Analysis of current–topography interaction in remote sensing imaging procedures for shallow water topography     

Xiaozhen Wang  Huaguo Zhang  Weibing Guan  Bin Fu 《Journal of Oceanography》2017,73(4):449-462

Underwater topography can be imaged using remote sensing methods. Numerous studies have been conducted to understand the imaging mechanism of shallow water topography. However, current–topography interaction constitutes the weakest link in the remote sensing imaging mechanism of underwater topography. In addition, few studies focused on different topography patterns. Current velocity is highly correlated with bathymetry, and velocity gradient is used as an indicator of sea surface roughness. In this research, we analyzed the distribution characteristics of current velocity and velocity gradient in different cases using a 3-dimensional (3-D) hydrodynamic model to discuss the current–topography interaction part of the remote sensing imaging mechanism, especially the modulation by current parallel or normal to the underwater topography, both positive and negative. Results showed remarkable agreement between 3-D current analysis and surface velocity analysis. Parallel and normal currents had different responses to different topography types. The distribution of surface current gradient showed opposite features over negative and positive topography in parallel and normal current fields. This can be used to distinguish negative topography from positive topography with different current directions to a certain extent.  相似文献   

GCM Simulations of Stable Isotopes in the Water Cycle in Comparison with GNIP Observations over East Asia   总被引：1，自引：0，他引：1       下载免费PDF全文

ZHANG Xinping  SUN Zhian  GUAN Huade  ZHANG Xinzhu  Wu Huawu  Huang Yimin 《Acta Meteorologica Sinica》2012,26(4):420-437

In this paper, we examine the performance of four isotope incorporated GCMs, i.e., ECHAM4 (University of Hamburg), HadCM3 (Hadley Centre), GISS E (Goddard Institute of Space Sciences), and MUGCM (Melbourne University), by comparing the model results with GNIP (Global Network of Isotopes in Precipitation) observations. The spatial distributions of mean annual δD and mean annual deuterium excess d in precipitation, and the relationship between δ18 o and δD in precipitation, are compared between GCMs and GNIP data over East Asia. Overall, the four GCMs reproduce major characteristics of δD in precipitation as observed by GNIP. Among the four models, the results of ECHAM4 and GISS E are more consistent with GNIP observed precipitation δD distribution. The simulated d distributions are less consistent with the GNIP results. This may indicate that kinetic fractionation processes are not appropriately represented in the isotopic schemes of GCMs. The GCM modeled MWL (meteoric water line) slopes are close to the GNIP derived MWL, but the simulated MWL intercepts are significantly overestimated. This supports that the four isotope incorporated GCMs may not represent the kinetic fractionation processes well. In term of LMWLs (local meteoric water lines), the simulated LMWL slopes are similar to those from GNIP observations, but slightly overestimated for most locations. Overall, ECHAM4 has better capability in simulating MWL and LMWLs, followed by GISS E. Some isotopic functions (especially those related to kinetic fractionation) and their parameterizations in GCMs may have caused the discrepancy between the simulated and GNIP observed results. Future work is recommended to improve isotopic function parameterization on the basis of the high-resolution isotope observations.  相似文献   

Spatiotemporal distributions of δD in atmospheric water vapor based on TES Data during 2004–2009          下载免费PDF全文

章新平  张新主  关华德  黄一民  吴华武 《Acta Meteorologica Sinica》2012,26(6):683-699

The spatial and temporal distributions of the stable isotopes such as HD¹⁶O (or ¹H²H¹⁶O, or HDO) and H₂ ¹⁸O in atmospheric water vapor are related to evaporation in source places, vapor condensation during transport, and vapor convergence and divergence, and thus provide useful information for investigation and understanding of the global water cycle. This paper analyzes spatiotemporal variations of the content of isotope HDO (i.e., δ _D), in atmospheric water vapor, namely, δ _{D v}, and the relationship of δ _{D v} with atmospheric humidity and temperature at different levels in the troposphere, using the HDO and H₂O data retrieved from the Tropospheric Emission Spectrometer (TES) at seven pressure levels from 825 to 100 hPa. The results indicate that δ _{D v} has a clear zonal distribution in the troposphere and a good correspondence with atmospheric precipitable water. The results also show that δ _{D v} decreases logarithmically with atmospheric pressure and presents a decreasing trend from the equator to high latitudes and from lands to oceans. Seasonal changes of δ _{D v} exhibit regional differences. The spatial distribution and seasonal variation of δ _{D v} in the low troposphere are consistent with those in the middle troposphere, but opposite situations occur from the upper troposphere to the lower stratosphere. The correlation between δ _{D v} and temperature has a similar distribution pattern to the correlation between δ _{D v} and precipitable water in the troposphere. The stable isotope HDO in water vapor (δ _{D v}), compared with that in precipitation (δ _{D p}), is of some differences in spatial distribution and seasonal variation, and in its relationship with temperature and humidity, indicating that the impacts of stable isotopic fractionation and atmospheric circulation on the two types of stable isotopes are different.  相似文献   

Air–sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal     

Guoxiong Wu  Yue Guan  Yimin Liu  Jinghui Yan  Jiangyu Mao 《Climate Dynamics》2012,38(1-2):261-279

In spring over the southern Bay of Bengal (BOB), a vortex commonly develops, followed by the Asian summer monsoon onset. An analysis of relevant data and a case study reveals that the BOB monsoon onset vortex is formed as a consequence of air–sea interaction over BOB, which is modulated by Tibetan Plateau forcing and the land–sea thermal contrast over the South Asian area during the spring season. Tibetan Plateau forcing in spring generates a prevailing cold northwesterly over India in the lower troposphere. Strong surface sensible heating is then released, forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern BOB. This southwesterly induces a local offshore current and upwelling, resulting in cold sea surface temperatures (SSTs). The southwesterly, together with the near-equatorial westerly, also results in a surface anticyclone with descending air over most of BOB and a cyclone with ascending air over the southern part of BOB. In the eastern part of central BOB, where sky is clear, surface wind is weak, and ocean mixed layer is shallow, intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer, resulting in the development of a unique BOB warm pool in spring. Near the surface, water vapor is transferred from northern BOB and other regions to southeastern BOB, where surface sensible heating is relatively high. The atmospheric available potential energy is generated and converted to kinetic energy, thereby resulting in vortex formation. The vortex then intensifies and moves northward, where SST is higher and surface sensible heating is stronger. Meanwhile, the zonal-mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex, and the vortex turns eastward. Eventually, southwesterly sweeps over eastern BOB and merges with the subtropical westerly, leading to the onset of the Asian summer monsoon.  相似文献   

1988-2009年全球地面风速变化趋势研究   总被引：1，自引：0，他引：1  

郑崇伟  李思祥  王冠  仇晓庆 《气象与环境科学》2012,35(Z1)

利用来自ESE的1988-2009年高精度、高分辨率的CCMP风场资料,对全球0.25°×0.25°每个网格点上地面风速的逐年变化趋势进行分析.研究发现:近22 a期间,全球大部分区域的地面风速以显著性递增趋势为主导,递增趋势较强的区域主要分布于南极大陆的临海区域、格陵兰岛的临海区域;显著性逐年线性递减以及地面风速无明显变化趋势的区域主要散布于全球各地的一些零星区域,且不同地区地面风速的变化趋势由不同季节主导.  相似文献   

中央电视台新台址建设CCTV中央大楼基坑支护及降水设计、施工重点     

沈元红  王东梅 《城市地质》2010,5(4):49-52

随着经济建设及城市建筑的发展,近年来我国的各类建筑与市政工程得到了飞速发展,随之而来的深基坑工程越来越多、越来越复杂,对基坑支护、降水的要求亦越来越高。本文以中央电视台新台址建设CCTV中央大楼基坑工程为例,介绍了对基坑标高复杂、地下水情况复杂的深大基坑的支护、降水设计及施工重点,详细分析了支护、降水特点,简要阐明了设计参数要点及施工重点、难点。此工程的设计、施工经验可广泛应用于众多深基坑工程中,对广大设计、施工人员亦有一定的借签意义。  相似文献   

台风“榴莲”陆上维持及暴雨增幅的大尺度环流特征   总被引：1，自引：1，他引：0  

王黎娟  卢珊  管兆勇  何洁琳 《气候与环境研究》2010,15(4):511-521

利用"CMA-STI热带气旋最佳路径集"、NCEP/NCAR再分析资料及地面加密观测资料,分析了2001年0103号台风"榴莲"陆上维持及暴雨增幅的大尺度环流特征。结果表明,"榴莲"登陆后正好位于低压带中,中纬度西风槽加强南伸,构成典型的"北槽南涡",阻碍西太平洋副热带高压西伸,使得"榴莲"陆上长时间维持。西风槽后的西北气流将中纬度冷空气输送至低纬,在"榴莲"环流北部外围与东南风暖湿气流汇合,有利于强降水发生。此外,索马里和100°E越赤道气流增强显著,加强西南季风,从阿拉伯海东部,经孟加拉湾和中南半岛中南部,直至南海北部到广西大部形成一条完整的水汽输送带,充沛的水汽直达"榴莲"东北侧,有利于该时段暴雨增幅。低纬夏季风10～20天低频振荡处于极端活跃位相时,低纬低频西风偏北及低频水汽向北输送至广西南部,有利于低层辐合并提供充足水汽,对"榴莲"暴雨增幅有重要作用。  相似文献   

大型自动气象监测网及数据采集中心的设计及应用   总被引：5，自引：0，他引：5  

伍光胜  敖振浪  李源鸿  蔡耿华 《气象》2010,36(3):128-135

通过分析我国自动气象监测系统的现状和存在的问题,基于通用分组数据业务、网络通信技术和数据处理技术,设计一种新型、安全、可靠的大规模自动气象站资料快速传输和并发处理系统。详细地阐述了系统的设计思路、通信模式、网络构架、传输协议、工作流程、软件设计、技术特点。该系统的设计方法对于规模大、无人值守、数据实时采集、数据突发传输的不同应用系统的开发具有指导意义。  相似文献   

与图像内容相关的色域映射算法研究   总被引：2，自引：0，他引：2  

许向阳  朱元泓  桑凤仙 《武汉大学学报(信息科学版)》2012,37(5):626-629

通过对经典色域映射算法的调查分析,总结归纳了映射执行中影响图像质量的各个相关因素,在分析其影响权重的基础上建立了一个最佳的映射模型,设计实现了一个与图像内容相关的色域映射算法。测试实验验证,新算法优于ICC推荐的HPMINDE和SGCK算法,确保转换图像的视觉效果最佳。  相似文献   

Intercomparison of stable isotopes in precipitation simulated by GCMs with GNIP survey over East Asia     

XinPing Zhang  ZhiAn Sun  HuaDe Guan  XinZhu Zhang 《寒旱区科学》2012,4(4):0330-0341

Using the isotope enabled ECHAM4, GISS E and HadCM3 GCMs, the spatial distribution of mean δ¹⁸O in precipitation, mean seasonality and the correlations of δ¹⁸O in precipitation with temperature and precipitation amount are analyzed. The simulated results are in agreement with stable isotopic features by GNIP observations. Over East Asia, the distribution of δ¹⁸O in precipitation is of marked latitude effect and altitude effect. The latitude effect is covered by the continent effect in some regions. The largest seasonality of δ¹⁸O in precipitation appears in eastern Siberia controlled by cold high pressure, and the smallest seasonality is in the western Pacific controlled by the subtropical high. Relatively weak seasonality appears in middle latitudes where oceanic and continental air masses frequently interact. However, three GCMs show significant systematic lower δ¹⁸O for inland mid-high latitudes than GNIP data, which is related to the used isotopic scheme in GCMs. Temperature effect occurs mainly in inland mid-high latitudes. The higher the latitude and the closer the distance to inland is, then the stronger the temperature effect. Amount effect occurs mainly in low-mid latitudes and monsoon areas, with the strongest effect in low-latitude coasts or islands. However, three GCMs provide virtually non-existent amount effect in arid regions over Central Asia. The enrichment action of stable isotopes in falling raindrops under a cloud base, which is enlarged by these modes, is responsible for such a result. A significant difference between spatial distributions of δ¹⁸O statistics by GCMs simulations and by GNIP observations is that the standard deviation of GCMs statistics is greater than that of GNIP statistics. In contrast, by comparing parallel time series at a single station, the standard deviations of GCMs simulations are smaller than that of GNIP observations.  相似文献