地球科学最新文献

Recent advancements in state-of-the-art generative deep-learning models, particularly diffusion models, have significantly enhanced the capability to produce realistic and diverse synthetic images and videos. These advancements have had a profound impact on fields such as computer vision and natural language processing. In this study, we leverage this cutting-edge generative model to refine Numerical Weather Prediction (NWP) precipitation outputs. By conditioning the generative model with fundamental meteorological variables simulated by the Weather Research and Forecasting model, we aim to reproduce the high-resolution satellite precipitation product, specifically CMORPH. Benefiting from the superior ability of generative diffusion models to learn the distribution of target data, these models excel in providing detailed and accurate precipitation estimations over the raw NWP outputs and traditional predictive models. With this presented pipeline, we provide valuable insights and practical tools for refining precipitation forecasting while preserving its extremities and variability thus better guiding decision making regarding weather dependent activities.

This study investigates the sources and regional attributions of nitrogen oxides (NO_x) in the upper troposphere|upper tropospheric (UT) during the Asian Summer Monsoon (ASM). The importance of South Asia (SA) and East Asia (EA) contributions is the subject of main interest. Using artificial tracers in a chemistry-climate model, simulations with tracers from surface anthropogenic and lightning sources in SA and EA are conducted. Model results are validated with airborne observations from the Asian Summer Monsoon Chemical and Climate Impact Project (ACCLIP) campaign in 2022 over the West Pacific. Good agreement between modeled and observed NO_x is found in the UT. The results indicate that within the ASM anticyclone, both SA and EA sources significantly contribute to the UT NOx, with contributions of 41% and 36%, respectively. While in the ACCLIP region during 2022, EA sources play a more important role, accounting for 50% compared to 19% from SA sources.

We use atmospheric profiles from ERA5, JRA55, and MERRA2 between 1993 and 2023 to estimate Earth's global clear-sky longwave feedback strength on the seasonal and interannual timescale. Differences in the relationship of relative humidity with skin temperature prior to 2008 lead to interannual feedback strengths between 1.34 Wm⁻² K⁻¹ (JRA55) and 1.89 Wm⁻² K⁻¹ (MERRA2). Restricting the analysis to the last 16 years yields more consistent interannual estimates of 2.05 Wm⁻² K⁻¹ on average, which is larger than the overall seasonal estimate of 1.91 Wm⁻² K⁻¹. The mid-tropospheric drying causing this difference suggests a substantial influence of ENSO variability on the interannual timescale. This indicates a long-term feedback strength smaller than 2.0 Wm⁻² K⁻¹, which is already at the lower end of previous estimates; emphasizing the importance of accurate long-term RH measurements to reliably project Earth's clear-sky feedback strength.

Despite growing interest and investment in salt-marsh restoration, relatively few marshes subjected to restoration efforts have been systematically monitored to assess physical restoration trajectory or success. In south San Francisco Bay, California, USA, where 83% of wetlands were lost via human manipulation, the largest wetland restoration effort on the US west coast is currently underway, restoring approximately 6000 ha of former salt-production ponds to mixed habitats. The Whale Tail–Cargill Mitigation salt-marsh complex in south San Francisco Bay has a century-long history of drainage, industrial use as salt-production ponds and subsequent restoration and recovery. Restoration of the 20 ha Cargill Mitigation Marsh was initiated in the late 1990s when the levee surrounding the subsided, former salt-production pond was breached in two locations, enabling conversion back to salt-marsh habitat in the subsequent decades. Here, we present time-series measurements of sediment fluxes in the primary tidal creek entering the salt-marsh complex, which are compared to decadal-scale sedimentation patterns determined from repeat elevation surveys and cores collected at the study site. All three methods show net sediment import to the restored marsh. The greatest equivalent sedimentation rates occurred early in the restoration, with generally decreasing rates through time. The long-term average, as determined from cores and expressed as a vertical sedimentation rate, is approximately 1.8 cm year⁻¹. Rates from the elevation data are between 1.4 and 2.6 cm year⁻¹, with higher rates earlier in the restoration. The most recent estimates, computed from time-series instrument deployments, indicate seasonal variability in sediment import. Annualized rates are lower in winter, approximately 0.1 cm year⁻¹, and higher in summer, approximately 1.7 cm year⁻¹. Although our measured long-term equivalent sedimentation rates are considerably greater than the current local relative sea-level rise (SLR) of 0.3 cm year⁻¹, an increase in SLR or decrease in available suspended sediment would threaten the ability of the marsh to keep pace with SLR and avoid drowning in the future.

Given the considerable influence of surface soil freeze‒thaw cycles on the surface energy balance, hydrological processes, and ecosystems, there is significant interest in exploring changes in surface soil freeze‒thaw cycles in the context of climate warming. In this study, we investigated changes in the duration of seasonal surface soil freeze‒thaw cycles across China and subregions divided by climate and ecosystem types (temperate and warm‒temperate deserts of northwestern China, temperate grasslands of Inner Mongolia, temperate humid and subhumid zones of northeastern China, warm‒temperate humid and subhumid zones of North China, and high‒elevation and cold zones of the Tibetan Plateau) from 1981 to 2017 and examined their relationships with meteorological elements using both homogenized weather station data and gridded observations. The results showed that the freeze start date has been delayed by 8.6 days and that the freeze end date has advanced by 8.6 days, resulting in a shortened freeze duration by 17.2 days in China. This change was most pronounced in the high‒elevation and cold zones of the Tibetan Plateau, with a shortened freeze duration by 25.2 days, and the weakest change was present in the temperate humid and subhumid zones of northeastern China. Nationwide, the decreasing trend of the freeze duration first increased but then decreased with increasing elevation, and it consistently decreased with increasing latitude. Changes in the freeze duration are significantly correlated with the following factors: air temperature in spring, autumn and winter, snow depth in spring, autumn and winter; and vegetation in autumn. Distinct regional differences exist in these relationships. These results provide a new understanding of surface freeze‒thaw cycle changes and their causes in China.

The identification and evaluation of abiotic methane remain an active research area due to uncertainties in traditional indicators that may lead to “false-positive” detections. As an emerging isotopic tool, methane clumped isotope can provide novel information about the generation and post-generation processes of methane gases. Using six deep natural gas samples from the Songliao Basin, we explored the potential of clumped isotopes in identifying abiotic methane. The results indicate that the Δ¹³CH₃D values of all samples are consistent with the thermodynamic equilibrium values at the inferred formation temperatures, whereas the Δ¹²CH₂D₂ values show small but detectable deficits (1∼6‰) relative to equilibrium. This particular non-equilibrium clumped isotopic signature of natural gas from the Songliao Basin is similar to the clumped isotopic signature of abiotic methane predicted by an isotopologue-specific kinetic model, suggesting a possible contribution of abiotic methane in the studied natural gases. However, we found that the mixing of abiotic and thermogenic gases could not fully explain the isotope data of all the samples. The proportion of abiotic gas calculated based on clumped isotopes would be underestimated because methane isotopic bond re-ordering at the late burial temperatures partially erases the disequilibrium signatures inherited from the original mixtures. The carbon isotopic reversals in C₁–C₃ of the samples provide additional constraint for evaluating the contribution of abiotic gas. Therefore, the coupling of intra-molecular clumped isotope and inter–molecular carbon isotope signatures may be a more robust approach for identifying abiotic methane, which can help us to quantitatively evaluate abiotic methane in petroleum systems.

Extreme hydroclimates impact sediment fluxes from mountainous catchments to the oceans. Given modern global warming, a challenge is to assess the sensitivity of erosion in mountainous catchments to extreme climate perturbations. Here, we reconstruct paleo-sedimentary fluxes across an abrupt global warming, the Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma), using sedimentary archives and numerical modeling. In the Tremp Basin (Southern Pyrenees, Spain), our results demonstrate that depositional volumetric rates of siliciclastic sediments increased two-fold during the PETM. According to the BQART and stream power law models, changes in mean annual temperature and precipitation explain only 9%–27% of the flux increase. This comparison between field data and model predictions suggests that even with high uncertainty on paleoclimate data, extreme rainfall events and landslides may have been crucial sediment generation processes during the PETM. This is consistent with predictions of enhanced climate variability in a warmer world, leading to significant sediment flushing.

Atmospheric rivers (ARs) are elongated areas of pronounced atmospheric water vapor transport that play an important role in the hydrological cycle over North America during winter. We investigate the sources of winter seasonal AR predictability over North America using average predictability time (APT) analysis. The skill of seasonal AR frequency predictions, in dynamical model forecasts provided by the Seamless System for Prediction and Earth System Research, is nearly entirely attributable to three physically interpretable APT modes that together represent about 19% of the total seasonal AR frequency variance. These three modes represent the AR response to the El Niño-Southern Oscillation, anthropogenic forcing and equatorial heating over the eastern flank of the western Pacific warm pool, respectively. We further show that these three modes, calculated from AR frequency, explain nearly all winter seasonal precipitation forecast skill over North America.

Among the subsurface geophysical methods used in the critical zone investigations, induced polarization (IP) shows great vitality thanks to its unique ability to assess porosity via bulk conduction and estimate permeability through surface conduction and/or polarization. However, such an advantageous separation between bulk and surface is mostly implemented by multi-salinity experiments in the laboratory, which is incredibly difficult to realize in the field. One promising approach to address such an obstinate issue is to gauge the surface conductivity (σ_s) from the quadrature conductivity (σ″) or normalized chargeability (M_n) with the ratios between (l = σ″/σ_s, l_mn = M_n/σ_s). While these ratios are known not to be universal, the underlying principles are not fully understood and relevant theoretical studies are rare, which makes quantitative IP applications difficult. Here we scrutinize the conduction and polarization mechanisms of geomaterials and pinpoint that the two ratios are inherently functions of salinities and frequencies rather than only determined by the properties of the electrical double layer (EDL), hence representative samples from the investigated field must be calibrated in the laboratory and a characteristic frequency should be chosen for their usage. Besides the macro-scale ratios l and l_mn, we define two micro-scale ratios χ and χ_mn directly from the EDL, such that the new ratios exclude the effect of salinity and frequency and offer the opportunity to characterize and monitor changes of the EDL. Our study demonstrates that the existing macro-scale ratios converge toward the values of novel micro-scale ratios at high water salinity.