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31.
航管二次监视雷达会出现假目标,尤其是在低俯仰角状态下,会极大地降低其性能。对低俯仰状态下假目标消除进行研究,提出了一种新的假目标识别方法。在对航管二次监视雷达几种典型假目标的原因进行分析基础之上,重点研究了航管二次监视雷达低俯仰角情况下假目标的综合识别方法、反射物列表实时更新、灵敏度时间程序控制以及功率程序控制技术等消除对策。在广汉机场的航管二次雷达系统上进行了验证,出现的假目标均被滤除,效果符合标准。 相似文献
32.
文章对近50a（1961—2010年）内蒙古呼伦贝尔地区的年、汛期和冬春季降水量和降水距平百分率（R%）作了统计,发现年R%和冬春季R%呈上升趋势,汛期R%略呈下降趋势;通过对年R%与大气环流指数、海温的相关分析发现：前期副热带高压（副高）、北半球极涡、大西洋欧洲环流C型、西藏高原位势高度和印缅槽（南支槽）强度指数等均与年R%密切相关,当北半球极涡收缩、强度减弱,副高扩张、强度加强,西藏高原位势高度偏高,南支槽减弱时,有利于来年呼伦贝尔地区降水,否则,相反。此外,前一年夏季北印度洋海域和赤道东太平洋海域海温对呼伦贝尔地区来年降水有显著影响,这两块海区的海温和上述环流指数可考虑作为呼伦贝尔地区年降水的预测信号使用。 相似文献
33.
5预测模型和预测试验5.1预测模型与算法5.1.1模型结构 预测模型结构中包括两个处理过程：在第一步处理过程中主要考虑的是实时样本与历史样本前期大气环流场和其他影响因素的前期场（如：前一年2月-当年1月,或前一年的4个季度）的动态变化过程的相似情形,经过第一步处理后我们可以获得两个描述指标, 相似文献
35.
The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important
role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion
of an abandoned section of the Huanghe (Yellow) River Delta. The theory of physical scale models is discussed and a method
for constructing the representative seabed section is developed. The results indicate that during the period initially after
the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction
that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the
beach profile equilibrated with a point of balance present on the profile. The experimental results indicate that the volume
of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction
with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively
comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and
prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce
the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion. 相似文献
36.
The erosion mechanisms of abandoned coastal section are understood detailedly by flume experiment, which play an important role to the offshore engineering facilities. A movable-bed physical model has been used to investigate the coastal erosion of an abandoned section of the Huanghe (Yellow) River Delta. The theory of physical scale models is discussed and a method for constructing the representative seabed section is developed. The results indicate that during the period initially after the abandonment of the delta the entire bed experienced rapid erosion because the seabed was steep and prone to liquefaction that resulted from storm wave action. After this initial period, a balance of erosion and accretion was established, and the beach profile equilibrated with a point of balance present on the profile. The experimental results indicate that the volume of deposition was about half that of the erosion. Wave action may also induce significant stratal changes through its interaction with the soft seabed. The major morphological features developed in the model delta section were found to be qualitatively comparable with those observed in the prototype. A distorted modeling law that maintains the similarity of the modeled and prototype equilibrium beach profiles is proposed. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature, and the model also successfully reproduced three historical evolutionary stages of erosion. 相似文献
37.
近50年来中国极端降水趋势与物理成因研究综述 总被引：6，自引：2，他引：4
对中国近50年来极端降水事件的研究表明,在全球变暖背景下极端降水事件的频率和强度均有升高的趋势,但存在明显的区域差异。观测分析表明长江中下游,东南地区和西北的部分区域极端降水有增加趋势,而华北、东北和西南的部分地区有减少趋势。现阶段不同模式模拟的结果还存在差异,但总的预测结论表明中国极端降水有极化的趋势。首先从统计学角度通过分析均值和极值的关系,探讨了极端降水事件概念的界定,然后分析了不同区域极端降水的变化趋势。在综述中国极端降水研究的基础上,以极端降水变化趋势较为复杂的长江流域作为典型气候区,从海—气相互作用角度对影响极端降水的物理机制和过程进行了总结。分析表明能够反映极端降水本质特性的定义和影响极端降水的物理过程还需要进一步研究,并且随着研究深入,新的影响极端降水的因子也会被逐渐发现。 相似文献
38.
本文提出了一种基于搭载平流层飞行器对平流层大气风场进行原位探测的探测系统，并详细介绍了其工作原理、计算公式和风洞实验结果。实验室测试中，该探测系统的理论测量误差值≤2.5 m/s。在常温下的风洞试验中，该系统表现出了良好的工作性能、系统稳定性和测量准确度。在和实验室的风向、风速对比试验中的相关性均超过了0.99，风速的平均绝对偏差为0.67 m/s，风向的绝对平均偏差为2.4°。2022年，中国气象局气象探测中心利用平流层超压气球搭载该系统在海拔19 km的平流层大气中进行了原位探测试验，对所搭载平台周围的风速和风向进行了探测，并对探测结果进行了比对分析。与平台轨迹算法进行比对结果显示，该系统具有较好的一致性；与NCEP_FNL再分析数据进行比对，显示出东西向风速的相关性较好，达到了0.795，而南北风速的相关性较差，仅为0.33。试验结果表明，在平流层飞行器上搭载该探测系统可以有效地探测平流层大气风场，对于获得平流层大气环境数据集、提供大气环境预报服务、开发平流层浮空器、监测平流层飞行器周围的大气环境、规划飞行路线和区域停留等方面具有巨大的应用潜力。 相似文献
39.
通过采用Car-Parrinello分子动力学方法对掺杂Ti前后的NaAlH4(001)2×2×1超晶胞表面晶体在333 K(60 ℃)温度条件催化脱氢的空间构型做了理论研究,发现掺杂Ti的合金中AlH4团的其中两个Al—H键长分别从约1.64 (1 =0.1 nm)增大至1.74和1.93 ,而未掺杂合金表面中AlH4团的4个Al—H键长基本不变,这意味着掺杂Ti相对未掺杂的合金更易于放氢.但在模拟温度条件下并未发现Ti-Al成键趋 相似文献