The ionosphere over Genova during the solar eclipse of February 15, 1961

Summary The behaviour of the ionosphere over Genova during the solar eclipse of February 15, 1961 is investigated. For theE-layer the effect was very marked, but the value obtained for the recombination coefficient is above normal. The effect of the eclipse was also observed on theF2 layer; however, the behaviour here appears affected by the simultaneous occurrence of an ionospheric perturbation. Finally, the maximum reduction of the ionospheric absorption on 2 and 3 Mc/s during the eclipse was found to be of the order of about 12 db.This report belongs to a set of investigations on geophysical effects of the solar eclipse of February 15th, 1961 carried out by the «Istituto Geofisico, Università di Genova», and made possible through a financial support of the «Consiglio Nazionale delle Ricerche».     

Scattering of radio waves from the ionosphere in presence of time varying random irregularities

Summary In this paper the modified formula for scattering cross-section of radio waves from the ionosphere has been deduced in presence of time-varying random irregularities. The anisotropic behaviour of the medium which arises due to the presence of the geomagnetic field along with the time-varying irregularities of the medium has been considered. The derived expression for the dielectric tensor for the above medium has been utilised to obtain the required cross-section. The latitude, altitude, azimuth and polarisation angle dependence of scattering of radio waves from the ionosphere has been shown. The evaluated formula may be verified experimentally and the importance of the geomagnetic field and irregularities may then be analysed.     

Testing IR flux during solar eclipse

A Ridgeley, G Grayer, D Mehmet and B Sheen report on a further experiment on IR flux during the solar eclipse in Lusaka, 2001.     

Observations of the ionosphere in the equatorial anomaly region using WISS during the total solar eclipse of 22 July 2009

An exceptionally long total solar eclipse occurred over the Yangtze River Basin in the mid-latitudes of China on 22 July 2009. The moon’s umbral shadow crossed through the ionospheric equatorial anomaly region. During the solar eclipse, new ionospheric behaviors were observed using a multi-station sounding approach. These new phenomena include: (1) visible Doppler spreading of F layer echoes at multiple group distances during the solar eclipse period, (2) strong ionospheric response near the peak of the northern equatorial anomaly crest and (3) synchronous oscillations in the E_s and F layer during the recovery phase of the solar eclipse.     

Wave response of the ionosphere to the partial solar eclipse of August 1, 2008

Quasi-periodic variations in the Doppler shift of the HF range frequency at a vertical path and critical frequency of the F ₂ layer caused by wave disturbances in the ionosphere on the day of the partial (the magnitude was about 0.42) solar eclipse and on background days are analyzed. For the spectral analysis, the window Fourier transform, adaptive Fourier transform, and wavelet analysis were jointly used. It is shown that on the day of the eclipse and the background day, spectral characteristics of wave disturbances within the 150–200 km height range differed substantially. The changes in the spectral composition began approximately 30–35 min after the solar eclipse beginning and lasted more than 1.5 h.     

A search for atmospheric pressure waves from the total solar eclipse of 9 March 1997

Solar eclipses are well defined forcing functions for atmospheric disturbances, including pressure disturbances, and are therefore important in studies of pressure waves in the Earth’s atmosphere. For the total solar eclipse of 9 March 1997 three microbarometers were deployed at ground level over the South East of the UK. They delivered excellent pressure records from several hours before the Moon’s penumbral shadow first made Earthfall, to about 60 h after the penumbral shadow left the Earth. The pressure records are richly structured, and consequently stringent criteria are defined for the detection of eclipse effects. Though no pressure waves of eclipse origin have been identified, useful upper limits to wave amplitudes are established.     

Variations in the amplitude and phase of VLF radiowaves in the ionosphere during the August 1, 2008, solar eclipse

Time variations in the amplitude and phase of signals of the Russian telecommunication station (the frequency is 25 kHz) on the Arkhangelsk—Kharkov path with a length of about 1600 km on the day of the August 1, 2008 solar eclipse (SE) and on the adjacent days are analyzed. Two types of effects are detected. An increase of the signal amplitude by approximately 32% in comparison with the background days and the 2.1 μs time shift of the signal during 2—2.5 h is referred to the first type. Changes in the spectral composition of the quasiperiodic disturbances in the ionosphere presented the second type of the effects. For spectral analysis of the quasiperiodic variations in the amplitude and phase of the radio signal, the window Fourier transform, adaptive Fourier transform, and wavelet transformation were applied simultaneously. In the period of SE and after it, oscillations with periods of 10—15 min (according to the amplitude data) and also about 10 and 18 min (according to the phase data) were intensified. Based on radio signal characteristics, the parameters of ionospheric disturbances are estimated.     

Disturbances in the ionosphere and atmosphere caused by the solar eclipse of August 11, 1999

Results of comparing ionospheric radio noise at wavelength of 2 m at midlatitudes to the data of the ionospheric vertical sounding during the partial phase of the solar eclipse of August 11, 1999, are presented. Disturbances in the ionospheric layers, radio noise of the ionospheric plasma, and variations and fluctuations in the atmospheric pressure at the Earth surface during the eclipse are considered. The parameters of the Lamb wave, which propagated with velocity of 300 m/s from the region of the total phase of the eclipse are determined. The Lamb wave characteristics in the summer midlatitude and auroral ionosphere have been compared.     

Effects of the solar eclipse of March 29, 2006, in the ionosphere and atmosphere

The observations of the effects of the partial (about 77%) solar eclipse (SE) of March 29, 2006, in the ionospheric plasma are presented. The experimental data were obtained using the Kharkov incoherent scatter radar. At the moment of the maximum phase of SE, a decrease in the critical frequency of the ionospheric F ₂ layer by 18%, a depletion of the density in the F ₂ layer maximum by 33%, and an increase in the maximum height z _m by 30 km were observed. The solar eclipse caused a decrease in the electron and ion temperatures by 150–300 and 100–200 K, respectively, within the height range 210–490 km. An increase in the relative density of the hydrogen ions during the maximum phase of SE by 20–25% within the height range 900–1200 km is detected. Calculations of the parameters of dynamical processes and thermal regime of the ionospheric plasma during SE are performed.     

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.     

The basic characteristics of the scintillation of radio waves after passing through the ionosphere

Резюме Анализируются величины, пригодные для характеристики сцинтилляций плоской волны после прохождения через ионосферу, которые одновременно позволяют провести сравнение сцинтилляций с геофизическими параметрами ионосферы и геометрией распространения волн. Предположим, что источником сцинтилляций являются изотропные области повыпенной электронной концентрации в тонком слое, где происходит слабое рассеяние. Для распределения амплитуды сцинтилляций предлагаетсят-распределение Накагами, показательт которого одновременно пригоден в качестве основного параметра сцинтилляции из корреляционной теории сцинтилляций были выведены выражения для рассеяния амплитуды и фазы и взаимные корреляции амплитуды или фазы на различных частотах. Для расчетов таких рассеяний было выбрано две модели функции корреляции флуктуаций показателя преломления (Гаусса и Бесселя), а для вывода были использованы спектральные функции по методу Татарского. В заключение для упомянутых моделей были выведены выражения для среднего числа превышений данного уровня и среднего числа максимумов амплитуды сцинтилляций; такие средние числа могут с успехом служить в качестве приближенных характеристик сцинтилляций. Полученные результаты сравниваются с опубликованными результатами измерений и указывается на некоторые недостатки в теоретических моделях сцинтилляции, применяем. в качестве основния для интерпретации результатов измерений.

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Address: Boční II, Praha 4-Spořilov.     

Wave disturbances in the ionosphere during a lasting solar activity minimum

Using the Kharkov incoherent scatter radar, observations of wave disturbances in electron concentration N in the ionosphere at heights of 120–600 km are conducted. The measurements were carried out in the periods of the spring and fall equinoxes and winter and summer solstices. The height-time dependences of the absolute ΔN and relative ΔN/N amplitudes of wave disturbances, as well as their spectral composition, were analyzed. It is shown that wave disturbances in the ionosphere with periods of 10–180 min were present at almost any time of the day and in all seasons. Their absolute and relative amplitudes varied from 6 × 10⁹ to 6 × 10¹⁰ m⁻³ and from 0.01 to 0.5, respectively. The maximum values of ΔN and ΔN/N were observed at a height of ∼200 km. The passage of the solar terminator changed substantially the wave disturbance parameters.     

Numerical modelling of spectral sky radiance during a total solar eclipse

Ground-based observations of the spectral sky radiance within the totality region during a total solar eclipse are of significant interest because the contribution from direct and single scattered light from the solar disk is eliminated. In the present paper, we develop a numerical model of the spectral sky radiance during totality, evaluate the contribution of double scattered sunlight to the sky radiance at totality and compare it to solar corona emissions. The results show that the single scattered coronal light is the major contaminant in ground-based observations of the corona, opposite to what was believed before. For observation directions outside the corona the double scattered sun radiation dominates over the single scattered coronal light.     

Observational effort to record Fresnel patterns during a total solar eclipse

Summary The observation of Fresnel diffraction patterns at 2nd and 3rd contact and efforts to correlate the time elements of a total solar eclipse at low elevation are discussed. The measurements were intended to determine atmospheric refraction at three optical wavelengths. A laboratory model of the system sun-moon-earth was employed for testing the recording instruments at the fast response times that are necessary for such observations.

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Zusammenfassung Diskutiert werden die Vorbereitungen zur Beobachtung von Fresnelschen Beugungsstreifen im Mondschatten, wenn 2. und 3. Kontakt einer Sonnenfisternis in die Sonnenaufgangszone fallen (streifender Lichteinfalt). Bei Kenntnis des Mondrandes kann man die Auswertung der Beugungsfiguren mit den Konjunktionszeiten korrelieren. Vergleiche mit den errechneten Ephemeriden ermöglichen eine Bestimmung der atmosphärischen Refraktion. Ein Modell diente zur Prüfung der Beobachtungsapparaturen.

     

On the transformation of planetary waves of tropospheric origin into waves in radio wave absorption in the lower ionosphere

Summary Calculations are carried out of upward propagation of a tropospherically forced 10-day planetary wave into the upper middle atmosphere with the use of the COMMA-R model of the University of Cologne, of its transformation into a wave in electron density by means of the model of the Comenius University, and of its final transformation into a wave in radio wave absorption in the lower ionosphere applying the computer code of the Geophysical Institute. The calculations show that the absorption may be used for investigating the planetary wave activity, particularly of its long-term trends. The possibility of propagation of planetary waves from the winter hemisphere to the summer hemisphere is illustrated, which could contribute to explanation of the occurrence of travelling planetary waves in the mesosphere in summer.Dedicated to the Memory of Professor Karel P     

基于GPS技术实时监测2009年7月22日日全食期间长三角区域电离层TEC变化

2009年7月22日上午发生的日全食是21世纪持续时间最长的日全食,其全食带覆盖了中国中部的长江流域,为研究日全食对电离层的影响提供了一次难得的机会.为此本文通过卡尔曼滤波算法实现了实时求解TEC和GPS系统硬件延迟,为实时监测日全食期间电离层变化提供了绝对的电离层TEC.采用上海和浙江区域内GPS网的观测数据,建立了实时区域电离层延迟模型,进而计算出了实时的VTEC和TEC变化率.同时考虑太阳和地磁活动参数,综合上述方法详细分析和讨论了长三角区域在此次日全食期间的TEC变化的电离层异常现象.     

Physical processes in the middle ionosphere accompanying the solar eclipse of January 4, 2011, in Kharkov

Aperiodic and quasi-periodic variations in the critical frequency of the F2 layer and Doppler frequency shift of radiowaves at vertical paths on the day of a partial (the magnitude was ～0.78) solar eclipse and on background days are analyzed. According to the experiment, the relative decrease in the electron concentration was 0.41 (0.46 according to calculations) and 0.50 (0.53 according to calculations) in the E region and in the lower part of the F region of the ionosphere. At a height of the main maximum of the electron concentration, the relative decrease in the electron concentration was 0.52 (0.51 according to calculations). It is shown that on the day of the eclipse and on the background day, the characteristics of wave disturbances within the height range 160–240 km were substantially different. Changes in the spectral composition began 30 min after the eclipse occurrence and, depending on the period, lasted from 2 to 4 h. The calculation results of the main parameters of the medium and signal correspond to the observational results.     

Shadow bands during the total solar eclipse of 26 February 1998

We have recorded shadow bands just before and just after the total phase of the solar eclipse of 26 February 1998, using four silicon photodiodes on the corners of a square 105 mm side. At two earlier eclipses, 11 July 1991, 3 November 1994, recordings were made using two silicon photodiodes separated by 100 mm. The analyses of these earlier eclipses have already been published in detail, and therefore here we concentrate on the analysis of the recordings made on 26 February 1998. Samples of the time series are presented, along with cross-correlation functions and power spectra. The power spectra are broadly in accord with the shadow band theory of Codona (Codona, C., 1986. The scintillation theory of eclipse shadow bands. Astron. Astrophys. 164, 415–427). This is also the case for the two earlier eclipses, but there are instructive differences between the three occasions.     

The solar corona during the eclipse of August 1, 2008

A new telescope has been created to investigate the solar corona during eclipses. One lens simultaneously forms three corona images occurring as coronal radiation passes through three polarizers with transmission directions rotated 0°, 60°, and 120° relative to the selected direction; in addition, one image is formed without the polarizer. The telescope was used for solar corona observation during the eclipse of August 1, 2008. We obtained the distributions of polarization brightness, K corona brightness, degree of K corona polarization, and total degree of polarization as well as polarization directions depending on the latitude and radius in the sky plane. Radial distributions of the electron density depending on latitude were calculated. The coronal plasma temperature was determined for different corona structures under the assumption of hydrostatic equilibrium.     

电离层人工调制激发的VLF波在磁层的传播特性及应用研究

电离层人工调制可以激发甚低频（VLF）波,其中向上传播进入磁层的VLF波,不但能够用来研究磁层中的各种物理现象,且具有人工沉降高能粒子,消除辐射带等实际用途.本文使用射线追踪方法,模拟电离层调制激发的VLF波在磁层的传播路径,分析激发纬度和调制频率对传播路径和传播特性的影响;并基于低频波的色散方程和波粒共振条件,分析VLF波传播路径上与磁层高能粒子的最低共振能及其分布.研究表明,VLF波通过在磁层来回反射向更高的L-shell传播,最终稳定在某一L-shell附近.以较低的调制频率或者从较高的纬度激发的VLF波能够传播到更高的L-shell,但是,当激发纬度过高时,低频波也可能不发生磁层反射而直接进入电离层和大气层.低频波在磁层的传播过程中,在较高的纬度或者较低的L-shell能够与较高能量的电子发生共振相互作用,在较高的L-shell并且低纬地区,能够与较低能量的电子发生共振相互作用.共振谐数越高,能发生波粒共振的电子能量越高.