The role of suprathermal particle measurements in CrossScale studies of collisionless plasma processes     

Mike Hapgood  Chris Perry  Mick Denton 《Planetary and Space Science》2011,59(7):618-629

The CrossScale mission will advance our understanding of fundamental plasma processes in collisionless plasmas. It will exploit the excellent natural plasma laboratory provided by the Earth’s magnetosphere and the near-Earth solar wind and, in particular, carry out multi-scale studies that will strongly complement plasma studies in ground-based laboratories. Previous studies of collisionless plasmas in space environments across the solar system have shown the ubiquitous nature of suprathermal particles and that these particles exhibit a power-law energy spectrum. In this paper we discuss the great significance of these suprathermal particles for CrossScale studies. We show that the presence of these particles is a natural consequence of the collisionless regime as they can propagate across the heliosphere with little spectral change and are not thermalised by collisions. They are a key indicator of the non-equilibrium nature of collisionless plasmas and an important source of free energy that can drive plasma processes. We discuss how these suprathermal particles influence the overall properties of the plasma. In particular, the energy distribution of particles follows a Kappa, rather than Maxwellian, distribution and thus the plasma does not have a single thermodynamic temperature. We also discuss the importance of the suprathermal tail as a tool to diagnose the processes responsible for particle energisation in collisionless plasmas. Such energisation is a common feature in collisionless plasmas, especially in terms of the primary science targets for CrossScale: reconnection, shocks and turbulence. Finally we also touch on the value of using CrossScale studies to provide ground truth measurements for a number of astrophysical techniques that exploit the effects of energetic electrons in the distant universe. Throughout the paper, we stress that suprathermal (30 keV-1 MeV) measurements are essential to fully characterise particle distributions. We show that such measurements will benefit greatly from the improved spatial and temporal resolution (compared to Cluster) that is proposed for the HEP instrument on CrossScale.  相似文献   

Nonthermal emission from the radio relic of the galaxy cluster A2256     

G. Siemieniec‐Ozieblo  B.M. Pasternak 《Astronomische Nachrichten》2011,332(6):649-654

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奥运会及残奥会期间北京市区大气颗粒物污染特征及微观形貌类型   总被引：1，自引：1，他引：0  

邵龙义  刘君霞  宋晓焱  牛红亚  张芳 《现代地质》2010,24(2)

2008年8月和9月,北京市成功举办了第29届奥运会和第13届残奥会,对这段时间在北京市区(中国矿业大学校园综合楼五层,距奥运村3 km)采集的大气颗粒物的质量浓度和微观形貌类型进行了研究。结果表明:奥运会期间,北京市区大气PM10和PM2.5的日均质量浓度分别小于国家PM10二级标准(150μg/m3)和美国EPA的PM2.5二级标准(65μg/m3),12 h的质量浓度范围分别为7.64~81.63μg/m3和1.91~54.59μg/m3;残奥会期间,12 h的PM10质量浓度范围为33.83~106.36μg/m3,没有超标,PM2.5质量浓度变化范围为15.29~88.30μg/m3,其中出现了3 d超标天,分别为9月6日、7日和14日;从奥运期间PM2.5/PM10的比值(0.26~0.86,大部分值大于0.5)可以看出,奥运期间北京大气颗粒物以细粒子为主。与往年相比,颗粒物质量浓度出现大幅下降趋势。场发射扫描电镜观察显示,奥运会和残奥会期间样品的微观形貌类型主要有球形颗粒、烟尘集合体、不规则矿物和未知颗粒,其数量-粒径分布主要呈单峰分布,峰值均在0.1~0.2μm范围,其中球形颗粒明显占多数。各种分析数据均显示,残奥会期间样品比奥运会期间样品污染要严重。  相似文献   

Observations of ionospheric flows and particle precipitation following a Sudden Commencement     

E. Nielsen  F. Honary 《Annales Geophysicae》2000,18(8):908-917

On May 4, 1998, at 0227 UT an interplanetary shock crossed the WIND spacecraft, and half an hour later a Sudden Commencement occurred. Coinciding with the Sudden Commencement a rapid intensification of the flux of particle precipitation into the ionosphere was observed. Evidence is presented that the ionospheric electric fields were influenced by the associated dynamic variations of the ionospheric conductivities. Following the initial phase the ionospheric flow speeds increased rapidly over the next 20 min to more than 2000 m/s, in agreement with an increased effective coupling of the solar wind energy to the magnetosphere following the interplanetary shock that caused the Sudden Commencement. These strong flows were meandering in latitude, a type of plasma flow modulation that has been reported before to occur during Omega band events: a string of alternating field-aligned currents propagating eastward. The riometer absorption was found to be at a minimum in regions associated with outward directed field aligned currents. The riometer absorption regions (the regions of particle precipitation) were drifting with E × B drift speed of the ionospheric electrons.  相似文献   

乌鲁木齐地区雪和雨对气溶胶湿清除能力的比较研究   总被引：6，自引：0，他引：6  

李霞  杨青  吴彦 《中国沙漠》2003,23(5):560-564

根据2002年乌鲁木齐地区逐日逐时SO₂、NO₂和PM₁₀粒子浓度监测资料,针对冬季固态降水、夏季液态降水对三种气溶胶颗粒物的湿清除能力进行了统计分析。粗略得出乌鲁木齐地区冬季微量降水日,气溶胶颗粒物浓度呈现增加趋势;而夏季微量降雨能够减小气溶胶颗粒物浓度。超过微量降水量的日子里,在冬季三种颗粒物的浓度明显高于夏季的情形下,每1 mm降雪量对气溶胶的清除率大于夏季每1 mm雨的清除能力。同时拟合结果表明降水日气溶胶浓度的改变量与其前一日气溶胶浓度值存在较好的相关特性。  相似文献   

辽宁冬季城市空气质量分布状况综合研究   总被引：5，自引：0，他引：5       下载免费PDF全文

马雁军  刘宁微  王扬锋 《气象与环境学报》2007,23(3):15-18

利用2006年12月辽宁14个城市的大气环境现状监测资料和沈阳、鞍山、抚顺、本溪4城市可吸收入颗粒物(PM10,PM2.5和PM1)的监测资料,对辽宁冬季各城市的空气质量分布状况进行了综合研究。结果表明:辽宁14个城市的冬季空气质量分布状况为优、良和轻微污染3个等级,其中铁岭、营口和辽阳的空气质量有28 d为良及以上等级;空气质量级别为轻微污染日数最多的城市是本溪,共计12 d;其次是葫芦岛、沈阳、鞍山、抚顺、盘锦、阜新,共计7—10 d。各城市的首要污染物是PM10。由于冬季燃煤量的增加,沈阳、鞍山、抚顺和本溪4城市PM2.5日平均浓度值的超标率为77.4%—90.3%。  相似文献   

Effect of sediment particles on the velocity profile of sediment-water mixtures in open-channel flow     

Lei Zhang  Jianzhao Guan  Deyu Zhong  Yousheng Wang 《国际泥沙研究》2023,38(3):361-373

The presence of sediment particles in open-channel flow has an important effect on turbulence; thus, an empirical, turbulent eddy viscosity formula was established for application in the limit for low concentrations. The current study establishes a theoretical relation for the mixture viscosity based on the two-phase mixture model. The percentage contribution of the three mechanisms of mixture viscosity,namely, fluid turbulence(FT), particle turbulence(PT), and inter-particle collisions(IPCs), w...  相似文献   

Experimental study of the settling of twin spherical particles released side by side: The impact of particle size,fluid viscosity,initial spacing,and particle density     

Yang Xiao  Jieqing Liu  Pei Zhang  Jian Zhou  Dongfang Liang  Zhihao Wang  Taotao Zhang  Saiyu Yuan  Hongwu Tang 《国际泥沙研究》2023,38(1):83-96

The settling of solid particles in a fluid is an important process that needs to be considered in many fields of research. For example, the interactions among particles and between particles and the surrounding fluid are important topics in studying suspended sediment transport and water clarification. In this paper, the settling processes and interactions of twin spherical particles released side by side were experimentally studied. The Reynolds number varied in the range of 1-300, which is wit...  相似文献   

Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress-controlled titanomagnetite (Fe_2.4Ti_0.6O₄) particles—I. Magnetic hysteresis properties     

R. Keller  & E. Schmidbauer 《Geophysical Journal International》1999,138(2):319-333

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Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress-controlled titanomagnetite (Fe_2.4Ti_0.6O₄) particles—II. Rotational hysteresis losses     

R. Keller  & E. Schmidbauer 《Geophysical Journal International》1999,138(2):334-342

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