Ionospheric measurements during the CRISTA/MAHRSI campaign: their implications and comparison with previous campaigns

The CRISTA/MAHRSI experiment on board a space shuttle was accompanied by a broad campaign of rocket, balloon and ground-based measurements. Supporting lower ionospheric ground-based measurements were run in Europe and Eastern Asia between 1 October–30 November, 1994. Results of comparisons with long ionospheric data series together with short-term comparisons inside the interval October-November, 1994, showed that the upper middle atmosphere (h =80–100 km) at middle latitudes of the Northern Hemisphere in the interval of the CRISTA/MAHRSI experiment (4–12 November, 1994) was very close to its expected climatological state. In other words, the average results of the experiment can be used as climatological data, at least for the given area/altitudes. The role of solar/geomagnetic and “meteorological” control of the lower ionosphere is investigated and compared with the results of MAP/WINE, MAC/SINE and DYANA campaigns. The effects of both solar/geomagnetic and global meteorological factors on the lower ionosphere are found to be weak during autumn 1994 compared to those in MAP/WINE and DYANA winters, and they are even slightly weaker than those in MAP/SINE summer. The comparison of the four campaigns suggests the following overall pattern: in winter the lower ionosphere at northern middle latitudes appears to be fairly well “meteorologically” controlled with a very weak solar influence. In summer, solar influence is somewhat stronger and dominates the weak “meteorological” influence, but the overall solar/meteorological control is weaker than in winter. In autumn we find the weakest overall solar/meteorological control, local effects evidently dominate.     

On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

Previous work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to 2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.     

曲靖非相干散射雷达电离层F区日间电子温度变化特征初步分析

利用曲靖非相干散射雷达2017—2018年春夏季观测数据首次分析了电离层日间150～450km电子温度的地方时与高度变化特征及其与电子密度的相关性.发现hmF2及以上的电子温度在日出日落时具有两个峰值,在11∶00—16∶00LT之间变化较小,高度越高午后上升的时间越早;从150km开始迅速增加,在约220km达到最大值,然后开始降低,在约300～350km达到最小值,最后单调上升;200km以下电子温度与电子密度成正相关(主要由热传导控制),200～450km之间存在明显的反相关(光电离过程占主导),电子-离子温度差与电子密度对数之间存在近似线性关系,电子温度逐日变化与光电离因子的变化趋势相似,这种相关性在中午与午后更明显;以上结果与其他非相干散射雷达观测和电离层模型计算结果基本一致,但也存在一些差别,需要结合更多数据深入分析.     

Irregular structures of the F layer at high latitudes during ionospheric heating

Results on heating the ionospheric F region above Tromsø, Norway are presented. The ionosphere was monitored by satellite tomography and amplitude scintillation methods as well as the EISCAT incoherent scatter radar. No effect of heating was observed in the daytime. In the evening and in the pre-midnight sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped the heating cone, where the electron density decreased and irregularities exceeding 10 km in size appeared. Between the heating periods the F layer was restored to its horizontal shape. The anisotropic parameters of small-scale irregularities with scale lengths of hundreds of metres were also determined. It was found that the perpendicular anisotropy points in the direction of F region plasma flow. In some cases the results can be explained by assuming that the small-scale irregularities were generated within the heating cone and drifted out of the heating region where they were subsequently observed.     

液闪法测量水中氚放射性活度的淬灭效应

采用液体闪烁计数法进行放射性同位素测量时存在淬灭效应,而且几乎每个样品的淬灭程度都不同,并影响测量精度。采用液体闪烁计数法测量水中氚的放射性活度,淬灭是难以避免的,因此要进行淬灭校正,才能使不同淬灭程度的样品的测量结果具有可比性。淬灭校正的方法有很多,外标准校正法是一种比较可靠的方法。文章采用氚外标准校正法进行实验,得出淬灭校正曲线即探测效率E与淬灭参数SQP(E)的关系式为E=0.001 3SQP(E)-0.707 6,经过样品验证,该曲线是可靠的。采用外标准校正法适合于大批样品的测量。     

基于陆态网络GPS数据的电离层空间天气监测与研究

中国大陆构造环境监测网络(简称陆态网络)是以全球卫星导航定位系统(GNSS)为主,辅以多种空间观测技术,实时动态监测大陆构造环境变化,探求其对资源、环境和灾害的影响的地球科学综合观测网络.基于陆态网络约200个基准站的GPS观测数据,本文探讨了其在电离层空间天气监测与研究方面的应用.包括磁暴期间电离层暴扰动形态,大尺度电离层行进式扰动,太阳耀斑引起的电离层骚扰和低纬电离层不规则体结构等.研究结果表明:陆态网络布局合理,观测数据质量良好,完全可用于中国及周边地区电离层空间天气监测与研究,为进一步开展我国电离层空间天气预警和预报奠定了观测基础.     

Two types of ELF hiss observed at Varanasi, India

The morphology of ELF hiss events observed at low-latitude ground station Varanasi (L = 1.07, geomagnetic latitude 14°55′N) are reported, which consist of two types: (1) events which propagated in ducted mode along the geomagnetic field line corresponding to observing station Varanasi and (2) events which propagated in ducted mode along higher L-values (L = 4–6), after reaching the lower edge of ionosphere excite the Earth-ionosphere wave guide and propagate towards equator to be received at Varanasi. To understand the generation mechanism of ELF hiss, incoherent Cerenkov radiated power from the low latitude and middle latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave-particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF hiss.     

Multi-instrument study of footprints of magnetopause reconnection in the summer ionosphere

Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the B_z component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR field-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed significantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic field lines and those opened along which magnetosheath ions precipitate.     

电离层闪烁对GNSS接收机性能影响比较分析

电离层闪烁是引起GNSS接收机性能降低甚至失锁的重要环境干扰因素。利用实测数据,比较分析了不同电离层闪烁活动强度下,不同GNSS系统（BD和GPS）接收机的定位性能。结果表明：电离层闪烁较弱时（S4〈0．3）,两种接收机均可以实现基本的定位功能;电离层闪烁较强（S4〉0.7）,且持续时间较长时,不同GNSS接收机将出现定位结果的抖动、跳变或失去定位能力;GNSS接收机应对电离层闪烁影响的能力与接收机设计相关。研究结果可作为抗闪烁接收机开发或闪烁影响分级的参考。     

电离层氧离子83.4 nm辐射计算方法

氧离子83.4 nm辐射是由氧离子辐射跃迁产生的,是电离层极紫外日辉辐射中辐射强度较高的信号之一.从空间对其进行成像为高层大气状态的监测提供了一种强有力的方法.为了准确的描述辐射强度的分布情况,本文在MSISE-00大气模型下,用AURIC计算氧离子83.4 nm辐射的初始体辐射率、电离层氮气分子、氧气分子以及氧原子的密度分布,接着,用Chapman函数生成氧离子密度分布,计算共振散射作用下的体辐射率.然后,给出在不同的初始辐射率情况下,沿天底方向观测的辐射强度对比.最后,与Anderson的计算结果作了两组对比,指出由电子碰撞产生的初始体辐射率占比提高16%,总的辐射强度会提高30%.本文的工作为低热层大气氧离子密度和光电子通量的探测提供支持,这对电离层电子密度反演具有理论意义.