The growth and breakup processes of raindrops within a cloud influence the rain intensity and the sizes of raindrops on the surface. The Doppler velocity spectrum acquired by a vertically pointing radar (VPR) contains information on atmospheric turbulence and the size classification of falling hydrometeors. In this study, the four types of Convective Cells (CC) during precipitation events with more than 700 mm of precipitation in southern China are described. The characteristics of four types of CCs correspond to the isolated convection, the early stage, the mature stage, and the decline stage of organizational convection, in that order. Microphysical analysis using retrieval of vertical air motion (Vair) and raindrop evolution in clouds from Doppler velocity spectra collected by C-band VPR revealed the growth and breakup of falling raindrops with dynamic impact. Larger raindrops appear in the early stages and are accompanied by ice particles, which are impacted by the falling path᾽s downdraft. Raindrop aggregation, which is primarily related to the alternation of updraft and downdraft, accounts for the mature stage᾽s high efficiency of surface rainfall. The CCs in the decline stage originate from the shallow uplift in the weak and broad downdraft under conditions of enough water vapor. The updraft dominates the stage of isolated convection. Observations of convective cells could be more accurately represented in model evaluations.
The south-western Ordos Basin is rich in low-middle rank coalbed methane (CBM) resources; while the geochemical characteristics and genetic mechanism of CBM are not clear. Herein, according to geological and geochemical test data from gas and coal seam water from CBM wells in Bingchang, Jiaoxun, Huangling, Yonglong, and Longdong minging areas, we systematically studied the geochemical characteristics, generation, and evolution mechanism of CBM in Jurassic Yan’an Formation in the south-western Ordos Basin. The results show that the CH4 content of whole gas is in the range of 42.01%–94.72%. The distribution ranges of the δ13C-CH4 value is −87.2‰ to −32.5‰, indicating diverse sources of thermogenic gas and biogenic gas. The microbial methane is mainly generated by a CO2 reduction pathway, with certain methyl-type fermentation spots. The δ13C-CH4 has a positive correlation with burial depth, indicating the obvious fractionation of CBM. The relationship between the genetic types and burial depth of the CBM reservoir indicates that the favorable depth of secondary biogenic gas is less than 660 m. The Late Cretaceous Yanshanian Movement led to the uplift of the Ordos Basin, and a large amount of thermogenic gas escaped from the edge of the basin. Since the Paleogene Period, the coal reservoir in the basin margin has received recharge from atmospheric precipitation, which is favorable for the formation of secondary biogenic methane. The deep area, generally under 1000 m, mainly contains residual thermogenic gas. The intermediate transition zone is mixed gas. Constrained by the tectonic background, the genetic types of CBM in different mining areas are controlled by the coupling of burial depth, coal rank, and hydrogeological conditions. The Binchang mining area contains biogenic gas, and the development of CBM has achieved initial success, indicating that similar blocks with biogenic gas formation conditions is key to the efficient development of CBM. The research results provide a scientific basis for searching for favorable exploration areas of CBM in the south-western Ordos Basin.
In this study the changes of tropical cyclone (TC) size from 2001 to 2021 are analyzed based on linear and quadratic curve fittings of the National Hurricane Center (NHC) / Joint Typhoon Warning Center (JTWC) best track data, based on the radius of maximum wind (RMW) and the average radius of 34-kt wind (AR34), in three oceanic basins of the North Atlantic (NATL), the Western North Pacific (WPAC) and the Eastern North Pacific (EPAC). The computations are done separately for two categories of tropical cyclones: tropical storms (TS) and hurricanes (HT). Size changes of landfalling and non-landfalling TCs are also discussed. Results show that there is a great inter-basin variability among the changes in TC sizes. Major conclusions include: 1) overall, the inner cores of TSs have become larger in all three basins, with the increasing tendencies being significant in the NATL and WAPC, while those of HTs mostly get smaller or remain similar; 2) meanwhile, comparatively large inter-basin differences are observed for the TC outer core sizes, and the sizes of landfalling TCs; 3) particularly, a significant decrease in landfalling HT outer core size is observed over the EPAC; 4) in contrast, significant increases in landfalling TS inner core size are found over the NATL and WPAC. The presented analysis results could benefit future research about TC forecasts, storm surge studies, and the cyclone climate and its changes.
The variations in precipitation have displayed a complex pattern in different regions since the mid-to-late-Holocene. Cloud formation processes may have a significant impact on precipitation, especially during the tropical marine processes and summer monsoon which convey abundant water vapor to coastal southern China and inland areas. Here, we use two 7500 year sedimentary records from the Pearl River Delta and the closed Maar Lake, respectively, in coastal southern China to reconstruct the mid-to-late-Holocene humidity variability and explore its possible relationship with cloud cover modulated by the Earth’s magnetic fields (EMF). Our proxy records document an apparent increase in wetness in coastal southern China between 3.0 and 1.8 kyr BP. This apparent increase in humidity appears to be consistent with the lower virtual axial dipole moments and, in turn, with a lower EMF. This correlation suggests that the EMF might have been superimposed on the weakened monsoon to regulate the mid-to-late-Holocene hydroclimate in coastal southern China through the medium of galactic cosmic rays, aerosols, and cloud cover. However, further investigations are needed to verify this interaction.
Deep shale gas reservoirs commonly contain connate water, which affects the enrichment and migration of shale gas and has attracted the attention of many scholars. It is significant to quantitatively estimate the amounts of adsorbed and free water in shale matrix pores, considering the different impacts of pore water (adsorbed water and free water) on shale gas. In this paper, pore water in six deep shale samples from the Wufeng-Longmaxi Formations in the Luzhou area, southern Sichuan Basin, China, was quantitatively evaluated by saturation-centrifugation experiments. Further, the impact of shale material composition and microstructure on the pore water occurrence was analyzed. The results show that amounts of adsorbed and free water are respectively 1.7967–9.8218 mg/g (mean 6.4501 mg/g) and 9.5511–19.802 mg/g (mean 13.9541 mg/g) under the experimental conditions (30°C, distilled water). The ratio of adsorbed water to total water is 15.83%–42.61% (mean 30.45%). The amounts of adsorbed and free water are related to the pore microstructure and material compositions of shale. The specific surface area of shale controls the amount of adsorbed water, and the pore volume controls the amount of free water; organic pores developed in shale solid asphalt contribute specific surface area and pore volume, and inorganic pores developed in clay mineral contribute pore volume. Therefore, the pores of shale solid asphalt accumulate the adsorbed water and free water, and the pores of clay minerals mainly accumulate the free water.
Eleven tropical cyclones (TCs) affected Shanghai and crossed the same latitude as Shanghai from 2007 to 2018. According to similar tracks from best-track data, TCs that cause significant precipitation in Shanghai can be divided into three types: landfall TCs, nearshore northward TCs, and western TCs. Based on ERA5 reanalysis data, the dynamic synthesis method was used to synthesize TC circulation situations to compare thermal, dynamic, water vapor, and stability conditions within TC circulations during the period when they affected Shanghai. The conclusions are as follows. 1) When the three TC types are at the same latitude as Shanghai, they are all in the divergent field in the upper troposphere. For the landfall type, the subtropical high at 500 hPa is stronger and farther north than usual, and there is a high-pressure dam on the north side of the TCs. 2) The warm advection of the three TC types at 925 hPa is located in the northern quadrant of the TCs. The dynamic and water vapor conditions are good in the north-western quadrant of landfall and western TCs, and more favorable in the eastern quadrant of nearshore northward TCs. 3) The favorable effects of all three types on precipitation in Shanghai come from the boundary layer. Water vapor, upward motion, and instability conditions of landfall TCs are superior to the other two TC types. The best water vapor, dynamic, and convective instability conditions are at the northern boundary in Shanghai during landfall TCs, and the main sources of water vapor in Shanghai come from the eastern and northern boundaries. During nearshore northward TCs, the main contribution to precipitation is from the eastern boundary, while better dynamic and water vapor conditions come from the western and northern boundaries during western TCs. The above findings provide scientific and technical support for operational forecasting precipitation from TCs affecting mega-cities.
Organic matter is the basis for oil and gas generation, and the depositional environment controls its enrichment. The first member of the Qingshankou Formation (K2qn1) in Songliao Basin has a thick organic-rich shale and so is an important target section for shale oil exploration and development. In the Gulong Sag, shale samples from this unit were collected over the full length of the section. The characterization of the environments of deposition (EOD) of K2qn1 was improved by utilizing lithological characteristics, thin section observations, elemental compositions, and organic carbon concentrations. Combined with the normalization coefficients proposed in this paper, an organic matter correlation model was established to elucidate the factors that influence organic matter enrichment. From the bottom to the top of K2qn1, the lake depth gradually becomes shallower, the primary productivity first decreases and then increases, the reducing conditions become stronger and then weaker, the water salinity gradually decreases, the climate first becomes semi-humid and then warm and humid, and the input of terrigenous debris first decreases and then increases. A major marine transgression at the base of the K2qn1᾽s brought in nutrients to increase primary productivity, and the density-stratified reducing environment preserved and enriched organic matter. High primary productivity occurred during the middle of the deposition of the K2qn1, while terrigenous input is low. Organic matter is preserved in reduced deep lake environments, resulting in organic matter-rich black shale. The lake became shallower, and the salinity decreased in the upper part of K2qn1. Benthic organisms rapidly multiplied, consuming large amounts of oxygen and destroying the previously depositional environment, resulting in a reducing environment disturbed by benthic organisms with poor preservation conditions and the lowest organic matter content.
The Mesozoic fan deltas in the north-west margin of the Junggar Basin, as important petroleum reservoirs, exhibited complex facies change and internal structures with strong heterogeneity which were controlled by the transformation of slope-patterns, bringing great challenges to the study of sedimentary characteristics. The Upper Karamay Formation at north-west margin of the Junggar Basin was the objective in this paper which attempts to clarify the mechanism of sedimentary response and sand-body distribution of fan delta systems under the control of slope-pattern change. Based on a data set of cores, well logs and seismic, two types of slope-pattern were identified in the study area, which include steep-to-gentle in the south and gentle-to-steep in the north. The control of difference slope-patterns on the sand-body distribution was clarified based on the analysis of the sedimentary dynamics, facies characteristics, and depositional evolution of the fan deltas. The study shows that the transport mechanism of sediments on the steep-slope was dominated by debris flows, developing coarse-grained, thick-bedded lobes with poor structural maturity of clasts. On the gentle-slope, the deposition was dominated by hyperconcentrated-traction currents, forming relatively fine-grained, thin-bedded lobes with increased sandy matrix. The sand-bodies show frequent bar-channel transformation and channel down-cutting under the steep slope setting, which exhibit migration of isolated river channels on the gentle slopes. Under the steep-to-gentle pattern, the coase-grained sediments were mainly accumulated at slope toe, generally developed equiaxial lobes. However, the coarse-grained clasts were preserved both at proximal and distal lobes on the gentle-to-steep slopes, showing obvious lateral extension of the fan delta. The slope patterns controlled sedimentary respond rates of the fan deltas during lake level change. By comparing the modern cases of fan systems worldwide, the control of slope patterns on deposition of coarse-grained fans was clarified, providing insight into hydrocarbon exploration on basin margins.
The uniaxial compressive strength (UCS) of rocks is a critical index for evaluating the mechanical properties and construction of an engineering rock mass classification system. The most commonly used method for determining the UCS in laboratory settings is expensive and time-consuming. For this reason, UCS can be estimated using an indirect determination method based on several simple laboratory tests, including point-load strength, rock density, longitudinal wave velocity, Brazilian tensile strength, Schmidt hardness, and shore hardness. In this study, six data sets of indices for different rock types were utilized to predict the UCS using three nonlinear combination models, namely back propagation (BP), particle swarm optimization (PSO), and least squares support vector machine (LSSVM). Moreover, the best prediction model was examined and selected based on four performance prediction indices. The results reveal that the PSO–LSSVM model was more successful than the other two models due to its higher performance capacity. The ratios of the predicted UCS to the measured UCS for the six data sets were 0.954, 0.982, 0.9911, 0.9956, 0.9995, and 0.993, respectively. The results were more reasonable when the predicted ratio was close to a value of approximately 1.
Accurate approaches for estimating flow resistance in large alluvial rivers are fundamental for simulating discharge, sediment transport, and flood routing. However, methods for estimating riverbed resistance and additional resistance in the channel-bar landscapes remain poorly investigated. In this study, we used in situ river bathymetry, sediment, and hydraulic data from the Shashi Reach in the Yangtze River to develop a semi-empirical approach for calculating flow resistance. Our method quantitatively separates flow resistance into riverbed resistance and additional resistance and shows high accuracy in terms of deviation ratio (~20%), root-mean-square error (~0.008), and geometric standard deviation (~3). Additional resistance plays a dominant role under low-flow conditions but a secondary role under high flows, primarily due to the reduction in momentum exchange in channel-bar regions as discharge increases. Riverbed resistance first decreases and then increases, which might be attributed to bedform changes in the lower and transitional flow regimes as flow velocity increases. Overall, our findings further the understanding of dynamic changes in flow resistance in the channel-bar landscapes of large river systems and have important implications for riverine ecology and flood management.
Ecosystem service flow is essential for transporting, transforming, and maintaining ecosystem services and connecting supply and demand. This study attempted to quantitatively assess the supply and demand flows of ecosystem services in the Yangtze River Basin in 2000, 2010, and 2020; assess the evolution of the spatial patterns of ecosystem service flow at the provincial, watershed and urban agglomeration scales; and design a zoning standard for ecosystem service flow. The results showed as follows. 1) Between 2000 and 2020, the Yangtze River had a progressive drop in its freshwater supply, water conservation service and carbon sequestration service flows. The decline rates for these services were measured at 10.90%, 11.11%, and 5.17%, respectively. The climate regulation service flow exhibited a pattern of initial fall followed by a subsequent increase, characterized by a decline rate of 35.53%. 2) The lowest was the ecosystem service flow in the lower reaches of the Yangtze River and the Yangtze River Delta urban agglomeration. Freshwater supply service flow and water conservation service flow were the highest in the upper reaches of the Yangtze River and the Chengdu-Chongqing urban agglomeration. Carbon sequestration service flow and climate regulation service flow were the highest in the middle reaches of the Yangtze River Basin and the urban agglomeration in the middle reaches of the Yangtze River. 3) From 2000 to 2020, the change ratios of the area proportion of the confluence, flow, and outflow areas in the Yangtze River Basin were 1.06, 3.17, and 0.86, respectively. The results of this research could offer decision support for regulating ecosystem services in the Yangtze River Basin, promoting sustainable regional development and achieving rational use of the basin resources.
The accurate determination of geological age is a key to understanding the history and process of paleolake evolution and oil and gas exploration in continental lake basin. However, improving the accuracy of geological age has always been a difficult scientific problem. A 609-m-thick, continuous lacustrine mudstone and sandstone succession in Chezhen Sag (eastern China) provides an ideal middle Eocene sedimentary record for establishing a high-resolution stratigraphic chronology framework. Based on spectrum analysis and sliding window spectrum analysis of the natural gamma (GR) logging data of well Che 271 (C271) in Chezhen Sag, the periods of 405 kyr and 40.1 kyr were filtered by a Gaussian bandpass filter, and a “floating” astrochronological time scale (ATS) was established. The total number of 405 kyr eccentricity cycles were 13.6 and 40.1 kyr obliquity cycles were 138 which recorded from the upper member 4 (Es4U) to the member 3 (Es3) of the Eocene Shahejie Formation, and the depositional duration was 5.53 Myr. Correlation Coefficient (COCO) analysis and evolutionary Correlation Coefficient (eCoCo) analysis found that the optimal sedimentary rate of different strata. Sedimentary noise simulation revealed the history of paleolake water changes in the Middle Eocene in the Chezhen Sag, according to which four sequences are divided. The study shows that the lake level change of Chezhen Sag in the middle Eocene shows prominent 1.2 Myr cycles and an antiphase well-coupled relationship with obliquity modulation. Finally, we propose a model to explain the relationship between the orbital cycle and lake level change in the continental lake basin. When the obliquity of the earth increases, the middle and high latitudes of the earth will be closer to the sun, the direct sunlight will be higher, and the meridional sunshine will increase, thus accelerating the evaporation process of lake basin water. When the seasonal changes are obvious (maximum period of 1.2 Myr ultra-long obliquity), this effect is more significant. The relative lake level change based on the restoration of high-precision ATS has significant scientific and economic value for understanding the vertical evolution of continental stratigraphic sequences and the formation and distribution of oil and gas resources.
