We study Rayleigh-Brillouin scattering in gases of N2, O2, and SF6 molecules, Kr atoms, and He-Xe and He-CO2 mixtures at pressures ranging from 1 to 3 bar and using two different experimental setups. In one setup, we measure spectra of light scattered by thermal density fluctuations (spontaneous Rayleigh-Brillouin scattering); in the second setup density waves are induced in the overlap region of two counterpropagating laser beams (coherent Rayleigh-Brillouin scattering). We compare measured spectra to the Tenti models and to a recent model for mixtures. We find new values of the bulk viscosity, which is a parameter in line-shape models that allows for internal degrees of freedom. Both experiments agree on the value of the bulk viscosity. Our results indicate a need for new line-shape models for mixtures of molecules with internal degrees of freedom.

Abstract. An algorithm setup for the operational Aerosol Layer Height product for TROPOMI on the Sentinel-5 Precursor mission is described and discussed, applied to GOME-2A data, and evaluated with lidar measurements. The algorithm makes a spectral fit of reflectance at the O 2 A band in the near-infrared and the fit window runs from 758 to 770 nm. The aerosol profile is parameterised by a scattering layer with constant aerosol volume extinction coefficient and aerosol single scattering albedo and with a fixed pressure thickness. The algorithm's target parameter is the height of this layer. In this paper, we apply the algorithm to observations from GOME-2A in a number of systematic and extensive case studies, and we compare retrieved aerosol layer heights with lidar measurements. Aerosol scenes cover various aerosol types, both elevated and boundary layer aerosols, and land and sea surfaces. The aerosol optical thicknesses for these scenes are relatively moderate. Retrieval experiments with GOME-2A spectra are used to investigate various sensitivities, in which particular attention is given to the role of the surface albedo.From retrieval simulations with the single-layer model, we learn that the surface albedo should be a fit parameter when retrieving aerosol layer height from the O 2 A band. Current uncertainties in surface albedo climatologies cause biases and non-convergences when the surface albedo is fixed in the retrieval. Biases disappear and convergence improves when the surface albedo is fitted, while precision of retrieved aerosol layer pressure is still largely within requirement levels. Moreover, we show that fitting the surface albedo helps to ameliorate biases in retrieved aerosol layer height when the assumed aerosol model is inaccurate. Subsequent retrievals with GOME-2A spectra confirm that convergence is better when the surface albedo is retrieved simultaneously with aerosol parameters. However, retrieved aerosol layer pressures are systematically low (i.e., layer high in the atmosphere) to the extent that retrieved values no longer realistically represent actual extinction profiles. When the surface albedo is fixed in retrievals with GOME-2A spectra, convergence deteriorates as expected, but retrieved aerosol layer pressures become much higher (i.e., layer lower in atmosphere). The comparison with lidar measurements indicates that retrieved aerosol layer heights are indeed representative of the underlying profile in that case. Finally, subsequent retrieval simulations with two-layer aerosol profiles show that a model error in the assumed profile (two layers in the simulation but only one in the retrieval) is partly absorbed by the surface albedo when this parameter is fitted. This is expected in view of the correlations between errors in fit parameters and the effect is relatively small for elevated layers (less than 100 hPa). If one of the scattering layers is near the surface (boundary layer aerosols), the effect becomes surprisingly large, in such a way that the retrieved height of the sin...

Atmospheric lidar techniques for the measurement of wind, temperature, and optical properties of aerosols rely on the exact knowledge of the spectral line shape of the scattered laser light on molecules. We report on spontaneous Rayleigh-Brillouin scattering measurements in the ultraviolet at a scattering angle of 90 degrees on N(2) and on dry and moist air. The measured line shapes are compared to the Tenti S6 model, which is shown to describe the scattering line shapes in air at atmospheric pressures with small but significant deviations. We demonstrate that the line profiles of N(2) and air under equal pressure and temperature conditions differ significantly, and that this difference can be described by the S6 model. Moreover, we show that even a high water vapor content in air up to a volume fraction of 3.6vol.% has no influence on the line shape of the scattered light. The results are of relevance for the future spaceborne lidars on ADM-Aeolus (Atmospheric Dynamics Mission) and EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer).

The strong electronic absorption systems of the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands can be used to probe possible mass-variation effects on a cosmological time scale from spectra observed at high redshift, not only in H 2 but also in the second most abundant hydrogen isotopomer HD. High resolution laboratory determination of the most prominent HD lines at extreme ultraviolet wavelengths is performed at an accuracy of = 5 10 ÿ8 , forming a database for comparison with astrophysical data. Sensitivity coefficients K i d ln i =d ln are determined for HD from quantum ab initio calculations as a function of the proton-electron mass ratio . Strategies to deduce possible effects beyond first-order baryon/lepton mass ratio deviations are discussed. DOI: 10.1103/PhysRevLett.100.093007 PACS numbers: 33.20.ÿt, 06.20.Jr, 95.30.Dr, 98.80.Bp The observation of spectral features at high redshift (z 2-3) provides an opportunity to probe minute variations of some fundamental constants over time intervals of 10 10 years, corresponding to 80% of the lifetime of the Universe. For the fine structure constant evidence has been reported for a temporal drift at 5 significance [1]. Variation of another fundamental constant, the dimensionless proton-electron mass ratio m p =m e , may be probed through spectra of molecules. Recently, an indication for a possible decrease of was reported at = 2:45 0:59 10 ÿ5 over a time interval of 12 10 9 years [2,3]. This result is derived from a set of 76 H 2 spectral lines in two absorption systems at z 2:59 and z 3:02 in the line of sight towards quasars Q0405 ÿ 443 and Q0347 ÿ 383 [4]. From observations of the NH 3 inversion splitting in the astrophysical object B0218 357 at z 0:68, a tight constraint upon variation at = 0:6 1:9 10 ÿ6 was deduced [5]. These seemingly contradictory results might be reconciled by invoking the concept of a phase transition having occurred at z 1, transiting from a matter-dominated to a darkenergy-dominated Universe; variation of constants is hypothesized to occur only before the phase transition, henceThe comparison of spectral lines over cosmological time scales depends on the availability of spectral transitions that can be observed at high accuracy and at high redshift. Molecular hydrogen is the most abundant molecule in the Universe by orders of magnitude. The abundance of the deuterated HD species competes with other abundant molecules such as CO and CH such that it is worthwhile to consider the opportunity of using HD absorption for probing mass-variation effects. HD lines in the Lyman bands have indeed been observed in the object Q1232 082 at z 2:34 [7].To facilitate this opportunity, a set of highly accurate zero-redshift (laboratory) transition wavelengths of HD electronic absorption lines is required. Here we report on the spectral calibration of zero-redshift HD lines in the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands, referred to as Lv and Wv bands with v the vibrational quantum number, in the extreme ultraviolet range 100-11...

We report on the realization of a heavy "Bohr atom," through the spectroscopic observation of a Rydberg series of bound quantum states at principal quantum numbers n=140 to 230. The system is made heavy by replacing an electron inside a hydrogen atom by a composite H- particle, thus forming a H+H- Coulombically bound system obeying the physical laws of a generalized atom with appropriate mass scaling.