Meteor Outburst Profiles and Cometary Ejection Models

The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from the nucleus, including the mass distribution of ejected meteoroids.     

Observations of interplanetary meteoroids with TIRA

The Tracking and Imaging RAdar (TIRA) at the Research Establishment for Applied Science (FGAN) was used in the L-band (1.33 GHz) to observe the Leonid shower in 1999. The radar beam was pointed directly into the radiant in the constellation Leo to receive “head echoes” from meteoroids when they ablate in the atmosphere at altitudes around 100 km. Two hundred and eighty-seven meteors were observed during 21 h in the early hours of November 17 and 18, 1999. The individual velocities, radiants and rough heliocentric orbits are calculated. Criteria are derived from optically observed Leonids which are then applied to decide whether an echo was created by a Leonid or a background meteoroid. However, in most cases the accuracy in the observational data is not good enough to allow for a clear distinction. Only for 100 meteors the velocity errors were less than 10 km/s. Out of those, 71 could be excluded on a 3σ level to be a Leonid (95 are excluded on a 1σ level). This confirms the theory that the Leonids have dominantly sizes of optical meteoroids with no significant extension in the lower mass range. Therefore, the risk of meteoroid impacts on spacecraft does not increase considerably during a Leonid storm. Background measurements 9 days after the Leonids maximum were taken in 2001 which corroborated the overall results obtained in 1999.     

The Leonid outburst of 1996

There is strong anticipation that the Leonid meteor shower could produce storm-level activity in 1998 and/or 1999. The well-documented Leonid outburst in 1996 and the more poorly observed one in 1994 have been taken by many observers to imply that a storm is imminent, This article explores the possible relationship between the 1996 outburst in activity and possible Leonid storms. The curve of activity is found to be much closer to that of normal activity, although with greater hourly rates, than it is to the very brief, steeply rising activity curve of a storm. It is probable that the 1996 outburst is thus completely unrelated to any future storm which may appear.     

Television meteor radiant mapping

We have carried out double-station TV meteor observations between 1990 and 1994. The orbits of 326 meteors have been determined from doubly observed meteors, and radiant distributions are studied. The mean magnitude of the observed meteors was as faint as +4.7, since I.I. (Image Intensifier) and Video cameras were used. Radiants were widely distributed over the celestial sphere. The velocity distribution showed some similarity with the distribution predicted by the theoretical radiant distribution from comets rather than that from asteroids. In all 13 showers including both major and minor meteor showers were detected from radiant distributions of the observed meteors; from the orbital elements and meteor velocities as well as from the radiant directions.     

A procedure of selection of meteors from major streams for determination of mean orbits

A procedure of selection of meteoroids from major streams is suggested and applied to the IAU Lund photographic database modified by a check for internal consistency among orbital elements (3411 orbits). Limits for choice of stream members were defined by break points on the plots of the cumulative numberN _C vs. the Southworth-HawkinsD discriminant. For the break points were considered the points from which the dependenceN _C vs.D changes to a quasi-linear one, and with the increasingD, N _C changes only moderately. Except for the Taurids which desire a separate analysis, theN _C vs.D diagrams are presented for the following major meteoroid streams: Quadrantids, Lyrids, Aquarids, Capricornids, N and S Aquarids, Perseids, Orionids, Leonids and Geminids. The mean orbits, velocities and radiants of the streams are derived and compared with the osculating orbits of their parent bodies. The limitingD _B was found to be a function of the number of the stream membersN _CB. Omitting the exceptionally concentrated Geminids, the relation is in the formD _B = 0.058 *ln(N _CB) – 0.04.     

On the response of the neutral temperature at 78°N and 90 km altitude to solar proton events

We are able to determine neutral air temperatures by examining the fading times of meteor trail echoes in the upper mesosphere/lower thermosphere. It has been suggested that solar proton events may stimulate both dynamic and aeronomic changes in the middle atmosphere and we have endeavoured to investigate this. Despite a variety of approaches to determine the background temperature above which we might expect to see enhancements under conditions of strong proton precipitation, we are unable to detect any significant changes. We have repeated the search during selected seasons and also with various proton flux thresholds, similarly to no avail. We conclude, therefore, that at 90 km altitude, 78°N and 16°E, at least, we are unable to detect enhanced neutral temperatures due to solar proton events. At best, any enhancements, predicted to be of the order of a few K only, are likely to be completely masked by the day-to-day variability of the temperature field.     

昆明全天空流星雷达观测中高层大气温度

利用昆明电波观测站（25.6°N,103.8°E）两台不同工作频率的全天空流星雷达在2011年特殊联合观测试验期间的数据,基于Hocking的方法利用不同的温度梯度,在确定了昆明地区中层顶位于流星峰值高度之上的情况下,反演了昆明地区上空88 km和85 km高度的大气温度,并与Aura卫星观测的温度进行比较.对比研究发现,两台流星雷达可以分别正确获得88 km和85 km高度的大气温度,但其中由全球温度梯度模式反演得到的大气温度与卫星观测温度相关性不是很好,而利用卫星观测的温度梯度,两台雷达反演出的大气温度与卫星观测温度存在很好的相关性.结果表明了准确的温度梯度在流星雷达观测大气温度过程中是至关重要的.     

地应力和瓦斯压力作用下深部煤与瓦斯突出试验

基于目前煤与瓦斯突出模拟试验均为人为控制突出口打开的实际情况,自主研制了可改变轴压、围压和孔隙压,实现突出口自行打开的煤与瓦斯突出模拟仪。以典型高瓦斯矿井-阜新孙家湾矿为例,试验模拟了煤层开采深度分别为900、 1 100、1 300 m时,突出煤层临近工作面区域在地应力和瓦斯压力共同作用下诱导发生煤与瓦斯突出全过程。试验利用轴压、围压模拟地应力作用,孔隙压模拟瓦斯压力作用。经相似理论计算确定了3种开采深度下轴压和围压值、孔隙压逐级增加得到了突出时瓦斯压力,并拟合了关系曲线。研究结果表明：开采深度、轴压、围压、瓦斯压力与突出距离、突出强度间均呈幂指数增加规律。随深度增加,地应力与瓦斯压力对突出影响增量逐渐减小。瓦斯压力对突出影响作用存在3阶段特征,分别为急剧影响增加阶段、稳定影响增加阶段和缓慢影响增加阶段,确定了瓦斯压力对突出影响变化率最大值,即瓦斯压力变化异常区与稳定区分界点为0.75 MPa,对应开采深度为350 m,与前人理论分析结果基本吻合。由此可以推断,随深部开采,地应力与瓦斯压力共同作用下煤与瓦斯突出频度将增加,但强度和破坏程度增加率将趋于平缓。所得结论对该矿深部煤与瓦斯突出机制认识和预测防治具有参考意义。     

煤和瓦斯突出与地应力之关系

本文以声发射粗估法地应力测量,研究谢二煤矿煤和瓦斯突出与地应力之关系。研究结果表明,煤与瓦斯突出与地应力呈正相关关系。也就是说,凡煤与瓦斯突出地带均属地应力超常地带,而安全地带的地应力值则正常或偏低.