Distribution and characteristics of marine habitats in a subpolar bay based on hydroacoustics and bed shear stress estimates—Potter Cove,King George Island,Antarctica     

Anne-Cathrin Wölfl  Chai Heng Lim  H. Christian Hass  Sebastian Lindhorst  Gabriela Tosonotto  Karsten Alexander Lettmann  Gerhard Kuhn  Jörg-Olaf Wolff  Doris Abele 《Geo-Marine Letters》2014,34(5):435-446

Marine habitats worldwide are increasingly pressurized by climate change, especially along the Antarctic Peninsula. Well-studied areas in front of rapidly retreating tidewater glaciers like Potter Cove are representative for similar coastal environments and, therefore, shed light on habitat formation and development on not only a local but also regional scale. The objective of this study was to provide insights into habitat distribution in Potter Cove, King George Island, Antarctica, and to evaluate the associated environmental processes. Furthermore, an assessment concerning the future development of the habitats is provided. To describe the seafloor habitats in Potter Cove, an acoustic seabed discrimination system (RoxAnn) was used in combination with underwater video images and sediment samples. Due to the absence of wave and current measurements in the study area, bed shear stress estimates served to delineate zones prone to sediment erosion. On the basis of the investigations, two habitat classes were identified in Potter Cove, namely soft-sediment and stone habitats that, besides influences from sediment supply and coastal morphology, are controlled by sediment erosion. A future expansion of the stone habitat is predicted if recent environmental change trends continue. Possible implications for the Potter Cove environment, and other coastal ecosystems under similar pressure, include changes in biomass and species composition.  相似文献   

Preface to the special memorial issue for Professor Donald V. Helmberger          下载免费PDF全文

Thorne Lay  Xiaodong Song 《地震科学（英文版）》2022,35(1):1-2

Donald Vincent Helmberger,Ph.D.and Smits Family Professor of Geophysics Emeritus at Caltech(Figure 1),one of the primary founders of seismic waveform modeling,w...  相似文献   

Effects of meteorological and hydrogeological factors on gross recharge percentage at unconfined sandy aquifers with an equatorial climate     

Stephen Boon Kean Tan  Eng Ban Shuy  Lloyd Hock Chye Chua 《水文研究》2007,21(18):2493-2503

A thorough understanding of rainfall recharge processes and their controlling factors is essential for management of groundwater systems. This study investigates the effects of various meteorological and hydrogeological factors on the gross recharge percentages, the rainfall–recharge relationships and the recharge threshold values for unconfined sandy aquifers under an equatorial climate. Among the meteorological factors investigated, rainfall intensity was found to have the most significant impact on the gross recharge rate. The effects of potential evaporation rate, relative humidity and air temperature on the gross recharge percentage were significant when the vadose zone thickness is larger than 2·5 m. The recharge threshold values were found to depend strongly on the vadose zone thickness. The rainfall–recharge relationships could generally be well defined by a normal–log relationship. The rainfall–recharge relationships derived here are applicable to yield estimates of gross recharge percentages for unconfined sandy aquifers under an equatorial climate, using rainfall intensity and vadose zone thickness as input variables. In this study, a theory was developed and validated to provide physical explanations for the observations, based on the residence time of the percolated rainwater within the vadose zone. Among the soil hydraulic parameters tested, porosity and saturated hydraulic conductivity were found to have the most pronounced effects on the gross recharge percentage. Utilizing the sensitivity results and the theory derived, an approach was developed for extending the application of the derived rainfall–recharge relationships to other sand textures. The approach was found to be capable of producing rough and fast estimations of gross recharge percentage for other sand textures. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

METEOROLOGICAL DATA REQUIRED IN THE HYDROLOGICAL SERVICE     

Dr. Eng. Julian LAMBOR 《水文科学杂志》2013,58(2):44-47

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Projected changes in meteorological drought over East Africa inferred from bias-adjusted CMIP6 models     

Ayugi  Brian  Shilenje  Zablon Weku  Babaousmail  Hassen  Lim Kam Sian  Kenny T. C.  Mumo  Richard  Dike  Victor Nnamdi  Iyakaremye  Vedaste  Chehbouni  Abdelghani  Ongoma  Victor 《Natural Hazards》2022,113(2):1151-1176

Natural Hazards - The ongoing global warming has caused unprecedented changes in the climate system, leading to an increase in the intensity and frequency of weather and climate extremes. This...  相似文献   

EChO payload electronics architecture and SW design     

M. Focardi  A. M. Di Giorgio  M. Farina  M. Pancrazzi  R. Ottensamer  T. L. Lim  S. Pezzuto  G. Micela  E. Pace 《Experimental Astronomy》2015,40(2-3):813-839

EChO is a three-modules (VNIR, SWIR, MWIR), highly integrated spectrometer, covering the wavelength range from 0.55 μ m to 11.0 μ m. The baseline design includes the goal wavelength extension to 0.4 μ m while an optional LWIR module extends the range to the goal wavelength of 16.0 μ m. An Instrument Control Unit (ICU) is foreseen as the main electronic subsystem interfacing the spacecraft and collecting data from all the payload spectrometers modules. ICU is in charge of two main tasks: the overall payload control (Instrument Control Function) and the housekeepings and scientific data digital processing (Data Processing Function), including the lossless compression prior to store the science data to the Solid State Mass Memory of the Spacecraft. These two main tasks are accomplished thanks to the Payload On Board Software (P-OBSW) running on the ICU CPUs.  相似文献   

The 69-μm forsterite band as a dust temperature indicator     

J. E.Bowey  M. J.Barlow  F. J.Molster  A. M.Hofmeister  C.Lee  C.Tucker  T.Lim  P. A. R.Ade  L. B. F. M.Waters 《Monthly notices of the Royal Astronomical Society》2002,331(1):L1-L6

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Geological overview and cratering model for the Haughton impact structure,Devon Island,Canadian High Arctic     

Gordon R. Osinski  Pascal Lee  John G. Spray  John Parnell  Darlene S. S. Lim  Theodore E. Bunch  Charles S. Cockell  Brian Glass 《Meteoritics & planetary science》2005,40(12):1759-1776

Abstract— The Haughton impact structure has been the focus of systematic, multi‐disciplinary field and laboratory research activities over the past several years. Regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to ?1880 m. New ⁴⁰Ar–³⁹Ar dates place the impact event at ?39 Ma, in the late Eocene. Haughton has an apparent crater diameter of ?23 km, with an estimated rim (final crater) diameter of ?16 km. The structure lacks a central topographic peak or peak ring, which is unusual for craters of this size. Geological mapping and sampling reveals that a series of different impactites are present at Haughton. The volumetrically dominant crater‐fill impact melt breccias contain a calcite‐anhydrite‐silicate glass groundmass, all of which have been shown to represent impact‐generated melt phases. These impactites are, therefore, stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets. The crater‐fill impactites provided a heat source that drove a post‐impact hydrothermal system. During this time, Haughton would have represented a transient, warm, wet microbial oasis. A subsequent episode of erosion, during which time substantial amounts of impactites were removed, was followed by the deposition of intra‐crater lacustrine sediments of the Haughton Formation during the Miocene. Present‐day intra‐crater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the High Arctic. Modern modification of the landscape is dominated by seasonal regional glacial and niveal melting, and local periglacial processes. The impact processing of target materials improved the opportunities for colonization and has provided several present‐day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain.  相似文献   

The effect of dissipation on the generation of density structure by magnetohydrodynamic waves     

A. J. Lim  S. A. E. G. Falle  T. W. Hartquist 《Monthly notices of the Royal Astronomical Society》2005,357(2):461-470

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Performance of Jacobi preconditioning in Krylov subspace solution of finite element equations     

F.‐H. Lee  K.K. Phoon  K.C. Lim  S.H. Chan 《国际地质力学数值与分析法杂志》2002,26(4):341-372

This paper examines the performance of the Jacobi preconditioner when used with two Krylov subspace iterative methods. The number of iterations needed for convergence was shown to be different for drained, undrained and consolidation problems, even for similar condition number. The differences were due to differences in the eigenvalue distribution, which cannot be completely described by the condition number alone. For drained problems involving large stiffness ratios between different material zones, ill‐conditioning is caused by these large stiffness ratios. Since Jacobi preconditioning operates on degrees‐of‐freedom, it effectively homogenizes the different spatial sub‐domains. The undrained problem, modelled as a nearly incompressible problem, is much more resistant to Jacobi preconditioning, because its ill‐conditioning arises from the large stiffness ratios between volumetric and distortional deformational modes, many of which involve the similar spatial domains or sub‐domains. The consolidation problem has two sets of degrees‐of‐freedom, namely displacement and pore pressure. Some of the eigenvalues are displacement dominated whereas others are excess pore pressure dominated. Jacobi preconditioning compresses the displacement‐dominated eigenvalues in a similar manner as the drained problem, but pore‐pressure‐dominated eigenvalues are often over‐scaled. Convergence can be accelerated if this over‐scaling is recognized and corrected for. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献