Ground-Water Tracing with Injected Helium     

S. K. Gupta  L. Stephen Lau  Philip S. Moravcik 《Ground water》1994,32(1):96-102

Helium has several characteristics that make it attractive for use as a tracer in hydrological studies. Two types of experiments were conducted to investigate applicability of helium as a tracer of ground-water movement. The experiments included studies using laboratory sand and soil columns and field ground-water tracing in a basaltic aquifer. A water helium analyzer comprised of a thin quartz glass membrane and diode ion pump (making use of the preferential permeation of helium through the quartz glass into an evacuated space) was developed and used for the experiments. Results of our studies demonstrated that breakthrough curves of specific conductance and helium were similar under saturated conditions. In the unsaturated sand/soil columns, breakthrough curves of helium were retarded relative to specific conductance reducing the usefulness of helium as a tracer.  相似文献   

Incremental time—space finite strip method for non-linear structural vibrations     

Y. K. Cheung  S. L. Lau 《地震工程与结构动力学》1982,10(2):239-253

Based on an incremental Hamilton's principle a versatile and systematic computer method for analysing non-linear structural vibrations is developed in this paper. The essence of the proposed method can be regarded as an incremental harmonic balance method associated with a finite strip procedure in the time-space domain. Only linearized equations in terms of frequency increment, amplitude increments, etc. have to be formulated and solved in each incremental step. This method is applicable to highly non-linear problems and may be generalized to related non-linear periodic structural motions such as dynamic stability, flutter and some motions of a rotating body, etc. To show the effectiveness and versatility of this method, a typical time-space finite strip for beam problems is worked out and examples for a wide variety of vibration problems including free and forced vibrations, super- and sub-harmonic resonances, and complicated phenomena such as internal resonance are computed. Comparisons with previous results are also made.  相似文献   

Application of MODIS satellite products to the air pollution research in Beijing     

LI Chengcai  MAO Jietai  Alexis K. H. Lau  YUAN Zibing  WANG Meihua  LIU Xiaoyang 《中国科学D辑(英文版)》2005,48(Z2)

The direct correlation between NASA MODIS aerosol optical depth (AOD) products and the air pollution index (API) in Beijing was found relatively low based on the long-term comparison analysis. The correlation improved to some extent after taking account of the seasonal variation of scale height and the vertical distribution of aerosols. The correlation coefficient further improved significantly after considering the influencing factor of Relative Humidity (RH). This study concluded that satellite remote-sensing could serve as an efficient tool for monitoring the spatial distribution of particulate pollutants on the ground-level, as long as corrections have been made in the two aforementioned processes. Taking advantage of the MODIS information, we analyzed a pollution episode occurring in October 2004 in Beijing. It indicated that satellite remote-sensing could describe the formation process of the ground-level pollution episode in detail, and showed that regional transport and the topography were crucial factors to air quality in Beijing. The annual averaged distribution in the urban area of Beijing and its surroundings could be also obtained from the high-resolution retrieval results, implicating that high-resolution satellite remote-sensing might be potential in monitoring the source distribution of particulate pollutants.  相似文献   

Tropical convective responses to microphysical and radiative processes: a sensitivity study with a 2-D cloud resolving model   总被引：1，自引：0，他引：1  

X. Li  C.-H. Sui  K.-M. Lau  W.-K. Tao 《Meteorology and Atmospheric Physics》2005,90(3-4):245-259

Summary Prognostic cloud schemes are increasingly used in weather and climate models in order to better treat cloud-radiation processes. Simplifications are often made in such schemes for computational efficiency, like the scheme being used in the National Centers for Environment Prediction models that excludes some microphysical processes and precipitation-radiation interaction. In this study, sensitivity tests with a 2-D cloud resolving model are carried out to examine effects of the excluded microphysical processes and precipitation-radiation interaction on tropical thermodynamics and cloud properties. The model is integrated for 10 days with the imposed vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. The experiment excluding the depositional growth of snow from cloud ice shows anomalous growth of cloud ice and more than 20% increase of fractional cloud cover, indicating that the lack of the depositional snow growth causes unrealistically large mixing ratio of cloud ice. The experiment excluding the precipitation-radiation interaction displays a significant cooling and drying bias. The analysis of heat and moisture budgets shows that the simulation without the interaction produces more stable upper troposphere and more unstable mid and lower troposphere than does the simulation with the interaction. Thus, the suppressed growth of ice clouds in upper troposphere and stronger radiative cooling in mid and lower troposphere are responsible for the cooling bias, and less evaporation of rain associated with the large-scale subsidence induces the drying in mid and lower troposphere.  相似文献   

Contrasting Indian Ocean SST variability with and without ENSO influence: A coupled atmosphere-ocean GCM study     

Jin-Yi Yu  K. M. Lau 《Meteorology and Atmospheric Physics》2005,90(3-4):179-191

Summary In this study, we perform experiments with a coupled atmosphere-ocean general circulation model (CGCM) to examine ENSO’s influence on the interannual sea-surface temperature (SST) variability of the tropical Indian Ocean. The control experiment includes both the Indian and Pacific Oceans in the ocean model component of the CGCM (the Indo-Pacific Run). The anomaly experiment excludes ENSO’s influence by including only the Indian Ocean while prescribing monthly-varying climatological SSTs for the Pacific Ocean (the Indian-Ocean Run). In the Indo-Pacific Run, an oscillatory mode of the Indian Ocean SST variability is identified by a multi-channel singular spectral analysis (MSSA). The oscillatory mode comprises two patterns that can be identified with the Indian Ocean Zonal Mode (IOZM) and a basin-wide warming/cooling mode respectively. In the model, the IOZM peaks about 3–5 months after ENSO reaches its maximum intensity. The basin mode peaks 8 months after the IOZM. The timing and associated SST patterns suggests that the IOZM is related to ENSO, and the basin-wide warming/cooling develops as a result of the decay of the IOZM spreading SST anomalies from western Indian Ocean to the eastern Indian Ocean. In contrast, in the Indian-Ocean Run, no oscillatory modes can be identified by the MSSA, even though the Indian Ocean SST variability is characterized by east–west SST contrast patterns similar to the IOZM. In both control and anomaly runs, IOZM-like SST variability appears to be associated with forcings from fluctuations of the Indian monsoon. Our modeling results suggest that the oscillatory feature of the IOZM is primarily forced by ENSO.  相似文献   

Statistical analysis of tropical disturbances over the South China Sea during 1997�C2006     

LAU Kai Hon 《中国海洋大学学报(英文版)》2011,10(2):99-105

Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 de-veloping tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.  相似文献   

Probing the Deepest Limits of the Earth’s Biosphere     

Thomas L. Kieft  T.C. Onstott  Maggie C. Y. Lau  Barbara Sherwood Lollar 《《地质学报》英文版》2018,92(Z1):195-195

  相似文献   

Human damage assessments of coastal flooding for Hong Kong and the Pearl River Delta due to climate change-related sea level rise in the twenty-first century     

Yu  Qiwei  Lau  Alexis K. H.  Tsang  Kang T.  Fung  Jimmy C. H. 《Natural Hazards》2018,92(2):1011-1038

Natural Hazards - The adverse impact of climate change-associated extreme weather events is becoming more significant globally, particularly the flood impact on coastal and low-lying areas such as...  相似文献   

Rapid tidal marsh development in anthropogenic backwaters     

Brian Yellen  Jonathan Woodruff  Caroline Ladlow  David K. Ralston  Sarah Fernald  Waverly Lau 《地球表面变化过程与地形》2021,46(3):554-572

Tidal marsh restoration and creation is growing in popularity due to the many and diverse sets of services these important ecosystems provide. However, it is unclear what conditions within constructed settings will lead to the successful establishment of tidal marsh. Here we provide documentation for widespread and rapid development of tidal freshwater wetlands for a major urban estuary as an unintended result of early industrial development. Anthropogenic backwater areas established behind railroad berms, jetties, and dredge spoil islands resulted in the rapid accumulation of clastic material and the subsequent initiation of emergent marshes. In one case, historical aerial photos document this transition occurring in less than 18 years, offering a timeframe for marsh development. Accretion rates for anthropogenic tidal marshes and mudflats average 0.8–1.1 and 0.6–0.7 cm year⁻¹, respectively, equivalent to two to three times the rate of relative sea level rise as well as the observed accretion rate at a 6000+ year-old reference marsh in the study area. Paired historical and geospatial analysis revealed that more than half of all the tidal wetlands on the Hudson River were likely triggered by anthropogenic development since the onset of the industrial era, including two-thirds of the emergent cattail marsh. These inadvertently constructed tidal wetlands currently trap roughly 6% of the Hudson River's sediment load. Results indicate that when sediment is readily available, freshwater tidal wetlands can develop relatively rapidly in sheltered settings. The study sites serve as useful examples to help guide future tidal marsh creation and restoration efforts.  相似文献   

Investigation of the 20 August 2005 fatal landslide at Fu Yung Shan Tsuen, Hong Kong     

K. K. S. Ho  P. A. Chao  T. M. F. Lau  S. De Silva 《Landslides》2013,10(3):285-297

On 20 August 2005, a landslide with a volume of about 400  m³ occurred at Fu Yung Shan Tsuen, Tsuen Wan in Hong Kong during a severe rainstorm with a return period of about 100  years on a hillside that has been disturbed locally by past human activities. The incident resulted in one fatality and permanent evacuation of residents of four squatter structures in the vicinity. A forensic investigation into the landslide was carried out to review the mechanism and probable causes of the landslide. The key contributory factors in the landslide were diagnosed. The investigation concluded that the landslide was probably caused by the loss of soil suction and transient build-up of groundwater pressure in the near-surface soil materials following prolonged and intense rainfall. The paper presents the methodology adopted for the landslide study, findings of the investigation and the lessons learnt from this fatal landslide.  相似文献