface wave plasmas sustained at atmospheric pressure
Spectrochimica Acta Part B: Atomic Spectroscopy, 2019Co-Authors: Juana Martinezaguilar, J Munoz, M D Calzada, Cristina Gonzalezgago, Eduardo Castanosmartinez, Rocio RinconAbstract:Abstract In this paper, a discussion about the influence of the gas flow on the axial distribution of plasma densities, temperatures and Thermodynamic Equilibrium degree in argon surface-wave discharges sustained at atmospheric pressure is presented. It was found that increasing the gas flow produces a decrease in gas temperature and electron density which is explained in terms of a decrease of residence time of both heavy particles and electrons. Moreover, the dependence of the dynamics of argon molecular ions on gas temperature also explains the decrease in electron density and the increase in the population of 4p excited levels. Thermodynamic Equilibrium is also affected by gas flow, whose increase drives the 5p levels out of partial Saha Equilibrium, although they remain in the collisional regime for their population processes. Furthermore, the linear power density was measured to complete the characterization of surface-wave plasmas with different gas flows. From the linear power density, it is possible to conclude that increasing the gas flow means that the energy supplied to the discharge is being used not only for ionization processes, but also for the excitation of argon atoms from the ground to metastable states, thus, increasing the populations of 4p levels.
-
departure from local Thermodynamic Equilibrium in argon plasmas sustained in a torche a injection axiale sur guide d ondes
Spectrochimica Acta Part B: Atomic Spectroscopy, 2015Co-Authors: Rocio Rincon, J Munoz, M D CalzadaAbstract:Abstract Plasma torches are suitable plasma sources for a wide range of applications. The capability of these discharges to produce processes like sample excitation or decomposition of molecules inside them depends on the density of the plasma species and their energies (temperatures). The relation between these parameters determines the specific state of Thermodynamic Equilibrium in the discharge. Thus, the understanding of plasma possibilities for application purposes is related to the knowledge of the plasma Thermodynamic Equilibrium degree. In this paper a discussion about the Equilibrium state for Ar plasmas generated by using a Torche a Injection Axiale sur Guide d'Ondes, TIAGO device, is presented. Emission spectroscopy techniques were used to measure gas temperature and electron density at the exit of the nozzle torch and along the dart. Boltzmann-plots as well as bp parameters were calculated to characterize the type and degree of departure from partial Local Saha Equilibrium (pLSE). This study indicates that the closer situation to Local Thermodynamic Equilibrium (LTE) of the plasma corresponds to larger Ar flows which highlights the importance of the nitrogen (atmosphere surrounding the plasma) in the kinetics of Ar-TIAGO discharges.
-
experimental investigation and characterization of the departure from local Thermodynamic Equilibrium along a surface wave sustained discharge at atmospheric pressure
Journal of Applied Physics, 1996Co-Authors: M D Calzada, M Moisan, A Gamero, A SolaAbstract:Surface‐wave‐sustained discharges (SWDs) form a particular class of high frequency (HF) discharges: their HF sustaining field is provided by a traveling wave that transfers energy as it propagates along the discharge column, yielding a plasma column with an axially decreasing electron density. SWDs have proved to be ideal for investigating experimentally and theoretically both the HF field and discharge aspects of HF plasma sources at reduced gas pressure. In this article, SWDs are utilized at atmospheric pressure to gain insight into the departure from Thermodynamic Equilibrium (TE) of HF sustained discharges. This departure is found to increase significantly as the electron density decreases along the plasma column whereas the gas temperature and the power absorbed per electron do not vary axially. The two‐temperature plasma model provides an adequate description of this departure from TE.
