Long-term Variability of Martian Atmospheric Water Vapor Abundances from PFS/MEX Observations

ABSTRACT Currently, a variety of land surface temperature (LST) products generated from thermal infrared bands have been already accumulated. Compared to the thermal infrared band, the mid-infrared band exhibits higher transmittance and greater robustness under humid atmospheric conditions, offering potential for further improving LST retrieval accuracy. However, the mid-infrared band presents larger variability in emissivity and higher estimation difficulty, limiting the effectiveness of LST retrieval using mid-infrared remote sensing data sources. This study proposed a MODIS night-time mid-infrared LST retrieval algorithm that integrates reflectance spectral characteristics to estimate emissivity. A few-shot machine learning model was established to build the correlation between MODIS optical band reflectance and mid-infrared band emissivity within a simulated dataset accounting for mixed spectral components, then applied to real observational data. Validation results from SURFRAD ground stations indicate an overall RMSE of 2.5521 K for this new algorithm, with values of 2.5558 K under dry atmospheric conditions and 2.5021 K under humid atmospheric conditions. The new algorithm can accurately retrieve night-time LST without significant error increasing as atmospheric water vapor content rises. Future work will further study on fields including eliminating daytime solar radiance effects, conducting multi-surface-type validation, and reducing dependence on external parameters.

High-temperature oxidation behavior of WC-12Co cemented carbide in dry air and water vapor atmospheres

Late-spring vertical profiles in atmospheric water vapor stable isotopes reveal westerlies moisture transport across the Himalaya into the Asian Water Towers.

The thermal decomposition of nickel hydroxide (Ni(OH)2) was investigated using thermoanalytical techniques with a specific focus on the multistep kinetic behavior and the effect of the partial pressure of water vapor (p(H2O)). The thermal decomposition process was modeled as a four-step kinetic process, comprising the dehydration of absorbed or included water, a two-step primary reaction process yielding nickel oxide (NiO), and the evolution of the trapped water molecules as the crystal growth of NiO progressed. The kinetic characteristics of the individual reaction steps in the primary reaction process were revealed using advanced kinetic analysis methodologies for multistep reactions. A distinctive retardation effect of atmospheric water vapor pressure (p(H2O)ATM) was evidenced by systematically tracing the reaction process at varying p(H2O)ATM values. Combining the kinetic analysis methodologies for multistep reactions and universal kinetic description across different p(H2O) values, the individual reaction steps in the primary reaction process were described as a function of temperature, degree of reaction, and p(H2O)ATM. This approach was further extended to incorporate the effect of the self-generated water vapor pressure, thereby enabling the universal kinetic description covering all kinetic data in a stream of dry and wet N2 gases. The kinetic results indicated the initial reaction step in the primary reaction process as being regulative of the primary reaction process in the context of the physico-geometrical kinetic behavior and the effect of p(H2O). The novel kinetic findings are expected to provide the necessary information to refine the thermal processing of Ni(OH)2, yielding NiO with the desired properties and morphologies.

With the rapid development of software-defined radio (SDR) technology, a digital, software-reconfigurable, and flexible solution is provided for microwave radiometers, particularly suitable for atmospheric water vapor and oxygen detection with wideband, multi-channel requirements, significantly improving system efficiency. Meanwhile, digitization helps improve channel consistency and address nonlinearity issues, while the digital zero-balancing mechanism implemented through adaptive integration is more suitable for digital platforms. This paper proposes a digital Dicke-type radiometer system based on an SDR platform, using Xilinx RFSoC XCZU47DR (AMD, San Jose, CA, USA) as the core hardware to achieve single-chip integration of RF signal sampling, digital local oscillator generation, and signal processing. The system implements a 46-channel channelized receiver (23 channels each for K-band and V-band) on an FPGA using a polyphase filter bank. The prototype filters achieve 70 dB stopband attenuation and 0.5 dB passband ripple, with each polyphase branch requiring only 25 coefficients, significantly reducing hardware resource consumption. An adaptive integration method is proposed, where an adaptive switch controller dynamically adjusts the hot source injection time ratio by calculating the power difference between adjacent integration periods, enabling the Dicke zero-balancing mechanism to operate entirely in the digital domain. Furthermore, a complete hardware transfer model is established for three signal branches (antenna, hot source, and matched load), and full-chain calibration of all 46 channels is performed using a liquid nitrogen cold source, with calibration reliability verified through blackbody measurements. Experimental results demonstrate brightness temperature consistency better than 0.7 K, with a sensitivity of less than 0.15 K for the K-band and less than 0.21 K for the V-band at 1 s integration time.

The westerlies moisture transport underpins water security for over two billion people dependent on the Asian water towers (AWTs). However, the mechanisms by which large-scale westerlies-advected moisture is integrated into the AWTs' atmospheric water budget remain poorly understood due to observational gaps. Here, we combine three-dimensional observations of atmospheric water vapor stable isotopes with isotope-enabled modeling. We identify the conveyor mechanism that regulates the vertical moisture transport under calm conditions during the winter-spring period when the westerlies are dominant. Sharp vertical isotopic gradients show that large-scale westerlies-advected moisture is predominantly confined aloft, while local residual moisture persists near the surface. Our results show the interplay of the westerlies' subsidence at night with thermodynamically distinct local residual air, yielding thermal inversions and condensation that suppresses vertical mixing and decouples moisture between the free troposphere and the atmospheric boundary layer. This process constitutes a primary pathway for integrating westerlies-advected moisture into the local moisture budget without precipitation, sustaining near-surface moisture accumulation. Our results provide critical benchmarks for improving atmospheric models, refining climate projections of the intensifying water cycle over the AWTs, and advancing interpretations of isotopic records in regional climatic archives.

The subtropical wetlands of the Doon Valley function as significant net sources of greenhouse gases (GHGs), with methane (CH₄) dominating the radiative forcing (∼62% of CO₂-equivalent emissions) despite lower molar fluxes than carbon dioxide (CO₂). High-resolution field measurements reveal that CH₄ emissions are primarily controlled by anaerobic conditions, sustained soil moisture, elevated temperatures, and low dissolved oxygen, whereas CO₂ fluxes exhibit greater temporal variability and respond strongly to thermal regimes and ionic strength. A key biogeoclimatic insight is the seasonal decoupling of soil moisture and atmospheric water vapor (H2O), where summer drying coincides with peak humidity driven by energy-limited evapotranspiration. Pronounced spatial heterogeneity in gas fluxes further suggests that land-use context and modified hydrological pathways may interact with climatic drivers to influence wetland carbon dynamics. The wetland complex (221.39ha) emits approximately 0.0195 Mt CO₂-eq annually, underscoring its disproportionate role in regional GHG budgets. These findings reveal strong coupling among hydrological saturation, thermal regimes, redox conditions, and atmospheric moisture in regulating GHG emissions. The study underscores the high climate sensitivity of monsoon-dependent wetlands and highlights the need for targeted hydrological restoration and continuous monitoring to mitigate future amplification of emissions under warming scenarios.

Supramolecular organic frameworks (SOFs) with intrinsic porosity and appealing optoelectronic properties hold promise for the integrated capture and photocatalytic conversion of CO2 from the air. Unfortunately, SOFs that can efficiently reduce CO2 have never been reported so far. In this work, we demonstrate the construction of a porous SOF through host-guest binding between cucurbit[8]uril (CB[8]) and a tetraphenylethylene-based derivative for highly selective CO2 reduction in the atmosphere of water vapor and air under solar light. The abundant cationic nitrogen sites within the framework endow the SOF with a CO2 uptake capacity of 14.41 cm3 g-1 at 298 K and 1 bar. Initial slope selectivity calculations demonstrated that SOF possessed high separation capability of CO2 over N2 with selectivity up to 57 at 273 K. In addition, the SOF showed efficient light harvesting in the visible region with an optical gap of 2.19 eV. Benefitting from these unique features, the SOF catalyzed the reduction of CO2 with a stable CO production rate of 69.78 μmol h-1 g-1. This research paves the way to design porous SOF-based photocatalysts for biomimetic reduction of CO2 in a practical environment.

The actuality of Earth's Energy Imbalance is extremely associated with global warming and sea level rise, with a more noticeable warming trend being observed in the Arctic region. The aim of this study is to quantify the effects of various climatic factors on radiation at different latitudes in the Northern Hemisphere through the utilization of satellite and reanalysis datasets, in order to recognize the primary driving factors for the situation of global energy imbalance. Through the utilization of the ordinary least squares method and the random forest method, an analysis was conducted of the effects of sea ice concentration, sea surface temperature, cloud cover, atmospheric water vapor, and aerosols on the top-of-atmosphere radiation in the mid-low latitudes (0°-70°N) and high latitudes (70°-90°N) regions. It is indicated by the findings that in the mid-low regions, the main drivers of radiation are identified as cloud cover and aerosols, and in the high-latitude areas, obvious influences on radiation are exerted by the effects of TCC and AOD, but a notable increase is observed in the contribution of TCWV. Meanwhile, a critical role in shortwave radiation and net radiation is also played by sea ice concentration. However, a clear identification of the main driving factors behind the warming trend in the Arctic region is failed to be achieved by the research. The incorporation of more variables related to atmospheric dynamics with a larger time span can be made by future studies, and the time lag effect can be taken into account to better assess the impact of sea ice concentration on radiation.

The practical application of gas–solid photocatalytic hydrogen evolution is often limited by low water vapor utilization efficiency and the absence of continuous proton transport pathways. To mitigate these issues, we developed a solid‐state electrolyte based on a silica aerogel–potassium acetate composite. This electrolyte exhibits an ionic conductivity of 9.6 × 10 −4 S cm −1 and an interfacial double‐layer capacitance of 2480 μF cm −2 . Its hierarchical meso‐macroporous network facilitates the capture and capillary condensation of atmospheric water vapor, which establishes localized aqueous pathways for proton conduction. Integrating this composite electrolyte with a CsPbBr 3 ‐based photoactive layer to form an all‐solid‐state photocathode led to a notable suppression of charge recombination. This effect is attributed to the use of acetate ions as effective hole traps at the solid–solid interface. Consequently, the device achieved a steady‐state hydrogen evolution rate of 43.4 μmol h −1 under simulated sunlight (AM 1.5 G), corresponding to a solar‐to‐hydrogen (STH) conversion efficiency of 0.64%. This performance remained stable, with less than 40% decay, over continuous operation for 100 h, demonstrating the robustness afforded by the solid‐state design.

Tracking a semi-arid Eastern Mediterranean ecotone through integration of terrestrial and atmospheric earth observation data (2000-2024).

To advance our understanding of atmospheric processes and climate dynamics, improved knowledge of outgoing long-wave radiation (OLR) spectral emission is essential. The FORUM mission, selected for the ninth cycle of the European Space Agency’s Earth Explorer programme, is specifically designed to address the long-standing observational gap in the far-infrared (FIR) spectral region. When combined with measurements from the IASI-NG instrument, FORUM will provide complete spectral coverage of Earth’s OLR emission (spanning 100 to 2760 cm−1 wavenumber, or 3.62 to 100 μm wavelength), thereby enabling robust climate model validation and enhanced understanding of climate change processes. While IASI-NG’s primary mission is to support numerical weather prediction, FORUM is designed to measure key climate variables, which also enable the retrieval of atmospheric parameters in the troposphere and lower stratosphere. In this study, we assess the information content of FORUM and IASI-NG measurements for atmospheric profiling through a simulation-based approach. Synthetic retrieval products are generated using a linearized formulation of the retrieval transfer function, allowing an efficient and physically consistent evaluation of the sensitivity of the two instruments to atmospheric temperature and water vapor profiles. The analysis reveals a non-negligible sensitivity of FORUM to atmospheric temperature extending into the stratosphere, resulting in significant information content at altitudes higher than previously reported. This finding highlights the potential of far-infrared observations to contribute to atmospheric temperature profiling beyond the lower troposphere. The complementary capabilities of FORUM and IASI-NG suggest that their combined use can enhance the characterization of the atmospheric thermal structure. These results represent a first step toward evaluating the potential role of FORUM Level-2 products in future numerical weather prediction applications.

Zenith Tropospheric Delay (ZTD) and its associated atmospheric water vapor information constitute essential environmental variables for Earth observation (EO)-based atmospheric monitoring and environmental variable retrieval. High-quality ZTD products are therefore of great importance for the post-processing, refinement, and reconstruction of atmospheric environmental variables at regional scales. Among existing observation techniques, Global Navigation Satellite System (GNSS) measurements provide high-precision ZTD estimates and have become an important means for retrieving tropospheric delay and water vapor. However, the sparse and uneven spatial distribution of GNSS stations limits their direct applicability for continuous environmental monitoring. Reanalysis-based products, such as ERA5 provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), offer EO big data with excellent spatiotemporal continuity but suffer from pronounced systematic biases compared to precision GNSS retrievals, restricting their direct use in high-accuracy regional applications. To address these limitations, this study proposes a Residual Correction Kriging method for ZTD (RK ZTD) that integrates GNSS ZTD and ERA5 ZTD grids through a multi-source data fusion framework. High-precision GNSS ZTD is treated as reference data, and the differences between GNSS ZTD and ERA5 ZTD at modeling stations are defined as residuals to characterize the systematic bias in ERA5 ZTD grids. A Kriging interpolation algorithm is then employed to model the spatial distribution of these residuals and generate residual correction grids. By superimposing the interpolated residual grids onto the ERA5 ZTD grids, a refined and high-precision regional ZTD product is reconstructed. Experiments were conducted using observations collected in 2023 from 36 GNSS stations in the Netherlands, including 10 modeling stations and 26 independent validation stations, together with concurrent ERA5-derived ZTD grids. The results demonstrate that the proposed RK ZTD model provides spatially robust and high-precision ZTD products across the study region. The RK ZTD achieves a Root Mean Square Error (RMSE) of 5.70 mm, representing improvements of 58.4% and 35.4% compared with the original ERA5 ZTD (13.69 mm) and the GNSS-Kriging ZTD (8.82 mm), respectively. Moreover, the absolute bias is reduced to 0.41 mm, in contrast to 5.15 mm for the ERA5 ZTD, indicating that systematic biases are effectively mitigated. Spatial and seasonal analyses further confirm that the proposed method maintains stable performance across all seasons and significantly alleviates interpolation inaccuracies caused by sparse GNSS stations, even under extreme weather conditions such as Storm Ciarán, proving its value for advanced Earth environmental science applications.

Furanoids are relevant atmospheric volatile organic compounds originating from sources like the degradation of conjugated dienes and increasing biomass burning. This study is focused on the atmospheric fate of products derived from the ozonolysis of 2,5-dihydrofuran (2,5-DHF). Considering the Criegee mechanism as a principal reaction pathway, two main stabilized Criegee Intermediates (sCI) are formed: the sCI syn and anti conformers. First, the global ozonolysis reaction rate was theoretically calculated, yielding a value of 1.7 × 10-17 cm3 molecule-1 s-1 at the F12-CCSDT/cc-pVDZ-F12//M06-2X/6-311++G(3df,3pd) level of theory. This result shows excellent agreement with experimental data. The subsequent reactions of these sCI were investigated, including their unimolecular decompositions and bimolecular reactions with atmospheric water vapor. The main products formed in the presence of water are vinyl-hydroperoxide (VHP) and hydroxy-hydroperoxide (HHP) compounds. These products are atmospheric sources of OH radicals, H2O2, and different alkoxy radicals. Consequently, it can be concluded that the final products of ozonolysis of 2,5-DHF are potential sources of reactive species in the atmosphere.

ABSTRACT Recent advances in remote sensing have emphasized the need for precise Land Surface Temperature (LST) retrieval, critical for assessing Earth’s energy balance and geophysical processes at global and local scales. This study compares sixteen Split Window Algorithms (SWAs) for LST estimation and evaluates their sensitivity for ECOSTRESS (ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station) data to identify the most reliable methods. SW coefficients were derived from at-sensor signal simulations using the MODerate resolution atmospheric TRANsmittance (MODTRAN) Radiative Transfer Model (RTM) under varying conditions for the ECOSTRESS bands. Among the sixteen SWAs, some are independent of Atmospheric Columnar Water Vapour (ACWV) and View Zenith Angle (VZA), while others depend on one or both parameters. The sixteen SWAs evaluated in this study comprise thirteen previously published algorithms and three modified versions. The terms added in the modified SWAs involve the introduction of quadratic temperature difference terms and explicit VZA correction terms to improve the atmospheric correction. The comparison with simulated dataset, ECOSTRESS LST product, and SURFRAD (Surface Radiation Budget Network) in-situ observations revealed that among the sixteen SWAs, Cheb Du et al. (2015) algorithm and modified François et al. (1996) algorithm consistently outperformed mainly attributed to inclusion of quadratic term, which better account for atmospheric non-linearity. Using simulated data across a range of ACWV and VZA conditions, Cheb Du and modified François algorithms exhibited RMSEs of 0.36–2.00 K and 0.36–1.62 K, respectively. Validation against ECOSTRESS LST yielded a maximum RMSEs of 0.51 K (Cheb Du) and 0.59 K (Modified François), while SURFRAD in-situ observations resulted in RMSEs of 2.69 K, 2.75 K, and 2.71 K for Cheb Du, modified François, and the standard ECOSTRESS product, respectively. These results highlight the suitability of both SWAs for accurate LST retrieval in upcoming missions such as TRISHNA, GISAT-1A, and SBG.

Abstract Tropospheric delay is a crucial factor that limits precise point positioning (PPP) performance, especially at low altitude angles. Here, a remote sensing (RS)‐augmented method was developed to improve PPP performance with high‐quality zenith tropospheric delay (ZTD) derived from water vapor products of satellite GOES‐18. The GOES‐18 precipitable water vapor (PWV) was evaluated against the European Center for Medium‐Range Weather Forecasts Reanalysis 5 (ERA5) PWV, with a root mean square error (RMSE) of 2.50 mm. The derived ZTD was validated using International GNSS Service (IGS) ZTD showing RMSE of 16.20 mm. Data from 42 GPS and GLONASS observed IGS stations were collected. The results show that the RS‐augmented PPP improves convergence time and short‐term precision in the vertical component for both GPS + GLONASS (G + R) and GPS‐only compared to traditional PPP. For the G + R vertical component, the convergence time was shortened by 18.9% and the short‐term positioning accuracy improved by 17.4%. For the GPS‐only systems, the convergence time was shortened by 12.2% for the vertical components, while vertical component positioning accuracy increased by 19.5%. The 42 stations were categorized through different geographic conditions and atmospheric water vapor structures (ocean, coastline, and land) to analyze their convergence times and positioning accuracy. The results show that stations in ocean regions exhibited the greatest improvement in both convergence time and positioning accuracy. The improvement in convergence time was mainly related to the accuracy of the ZTD RMSE; the improvement in positioning accuracy was primarily influenced by the geographic conditions of the stations, such as station latitude.

ABSTRACT Geostationary (GEO) satellites are paramount for continuously monitoring our planet from a fixed position because of their high temporal resolution. It is essential to monitor the quality of these observations before they are used in retrieval or data assimilation. The Global Space-based Intercalibration System calibrates GEO satellite observations against low-Earth-orbit (LEO) observations; however, very few studies directly compare GEO-GEO observations . GEO-GEO intercomparisons also offer valuable insight into inter-sensor consistency on a diurnal scale and, more robustly, on a seasonal scale. In this work, we perform a detailed inter-comparison of the Brightness Temperatures (BTs) of the thermal infrared window channels of two GEO sensors, INSAT-3DR Imager and SEVIRI onboard Meteosat-8, using more than 1.5 billion collocated clear-sky observations. We also compute simulated observations for both these satellites using a radiative transfer model to quantify the differences between observed and simulated (O − M) BTs and their variability. We found INSAT-3DR observations are 1.21 K (at 10.8 µm) and 0.83 K (at 12 µm) warmer than the Meteosat-8 observations, with corresponding mean model BT differences of 0.96 K and 0.84 K, respectively. A sensitivity test revealed that these systematic BT differences are mainly due to satellite viewing geometry and atmospheric total column water vapour. The bias-corrected INSAT-3DR observations showed a residual mean diurnal bias of ∼ 1 K, whereas it was ∼ 0.1 K for Meteosat-8 in both channels. We also implemented a double-difference technique to investigate the cross-sensor agreement. We found a calibration anomaly in INSAT-3DR observations during Oct-Nov 2021 and Mar-Apr 2022. However, Meteosat-8 observations were radiometrically stable, highlighting their utility for correcting anomalies/biases in INSAT-3DR observations. In summary, this study is valuable for determining the accuracy of observations in the window channels, which further affects the retrieval of geophysical parameters, such as SST and its diurnal variation.

Comparative study of water vapor corrosion resistance in directionally solidified RE3Al5O12/Al2O3 eutectic ceramics at 1500℃: Effect of eutectic structure and rare earth elements

Tracking the non-uniformity in atmospheric water vapor over the north polar layered deposits on Mars using high-resolution observations by MRO/CRISM