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.
Crop type mapping using remote sensing is critical for global agricultural monitoring and food security. However, the complexity of crop planting patterns and spatial heterogeneity pose significant challenges to field data collection, thereby limiting the accuracy of remotely sensed crop mapping. This study proposed a new approach for rapidly collecting field crop data by integrating unmanned aerial vehicle (UAV) images with the YOLOv3 (You Only Look Once version 3) algorithm. The impacts of UAV flight altitude and the number of training samples on the accuracy of crop identification models were investigated using peanut, soybean, and maize as examples. The results showed that the average F1-score for crop type detection accuracy reached 0.91 when utilizing UAV images captured at an altitude of 20 m. In addition, a positive correlation was observed between identification accuracy and the number of training samples. The model developed in this study can rapidly and automatically identify crop types from UAV images, which significantly improves the survey efficiency and provides an innovative solution for acquiring field crop data in large areas.
This study employs the regional Climate-Weather Research and Forecasting model (CWRF) to first investigate the primary physical mechanisms causing biases in simulating summer precipitation over the Yangtze River Basin (YRB), and then enhance its predictive ability through an optimal multi-physics ensemble approach. The CWRF 30-km simulations in China are compared among 28 combinations of varying physics parameterizations during 1980−2015. Long-term average summer biases in YRB precipitation are remotely correlated with those of large-scale circulations. These teleconnections of biases are highly consistent with the observed correlation patterns between interannual variations of precipitation and circulations, despite minor shifts in their primary action centers. Increased YRB precipitation aligns with a southward shifted East Asian westerly jet, an intensified low-level southerly flow south of YRB, and a south-eastward shifted South Asian high, alongside higher moisture availability over YRB. Conversely, decreased YRB precipitation corresponds to an opposite circulation pattern. The CWRF control configuration using the ensemble cumulus parameterization (ECP), compared to other cumulus schemes, best captures the observed YRB precipitation characteristics and associated circulation patterns. Coupling ECP with the Morrison or Morrison-aerosol microphysics and the CCCMA or CAML radiation schemes enhances the overall CWRF skills. Compared to the control CWRF, the ensemble average of these skill-enhanced physics configurations more accurately reproduces YRB summer precipitation’s spatial distributions, interannual anomalies, and associated circulation patterns. The Bayesian Joint Probability calibration to these configurations improves the ensemble’s spatial distributions but compromises its interannual anomalies and teleconnection patterns. Our findings highlight substantial potential for refining the representation of climate system physics to improve YRB precipitation prediction. This is notably achieved by realistically coupling cumulus, microphysics, and radiation processes to accurately capture circulation teleconnections. Further enhancements can be achieved by optimizing the multi-physics ensemble among skill-enhanced configurations.
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.
Hydrocarbon exploration in the Dongying Sag is constrained by the development of many Cenozoic transtensional structures with complex patterns and dynamic mechanisms. This study uses seismic interpretation and analog modeling to investigate these transtensional structures. Significant results include dividing these transtensional structures into boundary fault, oblique rifting, and deep strike-slip fault controlled structures, according to the relationships between main and secondary faults. They developed in the steep slope zone, the central sag zone, and the slope zone, respectively. In profile, the transtensional structures formed appear to be semi-flower-like, step-like, or negative-flower-like. In plan-view, they appear to be broom-like, soft-linked, or en-echelon structures. Further, these transtensional structures are controlled by the oblique normal slip of boundary faults, by the oblique extension of sub-sags, and by the later extension of deep strike-slip faults. The geometric deformation of these transtensional structures is controlled by the angles between the regional extension direction and the strike of boundary faults, deep faults, or sub-sags, where a larger angle corresponds to less developed transtensional structures. Further, the transtensional structures in the Dongying Sag were created by multi-phase and multi-directional extensions in the Cenozoic— which is also controlled by pre-existing structures. The strike of newborn secondary faults was determined by the regional extension direction and pre-existing structures.
Sedimentation is a key process affecting wetland sustainability and carbon burial flux. In context of sea level rise, climate change and human activities, further understanding about the sedimentary dynamic in wetland is critical in predicting the landscape evolution or the change in carbon burial flux. In this study, based on the field hydrological observation in a mangrove system in the Nanliu River estuary, we found the net flux of suspended sediment to mangrove is 39−72 kg/m in tidal cycles with Turbidity Maximum Zone (TMZ) forming in surface layer and only is 9−18 kg/m in tidal cycles without TMZ. The higher net flux of suspended sediment to mangrove in tidal cycles with TMZ forming in surface layer is attributed to high SSC in rising tide and intense flocculation in mangrove. The significant discrepancy in sedimentation rate in the mangrove patches also can be explained by the probability of TMZ forming in the surface layer of estuary. In future, rapid sea level rising may lead to the change of TMZ pattern in estuary, which will result in non-negligible variation in sedimentation rate in wetlands. According to the present data of sedimentation rate in wetlands, the fragility of wetlands in river estuary may be miscalculated.
