Response of low latitude D-region ionosphere to the total solar eclipse of 22 July 2009 deduced from ELF/VLF analysis

Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (Geog. lat., 25.27° N; Geog. long., 82.98° E; Geomag. lat. = 14° 55’ N) was investigated using ELF/VLF radio signal. Tweeks, a naturally occurring VLF signal and radio signals from various VLF navigational transmitters are first time used simultaneously to study the effect of total solar eclipse (TSE). Tweeks occurrence is a nighttime phenomena but the obscuration of solar disc during TSE in early morning leads to tweek occurrence. The changes in D-region ionospheric VLF reflection heights (h) and electron density (n_e: 22.6–24.6 cm⁻³) during eclipse have been estimated from tweek analysis. The reflection height increased from ∼89 km from the first occurrence of tweek to about ∼93 km at the totality and then decreased to ∼88 km at the end of the eclipse, suggesting significant increase in tweek reflection height of about 5.5 km during the eclipse. The reflection heights at the time of totality during TSE are found to be less by 2–3 km as compared to the usual nighttime tweek reflection heights. This is due to partial nighttime condition created by TSE. A significant increase of 3 dB in the strength of the amplitude of VLF signal of 22.2 kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day. The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days.     

Ionospheric total electron content response to annular solar eclipse on June 21, 2020

The effects of physical events on the ionosphere structure is an important field of study, especially for navigation and radio communication. The paper presents the spatio-temporal ionospheric TEC response to the recent annular solar eclipse on June 21, 2020, which spans across two continents, Africa and Asia, and 14 countries. This eclipse took place on the same day as the June Solstice. The Global Navigation Satellite System (GNSS) based TEC data of the Global Ionosphere Maps (GIMs), 9 International GNSS Service (IGS) stations and FORMOSAT-7/COSMIC-2 (F7/C2) were utilized to analyze TEC response during the eclipse. The phases of the TEC time series were determined by taking the difference of the observed TEC values on eclipse day from the previous 5-day median TEC values. The results showed clear depletions in the TEC time series on June 21. These decreases were between 1 and 9 TECU (15–60%) depending on the location of IGS stations. The depletions are relatively higher at the stations close to the path of annular eclipse than those farther away. Furthermore, a reduction of about ?10 TECU in the form of an equatorial plasma bubble (EPB) was observed in GIMs at ~20° away from the equator towards northpole, between 08:00–11:00 UT where its maximum phase is located in southeast Japan. Additionally, an overall depletion of ~10% was observed in F7/C2 derived TEC at an altitude of 240 km (hmF2) in all regions affected by the solar eclipse, whereas, significant TEC fluctuations between the altitudes of 100 km ? 140 km were analyzed using the Savitzky-Golay smoothing filter. To prove TEC depletions are not caused by space weather, the variation of the sunspot number (SSN), solar wind (V_SW), disturbance storm-time (Dst), and Kp indices were investigated from 16th to 22nd June. The quiet space weather before and during the solar eclipse proved that the observed depletions in the TEC time series and profiles were caused by the annular solar eclipse.     

Changes in surface UV solar irradiance and ozone over the balkans during the eclipse of August 11, 1999

Intensive measurements of UV solar irradiance, total ozone and surface ozone were carried out during the solar eclipse of 11 August 1999 at Thessaloniki, Greece and Stara Zagora, Bulgaria, located very close to the footprint of the moon's shadow during the solar eclipse with the maximum coverage of the solar disk reaching about 90% and 96% respectively. It is shown that during the eclipse the diffuse component is reduced less compared to the decline of the direct solar irradiance at the shorter wavelengths. A 20-minute oscillation of erythemal UV-B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20-minute fluctuation in total ozone presumably caused by the eclipse induced gravity waves. The surface ozone measurements at Thessaloniki display a decrease of around 10–15 ppbv during the solar eclipse. Similarly, ozone profile measurements with a lidar system indicate a decrease of ozone up to 2 km during the solar eclipse. The eclipse offered the opportunity to test our understanding of tropospheric ozone chemistry. The use of a chemical box model suggested that photochemistry can account for a significant portion of the observed surface ozone decrease.     

Study of atmospheric air pollutants during the partial solar eclipse on 15 January 2010 over Udaipur: A semi-arid location in Western India

The paper describes behavior of surface ozone, its precursor gases, BC along with TOCC, TWVC, AOT1020 nm as well as UV and IR radiation intensities observed during the partial solar eclipse of 15th January, 2010 over Udaipur, where 52% solar disc is obscured due to the moon’s shadow. During the beginning to main eclipse phase, the deviation values of several air pollutants concentrations from eclipse to control day values vary in a small range from −9 to −2 ppb in case of surface ozone and −180 to −80 ppb for CO. The corresponding change in the values of BC observed from −3.3 to −.5 μg/m³. No significant change is found in NO₂, NO or in ratio of NO₂/NO values during the partial eclipse time. TOCC values decrease from 3 to 5 DU along with a reduction in UV radiation intensity from 20 to 35% from starting to the main eclipse phase. The AOT1020 nm values are found to increase from .2 to 1.0 along with a reduction in IR radiation intensity order of 50%. However, TWVC values decrease from .22 to .1 cm during the eclipse hours. The low level of dilution in surface ozone in eclipse period may be attributed with change in local atmospheric boundary layer dynamic conditions or limited air pollutants dispersion, in term of decreases in planetary boundary layer height, wind speed and hence ventilation coefficient in the same eclipse hours. Thus, present studies support the argument for the leading roles of photochemical reactions with its precursor gases under presence of solar radiation in surface ozone variability. Other possible controlling factors are advection of air pollutants from the polluted region as evident from backward wind trajectories and altering the local meteorological conditions.     

日全食期间中间层大气臭氧光化过程试验

利用包括活O_x、HO_x、和NO_x等成份在内的一维时变光化模式,研究了日全食时上中层大气臭氧和O₂(1△g)的变化特性,并通过与观测资料的比较进行了光化模式的试验.结果表明,日全食时太阳辐照变化对1.27μm气晖影响的高度比曙暮期间明显偏低,利用1.27μm气晖光度计测量大气臭氧的高度范围约为52-67km.1997年3月9日漠河日全食时测量的大气臭氧含量变化幅度为50％.这与考虑O_x、HO_x、和NO_x等成份的光化模式理论模拟结果基本一致.它表明在52-67km高度范围不存在臭氧亏损现象.      

2009年7月22日日全食期间电离层参量的变化

利用多个电离层垂测站的数据和IGS-TEC数据资料, 结合日地空间环境指数, 分析了2009年7月22日日全食期间中国地区电离层参量(反射回波最低频率fmin及f0F2和TEC)的变化特征. 结果表明, 日食发生后fmin迅速降低, 日食结束后fmin迅速恢复到正常水平; 在食甚时刻附近, f0F2和TEC出现明显的降低, 显示了明显的光食效应. 日食结束后5~6 h, f0F2和TEC出现不同程度的正扰动, 在驼峰区更明显; 日食结束后9~10 h, f0F2和TEC出现较显著的负扰动. 由于此次日食发生时伴随着中等强度的磁暴和低纬电场穿透等空间天气事件, 给此次日食电离层效应的深入分析带来很大困难.      

Statistical analysis of geomagnetic field variations during solar eclipses

We investigate the geomagnetic field variations recorded by INTERMAGNET geomagnetic observatories, which are observed while the Moon’s umbra or penumbra passed over them during a solar eclipse event. Though it is generally considered that the geomagnetic field can be modulated during solar eclipses, the effect of the solar eclipse on the observed geomagnetic field has proved subtle to be detected. Instead of exploring the geomagnetic field as a case study, we analyze 207 geomagnetic manifestations acquired by 100 geomagnetic observatories during 39 solar eclipses occurring from 1991 to 2016. As a result of examining a pattern of the geomagnetic field variation on average, we confirm that the effect can be seen over an interval of 180?min centered at the time of maximum eclipse on a site of a geomagnetic observatory. That is, demonstrate an increase in the Y component of the geomagnetic field and decreases in the X component and the total strength of the geomagnetic field. We also find that the effect can be overwhelmed, depending more sensitively on the level of daily geomagnetic events than on the level of solar activity and/or the phase of solar cycle. We have demonstrated it by dividing the whole data set into subsets based on parameters of the geomagnetic field, solar activity, and solar eclipses. It is suggested, therefore, that an evidence of the solar eclipse effect can be revealed even at the solar maximum, as long as the day of the solar eclipse is magnetically quiet.     

2009年7月22日日全食期间电离层总电子含量变化研究

利用中国区域内五个GPS台站(一个台站处于日全食区域、四个台站处于日偏食区域)观测数据, 研究2009年7月22日日全食期间电离层总电子含量(TEC)的变化, 结果表明, 日全食期间, 电离层TEC值经历了下降和恢复的过程, 最小TEC相对于最大食偏的时间延迟约为1～10min; 台站测得最小TEC的星下点(IPP)越靠近日全食带TEC下降量越大, 在日食期间武汉站(114.35°E, 30.53°N) TEC相对于各参考日期的TEC, 其平均下降量最大, 达到4.58TECU.      

Response of the mid-latitude D-region ionosphere to the total solar eclipse of 22 July 2009 studied using VLF signals in South Korean peninsula

In this paper, we analyze VLF signals received at Busan to study the the D-region changes linked with the solar eclipse event of 22 July 2009 for very short (∼390 km) transmitter–receiver great circle path (TRGCP) during local noon time 00:36–03:13 UT (09:36–12:13 KST). The eclipse crossed south of Busan with a maximum obscuration of ∼84%. Observations clearly show a reduction of ∼6.2 dB in the VLF signal strength at the time of maximum solar obscuration (84% at 01:53 UT) as compared to those observed on the control days. Estimated values of change in Wait ionospheric parameters: reflection height (h′) in km and inverse scale height parameter (β) in km⁻¹ from Long Wave Propagation Capability (LWPC) model during the maximum eclipse phase as compared to unperturbed ionosphere are 7 km and 0.055 km⁻¹, respectively. Moreover, the D-region electron density estimated from model computation shows 95% depletion in electron density at the height of ∼71 km. The reflection height is found to increase by ∼7 km in the D-region during the eclipse as compared to those on the control days, implying a depletion in the Lyman-α flux by a factor of ∼7. The present observations are discussed in the light of current understanding on the solar eclipse induced D-region dynamics.     

The solar eclipse and its associated ionospheric TEC variations over Indian stations on January 15, 2010

An annular solar eclipse occurred over the Indian subcontinent during the afternoon hours of January 15, 2010. This event was unique in the sense that solar activity was minimum and the eclipse period coincides with the peak ionization time at the Indian equatorial and low latitudes. The number of GPS receivers situated along the path of solar eclipse were used to investigate the response of total electron content (TEC) under the influence of this solar eclipse. These GPS receivers are part of the Indian Satellite Based Augmentation System (SBAS) named as ‘GAGAN’ (GPS Aided Geo Augmented Navigation) program. The eight GPS stations located over the wide range of longitudes allows us to differentiate between the various factors induced due to solar eclipse over the equatorial and low latitude ionosphere. The effect of the eclipse was detected in diurnal variations of TEC at all the stations along the eclipse path. The solar eclipse has altered the ionospheric behavior along its path by inducing atmospheric gravity waves, localized counter-electrojet and attenuation of solar radiation intensity. These three factors primarily control the production, loss and transport of plasma over the equatorial and low latitudes. The localized counter-electrojet had inhibited the equatorial ionization anomaly (EIA) in the longitude belt of 72°E–85°E. Thus, there was a negative deviation of the order of 20–40% at the equatorial anomaly stations lying in this ‘inhibited EIA region’. The negative deviation of only 10–20% is observed for the stations lying outside the ‘inhibited EIA region’. The pre-eclipse effect in the form of early morning enhancement of TEC associated with atmospheric gravity waves was also observed during this solar eclipse. More clear and distinctive spatial and temporal variations of TEC were detected along the individual satellite passes. It is also observed that TEC starts responding to the eclipse after 30 min from start of eclipse and the delay of the maximum TEC deviation from normal trend with respect to the maximum phase of the eclipse was close to one hour in the solar eclipse path.     

1981年7月31日漠河地区日食的外电离层效应

本文利用漠河(磁径190°17′E, 磁纬42°18′N)地区接收的哨声和同时观测的电离层资料, 采用南北半球电子浓度不一定对称的假设, 以电离层垂测资料和哨声联合换算的模式法, 得到了1981年7月31日哨声色散常数的日食效应;并粗略地测定了日食期间, 漠河上空沿磁力线分布的电子浓度剖面, 磁通量管电子含量和等效标高的部分结果;此外, 还初步讨论了日食的外电离层效应.      

Ionospheric responses to the 21 August 2017 great American solar eclipse – A multi-instrument study

Herein, we report on the ionospheric responses to a total solar eclipse that occurred on 21 August 2017 over the US region. Ground-based GPS total electron content (TEC) data along with ground-based measurements (Millstone Hill Observatory (MHO) and digital ionosondes) and space-based measurements (COSMIC radio occultation (RO) technique) allowed us to identify eclipse-associated ionospheric responses. TEC data at ~20°, ~30°, and ~40°N latitudes from the west to east longitudes show not only considerable depression but also wave-like characteristics in TEC both in the path of totality and away from it, exclusively on the day of eclipse. Interestingly, the observed depressions are associated with lesser (higher) magnitudes at stations over which the solar obscuration percentage was meager (significant), a clear indication of bow-wave-like features. The MHO observes a 30% reduction in F₂-layer electron densities between 180 and 220 km on eclipse day. Ionosonde-scaled parameters over Boulder (40.4°N, 100°E) and Austin (30.4°N, 94.4°E) show a significant decrease in critical frequencies while an altitude elevation is seen in the virtual heights of the F-layer only during the eclipse day and that decreases are associated with wave-like signatures, which could be attributed to eclipse-generated waves. The estimated vertical electron density profile from the COSMIC RO-based technique shows a maximum depletion of 40%. Relatively intense and moderate depths of TEC depression, considerable reductions in the F₂-layer electron densities measured by the MHO and COSMIC RO-measured densities at the F₂-layer peak, and elevations in virtual heights and reduction in the critical frequencies measured by ionosondes during the eclipse day could be due to the eclipse-induced dynamical effects such as gravity waves (GWs) and their associated electro-dynamical effects (modification of ionospheric electric fields due to GWs).     

日食对低纬地区f0F2和ICF的影响

研究了１９９５年１０月２４日日食过程中,我国低纬地区广州和海口的Ｆ２层临界频率ｆ０Ｆ２的高干扰重心频率ＩＣＦ变化过程,鉴于多次日 处低纬的两地ｆ０Ｆ２的日食变化形态不完全一样,以及多次日食期间同一地方ｆ０Ｆ２变化形态不完全一样,ＩＣＦ也并不像预想的那样降低,因而对于低纬电离层,动力学过程可能要比直接与太阳辐射有关的光化学过程起更为重要的作用。     

The response of sporadic E-layer to the total solar eclipse of July 22, 2009 over the equatorial ionization anomaly region of the Indian zone

The digital ionosonde located in Bhopal (23.2°N, 77.2°E), India has been used to investigate the responses of the Es layer in the equatorial ionization anomaly (EIA) crest to the total solar eclipse (TSE) of July 22, 2009. Results show the presence of intense Es layer during and after the eclipse period. The gravity waves induced by the solar eclipse propagated upward in the Es layer and produced the periodic disturbance. The results of the wavelet analysis display the presence of dominant oscillation of about 24–32, 16–20 and 8 min. The appearance of intense sporadic-E concomitantly with the signatures of gravity wave suggests that the wind shear introduced by the solar eclipse induced gravity wave might be the plausible mechanism behind the intensification of Es-layer ionization.     

A study on TEC reduction during the tail phase of the 21st June 2020 annular solar eclipse

Ionospheric response during the annular solar eclipse of June 21, 2020, has been examined in terms of the Total Electron Content (TEC) obtained from six Global Positioning System (GPS) receivers positioned in the Chinese-Taiwanese region. We have shown TEC variation from satellites designated by PRNs (Pseudo-Random Noise code) 2, 6, and 19. PRN wise TEC trend was observed to depend upon satellite-pass trajectory to the receiver's location during the eclipse period. A time lag of ~15–30 min is also observed in maximum TEC decrement after the phase of maximum eclipse. Instead of the percentage of eclipse magnitude, a reduction in TEC is seen more for the station for which the orbital track of respective satellites was in closer view relative to receivers for more hours of eclipse window. Additionally, the eclipse day diurnal variations are compared with the pre-eclipse day TEC trend, and observed results show a clear decrease in TEC values at all chosen stations after the eclipse onset then reached the lowest value a few minutes afterward the maximum eclipse phase.     

利用COSMIC掩星数据监测电离层的异常变化

分析了COSMIC掩星数据反演电子密度的方法,利用实例研究反演方法的特点,并采用ISR非相干散射雷达获取的电子密度数据进行验证,进而反演了长三角区域SHAO（IGS）站上空在日全食和太阳风暴期间的电子密度廓线图. 通过与平静日期间电离层电子密度进行比较,发现日全食及太阳风暴导致电离层发生的异常变化,从而提出COSMIC掩星数据反演电子密度在监测电离层变化时所具有的优势.      

Feasibility analysis of solar thermal propulsion system with thermal energy storage

Possessing relatively high specific impulse and moderate thrust levels, solar thermal propulsion (STP) is a promising candidate in spacecraft propulsion system. However, the traditional solar thermal propulsion system suffers from thrust failure in the shadow area, which seriously affects its applicability. In this paper, we investigate feasibility of regenerative solar thermal propulsion system (RSTP) incorporating thermal energy storage, which can effectively overcome unmatched synchronous working time and illumination time. A numerical model for RSTP considering the whole energy transfer process from light concentrating, heat storage, to thrust generation is built, which is verified by experiment measurements with relative errors less than 15 %. The result shows that the maximum time to complete heat storage is about 4000 s, which is within the illumination time for low Earth orbit. In the solar eclipse region, the thrust (F_t) and the specific impulse (I_sp) of the system increase with the propellant flow rate, which can reach about 2 N and 690 s, respectively. What’s more, the system can operate for around 100 s continuously at the maximum thrust in the shadow area. This work provides alternative approaches for microsatellite propulsion with high specific impulse, high thrust, and continuous operation despite presence of solar eclipse.     

Amateur observations of solar eclipses and derivation of scientific data

This work presents the educational approach of using total solar eclipse occurrences as a scientific process learning aid. The work reviews the basic scientific aims and experiments included in the observational programs “Total solar eclipse 1999 and 2006” (Stoev, A., Kiskinova, N., Muglova, P. et al. Complex observational programme of the Yuri Gagarin Public Astronomical Observatory and STIL, BAS, Stara Zagora Department for the August 11, 1999 total solar eclipse, in: Total Solar Eclipse 1999 – Observational Programmes and Coordination, Proceedings, Recol, Haskovo, pp. 133–137, 1999a (in Bulgarian); Stoeva, P.V., Stoev, A.D., Kostadinov, I.N. et al. Solar Corona and Atmospheric Effects during the March 29, 2006 Total Solar Eclipse, in: 11th International Science Conference SOLAR–Terrestrial Influences, Sofia, November 24–25, pp. 69–72, 2005).     

2009年6至7月华南地区电离层TEC扰动研究

电离层TEC（Total Electron Content）扰动与多种扰动源相关联．2009年6至7月期间存在地震和日全食的扰动源．利用广州地区GPS监测网在2009年6至7月连续监测到的TEC数据,通过采用前15天数据的滑动窗口对数据进行处理,从时间序列和空间分布两方面分析了华南地区电离层TEC扰动特征．结果显示,2009年6至7月华南地区电离层TEC扰动和该时期发生的地震以及日全食事件可能有关联;2009年7月多个地震发生引起的电离层扰动特征为,震前出现的是正异常,发震当天或震后有可能是正异常,也有可能是负异常;7月22日日全食当天TEC扰动为正异常,推测该正异常是地磁活动、地震活动及日全食综合效应的结果．