Geomagnetic Field Variations during the Total Solar Eclipse of 2 July 2019 in La Serena,Chile

Geomagnetism and Aeronomy - The total solar eclipse on July 2, 2019, has been studied by using data of the La Serena ground magnetic station in Chile located in the path of the totality (at...     

日本古代的一次可能的日全食与地球自转变化

利用古代日食观测记载研究地球自转长期变化的方法和已有的结果为基础，研究了日本的古书中记载的可能与古代一次日全食有关的“天门”传说，及朝鲜的古书中与此有关的记载。本文的结果支持一些学者认为这个传说是由发生于公元158年7月13日的日全食引起的观点，并在历书时ET系统下计算分析了该日食的参数，由此得到表示地球自转变化的△T值约为2．22小时。     

Geomagnetic Pc3 Pulsations During the Total Solar Eclipse on Aug 11, 1999

The solar eclipse on August 11, 1999, observed in the region covered by many geomagnetic observatories, has offered a unique opportunity to look for an effect of the eclipse on geomagnetic pulsations. The pulsation activity digital data have been taken from Budkov Observatory in the Czech Republic (in the X component only), from observatories in Germany (Niemegk, Fürstenfeldbruck, Bad Bergzabern), in Hungary (Nagycenk), and for comparison in South Africa (Hermanus, conjugate-point station), and in Finland (Sodankylä, far from the eclipse zone). At all these stations the field in all three component has been recorded. The pulsation amplitudes in the X component exhibit a long-term minimum near the time of the eclipse. Spectral analysis of selected short intervals confirmed this decrease and also revealed a decrease of the average pulsation period during the eclipse. Such a change in the amplitude or in the period was not observed outside of the eclipse interval or in other days. Investigation in some narrower frequency bands showed that the maximal decrease occurred in the 15–20 s band. All these changes can be found in records from all the stations near the eclipse totality belt, also in records at the conjugate-point station, where no eclipse occurred. No signature has been found in records at the station situated far from the eclipse zone.     

Features of the Ionospheric Total Electronic Content Response to the Annular Solar Eclipse of June 21, 2020

Geomagnetism and Aeronomy - The features of the annular solar eclipse of June 21, 2020, in variations of the ionospheric total electron content (TEC) were analyzed using GPS observations of the IGS...     

Lidar observation campaigns on diurnal variations of the sodium layer in Beijing and Wuhan,China

Based on observations from daytime lidars in eastern China,diurnal cycles of the sodium layer over Wuhan(30.5°N,114.6°E)and Beijing(40.5°N,116°E)are investigated.Diurnal variations of Na density,root mean square(RMS)layer width,and centroid height of the sodium layer are analyzed.Results reveal that the large diurnal cycles of the sodium layer are controlled mainly by 24-hr oscillations at the two observation sites.The diurnal variation of the sodium layer over Wuhan was modulated mainly by tidal perturbations during the lidar observation campaign.Conversely,the diurnal variation over Beijing was controlled principally by photoionization and photochemistry effects during another campaign,and there was little evidence of direct tidal perturbations.These comparisons suggest that the diurnal variation of the sodium layer perhaps has obvious regional characteristics across China.The variation can be either controlled mainly by tidal perturbations or by photoionization and photochemistry effects in different seasons.     

Total electron content of the ionosphere during thegeomagnetic storm on 10 January 1997

Measurements at GPS ground stations of the International GPS Service (IGS) havebeen used to derive the total electron content (TEC) of the ionosphere over Europe and overthree North American stations for the 6–11 January 1997 storm event. The derived TEC dataindicate large deviations from the average behaviour especially at high latitudes on thenight-side/early morning longitude sector.The high-latitude perturbation causes a well-pronounced positive phase on the day-sidesector over Europe.Both meridional winds as well as transient electric fields are assumed to contribute to thesignature of the ionospheric perturbation propagating from high to low latitudes. Theobservations indicate a subsequent enhanced plasma loss which is probably due to theequatorward expansion of storm induced composition changes.     

Solar flare effect on the geomagnetic field and ionosphere

This paper studies the ionospheric and geomagnetic response to an X6.2 solar flare recorded at 14:30 UT on December 13, 2001, in quiet geomagnetic conditions which allow the variations in the geomagnetic field and ionosphere measurements to be easily related to the solar flare radiation.By using measurements from the global positioning system (GPS) and geomagnetic observatories, the temporal evolution of ionospheric total electron content variation, vTEC_V, and geomagnetic field variations, δB, as well as their rates of variation, were obtained around the subsolar point at different solar zenith angles. The enhancement of both parameters was recorded one to three minutes later than the Geostationary Operational Environmental Satellite (GOES) programme recording; such delay tends to depend on the latitude, longitude, and solar zenith angle of the observatory's observations.The vTEC_V is related to the local time and the δB to the intensity and position of the ionospheric currents.The vTEC_V′s maximum value is always recorded later than the maximum values reached by δB and the X-ray intensity. The maximum δB is larger in the local morning than in the afternoon.The rates of vTEC_V and δB have two maximum values at the same time as the maximum values recorded by Hα (for each ribbon).This work shows the quantitative and qualitative relations between a solar flare and the ionospheric and geomagnetic variations that it produces.     

武汉超导重力仪观测最新结果和海潮模型研究

利用武汉台站GWR_C032超导重力仪观测资料,在对原始数据进行有效预处理的基础上作调和分析,获得反映地球内部介质特征的重力潮汐参数.基于卫星测高技术和有限元方法同时考虑验潮站数据作约束条件获得的多个全球海潮模型,利用负荷理论和数值褶积积分技术计算了重力负荷,对周日和半日频段内的重力潮汐参数实施负荷改正,提出了“负荷改正有效性”概念,研究了全球海潮模型适应性.数值结果说明,海潮改正的有效性高达91%（O1,NAO99）和92%（M2,ORI96）.基于11个海潮模型对主波（O1,K1,M2和S2）的负荷改正说明平均有效性为（86%,70%,73%和84%）,振幅因子与理论模型间的差异分别从（212%,155%,116%和080%）降到（031%,039%,034%和008%）,同时还说明利用NAO99和ORI96全球海潮模型能获得比其他模型更佳的负荷改正效果.文章还利用国际地球动力学计划网络其他7个台站的超导重力仪观测研究了全球海潮模型的适定性问题,结果说明不同模型中不同潮波具有明显的区域特点,早期构制的SCW80全球海潮模型仍可作为大地测量研究中的重要参考模型.     

Imaging of the Antarctic ionosphere: Experimental results

Ground-based dual-frequency GPS observations can be used to create images of electron density. This is well established for the Arctic ionosphere; here one of the first results is presented for the Antarctic. In this study, the GPS receivers in the Antarctic are supplemented with another GPS receiver onboard CHAMP. The aim of the study is to demonstrate the technique for investigating geophysical events, for example, an ionospheric disturbance period on 11 February 2004. The images have been validated by in-situ measurements from DMSP and CHAMP satellites, as well as Super Dual Auroral Radar Network (SuperDARN) convection patterns, which are able to confirm the location, presence, and transportation of large-scale plasma patches. This study indicates that although the convection still dominates in the high-latitude ionosphere, soft precipitation within the polar cap may play a role in the evolution of the polar patches. It also illustrates the potential for future multi-instrument studies of the Antarctic.     

A 22-year cycle in the F layer ionization of the ionosphere

The double-sunspot-cycle variation in terrestrial magnetic activity has been well known for about 30 years. In 1990 we examined and compared the low-solar-activity (LSA) part of two consecutive cycles and predicted from this database and from published results the existence of a double-sunspot-cycle variation in total electron content (TEC) of the ionosphere too. This is restricted to noontime when the semi-annual component is well developed. Since 1995 we have had enough data for the statistical processing for high-solar-activity (HSA) conditions of two successive solar cycles. The results confirm the LSA findings. The annual variation of TEC shows a change from an autumn maximum in cycle 21 to a spring maximum during the next solar cycle. Similar to the aa indices for geomagnetic activity the TEC data show a phase change in the 1-year component of the Fourier transform of the annual variation. Additionally we found the same behaviour in the F-layer peak electron density (N_max) over four solar cycles. This indicates that there exists a double-sunspot-cycle variation in the F-layer ionization over Europe too. It is very likely coupled with the 22-year cycle in geomagnetic activity.     

Solar eclipse of August 1, 2008, above Kharkov: 2. Observation results of wave disturbances in the ionosphere

Quasi-periodic variations in the power of incoherent scattered signals, caused by wave disturbances of the electron concentration in the ionosphere, are analyzed for the day of a partial solar eclipse and for a background day. The windowed and adaptive Fourier transforms and the wavelet transform are used for spectral analysis. The spectral parameters of the wave disturbances at altitudes of 100–500 km in the 10–120 min period range differed significantly on the day of the solar eclipse and on the background day. Variations in the spectrum began near the onset of the phase of maximum disk occultation and continued no less than 2 h. The amplitude of time variations N was 2 × 10⁹–4 × 10¹⁰ m^?3, and the relative amplitude was 0.10–0.15. Wave disturbances have been compared for five solar eclipses; the comparison shows a noticeable variation in the spectrum of the wave disturbances during these events.     

Disturbances in the topside ionosphere during solar flares

The results of studying the ionospheric response to solar flares, obtained from the data of the GPS signal observations and incoherent scatter radars and as a result of the model calculations, are presented. It is shown that, according to the GPS data, a flare can cause a decrease in the electron content at altitudes of the topside ionosphere (h > 300 km). Similar effects of formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, with the Arecibo incoherent scatter radar. The mechanism by which negative disturbances appear in the topside ionosphere during solar flares has been studied in this work based on the theoretical model of the ionosphere-plasmasphere coupling. It has been indicated that the formation of the electron density negative disturbance in the topside ionosphere is caused by an intense removal of O⁺ ions into the overlying plasmasphere under the action of an abrupt increase in the ion production rate and thermal expansion of the ionospheric plasma.     

武汉大学IGS电离层分析中心全球电离层产品精度评估与分析

2016年2月,武汉大学卫星导航定位技术研究中心（Wuhan University,WHU）正式成为新的国际GNSS服务组织（International GNSS Services,IGS）电离层联合分析中心（Ionosphere Associate Analysis Center,IAAC）.本文首次系统地评估和分析了武汉大学IGS电离层分析中心自2016年日常化运行以来（2016年1月到2018年9月,太阳活动低年）的全球电离层产品的精度,并与其他六家IAACs（CODE、JPL、ESA、UPC、EMR和CAS）进行了比较分析.结果表明：WHU的全球电离层产品能够长期稳定且有效地监测全球电离层总电子含量（Total Electron Content,TEC）的时空变化;和IGS综合全球电离层产品比较,WHU的模型均方根误差和CODE、JPL相差不大,均值约为1.4 TECU,产品一致性优于其他IAACs;和GPS实测电离层TEC比较,WHU的模型内符合精度和CODE基本相当,均值约为1.4 TECU,且与电离层活动水平和地理纬度存在显著的相关性;和Jason-2测高卫星VTEC比较,WHU的全球电离层产品的系统性偏差均值约为-0.7 TECU,在不同纬度约为-3.0到1.0 TECU,且与地理纬度存在近似抛物线函数的关系;WHU的模型外符合精度和CODE、JPL以及CAS基本一致,均值约为2.9 TECU,且在中高纬度地区优于低纬度地区,北半球优于南半球.

     

Penetration of electric field from the near ground atmospheric layer to the ionosphere

A mathematical model has been proposed for describing quasi-stationary atmospheric electric fields with approximate, but fairly accurate allowance for ionospheric conductivity. It is shown that some well-known models of electric field penetration from the Earth into the ionosphere have been deemed inadequate, though they work well in the atmosphere below 50 km. In these models, the arbitrarily specified boundary condition in the upper boundary of the atmosphere omits the existing good conductor or adds not existent conductor. The maximum possible field in our model is far less than in models where ionospheric conductivity is not taken into account, but vastly larger than in models based on the approximation with infinite Pedersen conductivity in the upper ionosphere.     

Dusty plasma in the midlatitude ionosphere during meteor showers

The emission (or modulation) line, which manifests itself during high-speed (the speed of entry into the atmosphere is about 70 km/s) meteor showers (Perseids, Orionids, Leonids), has been detected in the fluctuation spectra of ionospheric plasma radio noise at λ = 2 m. The line frequency varies from 12 to 60 Hz depending on activity of ionospheric ionization sources and local characteristics of a meteor shower, time of day, etc. The line has a width of 2–3 Hz and can have satellites. The dusty plasma characteristics have been estimated on the assumption that ionospheric noise is modulated or emitted due to dusty plasma oscillations.     

Observations and model calculations of an additional layer in the topside ionosphere above Fortaleza, Brazil

Calculations using the Sheffield University plasmasphere ionosphere model have shown that under certain conditions an additional layer can form in the low latitude topside ionosphere. This layer (the F3 layer) has subsequently been observed in ionograms recorded at Fortaleza in Brazil. It has not been observed in ionograms recorded at the neighbouring station São Luis. Model calculations have shown that the F3 layer is most likely to form in summer at Fortaleza due to a combination of the neutral wind and theE × B drift acting to raise the plasma. At the location of São Luis, almost on the geomagnetic equator, the neutral wind has a smaller vertical component so the F3 layer does not form.     

Long-term Changes in Total Solar Irradiance and Their Predictions

Geomagnetism and Aeronomy - The Total Solar Irradiance (TSI) index of solar activity attracts the attention of a wide scientific audience due to its direct influence on the Earth’s climate. A...