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  • RESEARCH ARTICLE
    Dongliang ZHANG, Yunpeng YANG, Min RAN, Bo LAN, Hongyan ZHAO, Qi LIU
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0906-9

    Over the past 2000 years, a high-resolution pollen record from the Yushenkule Peat (46°45′–46°57′N, 90°46′–90°61′E, 2374 m a.s.l.) in the south-eastern Altai Mountains of northwestern China has been used to explore the changes in vegetation and climate. The regional vegetation has been dominated by alpine meadows revealed from pollen diagrams over the past 2000 years. The pollen-based climate was warm and wet during the Roman Warm Period (0–520 AD), cold and wet during the Dark Age Cold Period (520–900 AD), warm and wet during the Medieval Warm Period (900–1300 AD), and cold and dry during the Little Ice Age (1300–1850 AD). Combined with other pollen data from the Altai Mountains, we found that the percentage of arboreal pollen showed a reduced trend along the NW-SE gradient with decreasing moisture and increasing climatic continentality of the Altai Mountains over the past 2000 years; this is consistent with modern distributions of taiga forests. We also found that the taiga (Pinus forest) have spread slightly, while the steppe (Artemisia, Poaceae and Chenopodiaceae) have recovered significantly in the Altai Mountains over the past 2000 years. In addition, the relatively warm-wet climate may promote high grassland productivity and southward expansion of steppe, which favors the formation of Mongol political and military power.

  • RESEARCH ARTICLE
    Huijun LU, Ru ZHANG, Li REN, Anlin ZHANG, Yiming YANG, Xiaopeng LI
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0911-z

    Understanding the damage behavior and cracking mechanism of brittle shale is crucial for hydraulic fracturing design. In this research, uniaxial compression tests are conducted on shale samples with different bedding plane orientations, and acoustic emission monitoring is implemented synchronously. The results indicate that the apparent elastic modulus increases with increasing bedding orientation. For the bedding orientations of 45° and 90°, the lateral deformation is anisotropic due to the bedding structure, revealing the anisotropic Poisson effect. A shear failure surface and tensile failure surfaces form parallel to the bedding plane for bedding orientations of 45° and 90°, respectively. For the bedding orientation of 0°, shear failure mainly occurs through the bedding planes. Additionally, the damage mechanism of shale is investigated by crack classification based on AE parameters. It is found that crack initiation is induced by the generation of shear cracks for the bedding orientation of 45°, whereas by the generation of tensile cracks for other bedding orientations. According to damage attributable to different type cracks, shear cracks dominate the damage behavior for bedding orientations of 0° and 45°, whereas tensile cracks dominate the damage behavior for bedding orientation of 90°. Finally, the information entropy is calculated by AE energy. A low value of information entropy, approximately 0.36, predicts failure with a low degree of instability for the bedding orientation of 0°, whereas a high value of information entropy, more than 1.5, predicts failure with a high degree of instability for other bedding orientations. This finding indicates that the failure behavior is gradual progressive damage for bedding orientation of 0°, whereas sudden damage dominates failure behavior for other bedding orientations.

  • RESEARCH ARTICLE
    Shuai ZHANG, Jing HAN, Bingke ZHAO, Zhigang CHU, Jie TANG, Limin LIN, Xiaoqin LU, Jiaming YAN
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0902-0

    Calibration error is one of the primary sources of bias in echo intensity measurements by ground-based radar systems. Calibration errors cause data discontinuity between adjacent radars and reduce the effectiveness of the radar system. The Global Precipitation Measurement Ku-band Precipitation Radar (GPM KuPR) has been shown to provide stable long-term observations. In this study, GPM KuPR observations were converted to S-band approximations, which were then matched spatially and temporally with ground-based radar observations. The measurements of stratiform precipitation below the melting layer collected by the KuPR during typhoon Ampil were compared with those of multiple radar systems in the Yangtze River Delta to determine the deviations in the echo intensity between the KuPR and the ground-based radar systems. The echo intensity data collected by the ground-based radar systems was corrected using the KuPR observations as reference, and the correction results were verified by comparing them with rain gauge observations. It was found that after the correction, the consistency of the echo intensity measurements of the multiple radar systems improved significantly, and the precipitation estimates based on the revised ground-based radar observations were closer to the rain gauge measurements.

  • RESEARCH ARTICLE
    Sijun ZHENG, Chen MENG, Jianhui XUE, Yongbo WU, Jing LIANG, Liang XIN, Lang ZHANG
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0896-7

    Three-dimensional green volume (TDGV) reflects the quality and quantity of urban green space and its provision of ecosystem services; therefore, its spatial pattern and the underlying influential factors play important roles in urban planning and management. However, little is known about the factors contributing to the spatial pattern of TDGV. In this paper, TDGV and land use intensity (LUI) extracted from high spatial resolution (0.05 m) remotely sensed data acquired by an unmanned aerial vehicle (UAV), anthropogenic factors

    LUI, Distance from buildings and Distance from roads.

    and natural factors

    Land formation time and Distance from water.

    were utilized to identify the spatial pattern of TDGV and the potential influencing factors in Lingang New City, a rapidly developed coastal town in Shanghai. The results showed that most of the TDGV was distributed in the western part of this new city and that its spatial variations were significantly axial. TDGV corresponded well with the chronologies of land formation, urban planning, and construction in the city. Generalized least squares (GLS) analysis of TDGV (grid cell size: 100 × 100 m) and its influencing factors showed that the TDGV in this new city was significantly negatively correlated with both LUI and distance from roads and significantly positively correlated with land formation time and distance from water. Distance from buildings did not affect TDGV. Additionally, the degree of influence decreased in the following order: distance from water>land formation time>distance from roads>LUI. These results indicate that the spatial pattern of TDGV in this new town was mainly affected by natural factors (i.e., the distance from water and land formation time) and that the artificial disturbances caused by rapid urbanization did not decrease the regional TDGV. The main factors shaping the spatial distribution of TDGV in this city were local natural factors. Our findings suggest that the improvement in local soil and water conditions should be emphasized in the construction of new cities in coastal areas to ensure the efficient provision of ecological services by urban green spaces.

  • RESEARCH ARTICLE
    Ying CHEN, Ruixue CAO, Yuting FENG, Hui ZHAO
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0914-9

    Summer phytoplankton blooms appear frequently off the Somali coast in the southwestern Arabian Sea (AS), where strong reversal monsoon and summer upwelling is prevailing. Distinct high chlorophyll-a (Chl-a) concentrations in summer were displayed in the western AS, especially in the region off the Somali coast. The spatial and inter-annual variations of the summer high Chl-a were studied using satellite data including ocean color and wind vectors. Under ocean conditions including monsoon winds, Ekman transport (ET) and Ekman pumping velocity (EPV), as well as geostrophic current and aerosol precipitation, the possible mechanisms of high Chl-a was investigated. The summer high Chl-a presented strong inter-annual variations in the southwestern AS. The results of simple correlation analysis indicated that there were good correlations between the ET and Chl-a, as well as between EPV and Chl-a. These implied that the ET and EPV may cause uplift of nutrients into the upper layer of the western AS from subsurface or coastal regions, inducing high Chl-a in the southwestern AS, especially in the region off the Somali coasts in summer. The multiple/partial correlation analysis implied further that EPV-induced upwelling may be more helpful than the ET-induced upwelling in the coastal region off Somalia, leading to probably more significant influence of EPV upwelling on the phytoplankton bloom than upwelling by ET. Aerosol precipitation in the southwestern AS also played an important role in high Chl-a in the deep offshore AS (i.e., Section B in Fig. 1(a)), as second only to ET and sea surface temperature (SST), and even higher than EPV. A novel finding is that the influence of aerosol optical thickness (AOT) is evident in the offshore region and the dust precipitation is more important sources to oligotrophic water. Both the stability of the upper ocean and the aerosol precipitation may play more evident roles in the open regions of the southwestern AS off Somali.

  • RESEARCH ARTICLE
    Shangbin CHEN, Huijun WANG, Yang WANG, Tianguo JIANG, Yingkun ZHANG, Zhuo GONG
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0913-x

    The study and exploration practice of shale gas accumulation has focused on the static system comparison, key parameters analysis, reservoir characteristics, enrichment mode etc. However, the research on dynamic recovery from the original hydrocarbon generation of shale gas to the present gas reservoir is still lacking. The burial history of shale gas reservoir can reflect the overall dynamic process of early formation and later transformation of shale gas reservoir. It controls the material basis of shale gas, the quality of reservoir physical properties, preservation conditions, gas content and formation energy, which is the core and foundation of shale gas accumulation process research. Herein, based on the five typical wells data in the Northeast Yunnan, including geochronological data, measured Ro values, core description records, well temperature data, paleoenvironment, paleothermal, etc., the burial history, thermal evolution history and hydrocarbon generation history of the Lower Silurian Longmaxi Formation were systematically restored via back stripping method and EASY%Ro model. The results show that 1) the differences in the burial history of marine shale in Longmaxi Formation can be divided into syncline type and anticline type. 2) The shale gas accumulation process can be divided into four stages, namely the source-reservoir-cap sedimentation period, initial accumulation period, main accumulation period, and adjustment period. 3) Based on the characteristics of burial history and preservation conditions, the areas with wide and gentle anticline, far away from the denudation area, and buried deeply with good fault sealing ability are priority structural locations for the shale gas exploration in northeast Yunnan.

  • RESEARCH ARTICLE
    Umair KHAN, Baoyi ZHANG, Jiangfeng DU, Zhengwen JIANG
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0881-1

    Surface and deep subsurface geological structural trends, stratigraphic features, and reservoir charac-teristics play important roles in assessment of hydrocarbon potential. Here, an approach that integrates digital elevation modelling, seismic interpretation, seismic attributes, three-dimensional (3D) geological structural modeling predicated on seismic data interpretation, and petrophysical analysis is presented to visualize and analyze reservoir structural trends and determine residual hydrocarbon potential. The digital elevation model is utilized to provide verifiable predictions of the Dhulian surface structure. Seismic interpretation of synthetic seismograms use two-way time and depth contour models to perform a representative 3D reservoir geological structure evaluation. Based on Petrel structural modeling efficiency, reservoir development indexes, such as the true 3D structural trends, slope, geometry type, depth, and possibility of hydrocarbon prospects, were calculated for the Eocene limestone Chorgali, upper Paleocene limestone Lockhart, early Permian arkosic sandstone Warcha, and Precambrian Salt Range formations. Trace envelope, instantaneous frequency, and average energy attribute analyses were utilized to resolve the spatial predictions of the subsurface structure, formation extrusion, and reflector continuity. We evaluated the average porosity, permeability, net to gross ratio, water saturation, and hydrocarbon saturation of early Eocene limestone and upper Paleocene limestone based on the qualitative interpretation of well log data. In summary, this integrated study validates 3D stratigraphic structural trends and fault networks, facilitates the residual hydrocarbon potential estimates, and reveals that the Dhulian area has a NE to SW (fold axis) thrust-bounded salt cored anticline structure, which substantiates the presence of tectonic compression. The thrust faults have fold axes trending from ENE to WSW, and the petrophysical analysis shows that the mapped reservoir is of good quality and has essential hydrocarbon potential, which can be exploited economically.

  • RESEARCH ARTICLE
    Mengjuan LIU, Lin DENG, Wei HUANG, Wanchen WU
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0923-8

    The impact of vertical resolution on the simulation of Typhoon Lekima (2019) is investigated using the Weather Research and Forecasting (WRF) model version 3.8.1. Results show that decreasing vertical grid spacing from approximately 1000 m to 100 m above 1 km height barely influences the simulated track. However, significant differences are found in the simulated tropical cyclone (TC) structure. The simulation with the coarsest vertical resolution shows a clear double warm-core structure. The upper warm core weakens and even disappears with the increase of vertical resolution. A broader eye and a more slantwise eyewall are observed with the increase of vertical resolution due to the vertically extended lower-level and upper-level outflow, which likely results in a weaker subsidence. Vertical grid convergence is evaluated with the simulated kinetic energy (KE) spectra. As the vertical grid spacing becomes finer than 200 m, convergent KE spectra are found in both the free atmosphere and the outer core of the TC. However, sensitivity tests reveal that the grid convergence is sensitive to the choice of the planetary boundary layer scheme.

  • RESEARCH ARTICLE
    Guomin CHEN, Xiping ZHANG, Qing CAO, Zhihua ZENG
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0900-2

    The predictions for Super Typhoon Lekima (2019) have been evaluated from official forecasts, global models, regional models and ensemble prediction systems (EPSs) at lead times of 1–5 days. Track errors from most deterministic forecasts are smaller than their annual mean errors in 2019. Compared to the propagation speed, the propagation direction of Lekima (2019) was much easier to determine for the official agency and numerical weather prediction (NWP) models. The National Centers for Environmental Prediction Global Ensemble Forecast System (NCEP-GEFS), Japan Meteorological Agency Global Ensemble Prediction System (JMA-GEPS) and Meteorological Service of Canada Ensemble System (MSC-CENS) are underdispersed, and the Shanghai Typhoon Institute Typhoon Ensemble Data Assimilation and Prediction System (STI-TEDAPS) is overdispersed, while the ensemble prediction system from European Centre for Medium-Range Weather Forecasts (ECMWF) shows adequate dispersion at all lead times. Most deterministic forecasting methods underestimated the intensity of Lekima (2019), especially for the rapid intensification period after Lekima (2019) entered the East China Sea. All of the deterministic forecasts performed well at predicting the first landfall point at Wenling, Zhejiang Province with a lead time of 24 and 48 h.

  • EDITORIAL
    Jie TANG, Jianfang FEI, Hui YU
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-021-0929-2