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1.
Lederer Susan M. Campins Humberto Osip David J. Schleicher David G. 《Earth, Moon, and Planets》1997,78(1-3):131-136
We report the identification of gas jets in comet Hale-Bopp in OH, NH, CN, C2 and C3. This is the first time OH and NH jets without an obvious optical dust jet counterpart have been identified in narrowband
comet images. We also confirm the existence of CN jets as reported by Larson et al. (1997) and Mueller et al. (1998). Jet
features can be seen in the March and April 1997 datasets, approximately a month before and after perihelion. Our results
contribute to the understanding of both the chemical properties of the comet as well as the physical mechanisms necessary
to produce these features.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
GuangShu Zhang YuXiang Zhao XiuShu Qie Tong Zhang YanHui Wang ChengPin Chen 《中国科学D辑(英文版)》2008,51(5):694-708
A narrowband radio interferometer has been developed and used to locate the entire sources of VHF radiations from a negative cloud-to-ground (CG) lightning discharge which contains 19 strokes. This system uses five antennas to form an array consisting of short- and long-baselines along two or- thogonal directions. The system error which comes from frequency conversion is reduced by phase detection through direct high frequency amplifying. An interactive graphic analysis procedure is used to remove the fringe ambiguities which exist inherently in interferometry and to determine the direction of lightning radiation sources in two dimensions (azimuth and elevation) as a function of time at a time resolution of microsecond orders. With the developed system, the whole progression process in time and space of a lightning flash can be reconstructed. In this paper, combining the synchronous data of electric filed change and VHF radiation, the whole processes of an example negative CG flash have been studied in detail. It is found that the preliminary breakdown event of the CG flash started from negative charge region and exhibited firstly a downward pregression and then an upward propagation. There were very intense and continuous radiations during stepped leaders which became much stronger when the first return stroke began. In contrast, there were less and only discrete radiations during dart leaders. Stepped leader and dart leader may transform to each other depending on the state of the ionization of the path. The progression speed of initial stepped leaders was about 105 ms?1, while that was about 4.1×106 and 6.0×106 ms?1 for dart leaders and dart-stepped leaders, respectively. M events produced hook-shaped field changes accompanied by active burst of radiations at their begin- nings. Followed these active radiation processes, M events appeared to contact finally into conducting main discharge channels. The mean progression speed of M events was about 7×107 ms?1, greater than that of the dart leaders and dart-step leaders. K events and attempted leaders were essentially the same as dart leaders except that they could not reach the ground and initiate return strokes. 相似文献
3.
对于高速自旋目标而言,为了获得聚焦效果良好的图像,通常要求雷达系统具有较高的脉冲重复频率(PRF)。当PRF不满足采样要求时,雷达接收到的通常是方位欠采样的回波数据,从而影响目标识别。本文根据压缩感知理论,结合自旋目标回波信号稀疏性的特点,建立方位欠采样的成像模型,并提出了基于压缩采样匹配追踪的窄带雷达高速自旋目标成像算法。该算法在对信号进行重构迭代中,采用回退策略,并结合回波信号稀疏性的具体参数,选取最优的支撑集,提高了算法的重构质量。仿真实验表明新算法在回波欠采样的情况下能很好地重构图像,尤其是在低信噪比的情况下。采用"误选数"和"均方误差"两个指标对CoSaMP算法重建信号的性能进行评价,结果表明该算法受雷达PRF和信噪比SNR的影响较小,算法稳定性好。 相似文献
4.
我国阵风锋类型与产生机制分析及其主观识别方法 总被引：2，自引：1，他引：1
文章总结了近些年我国学者对阵风锋所开展的相关研究,阐明了阵风锋的空间结构、类型及其特征,探讨了阵风锋窄带回波的形成机制,提出了阵风锋的主观识别方法,结果表明:从雷达探测资料分析,可将阵风锋分为两类,一类是雷暴母体静止型阵风锋,一类是雷暴母体运动型阵风锋,而前者还可以进一步分为两个子类型。阵风锋类型不同,阵风锋对雷暴母体的反馈作用也截然不同。阵风锋窄带回波的形成可概括为两种机制:第一种是大气折射指数梯度脉动导致的布拉格散射(Bragg Scattering),第二种是由昆虫对雷达波的粒子散射(Particle Scattering)导致。利用阵风锋雷达强度和径向速度回波特征,可以识别阵风锋的位置和范围,并对其外推做出预报。由于阵风锋是低层大气现象,所以需要应用较低仰角的雷达资料来识别。利用阵风锋雷达回波特征,配合气象卫星高分辨率可见光云图上呈现的中尺度对流云团和弧状云线的变化,结合地面中尺度观测网资料,可以综合识别阵风锋的形成、发展和消散。 相似文献
5.
Earth, Moon, and Planets - 相似文献
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We present the results of narrowband photoelectric observations of comet Hale-Bopp near perihelion, which were made with the
AZT-14telescope at the station Lisniki of Kyiv University Astronomical Observatory. The standard set of IHW cometary filters
was used. The total number of cometary observations was more than 500 during the interval March 13–April 29, 1997. The comet's
nuclear gas production rates Q of C2 and C3 were calculated using the stellar calibration for these filters. The calculations used the Haser model for a neutral cometary
atmosphere. The value Afρ, which is characteristic of the dust production rate, was determined too. Mean values of the production
rates near perihelion are log Q(C2) = 28.4; log Q(C3) = 27.2; (Afρ)BC = 6.0.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
用FY-2C静止气象卫星资料计算射出长波辐射通量密度 总被引：3，自引：0，他引：3
介绍用FY-2C静止气象卫星资料估算射出长波辐射(OLR)的方法,包括FY-2C OLR反演模式的建立、由FY-2C窗区通道1、窗区通道2、水汽通道遥测数据计算OLR的详细步骤;给出了FY-2C OLR产品的精度:与相近时刻的NOAA卫星OLR产品相对比,两颗星OLR产品的等值线图基本完全一致,图上绝大部分偏差0~10 W/m,最大偏差20 W/m;并给出了FY-2C OLR产品的实例及其初步应用。 相似文献
9.
根据阵风锋的回波特征, 该文设计了阵风锋自动识别算法。在速度场中,考虑辐合线识别;在强度场中,考虑窄带回波识别;根据窄带与辐合线的空间一致性,综合二者识别出阵风锋。基于该算法,以锋线闪烁和物理量输出两种方式实现了预警功能。最后利用地面自动气象站资料和2009年6月3日河南商丘、郑州及2009年6月5日安徽阜阳3个雷达站探测的阵风锋98个体扫样本资料检验了识别效果,并采用临界成功指数进行评估。结果表明:双向梯度法能有效滤除大范围降水回波而保留窄带回波;该算法只需考虑较低仰角层,大大提高识别效率。在速度场中采用的算法能有效识别出径向辐合线,同时也适用于低空径向风切变和辐合线的识别;利用临界成功指数对98个体扫样本进行识别率评估,识别率达到68.4%。 相似文献
10.
随着我国新一代多普勒天气雷达网进一步建设,雷达资料如何实现资源共享提上日程,以便充分发挥现代化设备的效益。为了丰富共享内容和提高时效性,广东省在CINRAD/SA雷达资料共享方面进行了一些摸索和实践,形成了目前比较成熟的业务流程。文章分析了CINRAD/SA雷达资料共享中所涉及的有关问题,如由于计算机性能、通信网络、产品申请列表等原因导致的缓存溢出、CPU过载、窄带过载等问题,并提出了相应的处理办法,同时还着重介绍了广东省CINRAD/SA雷达资料共享业务流程。 相似文献