Ionospheric F-region response to geomagnetic disturbances

The F2-region reaction to geomagnetic storms usually called as an ionospheric storm is a rather complicated event. It consists of so called positive and negative phases, which have very complicated spatial and temporal behavior. The main morphological features of ionospheric storms and the main processes governing their behavior were understood at the end of the 1900s and described in a series of review papers. During the recent decade there were many publications dedicated to the problem of ionospheric storms. In this paper a concept of ionospheric storm morphology and physics formulated at the end of the 1990s is briefly summarized and the most interesting results obtained in the 2000s are described. It is shown that the main features of the studies of the previous decade were: the use of GPS TEC data for analyzing the ionospheric storm morphology, attraction of sophisticated theoretical models for studying the processes governing ionospheric behavior in disturbed conditions, and accent to analysis of ionospheric behavior during prominent events (very strong and great geomagnetic storms). Also a special attention was paid to the pre-storm enhancements in foF2 and TEC.     

An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using global positioning system (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the TEC. During this storm, two TEC enhancements were observed at low- and mid-latitudes: the first enhancement was observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, while the second TEC enhancement is associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show response features that differ from those of the TEC during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers may have existed, i.e., the westward electric field and equatorward neutral wind effects.     

The mid-latitude field-aligned disturbances and their effect on differential GPS and VLBI

For the first time we propose a method for detecting the mid-latitude field-aligned disturbances (FADs) prolated on the magnetic field. The method is based on GPS detection of isolated ionosphere disturbances and analysis of the angle between the “GPS satellite-receiver” line-of-sight and the local magnetic field vector, for which maximum (minimum) of aperiodic variation of the total electron content (TEC) is registered.     

The lower ionosphere response to its disturbances by powerful radio waves

The paper presents data from some campaigns at Sura heating facility in 2011–1016. The experiments on probing of the artificial disturbed region of the lower ionosphere were carried out at two observation sites. One of them was located near Vasil’sursk 1 km from Sura facility (56.1°N; 46.1°E) and the other site was located at the Observatory (55.85°N; 48.8°E) of Kazan State University, 170 km to the East. Investigation of the features of the disturbed region of the lower ionosphere based on its diagnostics by the methods of the vertical sounding and oblique backscattering is the main goal of this paper. Ionosphere disturbance was fulfilled by the effect of the powerful radio wave of the ordinary or extraordinary polarization emitted by transmitters of the Sura facility with effective radiated power ERP = 50–120 MW at the frequency of 4.3, 4.7 and 5.6 MHz. Pumping waves were emitted with period from 30 s to 15 min. The disturbed region of the ionosphere in Vasil’sursk was probed by the vertical sounding technique using the partial reflexion radar at the frequency of 2.95 and 4.7 MHz. For the oblique sounding of the disturbed region the modified ionosonde Cyclon-M, operating at ten frequencies from 2.01 to 6.51 MHz was used at the Observatory site. On many heating sessions simultaneous variations of the probing partial reflection signals in Vasil’sursk and backscattered signals in Observatory were observed at the height at 40–100 km below the reflection height of the pumping wave. These observations were correlated with the pumping periods of the Sura facility. Possible mechanisms of the appearance of the disturbance in the lower ionosphere and its effect on the probing radio waves are discussed.     

IONOSAT – Ionospheric satellite cluster

The IONOSAT project (from IONOspheric SATellites) is proposed by National Space Agency of Ukraine for First European Space Program as a part of Space Weather (SW) Program. As it is commonly accepted, Space Weather means the changes of the conditions on the Sun, in solar wind, magnetosphere and ionosphere which may affect the operation and reliability of on-board and ground technological systems and threaten human health. In this chain ionosphere is specific and integral part of SW formation. Moreover, namely in the ionosphere main part of the energy absorption of Sun-activated sporadic corpuscular and radiation fluxes takes places. The excitation of ionosphere by falling fluxes produces its “luminescence” in wide frequency band – from ULF waves till ultraviolet – and by this ionosphere works as an efficient “screen” or SW indicator.A goal of the proposed project is long-term spatial–temporal monitoring of main field and plasma parameters of ionosphere with aim to further develop fundamental conceptions of solar-terrestrial connections physics, nowcasting and forecast of SW, and diagnostics of natural and technogenic hazards with the help of scientific payload installed on-board a cluster of 3 low-Earth orbit (LEO) microsatellites (tentative launch date – 2012 year).The state of the project proposal and realization plans are discussed.     

行星际闪烁功率谱的Fresnel现象与太阳风速度

讨论了弱散射条件下行星际闪烁(IPS)功率谱的Fresnel现象。数值计算结果表明,无行星际扰动存在时,IPS功率谱的膝点频率仍是Fresnel频率,在日张角。ε≤35°的范围内,Fresnel振荡现象仍然存在,极小值所在频率与太阳风电子密度为一维结构薄屏近似的解析结果相差不大。行星际扰动存在时,功率谱的膝点频率并未改变,扰动区太阳风速度决定着Fresnel振荡出现的频率。     

Geoeffectiveness of interplanetary shocks controlled by impact angles: A review

The high variability of the Sun’s magnetic field is responsible for the generation of perturbations that propagate throughout the heliosphere. Such disturbances often drive interplanetary shocks in front of their leading regions. Strong shocks transfer momentum and energy into the solar wind ahead of them which in turn enhance the solar wind interaction with magnetic fields in its way. Shocks then eventually strike the Earth’s magnetosphere and trigger a myriad of geomagnetic effects observed not only by spacecraft in space, but also by magnetometers on the ground. Recently, it has been revealed that shocks can show different geoeffectiveness depending closely on the angle of impact. Generally, frontal shocks are more geoeffective than inclined shocks, even if the former are comparatively weaker than the latter. This review is focused on results obtained from modeling and experimental efforts in the last 15?years. Some theoretical and observational background are also provided.     

基于T96模型的极尖区位形变化特性研究

基于T96模型,定义了极尖区的位形以及相关的描述参量(例如赤道向边界磁纬的最小值,纬向宽度,子午向和晨昏向的张角,倾斜度,扁平度,中心磁地方时等),讨论了太阳风动压(P_d)、行星际磁场(IMF)及磁暴强度对极尖区位形的影响.太阳风动压和磁暴强度越大,则极尖区的赤道向边界磁纬越小,纬向宽度越大,子午向和晨昏向的张角越大,倾斜度越大,扁平度越小;南向IMF B_z越强,则极尖区的赤道向边界磁纬越小,纬向宽度越小,子午向的张角越小,晨昏向的张角越大,倾斜度越大,扁平度越大;北向IMF B_z与南向IMF B_z的情况刚好相反;极尖区的中心磁地方时受IMF B_y控制,IMF B_y为正时,极尖区向昏侧移动,而IMF B_y为负时,极尖区则向晨侧移动,并且极尖区的中心磁地方时与IMF B_y之间有着良好的线性关系.将所得结果与前人的观测结果进行了简单比较,发现利用T96模型确定的极尖区位形与观测基本一致.     

根据行星际闪烁(IPS)的双频互谱估计太阳风速度

本文讨论了观测频率为232MHz和327MHz时,利用互谱的方法估计太阳风速度的可能性、考虑路径积分效应,结果表明在17°≤ε≤50°范围内,对于几种可能的太阳风速度分布,由互谱所得结果与太阳风速度值差别小于15%.     

多GNSS全球电离层建模特性及其精度检验

分别以GPS单系统和融合BDS,GPS,GLONASS三系统两种方案,采用载波相位平滑伪距观测值和球谐函数,构建了全球电离层延迟模型并进行了对比和分析.本文以GPS单系统和融合三系统两种方法反演了2014年1月每日电离层变化过程,解算得出了频间偏差的月综合产品,并对结果进行了对比和分析.事实上,三系统融合不仅增加了可观测的卫星数,而且改善了穿刺点的几何分布.分析结果表明,三系统融合反演全球电离层在精度上优于GPS单系统,均有5~10 TECU的提高.计算得到的频间偏差结果显示,GPS优于GIONASS,BDS稳定性则较次之.     

The solar wind control of the equatorial ionosphere dynamics during geomagnetic storms

The interplanetary magnetic field, geomagnetic variations, virtual ionosphere height h′F, and the critical frequency foF2 data during the geomagnetic storms are studied to demonstrate relationships between these phenomena. We study 5-min ionospheric variations using the first Western Pacific Ionosphere Campaign (1998–1999) observations, 5-min interplanetary magnetic field (IMF) and 5-min auroral electrojets data during a moderate geomagnetic storm. These data allowed us to demonstrate that the auroral and the equatorial ionospheric phenomena are developed practically simultaneously. Hourly average of the ionospheric foF2 and h′F variations at near equatorial stations during a similar storm show the same behavior. We suppose this is due to interaction between electric fields of the auroral and the equatorial ionosphere during geomagnetic storms. It is shown that the low-latitude ionosphere dynamics during these moderate storms was defined by the southward direction of the B_z-component of the interplanetary magnetic field. A southward IMF produces the Region I and Region II field-aligned currents (FAC) and polar electrojet current systems. We assume that the short-term ionospheric variations during geomagnetic storms can be explained mainly by the electric field of the FAC. The electric fields of the field-aligned currents can penetrate throughout the mid-latitude ionosphere to the equator and may serve as a coupling agent between the auroral and the equatorial ionosphere.     

A Review on the Ionospheric Research： Chinese Works During 2006-2008

This paper reviews various progresses on the ionospheric studies by the scientists in China during the last two years.The main contents concern the 4 aspects of the ionospheric research:(1)ionospheric weather and coupling with magnetosphere(polar and auroral ionosphere,ionospheric response to substorms,ionospheric storms);(2)mid-and low-latitude ionospheric climatology(ionospheric properties,yearly variations and solar activity dependence,long term variation);(3)ionospheric coupling with neutral atmosphere(gravity waves,tides,planetary waves,background upper atmosphere,and ionospheric response);and(4)ionospheric diagnostics(observation,modeling,and prediction).     

Ionospheric slab thickness – Analysis, modelling and monitoring

A review of the climatological and storm-time behaviour of the ionospheric slab thickness is presented based on long-time observations at a European mid-latitude site, Dourbes (50.1°N, 04.6°E), and on published results from other studies. An operational electron density and slab thickness monitoring system, established to provide real-time characterisation of the local ionospheric dynamics, is outlined together with some exemplary results.     

全球电离层对2000年4月6-7日磁暴事件的响应

利用分布于全球的电离层台站的测高仪观测数据,对扰动期间,foF2值与其宁静期间参考值进行比较,研究了2000年4月6—7日磁暴期间全球不同区域电离层的响应形态,并通过对比磁扰期间NmF2的变化与由MSISR90经验模式估算的中性大气浓度比(no／nN2)的变化,探讨了本次事件期间的电离层暴扰动机制．结果表明,在磁暴主相和恢复相早期,出现了全球性的电离层F2层负相暴效应．最大负相暴效应出现在磁暴恢复相早期,即电离层暴恢复相开始时间滞后于磁暴恢复相开始时间．在磁暴恢复相后期,一些台站出现正相扰动．研究结果表明,本次事件期间的电离层暴主要是由磁暴活动而诱发的热层暴环流引起的．     

Mid-latitude amplitude scintillation of GPS signals and GPS performance slips

Degradation of transionospheric radio signals and operation failures during ionospheric disturbances constitute a crucial factor of space weather influence on radio engineering satellite systems performance. We found that during the main phase of strong magnetic storms in 2000–2003 when the auroral oval expands into mid-latitudes, its southern boundary develops a region with intense small-scale electron density irregularities. Such irregularities may cause strong amplitude scintillations of GPS signals at both GPS operating frequencies. The another consequence of it was significant random GPS signal phase fluctuations, breaking-down of signal tracking, and sharp increasing of GPS positioning errors as a result.     

Ionospheric response to the storm-time disturbance of 29 May, 2010

The Ionospheric F2-layer peak parameters response to a magnetic storm had been investigated over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°), Jicamarca, Peru (11.95°S, 76.87°W, dip angle, 0.8°) and Hermanus, South Africa (34.42°S, 19.22°E, dip angle, −60.77°), using percentage enhancement/depletion values. Our results showed an enhancement in NmF2 at all of these stations. Averagely, pre-noon and post-noon peaks are highest at Ilorin during quiet time. The similar pattern observed for quiet condition between Ilorin and Jicamarca was due to their latitudinal positions. For disturbed NmF2 condition, Jicamarca and Ilorin recorded higher peaks at nighttime than during the daytime for the storms main phase, and the reverse over Hermanus. The nighttime and daytime increases were observed respectively at Ilorin and Hermanus during the recovery period. The hmF2 variation recorded higher enhancement at Jicamarca during the daytime and at Hermanus at nighttime during the main phase. During the recovery phase, the highest enhancement was recorded during the daytime at Jicamarca, and over Hermanus at nighttime. These observations find their explanation in the magnetospheric current, solar wind and E × B drift.     

Ionospheric correction using GPS Klobuchar coefficients with an empirical night-time delay model

We proposed an ionospheric correction approach called NKlob to mitigate the ionospheric delay errors. NKlob is a modification of the original GPS Ionospheric Correction Algorithm (ICA), which uses an empirical night-time model depending on the time, geomagnetic location and periodicities of the ionospheric behavior to replace the night-time constant delay in GPS ICA. Performance of NKlob was evaluated by the independent total electron contents (TECs) derived from Global Ionospheric Maps (GIMs) of the International GNSS Services (IGS) and Jason-2 altimetry satellite during 2013–2017. Compared to GIM TECs, NKlob corrects 51.5% of the ionospheric delay errors, which outperforms GPS ICA by 6.3%. Compared to Jason-2 TECs, NKlob mitigates the ionospheric errors by 58.1%, which is approximately 3.7% better than that of GPS ICA. NKlob shows significant improvement in low-latitude and equatorial regions with respect to GPS ICA, meanwhile exhibiting comparable performance at middle and high latitudes. Since NKlob only requires slight technical changes at the processing level of GPS receivers, we suppose that it can be easily implemented for better ionospheric delay corrections of real-time GPS single-frequency applications.     

Ionospheric oscillations caused by geomagnetic Pi2 pulsations and their observations by multipoint continuous Doppler sounding; first results

In 2004, we started operating a continuous Doppler sounding system to investigate ionospheric signatures of infrasonic, short period acoustic gravity waves and geomagnetic pulsations. Since January 2007, four stable 3.59 MHz transmitters have been in operation in the western part of the Czech Republic. Multipoint measurements enable us to investigate horizontal propagation of waves and disturbances in the ionosphere and to estimate horizontal distances over which these waves (disturbances) are correlated.     

Hierarchical Bayesian modeling of ionospheric TEC disturbances as non-stationary processes

We model regular and irregular variation of ionospheric total electron content as stationary and non-stationary processes, respectively. We apply the method developed to SCINDA GPS data set observed at Bahir Dar, Ethiopia $\left(11.6°\text{N,}37.4°\text{E}\right)$. We use hierarchical Bayesian inversion with Gaussian Markov random process priors, and we model the prior parameters in the hyperprior. We use Matérn priors via stochastic partial differential equations, and use scaled $\text{Inv}-{\chi }^2$ hyperpriors for the hyperparameters. For drawing posterior estimates, we use Markov Chain Monte Carlo methods: Gibbs sampling and Metropolis-within-Gibbs for parameter and hyperparameter estimations, respectively. This allows us to quantify model parameter estimation uncertainties as well. We demonstrate the applicability of the method proposed using a synthetic test case. Finally, we apply the method to real GPS data set, which we decompose to regular and irregular variation components. The result shows that the approach can be used as an accurate ionospheric disturbance characterization technique that quantifies the total electron content variability with corresponding error uncertainties.