An empirical ensemble rainfall nowcasting model using multi-scaled analogues     

Zou  Xinyan  Dai  Qiang  Wu  Kejie  Yang  Qiqi  Zhang  Shuliang 《Natural Hazards》2020,103(1):165-188

Natural Hazards - Short-term rainfall prediction with high spatial and temporal resolution is of great importance to rainfall-triggered natural hazards such as landslide, flood, and debris flow. An...  相似文献   

短期重现性地磁日变化感应电流集中分布与地震关系初步研究     

冯志生  姜楚峰  冯丽丽  李军辉  戴勇  黄颂  姚丽  章鑫  袁桂平  倪晓寅  戴苗  李鸿宇 《中国地震》2020,36(3):502-516

通过分析台站之间地磁垂直分量日变化相关性,研究中国大陆南北带地区90°E～110°E,2009～2018年地磁日变化感应电流线状集中分布现象与M_S≥6.0地震关系。统计发现,我国每月平均出现约2次感应电流集中分布现象,且10天左右内有原地重复出现现象——感应电流集中分布重叠异常,原地重现的集中分布感应电流日期间隔一般在10天左右以内,原地重现日期一般不连续,重现次数一般仅有2次。研究发现,我国南北带2009～2018年共出现重叠异常23次,20次重叠异常出现后18个月内重叠段发生M_S≥6.0地震,对应率高达87%,地震基本发生在重叠段端部250km以内,重叠段发生2次M_S≥6.0地震的比例较低,约35%;重叠段2个端部均发生M_S≥6.0地震的比例极小,仅约9%。部分重叠段走向与已经发现的上地幔和地壳高导带埋深走向基本一致,推测重叠异常发生在上地幔和地壳高导带附近,是来自上地幔和地壳内高导带附近的地震异常信息。目前已知,中国大陆强地震主要发生在上地幔高导层的隆起区一带及其壳内高导层发育地区,深部电性测深结果表明,大震易于发生在电导率急剧变化的梯度带,但这些地区何时发生地震还未得知,本文发现的重叠异常解释了这些地区1～2年内是否发生地震这一问题。  相似文献   

A TEM and EELS study of carbon in a melt fragment from the Gardnos impact structure     

Paula Lindgren  Lydia Hallis  Fredrik S. Hage  Martin R. Lee  John Parnell  Anders Plan  Alistair Doye  Ian MacLaren 《Meteoritics & planetary science》2019,54(11):2698-2709

A carbon‐rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high‐resolution techniques including focused ion beam‐transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available.  相似文献   

An efficient early warning system for typhoon storm surge based on time-varying advisories by coupled ADCIRC and SWAN   总被引：2，自引：0，他引：2  

Seung Won Suh  Hwa Young Lee  Hyeon Jeong Kim  Jason G. Fleming 《Ocean Dynamics》2015,65(5):617-646

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Nonlinear bacterial load‐streamflow response on a marine beach          下载免费PDF全文

Wai Thoe  Joseph Hun‐wei Lee 《水文研究》2015,29(6):1238-1251

Bacterial concentration (Escherichia coli) is used as the key indicator for marine beach water quality in Hong Kong. For beaches receiving streamflow from unsewered catchments, water quality is mainly affected by local nonpoint source pollution and is highly dependent on the bacterial load contributed from the catchment. As most of these catchments are ungauged, the bacterial load is generally unknown. In this study, streamflow and the associated bacterial load contributed from an unsewered catchment to a marine beach, Big Wave Bay, are simulated using a modelling approach. The physically based distributed hydrological model, MIKE‐SHE, and the empirical watershed water quality model (Hydrological Simulation Program – Fortran) are used to simulate streamflow and daily‐averaged E. coli concentration/load, respectively. The total daily derived loads predicted by the model during calibration (June–July 2007) and validation (July–October 2008) periods agree well with empirical validation data, with a percentage difference of 3 and 2%, respectively. The simulation results show a nonlinear relationship between E. coli load and rainfall/streamflow and reveal a source limiting nature of nonpoint source pollution. The derived load is further used as an independent variable in a multiple linear regression (MLR) model to predict daily beach water quality. When compared with the MLR models based solely on hydrometeorological input variables (e.g. rainfall and salinity), the new model based on bacterial load predicts much more realistic E. coli concentrations during rainstorms. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Evaluation of Hydraulic Properties of Aquitards Using Earthquake‐Triggered Groundwater Variation          下载免费PDF全文

Shih‐Jung Wang  Kuo‐Chin Hsu  Chein‐Lee Wang  Wen‐Chi Lai  Liang‐Tzu Hsu 《Ground water》2017,55(5):747-756

The hydraulic properties of aquitards are not easily obtained because monitoring wells are usually installed in aquifers for groundwater resources management. Earthquake‐induced crust stress (strain) triggers groundwater level variations over a short period of time in a large area. These groundwater anomalies can be used to investigate aquifer systems. This study uses a poroelastic model to fit the postseismic variations of groundwater level triggered by the Chi‐Chi earthquake to evaluate the hydraulic properties of aquitards in the Jhoushuei River alluvial fan (JRAF), Taiwan. Six of the adopted eight wells with depths of 70 to 130 m showed good agreement with the recovery theory. The mean hydraulic conductivities (K) of the aquifers for the eight wells are 1.62 × 10^?4 to 9.06 × 10^?4 m/s, and the thicknesses are 18.8 to 46.1 m. The thicknesses of the aquitards are 11.3 to 42.0 m. Under the isotropic assumption for K, the estimated values of K for the aquitards are 3.0 × 10^?8 to 2.1 × 10^?6 m/s, corresponding to a silty medium. The results match the values obtained for the geological material of the drilling core and those reported in previous studies. The estimated values were combined with those given in previous studies to determine the distribution of K in the first two aquitards in the JRAF. The distribution patterns of the aquitards reflect the sedimentary environments and fit the geological material. The proposed technique can be used to evaluate the K value of aquitards using inverse methods. The inversion results can be used in hydrogeological analyses, contaminant modeling, and subsidence evaluation.  相似文献   

Relation of CME Speed and Magnetic Helicity in CME Source Regions on the Sun during the Early Phase of Solar Cycles 23 and 24     

R.-S. Kim  S.-H. Park  S. Jang  K.-S. Cho  B. S. Lee 《Solar physics》2017,292(4):66

To investigate the relations between coronal mass ejection (CME) speed and magnetic field properties measured in the photospheric surface of CME source regions, we selected 22 disk CMEs in the rising and early maximum phases of the current Solar Cycle 24. For the CME speed, we used two-dimensional (2D) projected speed observed by the Large Angle and Spectroscopic Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), as well as a 3D speed calculated from the triangulation method using multi-point observations. Two magnetic parameters of CME source regions were considered: the average of magnetic helicity injection rate and the total unsigned magnetic flux. We then classified the selected CMEs into two groups, showing: i) a monotonically increasing pattern with one sign of helicity (group A: 16 CMEs) and ii) a pattern of significant helicity injection followed by its sign reversal (group B: 6 CMEs). We found that: 1) 3D speed generally shows better correlations with the magnetic parameters than the 2D speed for 22 CME events in Solar Cycle 24; 2) 2D speed and the magnetic parameters of 22 CME events in this solar cycle have lower values than those of 47 CME events in Solar Cycle 23; 3) all events of group B in Solar Cycle 24 occur only after the beginning of the maximum phase, a trend well consistent with that shown in Solar Cycle 23; 4) the 2D speed and the helicity parameter of group B events continue to increase in the declining phase of Solar Cycle 23, while those of group A events abruptly decrease in the same period. Our results indicate that the two CME groups have a different tendency in the solar cycle variations of CME speed and the helicity parameters. Active regions that show a complex helicity evolution pattern tend to appear in the maximum and declining phases, while active regions with a relatively simple helicity evolution pattern appear throughout the whole solar cycle.  相似文献   

Improvements on a unified dark matter model     

A. Del Popolo  Xi-Guo Lee 《Astronomy Letters》2017,43(10):635-643

We study, by means of a spherical collapse model, the effect of shear, rotation, and baryons on a generalized Chaplygin gas (gCg) dominated universes. We show that shear, rotation, and the baryon presence slow down the collapse with respect to the simple spherical collapse model. The slowing down in the growth of density perturbation is able to solve the instability of the unified dark matter (UDM) models described in previous papers (e.g., Sandvik et al. 2004) at the linear perturbation level, as also shown by a direct comparison of our model with previous results.  相似文献   

The role of eddies in solute transport and recovery in rock fractures: Implication for groundwater remediation          下载免费PDF全文

Seung Hyun Lee  In Wook Yeo  Kang‐Kun Lee  Won Sang Lee 《水文研究》2017,31(20):3580-3587

A better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough‐walled fractures. Six representative troughs in a rough‐walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration. This experimental study was enabled by a microscale visualization technique of micro particle image velocimetry. With increasing flow velocity (Re ≤ 2.86), no eddies were generated, and solutes along the main streamlines transported rapidly, whereas those near the wall moved slowly. A larger amount of solutes remained trapped at all troughs at Re = 2.86 than Re < 1. For Re = 8.57, weak eddies started to be developed at the troughs on the lee side, which little contributed to overall solute flushing in the fracture. Accordingly, a large of amount of water was needed for solute flushing. The flow condition of 1 < Re < 10, before a full development of eddies, was least favourable in terms of time and amount of remediation fluid required to reach a target concentration. After large eddies were fully developed at troughs on the lee side for Re = 17.13, solutes were substantially reduced by eddies with less amount of water. Fully developed eddies were found to enhance solute transport and recovery, as opposed to a general consensus that eddies trap and delay solutes. Direct inflow into troughs on the stoss side also made a great contribution to solute flushing out of the troughs. This study indicates that fully developed eddies or strong inflows at troughs are highly possible to form for Re > 10 and this flow range could be favourable for efficient remediation.  相似文献   

Regional modelling of permafrost thicknesses over the past 130 ka: implications for permafrost development in Great Britain          下载免费PDF全文

Jonathan P. Busby  Jonathan R. Lee  Sev Kender  Paul Williamson  Simon Norris 《Boreas: An International Journal of Quaternary Research》2016,45(1):46-60

The greatest thicknesses of permafrost in Great Britain most likely occurred during the last glacial–interglacial cycle, as this is when some of the coldest conditions occurred during the last 1 000 000 years. The regional development of permafrost across Great Britain during the last glacial–interglacial cycle was modelled from a ground surface temperature history based on mean annual temperatures and the presence of glacier ice. To quantify the growth and decay of permafrost, modelling was undertaken at six locations across Great Britain that represent upland glaciated, lowland glaciated, upland unglaciated and lowland unglaciated conditions. Maximum predicted permafrost depths derived in this academic study range between several tens of metres to over 100 m depending upon various factors including elevation, glacier ice cover, geothermal heat flux and air temperature. In general, the greatest maximum permafrost thicknesses occur at upland glaciated locations, with minimum thickness at lowland sites. Current direct geological evidence for permafrost is from surface or shallow processes, mainly associated with the active layer. Further research is recommended to identify the imprint of freeze/thaw conditions in permanently frozen porous rocks from beneath the active layer.  相似文献