scholarly journals Inhomogeneous He ii reionization in hydrodynamic simulations

2020 ◽  
Vol 496 (4) ◽  
pp. 4372-4382 ◽  
Author(s):  
Phoebe Upton Sanderbeck ◽  
Simeon Bird
Keyword(s):  
Radiative Transfer ◽  
Thermal State ◽  
Computational Cost ◽  
Spatial Inhomogeneity ◽  
Intergalactic Gas ◽  
Hydrodynamic Simulations ◽  
Density Relation ◽  
Free Parameters ◽  
The Impact

ABSTRACT The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 ≲ z ≲ 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for large volumes, the physics of He ii reionization is often approximated by a uniform ultraviolet background model that does not capture the spatial inhomogeneity of reionization. We have devised a model that implements the effects of He ii reionization using semi-analytic calculations of the thermal state of intergalactic gas – a way to bypass a full radiative transfer simulation while still realizing the physics of He ii reionization that affects observables such as the Lyman α forest. Here, we present a publicly available code that flexibly models inhomogeneous He ii reionization in simulations at a negligible computational cost. Because many of the parameters of He ii reionization are uncertain, our model is customizable from a set of free parameters. We show results from this code in mp-gadget, where this model is implemented. We demonstrate the resulting temperature evolution and temperature–density relation of intergalactic gas – consistent with recent measurements and previous radiative transfer simulations. We show that the impact of He ii reionization gives rise to subtle signatures in the 1D statistics of the Lyman α forest at the level of several percent, in agreement with previous findings. The flexible nature of these simulations is ideal for studies of He ii reionization and future observations of the He ii Lyman α forest.

scholarly journals Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution  Ly α forest spectra

2020 ◽  
Vol 494 (4) ◽  
pp. 5091-5109 ◽  
Author(s):  
Prakash Gaikwad ◽  
Michael Rauch ◽  
Martin G Haehnelt ◽  
Ewald Puchwein ◽  
James S Bolton ◽  
...  
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Intergalactic Medium ◽  
Thermal State ◽  
Neutral Hydrogen ◽  
High Spectral Resolution ◽  
Profile Fitting ◽  
Density Relation ◽  
Width Distribution ◽  
Hydrodynamical Simulations

ABSTRACT We compare a sample of five high-resolution, high S/N  Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F, similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8  km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.

scholarly journals Fast and Effective Techniques for LWIR Radiative Transfer Modeling: A Dimension Reduction Approach

2019 ◽  
Author(s):  
Nicholas Westing ◽  
Brett Borghetti ◽  
Kevin Gross
Keyword(s):  
Machine Learning ◽  
Radiative Transfer ◽  
Dimension Reduction ◽  
Real Time ◽  
Computational Cost ◽  
Hyperspectral Data ◽  
Machine Learning Algorithms ◽  
Atmospheric Effects ◽  
Atmospheric Compensation ◽  
The Impact

The increasing spatial and spectral resolution of hyperspectral imagers yields detailed spectroscopy measurements from both space-based and airborne platforms. Machine learning algorithms have achieved state-of-the-art material classification performance on benchmark hyperspectral data sets; however, these techniques often do not consider varying atmospheric conditions experienced in a real-world detection scenario. To reduce the impact of atmospheric effects in the at-sensor signal, atmospheric compensation must be performed. Radiative Transfer (RT) modeling can generate high-fidelity atmospheric estimates at detailed spectral resolutions, but is often too time-consuming for real-time detection scenarios. This research utilizes machine learning methods to perform dimension reduction on the transmittance, upwelling radiance, and downwelling radiance (TUD) data to create high accuracy atmospheric estimates with lower computational cost than RT modeling. The utility of this approach is investigated using the instrument line shape for the Mako long-wave infrared hyperspectral sensor. This study employs physics-based metrics and loss functions to identify promising dimension reduction techniques. As a result, TUD vectors can be produced in real-time allowing for atmospheric compensation across diverse remote sensing scenarios.

scholarly journals Impact of the Ambae, Raikoke and Ulawun eruptions in 2018-2019 on the global stratospheric aerosol layer and climate

2020 ◽  
Author(s):  
Corinna Kloss ◽  
Pasquale Sellitto ◽  
Bernard Legras ◽  
Jean-Paul Vernier ◽  
Fabrice Jégou ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Orthogonal Polarization ◽  
Transfer Model ◽  
Aerosol Layer ◽  
The Impact ◽  
Aerosol Plume

<p>Using a combination of satellite, ground-based and in-situ observations, and radiative transfer modelling, we quantify the impact of the most recent moderate volcanic eruptions (Ambae, Vanuatu in July 2018; Raikoke, Russia and Ulawun, New Guinea in June 2019) on the global stratospheric aerosol layer and climate.</p><p>For the Ambae volcano (15°S and 167°E), we use the Stratospheric Aerosol and Gas Experiment III (SAGE III), the Ozone Mapping Profiler Suite (OMPS), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Himawari geostationary satellite observations of the aerosol plume evolution following the Ambae eruption of July 2018. It is shown that the aerosol plume of the main eruption at Ambae in July 2018 was distributed throughout the global stratosphere within the global large-scale circulation (Brewer-Dobson circulation, BDC), to both hemispheres. Ground-based LiDAR observations in Gadanki, India, as well as in-situ Printed Optical Particle Spectrometer (POPS) measurements acquired during the BATAL campaign confirm a widespread perturbation of the stratospheric aerosol layer due to this eruption. Using the UVSPEC radiative transfer model, we also estimate the radiative forcing of this global stratospheric aerosol perturbation. The climate impact is shown to be comparable to that of the well-known and studied recent moderate stratospheric eruptions from Kasatochi (USA, 2008), Sarychev (Russia, 2009) and Nabro (Eritrea, 2011). Top of the atmosphere radiative forcing values between -0.45 and -0.60 W/m<sup>2</sup>, for the Ambae eruption of July 2018, are found.</p><p>In a similar manner the dispersion of the aerosol plume of the Raikoke (48°N and 153°E) and Ulawun (5°S and 151°E) eruptions of June 2019 is analyzed. As both of those eruptions had a stratospheric impact and happened almost simultaneously, it is challenging to completely distinguish both events. Even though the eruptions occurred very recently, first results show that the aerosol plume of the Raikoke eruption resulted in an increase in aerosol extinction values, double as high as compared to that of the Ambae eruption. However, as the eruption occurred on higher latitudes, the main bulk of Raikoke aerosols was transported towards the northern higher latitude’s in the stratosphere within the BDC, as revealed by OMPS, SAGE III and a new detection algorithm for SO<sub>2</sub> and sulfate aerosol using IASI (Infrared Atmospheric Sounder Interferometer). Even though the Raikoke eruption had a larger impact on the stratospheric aerosol layer, both events (the eruptions at Raikoke and Ambae) have to be considered in stratospheric aerosol budget and climate studies.</p>

scholarly journals Impact of a New Radiation Package, McRad, in the ECMWF Integrated Forecasting System

2008 ◽  
Vol 136 (12) ◽  
pp. 4773-4798 ◽  
Author(s):  
J-J. Morcrette ◽  
H. W. Barker ◽  
J. N. S. Cole ◽  
M. J. Iacono ◽  
R. Pincus
Keyword(s):  
Radiative Transfer ◽  
Computational Cost ◽  
Vertical Plane ◽  
Radiative Transfer Model ◽  
Ensemble Prediction ◽  
Cold Bias ◽  
Transfer Model ◽  
Ensemble Prediction System ◽  
Forecasting System ◽  
The Impact

Abstract A new radiation package, “McRad,” has become operational with cycle 32R2 of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). McRad includes an improved description of the land surface albedo from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, the Monte Carlo independent column approximation treatment of the radiative transfer in clouds, and the Rapid Radiative Transfer Model shortwave scheme. The impact of McRad on year-long simulations at TL159L91 and higher-resolution 10-day forecasts is then documented. McRad is shown to benefit the representation of most parameters over both shorter and longer time scales, relative to the previous operational version of the radiative transfer schemes. At all resolutions, McRad improves the representation of the cloud–radiation interactions, particularly in the tropical regions, with improved temperature and wind objective scores through a reduction of some systematic errors in the position of tropical convection as a result of a change in the overall distribution of diabatic heating over the vertical plane, inducing a geographical redistribution of the centers of convection. Although smaller, the improvement is also seen in the rmse of geopotential in the Northern and Southern Hemispheres and over Europe. Given the importance of cloudiness in modulating the radiative fluxes, the sensitivity of the model to cloud overlap assumption (COA) is also addressed, with emphasis on the flexibility that is inherent to this new RT approach when dealing with COA. The sensitivity of the forecasts to the space interpolation that is required to efficiently address the high computational cost of the RT parameterization is also revisited. A reduction of the radiation grid for the Ensemble Prediction System is shown to be of little impact on the scores while reducing the computational cost of the radiation computations. McRad is also shown to decrease the cold bias in ocean surface temperature in climate integrations with a coupled ocean system.

scholarly journals Assimilating Compact Phase Space Retrievals (CPSRs): Comparison with Independent Observations (MOZAIC in situ and IASI Retrievals) and Extension to Assimilation of Truncated Retrieval Profiles

2018 ◽  
Author(s):  
Arthur P. Mizzi ◽  
David P. Edwards ◽  
Jeffrey L. Anderson
Keyword(s):  
Carbon Monoxide ◽  
Phase Space ◽  
Computational Cost ◽  
Lower Troposphere ◽  
Forecast Skill ◽  
Atmospheric Composition ◽  
Promising Alternative ◽  
Independent Observations ◽  
The Impact

Abstract. Assimilation of atmospheric composition retrievals presents computational challenges due to their high data volume and often sparse information density. Assimilation of compact phase space retrievals (CPSRs) meets those challenges and offers a promising alternative to assimilation of raw retrievals at reduced computational cost (Mizzi et al., 2016). This paper compares analysis and forecast results from assimilation of Terra/Measurement of Pollution in the Troposphere (MOPITT) carbon monoxide (CO) CPSRs with independent observations. We use MetOp-A/Infrared Atmospheric Sounding Interferometer (IASI) CO retrievals and Measurement of OZone, water vapor, carbon monoxide, and nitrogen oxides by in service AIrbus airCraft (MOZAIC) in situ CO profiles for our independent observation comparisons. Generally, the results confirm that assimilation of MOPITT CPSRs improved the WRF-Chem/DART analysis fit and forecast skill at a reduced computational cost (~ 35 % reduction) when compared to assimilation of raw or quasi-optimal retrievals (QORs). Comparison with the independent observations shows that assimilation of MOPITT CO generally improved the analysis fit and forecast skill in the lower troposphere but degraded it in the upper troposphere. We attribute that degradation to assimilation of MOPITT CO retrievals with a possible bias of ~ 14 % above 300 hPa. To discard the biased retrievals, in this paper we also extend CPSRs to assimilation of truncated retrieval profiles (as opposed to assimilation of full retrieval profiles). Those results show that not assimilating the biased retrievals: (i) resolves the upper tropospheric analysis fit degradation issue, (ii) has commensurate reductions in assimilation computation cost, and (iii) reduces the impact of assimilating the remaining unbiased retrievals because the total information content and vertical sensitivities are changed.

Investigating the Influence of Mean-Opacity (𝜅) Values on Interior-Atmosphere Modelling

2020 ◽  
Author(s):  
Jasmine MacKenzie ◽  
Philipp Baumeister ◽  
Mareike Godolt ◽  
John Lee Grenfell ◽  
Nicola Tosi
Keyword(s):  
Radiative Transfer ◽  
Temperature Profile ◽  
Parameter Space ◽  
Pure Iron ◽  
Computational Cost ◽  
Interior Structure ◽  
Robust Methods ◽  
Line Model ◽  
The Mean ◽  
The Impact

<p>Ever since the discovery of sub-Neptunes, exoplanets with masses < 20 M⊕ and radii < 4 R⊕, they have presented a distinct challenge in the exoplanet modelling community. When plotted on a mass-radius diagram, their bulk densities lie in a range spanning from that of pure iron to less than water. Such bulk densities are not necessarily indicative of the interior structure within, and when characterized using interior models the results are often varied in their morphology and highly degenerate. </p> <p> </p> <p>A semi-grey pressure-temperature profile approximation for an atmosphere is a popular choice in Interior-Atmosphere modelling as could allow us to estimate the radius contribution of an atmosphere as well as a full radiative transfer line-by-line model, but without the computational cost of a full 1-D radiative convective climate-chemistry model. Since the parameter space is large, thousands of interior-atmosphere model runs are required in order to quantify the potential degeneracies. Nevertheless, while the semi-grey approximation treats the problem in a more simplified manner than other more robust methods, which allows for faster analytical calculations, there are still underdetermined factors which make choosing the most appropriate value difficult without more data (e.g. atmospheric spectra and profiles). </p> <p> </p> <p>In this talk I will explore the impact of the different ways one chooses the value of one factor, the mean-opacity (

scholarly journals Assimilating compact phase space retrievals (CPSRs): comparison with independent observations (MOZAIC in situ and IASI retrievals) and extension to assimilation of truncated retrieval profiles

2018 ◽  
Vol 11 (9) ◽  
pp. 3727-3745 ◽  
Author(s):  
Arthur P. Mizzi ◽  
David P. Edwards ◽  
Jeffrey L. Anderson
Keyword(s):  
Carbon Monoxide ◽  
Phase Space ◽  
Data Assimilation ◽  
Computational Cost ◽  
Lower Troposphere ◽  
Forecast Skill ◽  
Promising Alternative ◽  
Independent Observations ◽  
The Impact

Abstract. Assimilation of atmospheric composition retrievals presents computational challenges due to their high data volume and often sparse information density. Assimilation of compact phase space retrievals (CPSRs) meets those challenges and offers a promising alternative to assimilation of raw retrievals at reduced computational cost (Mizzi et al., 2016). This paper compares analysis and forecast results from assimilation of Terra/Measurement of Pollution in the Troposphere (MOPITT) carbon monoxide (CO) CPSRs with independent observations. We use MetOp-A/Infrared Atmospheric Sounding Interferometer (IASI) CO retrievals and Measurement of OZone, water vapor, carbon monoxide, and nitrogen oxides by in-service AIrbus airCraft (MOZAIC) in situ CO profiles for our independent observation comparisons. Generally, the results confirm that assimilation of MOPITT CPSRs improves the Weather Research and Forecasting model with chemistry coupled to the ensemble Kalman filter data assimilation from the Data Assimilation Research Testbed (WRF-Chem/DART) analysis fit and forecast skill at a reduced computational cost compared to assimilation of raw retrievals. Comparison with the independent observations shows that assimilation of MOPITT CO generally improved the analysis fit and forecast skill in the lower troposphere but degraded it in the upper troposphere. We attribute that degradation to assimilation of MOPITT CO retrievals with a possible bias of  ∼ 14 % above 300 hPa. To discard the biased retrievals, in this paper, we also extend CPSRs to assimilation of truncated retrieval profiles (as opposed to assimilation of full retrieval profiles). Those results show that not assimilating the biased retrievals (i) resolves the upper tropospheric analysis fit degradation issue and (ii) reduces the impact of assimilating the remaining unbiased retrievals because the total information content and vertical sensitivities are changed.

In situ Quantification of the Impact of Episodic Enhanced Turbulent Events in Large Phytoplankton

2011 ◽  
Author(s):  
Percy L. Donaghay ◽  
Jan Rines ◽  
James Sullivan
Keyword(s):  
The Impact

Bayesian analysis reveals the impact of load partitioning on microstructural evolution in Ti-6Al-4V during in-situ tensile loading

Materialia ◽  
2021 ◽  
Vol 15 ◽  
pp. 100993
Author(s):  
N. Armstrong ◽  
P.A. Lynch ◽  
P. Cizek ◽  
S.R. Kada ◽  
S. Slater ◽  
...  
Keyword(s):  
Bayesian Analysis ◽  
Microstructural Evolution ◽  
Tensile Loading ◽  
The Impact

scholarly journals Solid-Phase Extraction Embedded Dialysis (SPEED), an Innovative Procedure for the Investigation of Microbial Specialized Metabolites

Marine Drugs ◽  
2021 ◽  
Vol 19 (7) ◽  
pp. 371
Author(s):  
Phuong-Y Mai ◽  
Géraldine Le Goff ◽  
Erwan Poupon ◽  
Philippe Lopes ◽  
Xavier Moppert ◽  
...  
Keyword(s):  
Solid Phase Extraction ◽  
Solid Phase ◽  
Chemical Space ◽  
Molecular Profile ◽  
Phase Extraction ◽  
Specialized Metabolites ◽  
Streptomyces Albidoflavus ◽  
Cultivation Process ◽  
The Impact

Solid-phase extraction embedded dialysis (SPEED technology) is an innovative procedure developed to physically separate in-situ, during the cultivation, the mycelium of filament forming microorganisms, such as actinomycetes and fungi, and the XAD-16 resin used to trap the secreted specialized metabolites. SPEED consists of an external nylon cloth and an internal dialysis tube containing the XAD resin. The dialysis barrier selects the molecular weight of the trapped compounds, and prevents the aggregation of biomass or macromolecules on the XAD beads. The external nylon promotes the formation of a microbial biofilm, making SPEED a biofilm supported cultivation process. SPEED technology was applied to the marine Streptomyces albidoflavus 19-S21, isolated from a core of a submerged Kopara sampled at 20 m from the border of a saltwater pond. The chemical space of this strain was investigated effectively using a dereplication strategy based on molecular networking and in-depth chemical analysis. The results highlight the impact of culture support on the molecular profile of Streptomyces albidoflavus 19-S21 secondary metabolites.

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