0608号超强台风"桑美"强度变化位涡诊断分析     

赵兵科  鲁小琴  万日金  张维 《地球科学进展》2011,26(5):528-537

利用位涡(PV)收支诊断和质点轨迹追踪等方法对2006年影响中国最严重的超强台风"桑美"强度变化的成因进行了分析和研究.结果表明:台风中心四周的垂直风切变、涡度、散度变化对台风强度变化有重要影响;通过位涡诊断揭示出在台风增强和减弱时,凝结潜热、垂直平流和水平平流起着不同的作用.在台风迅速发展之前和迅速发展初期,凝结潜热...  相似文献   

台风Nari(0116)登陆台湾过程中结构强度 变化的诊断分析   总被引：2，自引：1，他引：1  

胡姝  李英  魏娜 《大气科学》2013,37(1):81-90

利用中国气象局上海台风研究所整编的2001年《热带气旋年鉴》、美国NCEP最后分析FNL 1°×1°全球格点资料以及日本气象厅云顶亮温(TBB)资料等,对0116号台风Nari自北向南穿越台湾岛过程中的结构强度变化进行诊断分析,结果表明:(1)登陆过程中Nari云系结构从圆形变为半圆形,其环流西部对流云团旺盛,而东部为无云或少云区.Nari在岛上期间一直维持这种非对称结构特征.(2)在穿越台湾岛过程中,Nari西部环流内低空急流轴从其北侧逆时针延伸至南侧.一方面,切向风角动量的增加和传播有利于台风涡旋环流的加强,另一方面,低空急流附近的水汽通量辐合及急流轴左侧较强的正涡度区,有利于气旋性环流的长久维持.(3)Nari的结构强度变化与台湾岛地形及海峡效应有密切关系.Nari环流西部位于台湾岛迎风一侧上升运动加强,而Nari环流东部位于背风一侧上升运动则受抑制,对Nari形成半圆形非对称对流分布起积极作用;而台湾海峡的狭管效应加速台风通过气流,有利于Nari环流西部低空急流的形成和增强.(4)动能收支诊断表明,Nari登陆过程中动能的主要来源是动能制造项,水平辐合运动也对其提供动能.  相似文献   

Using mobile laser scanning data for automated extraction of road markings     

《ISPRS Journal of Photogrammetry and Remote Sensing》2014

A mobile laser scanning (MLS) system allows direct collection of accurate 3D point information in unprecedented detail at highway speeds and at less than traditional survey costs, which serves the fast growing demands of transportation-related road surveying including road surface geometry and road environment. As one type of road feature in traffic management systems, road markings on paved roadways have important functions in providing guidance and information to drivers and pedestrians. This paper presents a stepwise procedure to recognize road markings from MLS point clouds. To improve computational efficiency, we first propose a curb-based method for road surface extraction. This method first partitions the raw MLS data into a set of profiles according to vehicle trajectory data, and then extracts small height jumps caused by curbs in the profiles via slope and elevation-difference thresholds. Next, points belonging to the extracted road surface are interpolated into a geo-referenced intensity image using an extended inverse-distance-weighted (IDW) approach. Finally, we dynamically segment the geo-referenced intensity image into road-marking candidates with multiple thresholds that correspond to different ranges determined by point-density appropriate normality. A morphological closing operation with a linear structuring element is finally used to refine the road-marking candidates by removing noise and improving completeness. This road-marking extraction algorithm is comprehensively discussed in the analysis of parameter sensitivity and overall performance. An experimental study performed on a set of road markings with ground-truth shows that the proposed algorithm provides a promising solution to the road-marking extraction from MLS data.  相似文献   

Variation of diffuse attenuation coefficient of downwelling irradiance in the Arctic Ocean     

WANG Weibo  ZHAO Jinping 《海洋学报(英文版)》2014,33(6):53-62

The diffuse attenuation coefficient(Kd) for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition(CHINARE), including 18 stations and nine stations selected for irradiance profiles in sea water respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were obtained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of entering solar radiation. The linear relationship between averaging sea ice concentration(ASIC, from 158 Julian day to observation day) and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW(Alaskan Coastal Water), directly affects the amount of chlorophyll through taking more nutrient, and results in the higher attenuation coefficient in the layer of 30–60 m. Consequently, the spectral model of diffuse attenuation coefficient, the relationship between attenuation coefficient and chlorophyll and the linear relationship between the ASIC and the depth of maximum chlorophyll, together provide probability for simulating the process of diffuse attenuation coefficient during summer in the Arctic Ocean.  相似文献   

藏北高原地面加热场的变化及其对气候的影响   总被引：16，自引：9，他引：16  

季国良  时兴和  高务祥 《高原气象》2001,20(3):239-244

利用 1994— 1996年在藏北高原五道梁所观测得到的地面能量收支资料 ,结合同期的大气环流进行了分析研究。结果表明 :高原北部地面加热场强度的变化与高原西部相似 ,而与高原主体东半部的变化相反 ;冬季前期 11月的地面积雪过程对决定整个冬季地面加热场的性质具有重要的意义 ;高原冬季地面热状况的异常 ,引起夏季加热场的异常 ,这可能是造成大气环流异常的原因之一 ,从而影响我国的气候环境 ,因此对高原地面加热场的监测可以为短期气候预测提供依据。  相似文献   

华南前汛期雨涝强、弱年的确定及其环流特征对比   总被引：4，自引：1，他引：3  

罗艳艳  何金海  邹燕  孙蔡亮 《气象科学》2015,35(2):160-166

用区域性暴雨过程综合强度评估方法,在对1961—2010年华南前汛期逐场暴雨过程评估的基础上,通过定义华南区域雨涝强度指数(RWI),划分和确定了雨涝强、弱年,并对雨涝强、弱年的环流特征进行合成分析。结果显示:(1) RWI存在显著的年际变化和年代际变化特征。雨涝强度在1990s初以后呈现明显的增加趋势,雨涝强年明显增多。(2)雨涝强(弱)年,南亚高压偏南(北),副高位置偏西(东),欧亚中高纬500 hPa位势高度差值场自西向东呈现+ - +的波列分布,则有利(不利)于华南区域降水的发展和持续;(3)华南前汛期雨涝的强(弱)与大气低层来自华中—华南北部的偏北风输送加强(减弱)、高原东南侧的偏西风和经西太平洋—南海进入华南的西南风及水汽输送异常加强(减弱)有着密切的关系。而与来自孟加拉湾进入华南的偏南风及水汽输送强(弱)呈现反相关。(4)雨涝强(弱)年,冷空气活动频率较高(低),持续时间较长(短),强中心偏南(北)。且暖湿空气较早(晚)到达25 °N地区,并在30 °N以南地区维持时间较长(短),季风推进快(慢)。  相似文献   

近岸波浪在刚性植被区域传播的数值模型   总被引：2，自引：0，他引：2  

王磊  房克照  尹晶  孙家文 《海洋工程》2015,33(6):62-69

基于扩展型Boussinesq水波方程,建立了波浪在刚性植被覆盖的近岸海域传播的数值模型。通过在动量方程源项中引入拖曳阻力项考虑植被对波浪的衰减作用。控制方程采用有限差分和有限体积混合格式求解,模型稳定性强,具备间断捕捉能力,能有效模拟近岸区域波浪的传播变形、破碎和处理海岸动边界问题。利用所建立模型对典型物理模型实验进行模拟,计算结果与实验结果吻合良好,表明模型可用于波浪在刚性植被覆盖海域的数值计算。  相似文献   

Machine learning based mapping of the wave attenuation mechanism of an inclined thin plate     

《Applied Ocean Research》2015

The surface piercing and floating coastal defense structures can be applied as an alternative to conventional rubble mound structures in some specific circumstances. A partially submerged steeply inclined thin plate (ITP) is also one of the candidate alternative structures. Knowledge about the wave attenuation mechanism of ITP improves the engineer's ability to make more cost-effective design. From this motivation, the mechanism of ITP was modeled by artificial neural networks based on experimental data. It is particularly aimed to reveal some fundamental facts about the attenuation mechanism of ITP, which could not be previously attained solely by the conventional analysis of the relevant experimental data. Surface plots, which depict the relationships between the governing design variables were generated from the developed model. In this way, the influence of each individual parameter on the performance was decomposed in a more precise way. Based on the data-driven model outputs, it was inferred that the most dominant design variable is the wavelength. The ITP performance is enhanced with increasing submergence degree, an effect that becomes even more pronounced in severe wave climate conditions. In such wave conditions, decreasing inclination angles also improve the functionality of the structure. However, the generated data-driven model indicated that the combination of the examined variables can have a more complicated effect on the ITP performance, especially for the longer wave lengths.  相似文献   

海冰中侧向传播光衰减系数的解析验证     

赵进平  李涛  EHN Jens  BARBER David 《海洋学报(英文版)》2015,34(3):1-8

The attenuation of lateral propagating light(LPL) in sea ice was measured using an artificial light source in the Canadian Arctic during the 2007/2008 winter. The apparent attenuation coefficient μ(λ) for lateral propagating light was obtained from the measured logarithmic relative variation rate. In this study an analytical solution based on the strict optical theories is developed to validate the measured result. There is a good consistency between theoretical solution and measured data, by which a quite simple but very rigorous relationship among the light source, measurement geometry, and measured irradiance is established. The attenuation coefficients acquired by measurement and theory are the diffusion attenuation as an apparent optical property of ice, independent of the light source and shining condition. The attenuation ability of sea ice should be caused by the microstructure of sea ice, such as crystal size, ice density, brine volume, air inclusion, etc. It also includes the leak from both interfaces by directional scattering. It is verified that the measuring approach is operational and accurate to measure the attenuation of the LPL. The solution from this study did not tell the connection among the extinction and the inclusions of sea ice theoretically because of insufficient understanding.  相似文献   

中国人口省际流动重力模型的参数标定与误差估算   总被引：1，自引：2，他引：1  

赵梓渝  魏冶  杨冉  王士君  朱宇 《地理学报》2019,74(2):203-221

空间交互模型被广泛应用于地理要素关系强度的模拟,然而目前大量研究或建立在模型参数标定理想化、模式化的假设条件下,或是在暗箱中完成,由此导致模拟结果与实际的偏差却被严重低估。基于2015年中国春运期间人口省际流动的城市间O-D数据,在逐日、分市的研究精度下,实证推算人口流动重力模型变量的回归系数,探究模型代理变量影响效应的空间异质性,并评估重力模型在人口流动模拟上的误差。结果显示：① 重力模型参数标定的复杂性体现在交互对象代理变量影响程度的非对称性,和变量回归系数的空间异质性随研究精度加深显著加剧两个方面,因此模型参数标定的模式化将导致估算结果空间差异的趋势收敛;② 2015年春运期间中国人口省际流动距离衰减系数为1.970,在地级行政单元视角下,人口流出地距离衰减系数值域为0.712（驻马店）~7.699（乌鲁木齐）,人口流入地系数值域为0.792（三亚）~8.223（乌鲁木齐）;③ 应用重力模型模拟人口流动结果与实测流（百度迁徙数据）存在显著误差。就加权绝对平均误差而言,拟合总误差为85.54%,其中空间相互作用效应造成了86.09%的实测流与模拟流的最大误差,相对流出力、相对吸引力分别造成57.73%、49.34%的模型误差。因此,空间交互效应仍然是当前最难以模式化的因素。  相似文献