磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法

本文采用国际地磁参考场(1980IGRF,n=8)磁力线经验公式和三层模式电离层,结合哨声波沿磁力线传播所需电子浓度的横向梯度,给出了磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法;从而得出:(1)哨声色散值D不仅与电离层N_mF2正相关,而且与h_mF2也有明显相关性.当路径纬度ф₉₀≤10.5°(IGRF,n=8,下同)时,D与h_mF2负相关;>12时,正相关;在10.5°—12°之间时,正或负相关取决于路径顶点高度与h_m之差值.估算表明,三亚(磁纬7.04°N)收到的哨声中路径纬度ф₉₀≤10.5。的占94.5%,D与h_mF2负相关,这与观测结果一致.(2)所需抬升因子积分中值一般在7—31%之间.      

电离层离子丰度对哨声传播经度效应的影响

Iss-b卫星探测结果表明,|电离层离子丰度呈现经度变化.本文选取较真实的电离层模型参数,对130°E和114°E两个子午面内传播的低纬哨声进行了射线跟踪.我们发现,由于[O~+],[He~+]和[H~+]决定的电子浓度垂直梯度的经度变化,导致哨声传播特性的经度效应,使得130°E比114°E内传播的低纬哨声更好地满足透射条件:|μsinδ|≤1.与电子浓度的水平梯度的影响比较,离子丰度决定的电子浓度垂直梯度随经度的变化使哨声传播产生的经度效应明显得多.武昌(地理30.5°N,114.6°E;地磁19.3°N).和鹿儿岛(31.5°N,130.8°E;20.5°N)两台站观测到的哨声出现率的经度效应证实了本文的理论预言.     

1995年10月24日日食电离层效应的模式化研究

利用一个二维纬电离层理论模式模拟１９９５年１０月２４日日全食条件下东亚低纬电离层演变,探索低纬日食电离层效应。模式计算结果显示：日食散间日食区电离层电子与离子光致电离产生率减少使得Ｅ－Ｆ１区电离层光食效应显著,而较高部份电离层对日食影响的响应延迟。     

负相电离层骚扰及其日地相关关系

本文对1965—1982年, 我国境内的满州里(49°35′N, 117°27′E), 北京(40°00′N, 116°18′E), 重庆(29°30′N, 106°25′E), 广州(23°09′N, 113°21′E)和海口(20°00′N, 110°20′E)等五个电离层观测站的负相电离层骚扰形态, 用世界资料中心A出版的太阳地球物理资料中的太阳耀斑、射电、地磁和北京地磁台的地磁观测报告等资料与电离层骚扰的相关关系进行了分析研究.所得到的电离层骚扰形态变化规律和日地相关规律的结果对预报电离层骚扰是有益的.      

武昌哨声的传播特征及其与地磁活动的相关

本文利用武昌(磁纬19.2°N)连续三年的哨声观测资料,研究了武昌地区哨声传播的一般特征。着重对武昌哨声的传播路径进行了分析推断,并讨论了它们与地磁活动的相关特性。发现:武昌哨声的显著特征是色散与电离层f₀F₂有明显的正相关关系;其次常出现一类色散值稳定、出现率也很高的哨声。此外,对典型事件的分析及统计分析都表明武昌哨声出现率在地磁扰动时明显增高;哨声色散在磁暴急始后不久即有一个急剧的上升,上升幅度达18%至37%。      

哨声模波通过低纬电离层传播的某些特征

本文采用IGRF(1980)模型进行了哨声模三维射线跟踪计算, 研究了夜间哨声通过低纬电离层传播的射线与波法的特征.着重讨论了形成非导管哨声可透射路径的条件、射线的聚焦效应及射线的低纬截止.数值计算得到路径终纬度截止约在倾角纬度10.7°N.      

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.      

北美与东亚中纬地区电离层TEC变化的EOF建模和分析

考察了北美(30°N-50°N, 140°W-50°W)与东亚 (42.5°N-57.5°N, 65°E-140°E) 中纬地区电离层总电子含量 (TEC)的变化. TEC数据来自美国喷气动力实验室(JPL)约15年的全球电离层图 (Global Ionospheric Map, GIM)数据. 利用经验正交函数(Empirical Orthogonal Functions, EOF)得到上述两地区前三阶本征模及相关时间系数, 分别约占TEC 总变化的99.57%和99.79%. 结果表明, 两地区前三阶EOF分量所表现出的TEC变 化基本一致. 第一阶EOF分量表现为受太阳活动调制的半年变化; 第二阶EOF 分量表现为关于零磁偏线的经向电子浓度东西不对称结构, 计算表明该结构 与受地磁偏角控制的热层纬向水平风引起的等离子体向上漂移密切相关; 第三 阶EOF分量表现为磁倾控制的热层子午向风引起的等离子体向上漂移影响.      

低纬地区夜间电离层底部电子浓度与磁扰的关系

本文利用100kHz的低频无线电波资料,计算分析了1986—1987年期间,几种不同磁扰情况下,低纬地区夜间电离层中100km以下区域积分电子浓度及其变化的起因.结果表明:该区域电子浓度的变化与地磁扰动关系密切.在磁静日期间,其值较小,且随磁扰而变化,但比磁扰滞后1到2天.在磁暴后,其值较大,会出现几次剧烈起伏.该区域积分电子浓度的起伏可大于一个量级.沉降电子产生的动致辐射可能是引起该区域电子浓度变化的主要原因之      

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.      

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).     

地磁暴期间中国中低纬电离层的CIT研究

利用电离层层析成像技术(Computerized Ionospheric Tomography, CIT)处理115°E子午圈附近6个台站的GPS观测数据, 分析了2004年11月地磁暴期间中国中低纬电离层的响应情况. 结果表明, 电离层呈正相扰动, 且不同高度上的响应不同, 800 km以下电子密度有不同程度的增加, 且在峰值高度附近增幅最大, 800 km以上地磁暴的影响并不显著; 伴随地磁能量的注入, 赤道异常峰极向扩展; 随磁扰强度的降低, 电子密度也逐渐恢复至平静水平. 这些结果与以往的理论和观测结果一致, 初步估计扰动是由热层暴环流引起的, 并受到赤道异常峰移动的影响.      

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.     

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.     

2009年7月22日日全食电离层效应观测

首次利用廊坊中频雷达和武汉、嘉兴、廊坊等三站GPS对2009年7月22日日全食电离层效应进行了观测．日食期间,中频雷达D层78km高度上电子密度减小了约67％,电子密度为200cm^-3的高度上升了近10km,GPS／TEC减小了1TECU左右,其变化的最大相位与日食最大相位几乎同步;日食后,观测到周期为2个多小时的电离层扰动现象．     

Symmetry and asymmetry of ionospheric weather at magnetic conjugate points for two midlatitude observatories

Variations of the ionospheric weather W-index for two midlatitude observatories, namely, Grahamstown and Hermanus, and their conjugate counterpart locations in Africa are studied for a period from October 2010 to December 2011. The observatories are located in the longitude sector, which has consistent magnetic equator and geographic equator so that geomagnetic latitudes of the line of force are very close to the corresponding geographic latitudes providing opportunity to ignore the impact of the difference of the gravitational field and the geomagnetic field at the conjugate points on the ionosphere structure and dynamics. The ionosondes of Grahamstown and Hermanus provide data of the critical frequency (foF2), and Global Ionospheric Maps (GIM) provide the total electron content (TECgps) along the magnetic field line up to the conjugate point in the opposite hemisphere. The global model of the ionosphere, International Reference Ionosphere, extended to the plasmasphere altitude of 20,200 km (IRI-Plas) is used to deliver the F2 layer peak parameters from TECgps at the magnetic conjugate area. The evidence is obtained that the electron gas heated by day and cooled by night at the summer hemisphere as compared with the opposite features in the conjugate winter hemisphere testifies on a reversal of plasma fluxes along the magnetic field line by the solar terminator. The ionospheric weather W-index is derived from NmF2 (related with foF2) and TECgps data. It is found that symmetry of W-index behavior in the magnetic conjugate hemispheres is dominant for the equinoxes when plasma movement along the magnetic line of force is imposed on symmetrical background electron density and electron content. Asymmetry of the ionospheric storm effects is observed for solstices when the plasma diffuse down more slowly into the colder winter hemisphere than into the warmer summer hemisphere inducing either plasma increase (positive phase) or decrease (negative phase of W-index) in the ionospheric and plasmaspheric plasma density.