Atmospheric Model Research Articles

Designing a Fully‐Tunable and Versatile TKE‐l Turbulence Parameterization for the Simulation of Stable Boundary Layers

AbstractThis study presents the development of a so‐called Turbulent Kinetic Energy (TKE)‐l, or TKE‐l, parameterization of the diffusion coefficients for the representation of turbulent diffusion in neutral and stable conditions in large‐scale atmospheric models. The parameterization has been carefully designed to be completely tunable in the sense that all adjustable parameters have been clearly identified and the number of parameters has been minimized as much as possible to help the calibration and to thoroughly assess the parametric sensitivity. We choose a mixing length formulation that depends on both static stability and wind shear to cover the different regimes of stable boundary layers. We follow a heuristic approach for expressing the stability functions and turbulent Prandlt number in order to guarantee the versatility of the scheme and its applicability for planetary atmospheres composed of an ideal and perfect gas such as that of Earth and Mars. Particular attention has been paid to the numerical stability and convergence of the TKE equation at large time steps, an essential prerequisite for capturing stable boundary layers in General Circulation Models (GCMs). Tests, parametric sensitivity assessments and preliminary tuning are performed on single‐column idealized simulations of the weakly stable boundary layer. The robustness and versatility of the scheme are assessed through its implementation in the Laboratoire de Météorologie Dynamique Zoom GCM and the Mars Planetary Climate Model and by running simulations of the Antarctic and Martian nocturnal boundary layers.

Study on the reactions of n-pentanal and n-hexanal with Br atoms: Kinetics, gas-phase products, and SOA formation

Aldehydes are one of the most important oxygenated volatile organic compounds in the atmosphere, contributing to atmospheric radicals such as HO2 and RO2, which play a pivotal role in atmospheric chemistry and the oxidative capacity of the atmosphere. The kinetics, gas-phase products, and SOA formation of pentanal and n-hexanal initiated by Br atoms were studied in this work. The reaction rate constants of n-pentanal and n-hexanal reacting with Br atoms were determined to be (1.77 ± 0.25) × 10−11 cm3 molecule−1 s−1 and (2.07 ± 0.29) × 10−11 cm3 molecule−1 s−1 at 298 K and 760 Torr, respectively. Key gas-phase products, including smaller aldehydes, carboxylic acids, and alcohols, are known to contribute to atmospheric reactivity and have potential implications for air quality by promoting the formation of secondary pollutants and influencing the oxidative capacity of the atmosphere. The SOA yields were (5.24 ± 0.10)% and (6.00 ± 1.20)% for n-pentanal and n-hexanal, respectively, higher than the SOA yields of the aldehydes reaction initiated by OH radicals. The higher SOA yields observed from Br atoms oxidation compared to OH radical oxidation highlight the necessity to re-evaluate the role of halogen chemistry in atmospheric processes, particularly in regions where halogen compounds are prevalent. This research enhances our understanding of the atmospheric fate of aldehydes and highlights the importance of considering halogen-driven oxidation pathways in atmospheric models.

Discovery of SRGA J144459.2−604207 with the SRG/ART-XC telescope: A well-tempered bursting accreting millisecond X-ray pulsar

We report the discovery of the new accreting millisecond X-ray pulsar SRGA J144459.2−604207 using data of the SRG/ART-XC. The source was observed twice in February 2024 during the declining phase of the outburst. The timing analysis revealed a coherent signal near 447.9 Hz modulated by the Doppler effect due to the orbital motion. The derived parameters for the binary system are consistent with a circular orbit with a period of ∼5.2 h. The pulse profiles of the persistent emission, showing a sine-like part during half a period with a plateau in between, can be well modeled by emission from two circular spots that are partially eclipsed by the accretion disk. Additionally, during our observations with an exposure of 133 ks, we detected 19 thermonuclear X-ray bursts. All bursts have similar shapes and energetics, and none show any signs of an expanding photospheric radius. The burst recurrence times decreases linearly from ∼1.6 h at the beginning of observations to ∼2.2 h at the end and anticorrelate with the persistent flux. The spectral evolution during the bursts is consistent with the models of the neutron star atmospheres that are heated by accretion and implies a neutron star radius of 11–12 km and a distance to the source of 8–9 kpc. We also detected coherent pulsations during the bursts and showed that the pulse profiles differ substantially from those observed in the persistent emission. However, we could not find a simple physical model explaining the pulse profiles detected during the bursts.

Tropical Leaf Wax n‐Alkane and n‐Alkanoic Acid Reflect δD of Precipitation During Early Stages of Leaf Growth: Insights From an Isotope Labeling Experiment

AbstractThe hydrogen isotopic compositions of leaf‐wax n‐alkanes (δDalk) and n‐alkanoic acids (δDacid) reflect ambient climatic conditions (including precipitation δD values, δDprecip). However, the understanding of climatic conditions of exactly which period (i.e., early or entire period of the leaf's lifespan) these biomarkers preserve is still evolving. Previous studies on the δDalk and δDacid values, done only in extra‐tropical regions, mostly indicate that δDalk values are biased toward the early growing season whereas δDacid values are not biased toward any season. To decipher the seasonal bias in δDalk and δDacid records from tropics, we conducted a long‐duration experiment wherein deciduous and evergreen species were grown using normal water (δD = −2‰) during early stages of the leaf growth and later using isotopically labeled water (δD = 1,000‰). Our experiment revealed (a) in deciduous and evergreen species, δDalk and δDacid values reflect δDprecip during early stages of the leaf growth, (b) synchronous synthesis of n‐alkanes and n‐alkanoic acids, and (c) in deciduous species, minor incorporation of the previous year's photosynthates in leaf wax pool of the current year's mature leaves. Our study suggests that δDalk and δDacid records in the tropics are biased toward the climatic conditions prevailing during early stages of leaf growth. This bias should be considered while comparing the δDprecip values generated from leaf wax proxy records and isotope‐enabled atmospheric circulation models.

Envisioning a decision support system for the planning of alternative fuel bunkering operations in Singapore

Abstract In the coming decades, the global maritime industry will face a most formidable technological and societal challenge set by climate change – achieving net zero carbon emissions by 2050. To meet this target, ships are shifting towards the use of low-carbon alternative fuels such as ammonia and methanol. While this paradigm shift to the bunkering of greener fuels is encouraging, it also introduces a new and unique type of environmental risk in the unfortunate scenario of a spill. In the past decades numerous environmental studies have been conducted and mitigation techniques for petroleum oil spills have been developed. However, ammonia and methanol spills are comparatively less understood globally and in the region. There is a significant knowledge gap regarding how the complex atmosphere, hydrodynamic and environmental conditions of the Singapore Straits may influence the dispersion and assimilation of hypothetical ammonia or methanol plumes. Together with other emerging alternative fuels such as electricity and hydrogen, ammonia and methanol have different physical and chemical properties in ambient water compared to conventional LNG or petroleum oil which makes modelling the risk they pose to the environment more challenging. In view of these challenges, the key objective of our research is to develop an operationally running decision support system (DSS) that combines physics-based atmospheric and coastal hydrodynamic models that can forecast the marine and atmospheric plume dispersion of alternative fuels. This forecasting capability will be supplemented with data-driven and rule-based optimisation algorithms that can be used to determine the optimal mitigation scenarios which minimises the potential environmental impacts. Overall, the DSS will integrate observation data, models, mitigation scenarios, and decision-making tools pertaining to efficient and safe bunkering operations within Singapore’s ports. This is essential as the use of alternative fuels in maritime industry becomes more common in Singapore and around the world. Such a system will aid relevant authorities to better calculate risk and plan mitigation measures at designated bunkering locations and periods having optimal atmospheric, hydraulics, and environmental conditions. In this paper, we describe the potential consequences of alternative fuel spills, mitigation measures and a plan for assessing their environmental impact within the context of Singapore. We will review the limited current efforts to model ammonia spills in the literature and propose for a more integrated modelling approach through the DSS.

Should We Conserve Entropy or Energy when Computing CAPE with Mixed-Phase Precipitation Physics?

Abstract The rapidly increasing resolution of global atmospheric reanalysis and climate model datasets necessitates finding methods for computing convective available potential energy (CAPE) both efficiently and accurately. To this end, this article compares two common methods for computing CAPE which conserve either energy or entropy. Inaccuracies in these computations arise from both physical and numerical errors. For instance, computing CAPE with entropy conserved results in physical errors from nonequilibrium phase transitions but minimizes numerical errors because solutions are analytic at each height. In contrast, computing CAPE with energy conserved avoids these physical errors, but accumulates numerical errors that are grid-resolution-dependent because the numerical integration of a differential equation is required. Analysis of CAPE computed with large databases of soundings from the tropical Amazon and midlatitude storm environments shows that physical errors from the entropy method are typically 1%–3% as large as CAPE, which is comparable to the numerical errors from conserving energy with grid spacing of 25 and 250 m using explicit first-order and second-order integration schemes, respectively. Errors in entropy-based CAPE calculations are also insensitive to vertical grid spacing, in contrast to energy-based calculations whose error strongly scales with the grid spacing. It is shown that entropy-based methods are advantageous when intercomparing datasets with differing vertical resolution because they produce accurate and reasonably fast results that are insensitive to grid resolution, whereas a second-order energy-based method is advantageous when analyzing data with a consistent vertical resolution because of its superior computational efficiency. Significance Statement Convective available potential energy (CAPE) is a measure of instability in the atmosphere that helps forecasters and researchers understand when and where thunderstorms will form. The purpose of this article is to identify the most efficient and accurate methods for computing CAPE. Two methods are considered here, one that relates to the entropy (a measure of thermodynamic disorder) of an air parcel and one that relates to the energy of an air parcel. Results indicate that the entropy method is most accurate and insensitive to the resolution of the data used for the calculation (which can vary considerably), whereas the energy method uses the least computation time.

The analysis of the scatters of the filtered residuals of the GNSS stations from the crustal movement observation network of China

Through the analysis of the coordinate time series of the stations in the Crustal Movement Observation Network of China (CMONOC) from 2011 to 2019, it is found that the daily network scatters of the filtered residuals (called as SFR) of the station coordinate time series have obvious seasonal variation characteristics which reaches a maximum during summer and a minimum during winter. This phenomenon has not yet been further explained. Our analysis results demonstrate that the seasonal pattern of the daily SFR solutions is the temperature-dependent, such as small-scale atmospheric perturbation. The pattern of SFR series of the difference between the zenith wet delay (ZWD) calculated with GPS data and that calculated with meteorological data is similar to the SFR solutions computed using GPS data. The results mean that the estimated ZWD using GPS data does not fully capture the total real atmospheric variation. The atmospheric delay model in current GNSS analysis can effectively solve large-scale atmospheric delay estimation, but it may fail to deduct certain small-scale atmospheric disturbances. We think that a considerable portion of these small-scale disturbances are absorbed by the estimates of station positions.

IRDNet: An image-defogging algorithm based on dark channel prior

Abstract Image-defogging, as an important part of computer vision, has been widely used in intelligent driving, target recognition, satellite detection, underwater exploration and so on. Improving the performance of the defogging algorithm based on deep learning has practical significance for the completion of high-level vision tasks. This paper proposes an IRDNet algorithm by improving the image deep learning algorithm based on the RefineDNet framework and designing a new deep learning network structure. The proposed algorithm combines dark channel prior knowledge and atmospheric degradation model to decompose the input fogged images into dark channel images and degraded images, and then carries out feature extraction and detail enhancement for the two images by convolutional neural network. IRDNet introduces a fully connected convolutional structure, attention mechanism, and a pyramid structure to improve the performance of the overall defogging network. By testing on OTS datasets, we compare the IRDNet algorithm with traditional defogging methods, end-to-end deep learning defogging methods, and prior knowledge-guided deep learning defogging methods. Test results show that the performance of IRDNet is better than other methods, and the defogging network shows richer details of texture and more realistic colors.

Optical orthogonal frequency division multiplexing with differential index modulation

This paper proposes a differential index modulation (DIM) scheme to address the complex channel estimation challenges in optical orthogonal frequency division multiplexing with index modulation (OOFDM-IM). The main idea of the DIM scheme is to design a time-frequency dispersive matrix with unitary characteristics and perform index mapping based on the Lemer code principles. By applying differential operations, the DIM scheme enables decoding at the receiver without requiring channel estimation. The paper provides a detailed explanation of the design principles and theoretical bit error rate (BER) of the proposed scheme. Simulations based on the exponential Weibull atmospheric turbulence channel model are conducted to compare the DIM scheme with the existing OOFDM-IM scheme. Additionally, a carefully designed proof-of-concept experiment is performed to further validate the scheme’s effectiveness and feasibility. Both simulation and experimental results demonstrate that, compared to OOFDM-IM, the proposed scheme can entirely avoid complex channel estimation with a maximum signal-to-noise ratio (SNR) loss of no more than 4 dB, even under various turbulence intensities and higher-order modulation scenarios. This provides a valuable reference for OOFDM-IM in complex environments or where channel estimation is challenging.

Addressing atmospheric absorption in adaptive rectangular decomposition.

This paper focuses on the adaptive rectangular decomposition (ARD) scheme, a wave-based method employed for acoustic simulations. ARD holds promise for diverse applications. In architectural design, it can forecast acoustical parameters, facilitating the creation of spaces with superior sound quality. Moreover, in the domain of acoustic virtual reality, ARD can offer users a more immersive and lifelike acoustic environment. This enhancement proves advantageous for all of these applications, enabling the simulation of larger environments with heightened precision. Despite its notable efficiency, ARD faces a significant drawback: the absence of atmospheric absorption modeling. The principal aim of this study is to rectify this limitation, thereby augmenting the capabilities of the ARD algorithm.

Permafrost Region Greenhouse Gas Budgets Suggest a Weak CO2 Sink and CH4 and N2O Sources, But Magnitudes Differ Between Top‐Down and Bottom‐Up Methods

AbstractLarge stocks of soil carbon (C) and nitrogen (N) in northern permafrost soils are vulnerable to remobilization under climate change. However, there are large uncertainties in present‐day greenhouse gas (GHG) budgets. We compare bottom‐up (data‐driven upscaling and process‐based models) and top‐down (atmospheric inversion models) budgets of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) as well as lateral fluxes of C and N across the region over 2000–2020. Bottom‐up approaches estimate higher land‐to‐atmosphere fluxes for all GHGs. Both bottom‐up and top‐down approaches show a sink of CO2 in natural ecosystems (bottom‐up: −29 (−709, 455), top‐down: −587 (−862, −312) Tg CO2‐C yr−1) and sources of CH4 (bottom‐up: 38 (22, 53), top‐down: 15 (11, 18) Tg CH4‐C yr−1) and N2O (bottom‐up: 0.7 (0.1, 1.3), top‐down: 0.09 (−0.19, 0.37) Tg N2O‐N yr−1). The combined global warming potential of all three gases (GWP‐100) cannot be distinguished from neutral. Over shorter timescales (GWP‐20), the region is a net GHG source because CH4 dominates the total forcing. The net CO2 sink in Boreal forests and wetlands is largely offset by fires and inland water CO2 emissions as well as CH4 emissions from wetlands and inland waters, with a smaller contribution from N2O emissions. Priorities for future research include the representation of inland waters in process‐based models and the compilation of process‐model ensembles for CH4 and N2O. Discrepancies between bottom‐up and top‐down methods call for analyses of how prior flux ensembles impact inversion budgets, more and well‐distributed in situ GHG measurements and improved resolution in upscaling techniques.

China's methane emissions derived from the inversion of GOSAT observations with a CMAQ and EnKS-based regional data assimilation system

At present, inversions at higher temporal and spatial resolution tend to be in increasing demand. The resolution and precision of methane (CH4) inversions depend on quality of observations, transport model, and inversion scheme. Currently, most inversion-based estimates of CH4 in China use a global atmospheric transport model to relate emissions to observations, or a Lagrangian model to quantify the receptor-to-source sensitivity. Taking advantage of the ability that regional transport models have in mesoscale simulation, a regional inversion system was developed to infer China's CH4 emissions. The CMAQ (Community Multi-scale Air Quality) model was configured for forward simulation of CH4, including processes of emission, transport, diffusion, and chemical transformation. Furthermore, the Ensemble Kalman Smoother was extended to assimilate satellite observations with joint optimization scheme of concentrations and emissions to reduce the impact of initial uncertainty. We found that the posterior annual estimated emissions (53.30 Tg a−1) in 2020 were closer to the official reported figure (53.57 Tg a−1) than to the prior (63.80 Tg a−1), with a downward correction of 16.45% in prior estimates based on extrapolation of the bottom-up inventory, which likely led to overestimation. Moreover, under current observational coverage, monthly posterior estimates reflected region-dependent responses to local conditions. Generally, the regional assimilation system estimated annual and monthly CH4 emissions well, attributable to reliable CMAQ simulation, joint assimilation scheme, and careful selection of satellite retrievals. In addition, evaluation of the posterior estimates indicates that inversion delivers reasonable improvements, but amelioration of uncertainties in prior information and observations is still needed.

Spectroscopic survey of faint planetary-nebula nuclei

We present an analysis of 17 H-rich central stars of planetary nebulae (PNe) observed in our spectroscopic survey of nuclei of faint Galactic PNe carried out at the 10-m Hobby-Eberly Telescope. Our sample includes ten O(H) stars, four DAO white dwarfs (WDs), two DA WDs, and one sdOB star. The spectra were analyzed by means of NLTE model atmospheres, allowing us to derive the effective temperatures, surface gravities, and He abundances of the central stars. Sixteen of them were analyzed for the first time, increasing the number of hot H-rich central stars with parameters obtained through NLTE atmospheric modeling by approximately 20%. We highlight a rare hot DA WD central star, Abell 24, which has a Teff likely in excess of 100 kK, as well as the unusually high gravity mass of 0.70 ± 0.05 M⊙ for the sdOB star Pa 3, which is significantly higher than the canonical extreme horizontal-branch star mass of ≈0.48 M⊙. By investigating Zwicky Transient Facility light curves, which were available for our 15 northern objects, we found none of them show a periodic photometric variability larger than a few hundredths of a magnitude. This could indicate that our sample mainly represents the hottest phase during the canonical evolution of a single star when transitioning from an asymptotic giant branch star into a WD. We also examined the spectral energy distributions, detecting an infrared excess in six of the objects, which could be due to a late-type companion or to hot (≈103 K) and/or cool (≈100 K) dust. We confirm previous findings that spectroscopic distances are generally higher than found through Gaia astrometry, a discrepancy that deserves to be investigated systematically.

Evaluating the reliability of UAV-based carbon dioxide measurements in the lower troposphere

Vertical profiles of carbon dioxide (CO2) were captured in rural Ontario, Canada, using an Aeroqual Series 500 monitor mounted onboard an Uncrewed Aerial Vehicle (UAV). Measurements at various altitudes within the Transport Canada regulations height limit (5m – 95m) were compared to simultaneous measurements taken by an identical sensor at ground-level. Results demonstrate a high degree of agreement between onboard and ground-level observations, with a mean different of -6.02 ppm, and the majority of differences falling within the sensor’s factory calibration accuracy (±10 ppm + 5%). The study also demonstrates the ability to capture the homogeneity of CO2 in the lower troposphere, with Intraclass Correlation Coefficients (ICC) exceeding 0.75 at all altitudes, without the addition of turbulence by UAV flight. The vertical profiles captured in this study validate the use of UAV-based measurements for understanding the distribution and transport of greenhouse gases near the surface of the Earth. This research has implications for routine air quality monitoring to improve atmospheric models, environmental impact assessments and the development of targeted emission reduction strategies.

A regional ocean–atmosphere coupled model using CMA-TRAMS and LICOM: Preliminary results for tropical cyclone gale prediction over the northern South China Sea

This paper provides a comparative analysis of the performance of a high-resolution regional ocean–atmosphere coupled model in predicting tropical cyclone (TC) gales over the northern South China Sea. The atmosphere and ocean components of the coupled system are represented by the China Meteorological Administration's Tropical Regional Atmosphere Model for the South China Sea (CMA-TRAMS) and the LASG/IAP Climate system Ocean Model (LICOM), respectively. The Ocean Atmosphere Sea Ice Soil VersionH 3 (OASIS3) software has been utilized for the exchange of momentum, heat, and freshwater fluxes between these two components. An assessment of the coupled model's three-day predictions for five TCs’ gales was conducted. Preliminary findings indicate that the predicted TC tracks show less sensitivity to oceanic influences than the predicted TC intensities. Significant improvement in predicting the surface TC gales has been achieved through coupling the ocean model. This improvement is attributed to the impact of the warmer ocean's effect on TC intensification, counteracting the cooling effect of the cold wake. In summary, coupling has enhanced the model's predictive capabilities for TC gales. A detailed assessment of the coupled model's performance in predicting other tropical weather phenomena is forthcoming.摘要本文对一个具有我国自主知识产权的高分辨率区域海气耦合模式在南海北部台风大风预报性能进行对比分析. 该耦合模式的大气和海洋部分分别为中国气象局南海台风模式 (CMA-TRAMS) 和中国科学院大气物理研究所的海洋模式 (LICOM), 并用OASIS耦合器实现海气界面动量, 热量和淡水通量的交换. 本文对海气耦合模式预报5个台风的24, 48和72小时大风的性能进行了检验评估. 初步结果表明, 预报的台风路径对海洋影响的敏感性低于台风强度. 耦合模式使预报台风大风的准确性得到显著提高, 这一改进归结于海气耦合模式更为准确的海表温度对台风增强的影响, 从而抵消了冷尾流的降温效应. 总而言之, 耦合模式增强了模式对台风大风的预报能力. 关于海气耦合模式在其他热带天气中的预报能力评估将在未来工作中展示.

A network of cooler white dwarfs as infrared standards for flux calibration

ABSTRACT The accurate flux calibration of observational data is vital for astrophysics and cosmology because absolute flux uncertainties of stellar standards propagate into scientific results. With the ever higher precision achieved by telescopic missions (e.g. JWST) in the infrared (IR), suitable calibrators are required for this regime. The basis of the Hubble Space Telescope (HST) flux scale is defined by model fits of three hot (${T_\mathrm{eff}} > 30\, 000$ K) hydrogen-atmosphere (DA) white dwarfs, which achieve an accuracy better than 1 per cent at optical wavelengths but falls below this level in the IR range. We present a network of 17 cooler DA white dwarfs with ${T_\mathrm{eff}} < 20\, 000$ K as spectrophotometric flux standards that are equally, if not more, accurate at IR wavelengths. Cooler white dwarfs do not suffer from non-local thermal equilibrium effects in continuum flux or from ultraviolet metal line blanketing, have a larger sky density, are generally closer to Earth with little or negligible interstellar reddening, and have energy distributions peaking in the optical or near-IR. Using the latest grid of DA local thermal equilibrium atmosphere models with three-dimensional convection, the observed Space Telescope Imaging Spectrometer (STIS) and Wide Field Camera 3 (WFC3) fluxes of our network are accurate to 3 per cent over most of the range $1450\!\! - \!\!16\, 000$ Å, with a median standard deviation of 1.41 per cent. Fitting the HST STIS and WFC3 white dwarf spectral energy distributions (SEDs) and Balmer lines independently yields SEDs that agree within $3\sigma$, which demonstrates the precision of the models for our network.

JWST-TST High Contrast: Spectroscopic Characterization of the Benchmark Brown Dwarf HD 19467 B with the NIRSpec Integral Field Spectrograph

We present the atmospheric characterization of the substellar companion HD 19467 B as part of the pioneering James Webb Space Telescope Guaranteed Time Observer program to obtain moderate resolution spectra (R ∼ 2700, 3–5 μm) of a high-contrast companion with the NIRSpec integral field unit (IFU). HD 19467 B is an old, ∼9 Gyr, companion to a solar-type star with multiple measured dynamical masses. The spectra show detections of CO, CO2, CH4, and H2O. We forward model the spectra using Markov Chain Monte Carlo methods and atmospheric model grids to constrain the effective temperature and surface gravity. We then use NEWERA-PHOENIX grids to constrain nonequilibrium chemistry parameterized by K zz and explore molecular abundance ratios of the detected molecules. We find an effective temperature of 1103 K, with a probable range from 1000 to 1200 K, a surface gravity of 4.50 dex, with a range of 4.14–5.00, and deep vertical mixing, log10(K zz ), of 5.03, with a range of 5.00–5.44. All molecular mixing ratios are approximately solar, leading to a C/O ∼ 0.55, which is expected from a T5.5 brown dwarf. Finally, we calculate an updated dynamical mass of HD 19467 B using newly derived NIRCam astrometry, which we find to be 71.6−4.6+5.3MJup , in agreement with the mass range we derive from evolutionary models, which we find to be 63–75 M Jup. These observations demonstrate the excellent capabilities of the NIRSpec IFU to achieve detailed spectral characterization of substellar companions at high contrast close to bright host stars, in this case at a separation of ∼1.″6 with a contrast of 10−4 in the 3–5 μm range.

Unveiling the HD 95086 system at mid-infrared wavelengths with JWST/MIRI

Context. Mid-infrared imaging of exoplanets and disks is now possible with the coronographs of the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). This wavelength range unveils new features of young directly imaged systems and allows us to obtain new constraints for characterizing the atmosphere of young giant exoplanets and associated disks. Aims. These observations aim to characterize the atmosphere of the planet HD 95086 b by adding mid-infrared information so that the various hypotheses about its atmospheric parameters values can be unraveled. Improved images of cirsumstellar disks are provided. Methods. We present the MIRI coronagraphic imaging of the system HD 95086 obtained with the F1065C, F1140, and F2300C filters at central wavelengths of 10.575 µm, 11.3 µm, and 23 µm, respectively. We explored the method for subtracting the stellar diffraction pattern in the particular case when bright dust emitting at short separation is present. Furthermore, we compared different methods for extracting the photometry of the planet. Using the atmospheric models Exo-REM and ATMO, we measured the atmospheric parameters of HD 95086 b. Results. The planet HD 95086 b is detected at the two shortest MIRI wavelengths F1065C and F1140C. The contribution from the inner disk of the system is also detected. It is similar to that in the HR 8799 system. The outer colder belt is imaged at 23 µm. Background objects are observed in all filters. The mid-infrared photometry provides better constraints on the atmospheric parameters. We evaluate a temperature of 800–1050 K, consistent with one previous hypothesis that only used near-infrared data. The radius measurement of 1.0–1.14 RJup is better aligned with evolutionary models, but still smaller than predicted. These observations allow us to refute the hypothesis of a warm circumplanetary disk. Conclusions. HD 95086 is one of the first exoplanetary systems to be revealed at mid-infrared wavelengths. This highlights the interests and challenges of observations at these wavelengths.

Observations of Extremely Metal-poor O Stars: Weak Winds and Constraints for Evolution Models

Metal-poor massive stars drive the evolution of low-mass galaxies, both locally and at high redshift. However, quantifying the feedback they impart to their local surroundings remains uncertain because models of stellar evolution, mass loss, and ionizing spectra are unconstrained by observations below 20% solar metallicity (Z ⊙). We present new Keck Cosmic Web Imager optical spectroscopy of three O-type stars in the nearby dwarf galaxies Leo P, Sextans A, and WLM, which have gas-phase oxygen abundances of 3%–14% Z ⊙. To characterize their fundamental stellar properties and radiation-driven winds, we fit PoWR atmosphere models to the optical spectra simultaneously with Hubble Space Telescope far-ultraviolet (FUV) spectra and multiwavelength photometry. We find that all three stars have effective temperatures consistent with their spectral types and surface gravities typical of main-sequence dwarf stars. Yet, the combination of those inferred parameters and luminosity for the two lower-Z stars is not reproduced by stellar evolution models, even those that include rotation or binary interactions. The scenario of multiple-star systems is difficult to reconcile with all available data, suggesting that these observations pose a challenge to current evolution models. We highlight the importance of validating the relationship between stellar mass, temperature, and luminosity at very low Z for accurate estimates of ionizing photon production and spectral hardness. Finally, all three stars’ FUV wind profiles reveal low mass-loss rates and terminal wind velocities in tension with expectations from widely adopted radiation-driven wind models. These results provide empirical benchmarks for future development of mass-loss and evolution models for metal-poor stellar populations.

Ensemble Based Estimation of Wet Refractivity Indices Using a Functional Model Approach

AbstractThe estimation of the wet refractivity indices is crucial for applications like weather predictions or improving the accuracy of real‐time positioning techniques. Traditionally, solving the inverse tomography problem to estimate these atmospheric parameters has been challenging due to its ill‐posed nature and high computational demands, necessitating additional constraints. To overcome these challenges, the data assimilation method is proposed here to integrate Global Navigation Satellite System (GNSS) observations into a background model. In this study, the Ensemble Kalman Filter (EnKF) was served as the assimilation core to reduce the computational load and to enable the epoch‐wise estimation of wet refractivity indices. The Global Pressure and Temperature 3 (GPT3w) model was utilized as the background, and wet refractivity indices at each epoch were transformed into B‐spline coefficients, representing state vector parameters. Subsequently, GNSS derived zenith wet delay (ZWD) values were integrated into the model using the EnKF method. The study's region encompassed the western parts of Europe and incorporated approximately 893 GNSS stations. Evaluation spanned from 1 January 2017 to 31 December 2017. The estimated wet refractivity indices from the proposed method were compared with observations from 16 existing radiosonde stations, radio occultation data, and ZWD values from the 47 selected GNSS test stations. Additionally, calculated ZWD values, resulting from the integration of wet refractivity indices, were compared to the ZWD values from 47 test stations in the study region. The numerical results demonstrated that the proposed method achieved a root mean square error value of approximately 2.6 ppm, which was nearly 49% and 18% lower than that of the considered empirical and numerical atmospheric models, respectively.