A generalized approach for long-term modelling of extreme crest-to-trough wave heights

This paper deals with the long-term modelling of high sea waves. The solution is given for the return period of sea storms during which an arbitrary chosen number of waves, with crest-to-trough heights exceeding a fixed threshold, occur. This return period is derived starting from the Equivalent Triangular Storm (ETS) model, which associates a triangle to each actual storm and thus represents a significant wave height time series at a fixed location by means of a sequence of triangular storms. The short-term statistics is then applied to investigate the occurrence of large crest-to-trough wave heights during a given storm. Finally, by combining the statistical distribution of significant wave heights, the ETS model and the short-term wave statistics, the solution is given for the return periods R_N and R_N of a sea storm in which N or at least N waves higher than a fixed threshold occur. The values of R_N are then calculated, starting from data of two buoys moored in the Pacific Ocean and in the Mediterranean Sea.     

翡翠的矿物组成对其质量的影响

翡翠的质量主要取决于它的颜色和结构,就颜色而言,主要取决于其中的矿物组成和化学成分。翡翠主要由辉石族矿物、闪石族矿物、长石族矿物等组成。其中辉石族的矿物如硬玉、霓石、钠铬辉石、钙铁辉石,它们的存在和数量的多少及化学成分的变化对翡翠的质量影响很大。另外,闪石族矿物使翡翠的颜色偏暗,部分飘蓝花,直接影响翡翠的质量。     

基于LLS的多回击地闪及其雷电流幅值分布特征

为进一步研究多回击地闪参数分布特征,以便为雷电防护工程设计和雷电物理研究提供参考,根据湖北省雷电定位系统(LLS)2007年1月-2018年12月监测资料,采用计算机编程处理和数理统计方法,对多回击地闪次数、多重回击次数和不同类型多回击地闪雷电流幅值等参数进行了统计分析.结果 表明:多回击正地闪、负地闪和总地闪次数占其...     

2009年晚秋河北特大暴雪多普勒雷达特征分析

利用石家庄新乐CINRAD/SA雷达资料、加密自动站资料和四维变分同化风场反演资料,分析了2009年11月10-12日河北地区发生的有历史记录以来的特大暴雪天气过程。结果表明,这次特大暴雪过程可分为切变线回流降雪和西风槽降雪两个阶段。切变回流降雪回波为对流性层云和积云的混合云,西风槽降雪回波为层状云且无零度层亮带,对流性降雪回波的垂直结构与盛夏暴雨回波结构类似,是产生这次极端降雪的重要原因;径向速度场分布存在"牛眼"特征、零等速度线出现"S"形、反"S"形和不连续线。当同时出现暖平流、风向辐合及风速辐合时,降雪维持;当同时出现暖平流、风向辐散及风速辐散时,降雪减弱;从地面到1.2km的边界层内存在边界层辐合线,垂直风切变的辐合抬升使垂直运动增强、降雪强度增大。     

基于ADTD资料的浙江地区多回击地闪特征分析

利用2007-2018年浙江省ADTD闪电定位资料,分析了该地区多回击地闪分布及相关参数特征.结果表明:浙江省多回击地闪占总地闪的26.74％,其中正闪以单回击地闪为主;正、负闪平均回击数分别为1.04次和1.65次,最大回击数分别为5次和21次.回击数和地闪数存在较为一致的年际变化,正、负多回击地闪日变化分别呈多峰和...     

广义极值分布理论在重现期计算的应用

在气候统计学上,常用Weibull、Gumbel、Frechet统计分布函数对极端气候要素的分布进行拟合,广义极值分布理论综合了以上三种极值分布模型,在气候分析中得到了广泛应用。以南昌市年汛期日最大降水量为例,利用广义极值分布理论对其分布进行拟合,并对重现值及其置信区间进行计算,为气候要素极值的统计分析提供了一种新的手段。     

往返式探空观测资料的质量控制及不确定性分析

为了推动新型探测资料在数值预报模式中的应用,本文进行了往返式探空资料同化应用前重要的基础性研究工作。基于国内首次往返式探空观测资料,首先建立了面向业务化应用的往返式探空资料质量控制方案,通过对比和分析质量控制前后观测样本的统计特征,论证了质量控制方案的合理性,质量控制后探测要素抽样分布更为合理,要素间一致性得到提高。进而以数值天气预报高时间分辨率的模式预报场和同站址业务常规探空观测资料为参考,分析质量控制后资料的不确定性,结果表明往返探空探测精度达到了世界气象组织WMO（World Meteorological Center）规定的突破目标,部分探测要素甚至实现了理想目标,探测资料具有可用性。最后结合数值模式背景场探讨往返探空资料的可同化性,研究表明往返探空的风场观测和夜间温度观测满足变分同化系统的高斯、无偏假定,可直接同化;气压、湿度和日间温度观测在资料同化前需要开展偏差订正工作,从而更有效的发挥资料价值。本文的研究工作为今后往返探空资料在模式中的同化应用奠定了基础。     

关于海洋平台抗震设防水准的考虑

我国尚未制定海洋平台的抗震设计规范,本文首先将美国API-RP2A(2002)和GB17503-1998规范作分析对比,并结合美国南加利福尼亚地区和我国渤海海域地震活动性的情况,认为GBl7503-1998规范的抗震设防概率水准似乎过于保守。根据我国海域地震活动特征、海洋平台的设计基准期和设防目标等因素,参照相关行业工程抗震设防标准的经验,提出海洋平台用于强度设计的正常极限地震重现期取200年、用于延性设计的变形极限地震重现期取3000年,并与有关行业工程抗震设防标准进行了比较分析。     

“Racism in a Melting Pot…?” Trinidadian mid-life transnational migrants’ views on race and colour-class on return to their homes of descent

This paper deals with second-generation, one-and-a-half generation and “prolonged sojourner” Trinidadian transnational migrants, who have decided to ‘return’ to the birthplace of their parents. Based on 40 in-depth interviews, the paper considers both the positive and critical things that these youthful transnational migrants report about returning to, and living in, this multi-ethnic plural society and the salience of racial and colour-class stratification as part of their return migration experiences. Our qualitative analysis is based on the narratives provided by these youthful returnees, as relayed “in their own words”, presenting critical reflections on racism, racial identities and experiences as transnational Trinidadians. It is clear that it is contexts such as contemporary working environments, family and community that act as the reference points for the adaptation “back home” of this strongly middle-class cohort. We accordingly encounter a diverse, sometimes contesting set of racial issues that emerge as salient concerns for these returnees. The consensus is that matters racial remain as formidable legacies in the hierarchical stratification of Trinidadian society for a sizeable number. Many of our respondents reported the positive aspects of racial affirmation on return. But for another sub-set, the fact that multi-ethnic and multi-cultural mixing are proudly embraced in Trinidad meant that it was felt that return experiences were not overly hindered, or blighted by obstacles of race and colour-class. For these returnees, Trinidad and Tobago is seen as representing a 21st century “Melting Pot”. But for others the continued existence of racial divisions within society - between ethnic groups and among those of different skin shades - was lamented. In the views of these respondents, too much racial power is still ascribed to ‘near-whiteness’. But for the most part, the returnees felt that where race played a part in their new lives, this generally served to advantage them. However, although the situation in Trinidad appears to have been moderated by assumptions that it remains a racial ‘Melting Pot’, the analysis strongly suggests that the colour-class system of stratification is still playing an essential role, along with racial stereotyping in society at large.     

Charge source of cloud-to-ground lightning and charge structure of a typical thunderstorm in the Chinese Inland Plateau

GPS-synchronized measurements of electric (E) field changes induced by lightning flashes were recorded at six stations in the northeastern verge of the Tibetan Plateau. The height and magnitude of charge neutralized by 65 return strokes, including 16 negative cloud-to-ground (CG) flashes and 2 positive CG flashes, have been fitted with the nonlinear least-square method based on the E field changes of CG flashes observed in a typical thunderstorm with larger-than-usual lower positive charge center (LPCC). Results show that the height of the charge region neutralized by negative CG flashes ranges from 3 km to 5 km above the ground, corresponding to an ambient temperature between − 2 °C and − 15 °C. For the two positive CG flashes, the neutralized charge regions are located at a height of about 5.5 km and the ambient temperature is about − 18 °C, indicating the existence of upper positive charge in the thunderstorm.