Low-Level Westerly Winds,Topography, and Tropical Cyclogenesis of Arlene (2005): Observations and Model Simulations     

Jinwoong Yoo  Robert V. Rohli  Jennifer M. Collins 《The Professional geographer》2017,69(3):348-361

The evolution process of the low-level westerly winds over the eastern North Pacific is investigated to understand the tropical cyclogenesis (TCG) of Tropical Storm Arlene (2005) over the Intra-Americas Sea (IAS). Also considered are the influences of the topography of the Central American mountain region interacting with the low-level westerly winds on Arlene's TCG by comparing results from a modified-topography simulation of Arlene's TCG with those from a simulation with the original topography in the Weather Research and Forecast (WRF) model. Interactions among large-scale circulations associated with subtropical highs in both hemispheres and an anticyclone over the warm eastern North Pacific produced low-level westerly winds into the IAS. WRF model experiments with a virtually elevated terrain filling in mountain passes in Central America resulted in the delayed and suppressed development of the incipient storm. The model experiments suggest that the low-level winds and moisture fluxes from the eastern North Pacific passing through the low-level mountain passes in Central America could play a critical role in the TCG process and perhaps also sustenance of storms over the western Caribbean.  相似文献   

Sedimentological, geochemical and palaeontological evidence for a neoglacial cold event during the late Holocene in the continental shelf of the northern South Shetland Islands, West Antarctica     

Kyu-Cheul Yoo  Ho Il Yoon  Jin-Kyung Kim  & Boo-Keun Khim 《Polar research》2009,28(2):177-192

Two sediment cores obtained from the continental shelf of the northern South Shetland Islands, West Antarctica, consist of: an upper unit of silty mud, bioturbated by a sluggish current, and a lower unit of well-sorted, laminated silty mud, attributed to an intensified Polar Slope Current. Geochemical and accelerator mass spectrometry ¹⁴C analyses yielded evidence for a late Holocene increase in sea-ice extent and a decrease in phytoplankton productivity, inferred from a reduction in the total organic carbon content and higher C : N ratios, at approximately 330 years B.P., corresponding to the Little Ice Age. Prior to this, the shelf experienced warmer marine conditions, with greater phytoplankton productivity, inferred from a higher organic carbon content and C : N ratios in the lower unit. The reduced abundance of Weddell Sea ice-edge bloom species ( Chaetoceros resting spores, Fragilariopsis curta and Fragilariopsis cylindrus ) and stratified cold-water species ( Rhizosolenia antennata ) in the upper unit was largely caused by the colder climate. During the cold period, the glacial restriction between the Weddell Sea and the shelf of the northern South Shetland Islands apparently hindered the influx of ice-edge bloom species from the Weddell Sea into the core site. The relative increases in the abundance of Actinocyclus actinochilus and Navicula glaciei , indigenous to the coastal zone of the South Shetland Islands, probably reflects a reduction in the dilution of native species, resulting from the diminished influx of the ice-edge species from the Weddell Sea. We also document the recent reduction of sea-ice cover in the study area in response to recent warming along the Antarctic Peninsula.  相似文献   

Lituya Bay Landslide Impact Generated Mega-Tsunami 50th Anniversary   总被引：4，自引：0，他引：4  

Hermann M. Fritz  Fahad Mohammed  Jeseon Yoo 《Pure and Applied Geophysics》2009,166(1-2):153-175

On July 10, 1958, an earthquake M_w 8.3 along the Fairweather fault triggered a major subaerial landslide into Gilbert Inlet at the head of Lituya Bay on the southern coast of Alaska. The landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history. The mega-tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis. A cross section of Gilbert Inlet was rebuilt at 1:675 scale in a two-dimensional physical laboratory model based on the generalized Froude similarity. A pneumatic landslide tsunami generator was used to generate a high-speed granular slide with controlled impact characteristics. State-of-the-art laser measurement techniques such as particle image velocimetry (PIV) and laser distance sensors (LDS) were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup. The entire process of a high-speed granular landslide impact may be subdivided into two main stages: (a) Landslide impact and penetration with flow separation, cavity formation and wave generation, and (b) air cavity collapse with landslide run-out and debris detrainment causing massive phase mixing. Formation of a large air cavity — similar to an asteroid impact — in the back of the landslide is highlighted. A three-dimenional pneumatic landslide tsunami generator was designed, constructed and successfully deployed in the tsunami wave basin at OSU. The Lituya Bay landslide was reproduced in a three-dimensional physical model at 1:400 scale. The landslide surface velocities distribution was measured with PIV. The measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models.  相似文献   

Geology, Mineralogy and Geochemistry of Carbonate Replacement-Type Lead-Zinc-Silver Deposits in Janggun Mine, Republic of Korea     

Lee Hyun Koo Lee Chan Hee Yoo Bong Cheal Lee Jong Chang Department of Geology  Chungnam National University  Taejon  Korea 《中国地质大学学报(英文版)》2000,11(2)

INTRODUCTIONThe Janggun mine,Republic of Korea,is located in thesoutheast of the Seoul,about latitude36°5 1′N and longitude12 9°0 4′E. In this mine area is situated the Bonghwa m ineral-ized zone of the Taebaegsan mining district,Korea.The geo-logic setting of the region was described as the Samgeum riQuadrangle(Kim et al.,196 2 ) .The general and local geolo-gy near the mine area have been studied by L ee (196 7) ,Hwang and Reedman(1975 ) .This mine consists of four min-eral de…  相似文献   

Stochastic multi-site generation of daily rainfall occurrence in south Florida     

Tae-woong Kim  Hosung Ahn  Gunhui Chung  Chulsang Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):705-717

This paper presents a stochastic model to generate daily rainfall occurrences at multiple gauging stations in south Florida. The model developed in this study is a space–time model that takes into account the spatial as well as temporal dependences of daily rainfall occurrence based on a chain-dependent process. In the model, a Markovian method was used to represent the temporal dependence of daily rainfall occurrence and a direct acyclic graph (DAG) method was introduced to encode the spatial dependence of daily rainfall occurrences among gauging stations. The DAG method provides an optimal sequence of generation by maximizing the spatial dependence index of daily rainfall occurrences over the region. The proposed space–time model shows more promising performance in generating rainfall occurrences in time and space than the conventional Markov type model. The space–time model well represents the temporal as well as the spatial dependence of daily rainfall occurrences, which can reduce the complexity in the generation of daily rainfall amounts.  相似文献   

Common-offset domain reflection–diffraction separation with deep learning     

Paul Zwartjes  Jewoo Yoo 《Geophysical Prospecting》2023,71(1):85-101

Separation of diffracted from reflected events in seismic data is still challenging due to the relatively low amplitude of the diffracted wavefield compared to the reflected wavefield as well as the overlap in the kinematics of reflection and diffraction events. A workflow based on deep learning can be a simple and fast alternative, but using training data made by physics-based modelling is expensive and lacks diversity in terms of noise, amplitude, frequency content and wavelet. This results in poor generalization beyond the training data without retraining and transfer learning. In this paper, we demonstrate successful applications of reflection–diffraction separation using a conventional U-net architecture. The novelty of our approach is that we do not use synthetic data created from physics-based modelling, but instead use only synthetic data built from basic geometric shapes. Our domain of application is the pre-migration common-offset domain where reflected events resemble local geology and the diffracted wavefield consists of downward convex hyperbolic diffraction patterns. Both patterns were randomly perturbed in many ways while maintaining their intrinsic features. This approach is inspired by the common practice of data augmentation in deep learning for machine vision applications. Since many of the standard data augmentation techniques lack a geophysical motivation, we have instead perturbed our synthetic training data in ways to make more sense from a signal processing perspective or given our ‘domain knowledge’ of the problem at hand. We did not have to retrain the network to show good results on the field data set. The large variety and diversity in examples enabled to trained neural networks to show encouraging results on synthetic and field data sets that were not used in training.  相似文献   

Quality of hybrid location data drawn from GPS‐enabled mobile phones: Does it matter?     

Eun‐Hye Yoo  John E. Roberts  Youngseob Eum  Youdi Shi 《Transactions in GIS》2020,24(2):462-482

Despite their increasing popularity in human mobility studies, few studies have investigated the geo‐spatial quality of GPS‐enabled mobile phone data in which phone location is determined by special queries designed to collect location data with predetermined sampling intervals (hereafter “active mobile phone data”). We focus on two key issues in active mobile phone data—systematic gaps in tracking records and positioning uncertainty—and investigate their effects on human mobility pattern analyses. To address gaps in records, we develop an imputation strategy that utilizes local environment information, such as parcel boundaries, and recording time intervals. We evaluate the performance of the proposed imputation strategy by comparing raw versus imputed data with participants’ online survey responses. The results indicate that imputed data are superior to raw data in identifying individuals’ frequently visited places on a weekly basis. To assess the location accuracy of active mobile phone data, we investigate the spatial and temporal patterns of the positional uncertainty of each record and examine via Monte Carlo simulation how inaccurate location information might affect human mobility pattern indicators. Results suggest that the level of uncertainty varies as a function of time of day and the type of land use at which the position was determined, both of which are closely related to the location technology used to determine the location. Our study highlights the importance of understanding and addressing limitations of mobile phone derived positioning data prior to their use in human mobility studies.  相似文献   

Two‐dimensional lower bound analysis of offshore pile foundation systems          下载免费PDF全文

Jinbo Chen  Robert B. Gilbert  Yoo Sang Choo  Peter W. Marshall  James D. Murff 《国际地质力学数值与分析法杂志》2016,40(9):1321-1338

The objective of this paper is to present a simplified method to determine the pile foundation system capacity based on the lower bound theorem of plasticity. The motivations for determining the lower bound capacity are the following: (1) to evaluate the accuracy of solutions based on the upper bound method; (2) to provide a conservative and efficient solution to the system capacity; and (3) to provide information about load distribution among individual piles at the verge of failure for the pile system. The failure mechanisms for a single pile and for the pile system are assumed to be two‐dimensional. For a typical long offshore pile, the upper and lower bound analyses produce identical lateral capacities. A simplified failure surface for loads at the single pile head is proposed and verified through analysis of 16 case study piles. With this proposed failure surface for a single pile, the lower bound failure load of the pile foundation system is obtained using the elastic compensation method enhanced with the linear matching method. Comparing with the existing upper bound and finite element solutions, the proposed lower bound method is capable of accurately and efficiently predicting the ultimate capacity of a pile foundation system. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Evolution of hillslope soils: The geomorphic theater and the geochemical play     

Kyungsoo Yoo  Beth Weinman  Simon Marius Mudd  Martin Hurst  Mikael Attal  Kate Maher 《Applied Geochemistry》2011

How and how fast do hillslope soils form as the landscape’s morphology changes over time? Here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history. In Northern Sierra Nevada, California, the authors are investigating a tributary basin to the Middle Fork Feather River. A major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the Feather River at an elevation of ～700 m to the plateau at an elevation of ～1500 m. Hillslopes are significantly steeper below the knickpoint. The area’s total denudation rates are currently being constrained using cosmogenic radio nuclides, but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint. When compared with topographic attributes calculated from LIDAR data, physical erosion rates can be modeled as a linear function of ridge top curvature. Surprisingly, over the wide range of total denudation rates, soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes. Bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates. From three hillslopes with different physical erosion rates, the concentrations of Zr, which were considered conserved during dissolution and leaching, were determined and used as a proxy for the degree of mass losses via chemical denudation. There is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. Likewise, the saprolites show greater degrees of chemical denudation at the sites above the knickpoint, presumably because of the saprolites’ longer turnover time in the slowly eroding landscapes. In the two steep hillslopes below the knickpoint, no significant or systematic topgraphic trends were found for soil geochemistry. However, soils show increasing Zr enrichment in the downslope direction in the hillslope above the knickpoint, which suggests a critical denudation rate beyond which soils’ turnover time is too short to develop a geochemical catena. As detailed CRN-based soil production rates and catchment scale denudation rates are acquired, the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient.  相似文献   

Diagnosis and testing of low-level cloud parameterizations for the NCEP/GFS model using satellite and ground-based measurements     

Hyelim Yoo  Zhanqing Li  Yu-Tai Hou  Steve Lord  Fuzhong Weng  Howard W. Barker 《Climate Dynamics》2013,41(5-6):1595-1613

The objective of this study is to investigate the quality of clouds simulated by the National Centers for Environmental Prediction global forecast system (GFS) model and to examine the causes for some systematic errors seen in the simulations through use of satellite and ground-based measurements. In general, clouds simulated by the GFS model had similar spatial patterns and seasonal trends as those retrieved from passive and active satellite sensors, but large systematic biases exist for certain cloud regimes especially underestimation of low-level marine stratocumulus clouds in the eastern Pacific and Atlantic oceans. This led to the overestimation (underestimation) of outgoing longwave (shortwave) fluxes at the top-of-atmosphere. While temperature profiles from the GFS model were comparable to those obtained from different observational sources, the GFS model overestimated the relative humidity field in the upper and lower troposphere. The cloud condensed water mixing ratio, which is a key input variable in the current GFS cloud scheme, was largely underestimated due presumably to excessive removal of cloud condensate water through strong turbulent diffusion and/or an improper boundary layer scheme. To circumvent the problem associated with modeled cloud mixing ratios, we tested an alternative cloud parameterization scheme that requires inputs of atmospheric dynamic and thermodynamic variables. Much closer agreements were reached in cloud amounts, especially for marine stratocumulus clouds. We also evaluate the impact of cloud overlap on cloud fraction by applying a linear combination of maximum and random overlap assumptions with a de-correlation length determined from satellite products. Significantly better improvements were found for high-level clouds than for low-level clouds, due to differences in the dominant cloud geometry between these two distinct cloud types.  相似文献