Meteor fluxes and visual magnitudes from EISCAT radar event rates: a comparison with cross-section based magnitude estimates and optical data

Incoherent scatter radars (ISR) are versatile instruments for continuous monitoring of ionisation processes in the Earths atmosphere. EISCAT, The European Incoherent Scatter facility has proven effective also in meteor studies. The time resolution of the radar can be reduced to a few milliseconds, sufficient to resolve the passage of individual meteors through the narrow ISR beam. Methods for group and phase velocity determination of the meteoroids and the discrepancy between the results related to the target behaviour are presented. The radar cross sections of echoes associated with moving meteoroids (–meteor head echoes) are very small and increase with decreasing wavelength. The parent meteoroids are found to have visual magnitudes far below the detection limit of most optical observations. The equivalent visual magnitude limit of the smallest objects observed by EISCAT in the current experiments has been estimated by two different methods, both from the cross-section measurements and from the measured event rates. Both methods give a limit value of +10 for the smallest objects while the upper limit is +4. The lower limit of the visual magnitude for the collocated optical measurement system is +4. Thus the two detection systems observe two different meteor size ranges, with the radar almost reaching micrometeorite population. Meteor fluxes estimated from the event rates and the radar system parameters agree well with previous extrapolated values for this size range.     

SCIPION, a new flexible ionospheric sounder in Senegal

SCIPION is a new state of the art digital sounder that has been developed by France Telecom-CNET for ionospheric monitoring and research. Extensive data processing using DSP technology has resulted in a low power, low cost and full featured system for both vertical and oblique soundings. A SCIPION system is in the process of being installed in Dakar, Senegal, to study HF propagation in the sub-equatorial ionosphere. However, preliminary results have still been obtained during experiments wit a prototype system. In this paper, the system is described and some illustrative examples of its capabilities are shown.     

An analysis of anomalous weather and cli mate around the M S= 6.2 earthquake of Zhangbei region

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古代与现代海底黑矿型块状硫化物矿床矿石地球化学比较研究

选择西南太平洋冲绳海槽现代海底烟囱硫化物矿床、日本小坂矿山上向黑矿（第三纪）和中国西南呷村黑矿型矿床（三叠纪）进行了矿石地球化学比较研究。黑矿型矿床矿石吨位－品位模式与其他火山成因块状硫化物（ＶＭＳ）矿床类似，矿田（２０－５０ｋｍ＾２）矿石吨位与单个喷气－沉积型（Ｓｅｄｅｘ）矿床相当，金属总量４－６Ｍｔ，为矿田范围内热液流体搬运的最大金属量。与洋脊环境ＶＭＳ矿床相比，岛弧裂谷环境产出的黑矿型矿床相     

Roughness length and drag coefficient at two MONTBLEX-90 tower stations

Using MONTBLEX-90 mean velocity data, roughness lengths and drag coefficients are estimated at Jodhpur and Kharagpur. At Jodhpur, since the surface is not uniform the roughness length is estimated separately in three different subsectors within the range of prevailing wind directions and averages to 1.23 cm in the sector between 200° and 230° which is relatively flat with no obstacles on the ground. At Kharagpur, where the terrain is more nearly homogeneous, the average value (for all prevailing wind directions) is 1.94 cm. The drag coefficient C_D at Jodhpur shows variation both with the roughness subsector and with wind speed, the average over all directions increasing rapidly as themean wind speed Ū₁₀ at 10m height drops according to the power lawC _D = 0.05 Ū ₁₀ ^t-1.09 in trie range 0.5 < Ū₁₀ < 7 m s⁻¹. At Kharagpur, the drag coefficient is smaller than at Jodhpur by nearly 50% for the same range of wind speeds (> 3 ms⁻¹).     

Planning MONTBLEX — An overview

The multi-institutional experiment MONTBLEX aimed at sensing and studying the atmospheric boundary layer over the monsoon trough region of the northern plains of India during the summer monsoon of 1990. Four core facilities consisting of micro-meteorological towers and state-of-the-art instrumentation were created along the trough axis. This overview emphasizes the key features of project planning, management and execution, and provides detail? of all the experimental observation sites.     

Subsolar elevation of the equatorial electrojet

The subsolar elevation of the equatorial electrojet has been produced from satellite solstitial data available from 09 to 15 hr LT using a new approach with the general style of the overhead equivalent current system. It shows the bunching of the current around the dip equator; the return currents of the equatorial electrojet close to the flanks of the dip equator; the fast growth of the electrojet to its diurnal peak followed by a slow decay; and the contraction of its latitudinal extent around the meridian of its highest intensity. Comparison with the results of other workers using ground data suggests that the elevation from satellite data agrees better with that from ground data when the worldwideSq is removed from the ground data.     

川西螺髻山冰川侵蚀地貌研究

定量分析发现影响该地区冰斗形态的因素有海洋性较强的气候,朝向北(极向),朝向东和较大的地形起伏四种。槽谷的横剖面可以公式化为Y=a·X~b,槽谷形态不对称由冰川差异侵蚀和冻融差异所致。发现两种冰川侵蚀裂痕,即挤压剪切裂痕和拉张剪切裂痕。     

新矿物——钓鱼岛石的研究

钓鱼岛石是在我国台湾省钓鱼岛附近海域海底表层沉积物中发现的一种新矿物。钓鱼岛石为无色淡绿色到,薄板状,一轴晶负光性,晶体很小,一般在0.4×0.2×0.03mm~3以下,D=3.30,H_(v15)=1392.8kg/mm~2。电子探针定量分析(以相应氧化物为标样)结果(％):Na_2O4.54、Al_2O_3 93.00、Cr_2O_31.95、MgO0.10、CaO 0.10、SiO_2 0.23、K_2O 0.12,总量100.04。以氧为17计算的化学式为(Na_(0.87) K_(0.02) Mg_(0.02) Ca_(0.01);)_(0.92)(Al_(10.84)Cr_(0.15)Si_(0.02))_(11.01)O_(17)。经四圆单晶衍射证明,该矿物为六方晶系,空间群为P6_3/mmc,a=b=5.602(1)Ac=22.626(5)A,α=β=90°,γ=120°。     

电离层声重波扰动的高频无线电诊断

为了充分发挥现代数字式电离层探测仪在电离层结构与优动研究中的潜力,必须在传统的频高图真高换算的基础上,发展新的反演理论和算法.本文介绍了随时空缓变的各向异性电离层介质中无线电波包传播的广义射线方程组,讨论了计算波包射线几何路径以及计算波包参数,如频移、波矢、群时延等沿射线路径变化的传播正问题,并详细讨论了根据波包参量的测定值反演介质结构和扰动伏态的传播反问题.文中若干实验实例表明,这种反演理论和算法可用于数字式电离层探测仪记录的分析,它使高频无线电波探测技术成为研究全球电离层声重波一类扰动的有力工具。