ALBERT

Description: The carbon balance of peatlands is predicted to shift from a sink to a source this century. However, peatland ecosystems are still omitted from the main Earth system models that are used for future climate change projections, and they are not considered in integrated assessment models that are used in impact and mitigation studies. By using evidence synthesized from the literature and an expert elicitation, we define and quantify the leading drivers of change that have impacted peatland carbon stocks during the Holocene and predict their effect during this century and in the far future. We also identify uncertainties and knowledge gaps in the scientific community and provide insight towards better integration of peatlands into modelling frameworks. Given the importance of the contribution by peatlands to the global carbon cycle, this study shows that peatland science is a critical research area and that we still have a long way to go to fully understand the peatland–carbon–climate nexus.

Description: The present day’s thermal lithospheric thickness is usually calculated by one or two-dimensional steady-state heat conduction equation. Using the latest measured heat flow data of the North China Craton(NCC) and the one-dimensional steady-state heat conduction equation, the calculated thermal lithospheric thickness of the NCC is between 34.8-190 km. There are some regions, whose lithosphere is very thin, and the lithosphere adjacent to them is very thick, so the bottom boundary of the lithosphere fluctuates greatly. The last thinning of the NCC stopped at~24 Ma and then entered the thermal subsidence period. To study whether the fluctuates of the bottom boundary of the lithosphere can be maintained during the long-term thermal subsidence process, a thermal subsidence model was established. The modeling results show that after the thermal subsidence of 24 Ma, the fluctuates of the bottom boundary of the lithosphere are difficult to maintain, and the present day’s thermal lithospheric thickness of the NCC should not exceed 73 km, and the maximum surface heat flow value of the NCC is 75.6 mW·m〈sup〉-2〈/sup〉 due to the deep thermal state. The high heat flows anomaly in the NCC is more caused by shallow activities and cannot reflect the deep thermal state. After correction, the current thermal lithospheric thickness of the North China craton is ~73-190 km, and the bottom boundary of the lithosphere changes gently.

Description: Many theoretical and numerical studies have been carried out to understand the mechanisms for the meridional overturning circulation (MOC), especially how its strength varies with for example, the magnitude of Ekman pumping, the density contrast between the two polar regions, and the vertical diffusivity. However, these studies were mostly done under idealized configurations, it is still unclear how the strength of global MOC changes in the realistic climate as simulated by climate models and why it changes in the way it does. Here we first present climate simulations for the whole Phanerozoic (541 million years ago to now) performed using a fully coupled atmosphere-ocean general circulation model (GCM), CESM1.2. A snapshot of the climate was obtained for every 10 million years, from which a time series of the MOC strength was constructed. The strength here is defined as the maximum zonally integrated stream function at the equator and varies from 2 Sv to 32 Sv. Then we carried out many sensitivity experiments to test whether the MOC strength was due to change of climate or continental configuration. It is found that both the climate state and the continental figuration have significant influence on the MOC strength. We further identified the roles of the mid-latitude westerly winds and the polar density contrast in affecting the MOC strength, with the aid of idealized experiments done with MITgcm. It is found that the wind-induced Ekman pumping plays a more important role than the density contrast.

Description: Pore-scale numerical simulation plays an important role in comprehending water quality. Predicting the permeability of porous media via machine learning models is a crucial aspect of current research in pore-scale modelling. These models can create a mapping relationship between permeability and pore structure, serving as a regression task. However, directly applying 3D data of porous media to classical machine learning models is not possible, requiring the extraction of features from the pore structure. Deep learning models, as an advanced form of classical machine learning, have been successful in permeability prediction using 3D digital images, but come at a high computational cost. To address this, we propose an intuitive feature extraction method that extracts pore structure features from slices of 3D porous media and uses them as input for machine learning models. This not only reduces the amount of input data but also improves training efficiency, while maintaining excellent prediction accuracy. Moreover, due to the spatial continuity of the 2D pore structure features, we achieved improved prediction performance compared to classical machine learning models by using a long short-term memory (LSTM) neural network. The use of transfer learning further demonstrates the LSTM model's remarkable generalization ability.

Description: On May 22, 2021, an Mw7.4 earthquake occurred in Maduo, Qinghai, China. The epicenter was located at 34.59 degrees north latitude and 98.34 degrees east longitude. This paper uses ASF HyP3 and MintPy software to conduct time-series InSAR analysis by using the Sentinel-1 SAR images from 2018 to 2023, and then to study the temporal and spatial distribution of regional crustal deformation and the distribution of the seismic fault ruptures. The time-series InSAR analysis are taken in three groups: Pre-earthquake period from January 2018 to May 2021, Earthquake onset period from April 2021 to June 2021, and Post-earthquake period From June 2021 to January 2023. The LOS(Light of Sight) velocity results of the time series INSAR analysis in the three groups and three dimension velocity of GPS stations in this area are fused to obtain regional tectonic strain rates, co-seismic fault slips, and post-seismic displacements. The results show that crustal deformation before the earthquake is small, the range of the coseismic surface rupture of the Maduo earthquake overlaps with the abnormal area of the regional strain field obtained, and the post-seismic viscoelastic deformation is strongly correlated with Maduo earthquake fault.

Description: Although the impact of the Indian Ocean on the decaying pace of El Niño events has been documented previously, contrary to the consensus that the Indian Ocean Basin (IOB) mode favors the decay of El Niño via modulating the zonal wind anomalies in the tropical western Pacific, the contribution of the Indian Ocean Dipole (IOD) on the following year’s El Niño remains highly controversial. Through investigating the evolution of fast and slow decaying El Niño events, this study demonstrates that the positive IOD phase with a strong western pole prompts the termination of El Niño, whereas no significant effect of the IOD with a weak western pole. The responsible physical mechanism is that the strong western pole of a positive IOD can lead to a strong IOB pattern along with peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising (sinking) motions over the tropical Indian Ocean (western Pacific Ocean). The surface easterly wind anomalies on the western flank of the sinking motions stimulate oceanic upwelling equatorial Kelvin waves, which shoal the thermocline in the equatorial eastern Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of IOD induces a weak IOB mode that peaks in late spring, and the above cross-basin physical processes will not appear.

Description: Precise satellite clock product is an indispensable prerequisite for the real-time precise positioning service. To meet the requirement of numerous time-critical applications, real-time satellite clock corrections need to be broadcast to users with an update rate of 5 s or higher. With the rapid development of global navigation satellite systems (GNSS) over the past decades, abundant GNSS tracking stations and modern constellations have emerged, and the computation for multi-GNSS real-time clock estimation has become rather time-consuming. In this contribution, an efficient strategy is proposed to achieve high processing efficiency for multi-GNSS real-time clock estimation, wherein undifferenced method based on sequential least square is adopted. In the proposed strategy, parallel data processing and high-performance matrix operations are introduced to accelerate the processing of multi-GNSS clock estimation. The former is based on OpenMP (Open Multi-Processing), while the latter is achieved by the implementation of the Schur complement and the open-source library OpenBLAS. Multi- GNSS observations from 85 globally distributed tracking stations are employed for the generation of real-time precise clock products. The average elapsed time per epoch with the proposed strategy is 0.35, 0.68, and 2.30 s for GPS-only, dual-system, and quad-system solutions, respectively. Compared to the traditional serial strategy, the computation efficiency is significantly improved by 76.0%, 77.3%, and 77.7%, respectively. The accuracy of the estimated clocks is evaluated with respect to IGS final GPS clock products and GFZ final multi-GNSS clock products (GBM0MGXRAP), and multi-GNSS real-time precise point positioning (PPP) experiments are further carried out. All the results indicate that the proposed strategy is efficient, accurate, and can promise high-rate multi-GNSS real-time clock estimation.

Description: In recent years, the large Low Earth Orbit (LEO) constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems (GNSS) positioning performance. One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites. The GNSS-based Precise Orbit Determination (POD) will be exclusively performed to achieve this goal, where the Integer Ambiguity Resolution (IAR) plays a key role in acquiring high-quality orbits. In this study, we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations. We perform ambiguity-fixed LEO POD for four typical missions, including Gravity Recovery and Climate Experiment (GRACE) Follow-On (GRACE-FO), Swarm, Jason-3 and Sentinel-3, using the Uncalibrated Phase Delay (UPD) products generated by our GREAT (GNSS+ REsearch, Application and Teaching) software. The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits. There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias (OSB) and Integer Recovery Clock (IRC) products, indicating the good-quality of UPD products we generated. Compared to the float solution, the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites. Meanwhile, the benefit can be observed in laser ranging residuals as well, with a Standard Deviation (STD) reduction of 3–4 mm on average for the fixed solutions. Apart from the absolute orbits, the relative accuracy of the space baseline is also improved by 20–30% in the fixed solutions. The result demonstrates the superior performance of the ambiguity-fixed LEO POD, which appears as a particularly promising technique for POD of future LEO constellations.