地球科学最新文献

Observed El Niño-Southern Oscillation (ENSO) varies between decades with high ENSO amplitude and more extreme Eastern Pacific (EP) El Niño events and decades with low ENSO amplitude and mainly weak El Niño events. Based on experiments with the CESM1 model, ENSO may lock-in into an extreme EP El Niño-dominated state in a +3.7 K warmer climate, while in a −4.0 K cooler climate ENSO may lock-in into a weak El Niño-dominated state. The state shift of ENSO with global warming can be explained by the location and amplitude of the strongest warming over the eastern equatorial Pacific, which amplifies the Bjerknes feedback and allows a southward migration of the Intertropical Convergence Zone onto the equator, a prerequisite of extreme EP El Niños. In light of these results, we discuss to what extent the state of ENSO may be a tipping element in the climate system.

Entrainment and detrainment rates (ε and δ) constitute the most critical free parameters in mass flux schemes commonly employed for cumulus parameterizations. Recently, Zhu et al. (2021) introduced a new approach that utilizes aircraft observations to simultaneously estimate ε and δ for cumulus clouds, overcoming the limitation of other observation-based approaches that solely yield ε without offering insights into δ. This study aims to comprehensively evaluate the reliability of this new approach. First, evaluation using an Explicit Mixing Parcel Model demonstrates the capability of the new approach to back-calculate predetermined ε and δ based on the physical properties before and after the entrainment mixing. Second, evaluation using large-eddy simulations illustrates that the new approach yields consistent ε and δ profiles compared to the traditional approach. Sensitivity tests indicate a weak sensitivity of the estimated δ with the new approach to the entrained air source. A decrease in the proportion of cloudy air in the assumed detrained air leads to a reduction in the estimated δ, while ε remains unaffected. Finally, the most appropriate assumptions for entrained and detrained air are discussed. Estimating ε for cumulus parameterizations involves acquiring ambient air more than 500 m away from the cloud edge as entrained air. Due to implicit mean field approximations in the traditional approach, determining the optimal assumption for detrained air properties proves challenging. This study confirms the reliability of the new approach in estimating ε and δ, providing confidence in its application to extensive observational data and advancement in parameterization.

The Land Surface, Snow and Soil moisture Model Intercomparison Project (LS3MIP) offers valuable land surface hydrology products from the land modules of current Earth system models (ESMs). Historical hydrological variables from six ESMs driven by four meteorological forcing data sets (GSWP, WFDEI, CRU-NCEP, and Princeton) in Land Model Intercomparison Project (LMIP) have been extensively evaluated with various high-quality reference data sets over Chinese mainland. Compared with the reference data sets, the multi-model ensemble means (MMEs) of most hydrological variables are underestimated, while their annual trends show high spatial consistency, with sign consistency over 56%–85% of land area. After computing and ranking four statistical metrics (bias, correlation coefficient, normalized standard deviation, and unbiased root-mean-square biases) between simulations and references, it is found that the CLM5 has the best performance, while the GSWP3 exhibits the highest quality. Furthermore, the analysis of variance method (ANOVA) is then used to trace sources (model, atmospheric forcing data sets and their interactions) of the uncertainty of those modeling hydrological variables for 1900–2012 (1948–2012 for runoff) over China. The results indicate that the total uncertainty and its composition vary with time and decrease significantly in recent decades, reflecting the enhanced forcing data quality. Larger forcing uncertainty existed during the early twentieth century because less available observation data sets have been adopted to constrain climate variables. For all modeling hydrological variables, the model uncertainty plays the dominant role, suggesting that the quality of LMIP products largely relies on Land surface models.

Abstract—The paper presents an attempt to estimate the contribution of thermal processes in the Earth’s crust to earthquake generation. As a case study, the seismically active junction zone of the Chu depression and Kyrgyz ridge of the Northern Tien Shan is considered. The analysis is based on the previously constructed models of temperature, petrophysical characteristics, and elastic moduli. The silica content model derived from seismic tomography data is used to build a lithotype model. The thermal conductivity model is constructed and used in conjunction with the temperature model to create a depth model of the heat flow density. The shear stress and thermoelastic stress models derived from density, elastic moduli, and temperature models are compared with the distribution of earthquake hypocenters in the region. The comparison suggests that on the scale of the seismically active junction zone of the Chu depression and the Kyrgyz ridge of the Northern Tien Shan, seismicity is mainly determined by thermomechanical effect induced by hot ascending flow of acid magma rising from the upper mantle beneath the Muyunkum–Narat median massif.

Analysis of dissolved oxygen (O₂) in the Arctic's surface ocean provides insights into gas transfer between the atmosphere-ice-ocean system, water mass dynamics, and biogeochemical processes. In the Arctic Ocean's Canada Basin mixed layer, higher O₂ concentrations are generally observed under sea ice compared to open water regions. Annual cycles of O₂ and O₂ saturation, increasing from summer through spring and then sharply declining to late summer, are tightly linked to sea ice cover. The primary fluxes that influence seasonal variability of O₂ are modeled and compared to Ice-Tethered Profiler O₂ observations to understand the relative role of each flux in the annual cycle. Findings suggest that sea ice melt/growth dominates seasonal variations in mixed layer O₂, with minor contributions from vertical entrainment and atmospheric exchange. While the influence of biological activity on O₂ variability cannot be directly assessed, indirect evidence suggests relatively minor contributions, although with significant uncertainty. Past studies show that O₂ molecules are expelled from sea ice during brine rejection; sea ice cover can then inhibit air-sea gas exchange resulting in winter mixed layers that are super-saturated. Decreasing mixed layer O₂ concentrations and saturation levels are observed during winter months between 2007 and 2019 in the Canada Basin. Only a minor portion of the decreasing trend in wintertime O₂ can be attributed to decreased solubility. This suggests the O₂ decline may be linked to more efficient air-sea exchange associated with increased open water areas in the winter sea ice pack that are not necessarily detectable via satellite observations.