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Showing papers on "Radiative transfer published in 2004"


Journal ArticleDOI
TL;DR: In this article, the transitions of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients.
Abstract: Atomic and molecular data for the transitions of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are extrapolated to higher energies. These data, which are made publically available through the WWW at this http URL, are essential input for non-LTE line radiative transfer programs. An online version of a computer program for performing statistical equilibrium calculations is also made available as part of the database. Comparisons of calculated emission lines using different sets of collisional rate coefficients are presented. This database should form an important tool in analyzing observations from current and future (sub)millimetre and infrared telescopes.

1,407 citations


Journal ArticleDOI
TL;DR: Zhang et al. as discussed by the authors used a more advanced NASA Goddard Institute for Space Studies (GISS) radiative transfer model and improved ISCCP cloud climatology and ancillary data sets.
Abstract: [1] We continue reconstructing Earth’s radiation budget from global observations in as much detail as possible to allow diagnosis of the effects of cloud (and surface and other atmospheric constituents) variations on it. This new study was undertaken to reduce the most noticeable systematic errors in our previous results (flux data set calculated mainly using International Satellite Cloud Climatology Project–C1 input data (ISCCP-FC)) by exploiting the availability of a more advanced NASA Goddard Institute for Space Studies (GISS) radiative transfer model and improved ISCCP cloud climatology and ancillary data sets. The most important changes are the introduction of a better treatment of ice clouds, revision of the aerosol climatology, accounting for diurnal variations of surface skin/air temperatures and the cloud-radiative effects on them, revision of the water vapor profiles used, and refinement of the land surface albedos and emissivities. We also extend our previous flux results, limited to the top of atmosphere (TOA) and surface (SRF), to also include three levels within the atmosphere, forming one integrated vertical atmospheric flux profile from SRF to TOA, inclusive, by combining a new climatology of cloud vertical structure with the ISCCP cloud product. Using the new radiative transfer model and new input data sets, we have produced an 18-year at 3-hour time steps, global at 280-km intervals, radiative flux profile data set (called ISCCP-FD) that provides full- and clear-sky, shortwave and longwave, upwelling and downwelling fluxes at five levels (SRF, 680 mbar, 440 mbar, 100 mbar, and TOA). Evaluation is still only possible for TOA and SRF fluxes: Comparisons of monthly, regional mean values from FD with Earth Radiation Budget Experiment, Clouds and the Earth’s Radiant Energy System and Baseline Surface Radiation Network values suggest that we have been able to reduce the overall uncertainties from 10–15 to 5–10 W/m 2 at TOA and from 20–25 to 10– 15 W/m 2 at SRF. Annual mean pressure-latitude cross sections of the cloud effects on atmospheric net radiative fluxes show that clouds shift the longwave cooling downward in the Intertropical Convergence Zone, acting to stabilize the tropical atmosphere while increasing the horizontal heating gradient forcing the Hadley circulation, and shift the longwave cooling upward in the midlatitude storm zones, acting to destabilize the baroclinic zones while decreasing the horizontal heating gradient there. INDEX TERMS: 1620 Global Change: Climate dynamics (3309); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: Earth radiation budget, surface radiation budget (SRB), cloud vertical structure, ERBE, CERES, BSRN Citation: Zhang, Y., W. B. Rossow, A. A. Lacis, V. Oinas, and M. I. Mishchenko (2004), Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data, J. Geophys. Res., 109, D19105, doi:10.1029/2003JD004457.

1,076 citations


Journal ArticleDOI
TL;DR: In this paper, a new method for evaluating the radiative forcing, the climate feedback parameter (W m−2 K−1) and hence the effective climate sensitivity from any GCM experiment in which the climate is responding to a constant forcing is presented.
Abstract: [1] We describe a new method for evaluating the radiative forcing, the climate feedback parameter (W m−2 K−1) and hence the effective climate sensitivity from any GCM experiment in which the climate is responding to a constant forcing. The method is simply to regress the top of atmosphere radiative flux against the global average surface air temperature change. This method does not require special integrations or off-line estimates, such as for stratospheric adjustment, to obtain the forcing, and eliminates the need for double radiation calculations and tropopause radiative fluxes. We show that for CO2 and solar forcing in a slab model and an AOGCM the method gives results consistent with those obtained by conventional methods. For a single integration it is less precise but since it does not require a steady state to be reached its precision could be improved by running an ensemble of short integrations.

811 citations


Journal ArticleDOI
TL;DR: In this paper, a new method is presented which determines the aerosol light absorption from the simultaneous measurement of radiation passing through and scattered back from a particle-loaded /bre /lter.

520 citations


Journal ArticleDOI
TL;DR: In this article, the physical structure and chemical composition of two close-to-round starless cores in Taurus-Auriga, L1498 and L1517B, were characterized based on high angular resolution observations in at least two transitions of NH3,N 2H +,C S, C 34 S,C 18 O, and C 17 O, together with maps of the 1.2 mm continuum.
Abstract: We have characterized the physical structure and chemical composition of two close-to-round starless cores in Taurus-Auriga, L1498 and L1517B. Our analysis is based on high angular resolution observations in at least two transitions of NH3 ,N 2H + ,C S, C 34 S, C 18 O, and C 17 O, together with maps of the 1.2 mm continuum. For both cores, we derive radial profiles of constant temperature and constant turbulence, together with density distributions close to those of non-singular isothermal spheres. Using these physical conditions and a Monte Carlo radiative transfer model, we derive abundance profiles for all species and model the strong chemical differentiation of the core interiors. According to our models, the NH3 abundance increases toward the core centers by a factor of several (≈5) while N2H + has a constant abundance over most of the cores. In contrast, both C 18 O and CS (and isotopomers) are strongly depleted in the core interiors, most likely due to their freeze out onto grains at densities of a few 10 4 cm −3 . Concerning the kinematics of the dense gas, we find (in addition to constant turbulence) a pattern of internal motions at the level of 0.1 km s −1 . These motions seem correlated with asymmetries in the pattern of molecular depletion, and we interpret them as residuals of core contraction. Their distribution and size suggest that core formation occurs in a rather irregular manner and with a time scale of a Myr. A comparison of our derived core properties with those predicted by supersonic turbulence models of core formation shows that our Taurus cores are much more quiescent than representative predictions from these models. In two appendices at the end of the paper we present a simple and accurate approximation to the density profile of an isothermal (Bonnor-Ebert) sphere, and a Monte Carlo-calibrated method to derive gas kinetic temperatures using NH3 data.

518 citations


Journal ArticleDOI
05 Nov 2004-Science
TL;DR: Coupled surface plasmon polaritons (SPPs) are shown to provide effective transfer of excitation energy from donor molecules to acceptor molecules on opposite sides of metal films up to 120 nanometers thick, which could allow subwavelength-scale manipulation of light and provide an interface to the outside world.
Abstract: Coupled surface plasmon polaritons (SPPs) are shown to provide effective transfer of excitation energy from donor molecules to acceptor molecules on opposite sides of metal films up to 120 nanometers thick. This variant of radiative transfer should allow directional control over the flow of excitation energy with the use of suitably designed metallic nanostructures, with SPPs mediating transfer over length scales of 10–7 to 10–4 meters. In the emerging field of nanophotonics, such a prospect could allow subwavelength-scale manipulation of light and provide an interface to the outside world.

457 citations


Journal ArticleDOI
15 Jul 2004-Nature
TL;DR: Three-dimensional radiative transfer modelling of scattering polarization in atomic and molecular lines that indicates the presence of hidden, mixed-polarity fields on subresolution scales finds a ubiquitous tangled magnetic field with an average strength of ∼130 G.
Abstract: Deciphering and understanding the small-scale magnetic activity of the quiet solar photosphere should help to solve many of the key problems of solar and stellar physics, such as the magnetic coupling to the outer atmosphere and the coronal heating. At present, we can see only approximately 1 per cent of the complex magnetism of the quiet Sun, which highlights the need to develop a reliable way to investigate the remaining 99 per cent. Here we report three-dimensional radiative transfer modelling of scattering polarization in atomic and molecular lines that indicates the presence of hidden, mixed-polarity fields on subresolution scales. Combining this modelling with recent observational data, we find a ubiquitous tangled magnetic field with an average strength of approximately 130 G, which is much stronger in the intergranular regions of solar surface convection than in the granular regions. So the average magnetic energy density in the quiet solar photosphere is at least two orders of magnitude greater than that derived from simplistic one-dimensional investigations, and sufficient to balance radiative energy losses from the solar chromosphere.

441 citations


Journal ArticleDOI
TL;DR: A radiative lifetime of 110 ns is deduced from the measured decay rate and a determination of fluorescence quantum efficiency, which explains the relatively low observed fluorescence efficiency in isolated SWNTs.
Abstract: The temporal evolution of fluorescence from isolated single-wall carbon nanotubes (SWNTs) has been investigated using optical Kerr gating. The fluorescence emission is found to decay on a time scale of 10 ps. This fast relaxation arises from nonradiative processes, the existence of which explains the relatively low observed fluorescence efficiency in isolated SWNTs. From the measured decay rate and a determination of fluorescence quantum efficiency, we deduce a radiative lifetime of 110 ns.

299 citations


Journal ArticleDOI
TL;DR: In this article, a numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere is presented, where the authors consider three dimensions of the chromosphere.
Abstract: Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere

297 citations


Journal ArticleDOI
TL;DR: In this paper, the chemistry of the envelopes around a sample of 18 low-mass pre- and protostellar objects for which physical properties have previously been derived from radiative transfer modeling of their dust continuum emission are reported.
Abstract: This paper presents the first substantial study of the chemistry of the envelopes around a sample of 18 low-mass pre- and protostellar objects for which physical properties have previously been derived from radiative transfer modeling of their dust continuum emission. Single-dish line observations of 24 transitions of 9 molecular species (not counting isotopes) including HCO + , N 2 H + , CS, SO, SO 2 , HCN, HNC, HC 3 N and CN are reported. The line intensities are used to constrain the molecular abundances by comparison to Monte Carlo radiative transfer modeling of the line strengths. In general the nitrogen-bearing species together with HCO + and CO cannot be fitted by a constant fractional abundance when the lowest excitation transitions are included, but require radial dependences of their chemistry since the intensity of the lowest excitation lines are systematically underestimated in such models. A scenario is suggested in which these species are depleted in a specific region of the envelope where the density is high enough that the freeze-out timescale is shorter than the dynamical timescale and the temperature low enough that the molecule is not evaporated from the icy grain mantles. This can be simulated by a “drop” abundance profile with standard (undepleted) abundances in the inner- and outermost regions and a drop in abundance in between where the molecule freezes out. An empirical chemical network is constructed on the basis of correlations between the abundances of various species. For example, it is seen that the HCO + and CO abundances are linearly correlated, both increasing with decreasing envelope mass. This is shown to be the case if the main formation route of HCO + is through reactions between CO and H$_3^+$, and if the CO abundance still is low enough that reactions between H$_3^+$ and N 2 are the main mechanism responsible for the removal of H$_3^+$. Species such as CS, SO and HCN show no trend with envelope mass. In particular no trend is seen between “evolutionary stage” of the objects and the abundances of the main sulfur- or nitrogen-containing species. Among the nitrogen-bearing species abundances of CN, HNC and HC 3 N are found to be closely correlated, which can be understood from considerations of the chemical network. The CS/SO abundance ratio is found to correlate with the abundances of CN and HC 3 N, which may reflect a dependence on the atomic carbon abundance. An anti-correlation is found between the deuteration of HCO + and HCN, reflecting different temperature dependences for gas-phase deuteration mechanisms. The abundances are compared to other protostellar environments. In particular it is found that the abundances in the cold outer envelope of the previously studied class 0 protostar IRAS 16293-2422 are in good agreement with the average abundances for the presented sample of class 0 objects.

291 citations


Journal ArticleDOI
TL;DR: In this article, a rigorous and systematic intercomparison of codes used for the retrieval of trace gas profiles from high-resolution ground-based solar absorption FTIR measurements is presented for the first time.
Abstract: A rigorous and systematic intercomparison of codes used for the retrieval of trace gas profiles from high-resolution ground-based solar absorption FTIR measurements is presented for the first time. Spectra were analyzed with the two widely used independent, retrieval codes: SFIT2 and PROFFIT9. Vertical profiles of O 3 , HNO 3 , HDO, and N 2 O were derived from the same set of typical observed spectra. Analysis of O 3 was improved by using updated line parameters. It is shown that profiles and total column amounts are in excellent agreement, when similar constraints are applied, and that the resolution kernel matrices are also consistent. Owing to the limited altitude resolution of ground-based observations, the impact of the constraints on the solution is not negligible. It is shown that the results are also compatible for independently chosen constraints. Perspectives for refined constraints are discussed. It can be concluded that the error budget introduced by the radiative transfer code and the retrieval algorithm on total columns deduced from high-resolution ground-based solar FTIR spectra is below 1%.

Journal ArticleDOI
TL;DR: In this article, the authors review radiative processes responsible for X-ray emission in hard (low) and soft (high) spectral states of black-hole binaries and find that the main process in the hard state appears to be scattering of blackbody photons from a cold disk by thermal electrons in a hot inner flow, and any contribution from nonthermal synchrotron emission is at most small.
Abstract: We review radiative processes responsible for X-ray emission in hard (low) and soft (high) spectral states of black-hole binaries. The main process in the hard state appears to be scattering of blackbody photons from a cold disk by thermal electrons in a hot inner flow, and any contribution from nonthermal synchrotron emission is at most small. In the soft states, blackbody disk emission dominates energetically, and its high-energy tail is due to scattering by hybrid, thermal/nonthermal electrons, probably in active regions above the disk surface. State transitions appear to correspond to a variable inner radius of the cold disk driven by changes of the accretion rate. The existence of two accretion solutions, hot and cold, in a range of the accretion rate leads to hysteresis in low-mass X-ray binaries.

Journal ArticleDOI
TL;DR: Three major changes allowed us to improve DART accuracy by a factor of three: more accurate simulation of single and multiple scattering, use of a scheme that oversamples DART cells and a better account of the direction of radiation that gives rise to multiple scattered radiation.
Abstract: DART (Discrete Anisotropic Radiative Transfer) is a radiative transfer model that simulates remotely acquired images. It was originally developed to work in the short wavelengths (0.3–3 µm) within 3D natural scenes that are represented as matrices of rectangular cells containing trees, shrubs, grass, soil, etc. DART was recently modified to extend its domain of application and to improve its accuracy. This paper summarizes the major features of DART and presents the changes that were implemented for improving its accuracy. Presently, this model works with natural and urban landscapes, on the whole optical domain (thermal infrared included) and with a multispectral approach that uses optical data bases from 0.3 µm up to 15 µm. It simulates radiative transfer in the whole ‘atmosphere–Earth’ system and it accounts for the instrumental transfer function. Three major changes allowed us to improve DART accuracy by a factor of three: more accurate simulation of single and multiple scattering, use of a scheme tha...

Journal ArticleDOI
TL;DR: In this article, a multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) method for the determination of atmospheric aerosol properties is presented.
Abstract: [1] Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of the oxygen dimer O4 which can serve as a new method for the determination of atmospheric aerosol properties are presented. Like established methods, e.g., Sun radiometer and LIDAR measurements, MAX-DOAS O4 observations determine optical properties of aerosol under atmospheric conditions (not dried). However, the novel technique has two major advantages: It utilizes differential O4 absorption structures and thus does not require absolute radiometric calibration. In addition, O4 observations using this method provide a new kind of information: since the atmospheric O4 profile depends strongly on altitude, they can yield information on the atmospheric light path distribution and in particular on the atmospheric aerosol profile. From O4 observations during clear days and from atmospheric radiative transfer modeling, we conclude that our new method is especially sensitive to the aerosol extinction close to the ground. In addition, O4 observations using this method yield information on the penetration depth of the incident direct solar radiation. O4 observations at different azimuth angles can also provide information on the aerosol scattering phase function. We found that MAX-DOAS O4 observations are a very sensitive method: even aerosol extinction below 0.001 could be detected. In addition to the O4 absorptions we also investigated the magnitude of the Ring effect and the (relative) intensity. Both quantities yield valuable further information on atmospheric aerosols. From the simultaneous analysis of the observed O4 absorption and the measured intensity, in particular, information on the absorbing properties of the aerosols might be derived. The aerosol information derived from MAX-DOAS observations can be used for the quantitative analysis of various trace gases also analyzed from the measured spectra.

Journal ArticleDOI
TL;DR: In this article, a new type of solar irradiance scheme is developed based on radiative transfer models (RTM) using atmospheric parameter information retrieved from the Meteosat Second Generation (MSG) satellite (clouds, ozone, water vapour) and the ERS-2/ENVISAT satellites (aerosols, ozone).

Journal ArticleDOI
TL;DR: In this paper, the authors compare simulations from different versions of the GFDL Atmospheric Model 2 (AM2) that have widely varying strengths of cloud feedback to illustrate the differences between the two and highlight the potential for changes in cloud radiative forcing to be misinterpreted.
Abstract: Uncertainty in cloud feedback is the leading cause of discrepancy in model predictions of climate change. The use of observed or model-simulated radiative fluxes to diagnose the effect of clouds on climate sensitivity requires an accurate understanding of the distinction between a change in cloud radiative forcing and a cloud feedback. This study compares simulations from different versions of the GFDL Atmospheric Model 2 (AM2) that have widely varying strengths of cloud feedback to illustrate the differences between the two and highlight the potential for changes in cloud radiative forcing to be misinterpreted.

01 Jan 2004
TL;DR: A successor version of the SCIATRAN radiative transfer model (RTM) has been developed to perform radiative transport modeling in any observation geometry appropriate to measurements of the scattered solar radiation in the Earth's atmosphere as discussed by the authors.
Abstract: A successor version of the SCIATRAN radiative transfer model (RTM) has been developed to perform radiative transfer modeling in any observation geometry appropriate to measurements of the scattered solar radiation in the Earth’s atmosphere. The model is designed to be used as a forward model in the retrieval of atmospheric constituents from measurements of scattered solar light by satellite, ground-based, or airborne instruments in UV–Vis–NIR spectral region. Furthermore, it can be used to calculate air mass factors or fluxes. The new generation of the SCIATRAN model comprises all features of the latest SCIATRAN 1.2 RTM supporting additionally radiative transfer calculations in a spherical atmosphere. The program is written in FORTRAN 95 and suitable for parallel execution using the OpenMP standard. The wavelength range covered by the radiative transfer model is extended to 175–2380 nm including Schuman-Runge and Herzberg absorption bands of oxygen. The SCIATRAN 2.0 model exhibits the following new capabilities: (i) modeling of the scattered solar radiation in limb viewing geometry as well as any kind of measurements of the scattered radiation within the atmosphere, (ii) corresponding quasi-analytical calculation of weighting functions of atmospheric parameters, (iii) airmass factor calculations for ground-based, space and airborne measurements including off-axis geometry, (v) accounting for photochemically active species, i.e., radiative transfer calculations can be performed using solar zenith angle dependent vertical distributions of atmospheric species, (iv) height resolved radiation fluxes, including actinic fluxes for photolysis rate calculations, (vi) inelastic rotational Raman scattering in any supported viewing geometry, (vii) new effective approximations for radiative transfer modeling in presence of clouds. The SCIATRAN model is freely available via the world wide web for non-commercial scientific applications.

Journal ArticleDOI
TL;DR: In this paper, the formation and evolution of HII regions around the first stars formed at z = 10-30 were studied using a one-dimensional Lagrangian hydrodynamics code which self-consistently incorporates radiative transfer and non-equilibrium primordial gas chemistry.
Abstract: We study the formation and evolution of HII regions around the first stars formed at z=10-30. We use a one-dimensional Lagrangian hydrodynamics code which self-consistently incorporates radiative transfer and non-equilibrium primordial gas chemistry. The star-forming region is defined as a spherical gas cloud with a Population III star embedded at the center. We explore a large parameter space of host halo mass, gas density profile, and stellar luminosity. The formation of the HII region is characterized by initial slow expansion of a weak D-type ionization front near the center, followed by rapid propagation of an R-type front throughout the outer gas envelope. We find that the transition between the two front types is indeed a critical condition for the complete ionization of halos of cosmological interest. In small mass ( 80%) of both ionizing and photodissociating photons. In larger mass (> 10^7 M_sun) halos, the ionization front remains to be of D-type over the lifetime of the massive star, the HII region is confined well inside the virial radius, and the escape fractions are essentially zero. We derive an analytic formula that reproduces well the results of our simulations. We discuss immediate implications of the present results for the star formation history and early reionization of the Universe.

Journal ArticleDOI
TL;DR: In this paper, the authors compute the temperature of the gas in the surface layers of the disk in a self-consistent manner and find that in general the dust and gas temperatures are equal to within 10% for AV 0.1, which is above the location of the superheated surface layer in which the dust emission features are produced.
Abstract: Models for the structure of protoplanetary disks have thus far been based on the assumption that the gas and dust temperatures are equal. The gas temperature, an essential ingredient in the equations of hydrostatic equilibrium of the disk, is then determined from a continuum radiative transfer calculation, in which the continuum opacity is provided by the dust. It has long been debated whether this assumption still holds in the surface layers of the disk, in which the dust infrared emission features are produced. In this paper we compute the temperature of the gas in the surface layers of the disk in a self-consistent manner. The gas temperature is determined from a heating-cooling balance equation in which processes such as photoelectric heating, dissociative heating, dust-gas thermal heat exchange, and line cooling are included. The abundances of the dominant cooling species such as CO, C, C+, and O are determined from a chemical network based on the atomic species H, He, C, O, S, Mg, Si, and Fe. The underlying disk models to our calculations are the models of Dullemond, van Zadelhoff, & Natta. We find that in general the dust and gas temperatures are equal to within 10% for AV 0.1, which is above the location of the superheated surface layer in which the dust emission features are produced. High above the disk surface the gas temperature exceeds the dust temperature and can become—in the presence of polycyclic aromatic hydrocarbons—as high as 600 K at a radius of 100 AU. This is a region in which CO has fully dissociated, but a significant fraction of hydrogen is still in molecular form. The densities are still high enough for nonnegligible H2 emission to be produced. At radii inward of 50 AU, the temperature of the gas above the photosphere can reach up to ~104 K. In the disk surface layers, the gas temperature exceeds the virial temperature of hydrogen. Some of this material could possibly evaporate, but firm conclusions have to await fully self-consistent disk models, in which the disk structure and gas temperature determination will be solved iteratively.

Journal ArticleDOI
TL;DR: The results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments.
Abstract: We present a simple method to measure the radiative and nonradiative recombination rates of individual fluorescent emitters at room temperature. By placing a single molecule successively close and far from a dielectric interface and simultaneously measuring its photoluminescence decay and its orientation, both the radiative and nonradiative recombination rates can be determined. For CdSe nanocrystals, our results demonstrate that the fluorescence quantum efficiency, determined at the single-molecule level, is 98% in average, far above the value expected from conventional ensemble experiments. The bidimensional nature of the transition dipole is also directly evidenced from a single-particle measurement.

Journal ArticleDOI
TL;DR: In this paper, the authors present a theoretical model for primordial star formation, where the structure of the initial gas cores is described as virialized, quasi-hydrostatic objects in accord with recent high-resolution numerical studies.
Abstract: We present a theoretical model for primordial star formation. First we describe the structure of the initial gas cores as virialized, quasi-hydrostatic objects in accord with recent high-resolution numerical studies. The accretion rate can then be related to characteristic densities and temperatures that are set by the cooling properties of molecular hydrogen. We allow for rotation of the gas core, assuming angular momentum conservation inside the sonic point of the flow. In the typical case, most mass then reaches the star via an accretion disk. The structure of the inner region of this disk is described with the standard theory of viscous disks, but with allowance for the substantial energies absorbed in ionizing and dissociating the gas. The size of the protostar and its luminosity depend on the accretion rate, the energetics of the accreting gas, and the ability of the radiation to escape from the stellar accretion shock. We combine these models for the infall rate, inner disk structure, and protostellar evolution to predict the radiation field that is the basis for radiative feedback processes acting against infall (second paper in the series). For realistic initial angular momenta, the photosphere of the protostar is much smaller and hotter than in the spherical case, leading to stronger radiative feedback at earlier stages in the evolution. In particular, once the star is older than its Kelvin-Helmholtz time, contraction toward the main sequence causes a rapid increase in ionizing and far-ultraviolet luminosity at masses ~30 M? in the fiducial case. Since the cores out of which the first stars formed were much more massive than 30 M? and since feedback is dynamically unimportant at lower masses, we conclude that the first stars should have had masses 30 M?.

Journal ArticleDOI
TL;DR: In this paper, the evolution of chemistry and molecular line profiles through the entire star formation process, including a self-consistent treatment of dynamics, dust continuum radiative transfer, gas energetics, chemistry, molecular excitation, and line radiative transfers, is studied.
Abstract: Understanding the chemical evolution in star-forming cores is a necessary precondition to correctly assessing physical conditions when using molecular emission. We follow the evolution of chemistry and molecular line profiles through the entire star formation process, including a self-consistent treatment of dynamics, dust continuum radiative transfer, gas energetics, chemistry, molecular excitation, and line radiative transfer. In particular, the chemical code follows a gas parcel as it falls toward the center, passing through regimes of density, dust temperature, and gas temperature that are changing because of both the motion of the parcel and the evolving luminosity of the central source. We combine a sequence of Bonnor-Ebert spheres and the inside-out collapse model to describe dynamics from the pre-protostellar stage to later stages. The overall structures of abundance profiles show complex behavior that can be understood as interactions between freezeout and evaporation of molecules. We find that the presence or absence of gas-phase CO has a tremendous effect on the less abundant species. In addition, the ambient radiation field and the grain properties have important effects on the chemical evolution, and the variations in abundance have strong effects on the predicted emission-line profiles. Multitransition and multiposition observations are necessary to constrain the parameters and interpret observations correctly in terms of physical conditions. Good spatial and spectral resolution is also important in distinguishing evolutionary stages.

Journal ArticleDOI
TL;DR: In this paper, a new approach to derive tropospheric concentrations of some atmospheric trace gases from ground-based UV/vis measurements is described, which uses the sunlight scattered in the zenith sky as the light source and the method of Differential Optical Absorption Spectroscopy (DOAS) to derive column amounts of absorbers like ozone and nitrogen dioxide.
Abstract: . A new approach to derive tropospheric concentrations of some atmospheric trace gases from ground-based UV/vis measurements is described. The instrument, referred to as the MAX-DOAS, is based on the well-known UV/vis instruments, which use the sunlight scattered in the zenith sky as the light source and the method of Differential Optical Absorption Spectroscopy (DOAS) to derive column amounts of absorbers like ozone and nitrogen dioxide. Substantial enhancements have been applied to this standard setup to use different lines of sight near to the horizon as additional light sources (MAX - multi axis). Results from measurements at Ny-Alesund (79° N, 12° E) are presented and interpreted with the full-spherical radiative transfer model SCIATRAN. In particular, measurements of the oxygen dimer O4 which has a known column and vertical distribution in the atmosphere are used to evaluate the sensitivity of the retrieval to parameters such as multiple scattering, solar azimuth, surface albedo and refraction in the atmosphere and also to validate the radiative transfer model. As a first application, measurements of NO2 emissions from a ship lying in Ny-Alesund harbour are presented. The results of this study demonstrate the feasibility of long term UV/vis multi axis measurement that can be used to derive not only column amounts of different trace gases but also some information on the vertical location of these absorbers.

Journal ArticleDOI
TL;DR: An improved version of the RTTOV (Radiative Transfer for the Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder) fast radiative transfer model used operationally at the European Centre for Medium-Range Weather Forecasts (ECMWF) for the assimilation of Advanced TIROS Operational VOS radiances has been developed.
Abstract: An improved version of the RTTOV (Radiative Transfer for the Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder) fast radiative transfer model used operationally at the European Centre for Medium-Range Weather Forecasts (ECMWF) for the assimilation of Advanced TIROS Operational Vertical Sounder (ATOVS) radiances has been developed. This new model computes radiances for the Atmospheric Infrared Sounder and reproduces line-by-line radiances and Jacobians for the surface-sensing, water vapour and ozone channels of the ATOVS with significantly improved accuracy. The profile-dependent predictors used by the improved model to parametrize the atmospheric optical depths are based on the approach followed by the ECMWF fast radiative transfer model for the Infrared Atmospheric Sounding Interferometer (RTIASI). To improve the accuracy of the fast model in reproducing line-by-line radiances for the Infrared Atmospheric Sounder, modifications have been made to the predictors used in RTIASI by introducing a revised set of predictors for ozone and adding new predictors to model the water vapour continuum type absorption. To eliminate discontinuities in the water vapour Jacobians observed in RTIASI, data are now weighted prior to performing the regression. Copyright © 2004 Royal Meteorological Society

Journal ArticleDOI
TL;DR: In this paper, the radiative relaxation quantum yield of synthetic eumelanin was determined by correcting for pump beam attenuation and emission reabsorption in both eumelsin samples and fluorescein standards over a large range of concentrations.
Abstract: We report absolute values for the radiative relaxation quantum yield of synthetic eumelanin as a function of excitation energy. These values were determined by correcting for pump beam attenuation and emission reabsorption in both eumelanin samples and fluorescein standards over a large range of concentrations. Our results confirm that eumelanins are capable of dissipating >99.9% of absorbed UV and visible radiation through nonradiative means. Furthermore, we have found that the radiative quantum yield of synthetic eumelanin is excitation energy dependent. This observation is supported by corrected emission spectra, which also show a clear dependence of both peak position and peak width on excitation energy. Our findings indicate that photoluminescence emission in eumelanins is derived from ensembles of small chemically distinct oligomeric units that can be selectively pumped. This hypothesis lends support to the theory that the basic structural unit of eumelanin is oligomeric rather than heteropolymeric.

Journal ArticleDOI
TL;DR: In this article, the authors describe the underlying radiative transfer processes, drawing upon research conducted in shallow marine environments, and model the effect of water depth, substrate type, suspended sediment concentration, and surface turbulence.

Journal ArticleDOI
15 Jan 2004-Nature
TL;DR: This work examines the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions, and concludes that the indirect aerosol effect has a significant influence on radiative fluxes.
Abstract: Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected with droplet concentrations, but it has been difficult to determine the impact of these indirect effects on radiative forcing1,2,3. Here we provide observational evidence for a substantial alteration of radiative fluxes due to the indirect aerosol effect. We examine the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions—a continental site in Oklahoma with high aerosol concentrations, and an Arctic site in Alaska with low aerosol concentrations. We determine the cloud optical depth required to fit the observed shortwave downward surface radiation. We then use a cloud parcel model to simulate the cloud optical depth from observed aerosol properties due to the indirect aerosol effect. From the good agreement between the simulated indirect aerosol effect and observed surface radiation, we conclude that the indirect aerosol effect has a significant influence on radiative fluxes.

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TL;DR: In this paper, the authors present a time-dependent radiative model of the atmosphere of HD209458b and investigate its thermal structure and chemical composition, showing that 99.99% of the incoming stellar flux has been absorbed before reaching the 7 bar level.
Abstract: We present a time-dependent radiative model of the atmosphere of HD209458b and investigate its thermal structure and chemical composition. In a first step, the stellar heating profile and radiative timescales were calculated under planet-averaged insolation conditions. We find that 99.99% of the incoming stellar flux has been absorbed before reaching the 7 bar level. Stellar photons cannot therefore penetrate deeply enough to explain the large radius of the planet. We derive a radiative time constant which increases with depth and reaches about 8 hr at 0.1 bar and 2.3 days at 1 bar. Time-dependent temperature profiles were also calculated, in the limit of a zonal wind that is independent on height (i.e. solid-body rotation) and constant absorption coefficients. We predict day-night variations of the effective temperature of \~600 K, for an equatorial rotation rate of 1 km/s, in good agreement with the predictions by Showman &Guillot (2002). This rotation rate yields day-to-night temperature variations in excess of 600 K above the 0.1-bar level. These variations rapidly decrease with depth below the 1-bar level and become negligible below the ~5--bar level for rotation rates of at least 0.5 km/s. At high altitudes (mbar pressures or less), the night temperatures are low enough to allow sodium to condense into Na2S. Synthetic transit spectra of the visible Na doublet show a much weaker sodium absorption on the morning limb than on the evening limb. The calculated dimming of the sodium feature during planetary transites agrees with the value reported by Charbonneau et al. (2002).

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TL;DR: Jin et al. as discussed by the authors used a validated coupled ocean-atmosphere radiative transfer model to estimate the ocean surface albedo look up table in terms of four important physical parameters: solar zenith angle, wind speed, transmission by atmospheric cloud/aerosol, and ocean chlorophyll concentration.
Abstract: [1] Measurements at a sea platform show that the ocean surface albedo is highly variable and is sensitive to four physical parameters: solar zenith angle, wind speed, transmission by atmospheric cloud/aerosol, and ocean chlorophyll concentration Using a validated coupled ocean-atmosphere radiative transfer model, an ocean albedo look up table is created in terms of these four important parameters A code to read the table is also provided; it gives spectral albedos for a range of oceanic and atmospheric conditions specified by the user The result is a fast and accurate parameterization of ocean surface albedo for radiative transfer and climate modeling INDEX TERMS: 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 1620 Global Change: Climate dynamics (3309); 3339 Meteorology and Atmospheric Dynamics: Ocean/ atmosphere interactions (0312, 4504); 4552 Oceanography: Physical: Ocean optics; 1610 Global Change: Atmosphere (0315, 0325) Citation: Jin, Z, T P Charlock, W L Smith Jr, and K Rutledge (2004), A parameterization of ocean surface albedo, Geophys Res Lett, 31, L22301, doi:101029/ 2004GL021180

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TL;DR: In this paper, the evolution of chemistry and molecular line profiles through the entire star formation process, including a self-consistent treatment of dynamics, dust continuum radiative transfer, gas energetics, chemistry, molecular excitation, and line radiative transfers, is studied.
Abstract: Understanding the chemical evolution in star-forming cores is a necessary pre-condition to correctly assess physical conditions when using molecular emission. We follow the evolution of chemistry and molecular line profiles through the entire star formation process, including a self-consistent treatment of dynamics, dust continuum radiative transfer, gas energetics, chemistry, molecular excitation, and line radiative transfer. In particular, the chemical code follows a gas parcel as it falls toward the center, passing through regimes of density, dust temperature, and gas temperature that are changing both because of the motion of the parcel and the evolving luminosity of the central source. We combine a sequence of Bonnor-Ebert spheres and the inside-out collapse model to describe dynamics from the pre-protostellar stage to later stages. The overall structures of abundance profiles show complex behavior that can be understood as interactions between freeze-out and evaporation of molecules. We find that the presence or absence of gas-phase CO has a tremendous effect on the less abundant species. In addition, the ambient radiation field and the grain properties have important effects on the chemical evolution, and the variations in abundance have strong effects on the predicted emission line profiles. Multi-transition and multi-position ob servations are necessary to constrain the parameters and interpret observations correctly in terms of physical conditions. Good spatial and spectral resolution is also important in distinguishing evolutionary stages.