The hyperthermal ionization and high absolutemeteor velocities observed with HPLA radars

High Power Large Aperture (HPLA) radars generally observe very high meteor velocities averaging over 50 km s⁻¹. There are only a few events recorded around 30 km s⁻¹, while meteors at 20 km s⁻¹ or slower are very rare. This is a clear and debated contradiction to specular meteor radar results. A high plasma density condition contributes, but the dominating phenomenon is the hyperthermal ionization mechanism due to chemical dynamics of the ionization process. The observed high velocities can be explained in terms of high hyperthermal ionization cross-sections for collisions between ablated meteoroid metal atoms such as Na and/or Fe and atmospheric species.     

非迁移潮作用下的电离层赤道异常区单峰现象及其经度分布

当喷泉效应较弱而双峰结构发展不充分的时候,可能在赤道异常区仅能够观测到一个电子密度的峰值,称之为单峰现象.本文利用CHAllenging Minisatellite Payload卫星在2001-2010年的电子密度数据给出了单峰的发生规律,单峰在地方时早上08：00-10：00和下午16：00-19：00发生率高,发生位置在经度上呈现多波数分布,尤其在10：00-18：00明显：在分季时多呈现四波,而在冬至季时以三波为主.单峰发生多的经度,正好对应着双峰的结构特征较弱之处.究其原因,是非迁移潮的DE2和DE3分量调制了背景风场和大气发电机电场,在电场和喷泉效应减弱的经度,双峰结构难以形成时,就会表现为单峰结构.本文扩展了对单峰现象的地方时、季节和经度分布等规律的了解,明确了非迁移潮在其中施加的影响,由此,单峰同双峰现象一样可以用于研究非迁移潮对热层-电离层的作用.

     

The generation of ionization-shock front oscillations by a variable radiation flux

The effect of a time-varying radiation flux incident on an ionization front on the generation of ionization-shock front oscillations in the interstellar medium is analyzed analytically and numerically. We take into account both variations in the flux of ionizing radiation directly from the source that produces the ionization front and the absorption of energetic photons by the post-front plasma. Based on our calculations, we show that the time dependence of the radiation flux can be an additional factor (apart from small inhomogeneities in the interstellar medium) that contributes to the amplification of oscillations and to the kinetic energy input to the observed turbulent motions in H II regions.     

Acceleration of a spherical neutral shell produced by an ionization-shock front in an inhomogeneous interstellar medium

We numerically model the formation and acceleration of a neutral gas shell as an ionization-shock front propagates in a spherical cloud by taking into account the photoionization and radiative heating of the gas, the spectral radiative transfer. We suggest and implement an approximation of the cooling function that allows calculations to be performed in a wide range of gas ionization fractions and temperatures. The total mass, average velocity, and thickness of the shell have been determined. The results are compared with approximate formulas known in the literature. Based on the parameters of the shell found, we estimate its acceleration, characteristic scales, and the growth times of unstable perturbations. We analyze the influence of the cloud particle density, cloud radius, stellar temperature, and radiation spectrum on the integrated characteristics of the neutral gas in the layer between the ionization and shock fronts. The distribution of matter in the shell and its thickness are shown to differ significantly from those used in approximate models.     

高温热水孔逸出气氡观测实验研究

本文通过在漳州龙师１＃井开展的逸出气氡观测实验研究，认为逸出气氡作为新的地震前兆观测项目是可行的，可以进行平行样观测，同时可得到Ｒｎ气／Ｒｎ水比值，作为研究地下流体前兆的一个新的参数。并对应用电离法测量逸出气氡的连续自记观测技术进行了预研究试验。     

杯法测氡原理及应用

本文分析了α测氡方法及应用的现状,针对目前存在的问题,通过实验研究,提出了α杯法测氡技术。文中详细论述了α杯法测氡原理、功能、特点、工作方法和应用情况。结果表明:α杯法测氡的灵敏度高、操作简单、效率高、成本低、能够为寻找基岩地下水、探测隐伏地质构造、解决工程地质问题等提供了可靠依据,有进一步推广应用价值。     

与地震预报有关的电磁现象国际讨论会概况

与地震预报有关的电磁现象国际学术讨论会已于１９９３年９月６－８日在东京召开。这次学术讨论会的宗旨是，为世界各国学者提供一个公开讲坛以讨论与地震有关的电磁现象，并通过交叉学科与多科学相关领域相结合的方式探讨地震预报等问题。本文较详细地介绍了各国学者在这一领域中的最新成果。     

对流输运在TOI断裂形成等离子体云块中的作用研究

极盖等离子体云块是极区电离层常见特征之一,其形成演化过程是当前重要研究课题.光电离高密度等离子体在对流输送作用下从日侧穿过极隙,通过极盖到达夜侧,已成为共识.日侧磁场重联作用下的极区对流输运过程,在舌状等离子体结构（TOI）"断裂"形成极盖等离子体云块中发挥重要作用.利用极区全域GPS/TEC观测数据,结合SuperDARN雷达实测的对流速度,对等离子体云块形成过程进行案例研究,重点分析两种TOI断裂形成等离子体云块的发生机制.研究结果显示,等离子体对流输运过程在TOI断裂形成等离子体云块过程中发挥关键性作用,对流形态或局部对流速度矢量急剧变化都可能导致TOI结构不稳定,使TOI结构断裂形成等离子体云块.     

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.