Relative concentration of oxygen atoms and molecules at a height of 120 km according to the data of ionospheric measurements

It is convenient to use the semi-empirical model (SEM), developed by the authors earlier and describing the relation of the electron density at heights of the middle ionosphere (120–200 km) to the parameters of the thermosphere and the integral flux of the ionizing solar radiation, to estimate the gas composition characteristics using the data of ionospheric measurements [Shchepkin et al., 2008]. The ratios of the concentrations of oxygen atoms and nitrogen molecules to those of oxygen molecules and atoms at a height of 120 km are compared using two SEM versions. The first version is based on the usage of the coefficients obtained from the measurements of N(h) profiles at Moscow observatory. The electron densities at heights of 120–200 km, obtained at the Institute of Solar-Terrestrial Physics in 2003–2006 using the digisonde, were the experimental data for the second version.     

Disturbances in the F1 ionospheric layer in April 2005

Manifestations of ionospheric disturbances at heights from 120 km to the height h _m of the F2-layer maximum are analyzed. The geomagnetic disturbances on April 5, 12, and 13, 2005, are considered. These disturbances are characterized by a pronounced synchronous decrease in the electron concentration over the entire indicated height range. Using the method proposed by the authors, the noontime changes in the relative content of atomic and molecular oxygen at a height of 120 km are estimated. There are a distinct decrease in the ratio of atomic oxygen and molecular nitrogen concentrations and an increase in the ratio of oxygen molecule and atom concentrations.     

Large-scale disturbances of auroral origin during strong magnetic storms of October 29–31, 2003, and November 7–11, 2004, according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered according to measurements of the total electron content (TEC) during the magnetic storms of October 29–31, 2003, and November 7–11, 2004, has been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region (foF2) were used for this purpose. The variations in TEC and foF2 were similar for all events mentioned above. The previous assumption that the region of thickness 150–200 km in the vicinity of the ionospheric F region mainly contributes to TEC modulation was confirmed for the cases when the electron density disturbance at an F region maximum was not more than 50%. However, this region probably becomes more extensive in vertical when the electron density disturbance in the vicinity of the ionospheric F region is about 85%.     

Precursory phenomena observed in the total electron content measurements before great Hokkaido earthquake of September 25, 2003 (<Emphasis Type="Italic">M</Emphasis> = 8.3)

In this paper the analysis of the ionospheric total electron content (TEC) variations obtained with using GPS measurements before the Hokkaido earthquake (M = 8.3) is presented. Anomalous behavior of TEC was detected within several days before the main event. Anomaly appeared as the local TEC enhancement situated in the vicinity of the forthcoming earthquake epicenter. These structures occurred during 5 days prior to the shock at the same interval of local time. At the process of the earthquake approach the amplitude of modification was increased, and it has reached the 85–90% level relative to the non-disturbed conditions 18 hours before the earthquake. The area of strong positive disturbance has extended over 1500 km in latitudes and 4000 km in longitudes. The analysis have shown that according to the series of characteristics (its locality, affinity with the epicenter, dome-shaped zone of manifestation, characteristic time of existence) the detected ionospheric anomaly may be associated to the precursors of seismic activity.     

Geomagnetic Storm Effects at <Emphasis Type="Italic">F</Emphasis>1 Layer Altitudes in Various Periods of Solar Activity (Irkutsk Station)

The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150?190 km.     

基于等离子体GCPM模型对电离层薄壳模型高度的仿真研究

在基于GPS数据提取电离层总电子含量(TEC)的过程中,电离层薄壳高度的选择对解算电离层垂直TEC的精度有很大的影响.但由于不可能获得一个真实的从电离层D层到GPS卫星高度的电子密度剖面,关于电离层薄壳高度的选择一直是基于GPS数据解算电离层TEC方法中关注的一个问题.本文利用等离子体GCPM模型,对太阳活动高年(2002)和太阳活动低年(2008)情况下电离层有效薄壳高度的选择进行了仿真计算.结果表明,最佳的薄壳高度在2002年为560 km,而在2008年为695 km.通过对全球八个具有代表性地点的仿真计算,揭示了有效薄壳高度更复杂的变化特点.在白天,最佳薄壳的高度变化不大(500 km至750 km);但在夜晚,最佳薄壳高度变化范围很大,甚至可以超过2000 km.此外,本文还对不同卫星仰角的情况下斜向TEC转换为垂直TEC的误差进行了分析,结果表明:随着卫星仰角的增加,薄壳模型带来的转换误差基本上是单调减少的.因而,在实际应用中,尽可能地采用大仰角的卫星数据有助于提高解算的电离层垂直TEC的精度.最后,对全球不同地点的电离层TEC的仿真研究表明,在电子密度水平梯度较大的地区,应用电离层薄壳模型时会导致电子密度较高处的TEC被高估,而电子密度较低处的TEC被低估,在分析基于GPS数据提取的电离层TEC空间变化时要认识到这一点.     

Ionospheric behavior over Europe during the solar eclipse of 3 October 2005

An annular eclipse occurred over Europe in the morning hours of 3 October 2005. The well-defined obscuration function of the solar radiation during the eclipse provided a good opportunity to study the ionospheric/thermospheric response to solar radiation changes. Since the peak electron density behavior of the ionospheric F2 layer follows the local balance of plasma production, loss and transport, the ionospheric plasma redistribution processes significantly affect the shape of the electron density profile. These processes are discussed here based on a comparison of vertical incidence sounding (VS) and vertical total electron content (TEC) data above-selected ionosonde stations in Europe. The equivalent slab thickness, derived with a time resolution of 10 min, provides relatively good information on the variation of the electron density profile during the eclipse. The computations reveal an increased width of the ionosphere around the maximum phase. As indicated by the available measurements over Spain, the photo production is significantly reduced during the event leading to a slower increase of the total ionization in comparison with the neighboring days. The supersonic motion of the Moon's cool shadow through the atmosphere may generate atmospheric gravity waves that propagate upward and are detectable as traveling ionospheric disturbances at ionospheric heights. High-frequency (HF) Doppler shift spectrograms were recorded during the eclipse showing a distinct disturbance along the eclipse path. Whereas the ionosonde measurements at the Ebro station/Spain in the vicinity of the eclipse path reveal the origin of the wave activity in the lower thermosphere below about 180 km altitude, the similar observations at Pruhonice/Czech Republic provide arguments to localize the origin of the abnormal waves in the middle atmosphere well below the ionospheric heights. Although ionosonde and HF Doppler measurements show enhanced wave activity, the TEC data analysis does not, which is an indication that the wave amplitudes are too small for detecting them via this interpolation method. The total ionization reduces up to about 30% during the event. A comparison with similar observations from the solar eclipse of 11 August 1999 revealed a quite different ionospheric behavior at different latitudes, a fact that needs further investigation.     

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.     

Wave-like processes in the ionosphere under quiet and disturbed conditions. 1. Kharkov incoherent scatter radar observations

Wave-like disturbances (WDs) with periods of 30–120 min at altitudes of 125–500 km (100–1000 km in individual experiments) have been studied. The measurements of total duration more than 400 h have been performed under the conditions of a quiet ionosphere as well as during magnetic and ionospheric storms and two solar eclipses. It has been indicated that WDs exist almost permanently in the ionosphere. The effect of powerful energy sources leads to a change in the WD character and to variations in the WD spectral composition and amplitudes. The latter substantially vary during a day and depending on the disturbance of the ionosphere. The WD relative amplitudes vary from several percent to several tens of percent.     

Enhancement of OI 630.0 nm emission at mid-latitudes during an intense magnetic storm

All-sky camera (ASC), Global Positioning System (GPS), and ionosonde measurements were used to investigate the upper atmospheric variations at mid-latitude during the strong geomagnetic storm on October 29–31, 2003. An arc-shaped 630.0 nm emission was observed in the northern sky on all-sky images taken at Mt. Bohyun (36.2°N, 128.9°E, GMLAT=29°N) in Korea during 17:48–8:58 UT in the main phase of the geomagnetic storm on October 29. The NmF₂ and hmF₂ from the ionosonde show strong disturbances at that time. The vertical profiles of electron densities, calculated by the ionospheric tomographic method using ground-based GPS slant total electron contents measurements, show the largest value at ∼440 km height at 18:30 UT on October 29 when the enhancements of OI 630.0 nm emission were observed. The arc-shaped red emission observed during the main phase of the magnetic storm is likely a low-latitude red aurora due to its short duration of ∼1 h. The result implies that the plasmapause was at L=1.4–1.6 during the geomagnetic storm. The fact that the arc did not follow a constant L-value appears to suggest that neutral precipitation and a traveling ionospheric disturbance could also be the cause of the arc.     

不同太阳活动及地磁条件下的电导率分布变化

电离层电导率在不同的太阳活动和地磁条件下会发生变化. 本文通过中性大气经验模式NRLMSISE_00（Neutral Atmosphere Empirical Model_2000,简称NRLMSISE_00）和电离层经验模式IRI_2001（International Reference Ionosphere_2001,简称IRI_2001）计算电离层的电子、离子碰撞频率以及电导率,并简要讨论了120 km和300 km高度上的电导率在不同季节、不同太阳活动和地磁指数下的经纬分布. 结果显示,电导率的分布与日照密切相关,且随太阳活动的变化而变化. 磁暴时电导率随地磁活动的变化相对于随太阳活动的变化要小,在120?km高度,磁暴期间电导率在低纬地区和高纬地区发生不同变化,且Pedersen电导率和Hall电导率变化趋势相反,向两极靠近,电导率变化幅度略有增长;在300?km高度上,磁暴对低纬地区和高纬地区电导率的影响要比120?km处大,Pedersen电导率和Hall电导率变化趋势相同,且越向两极靠近电导率的变化幅度越大.     

Ionospheric disturbances in the east-Asian region during the geomagnetic period in November 2004

Results of the studies of ionospheric parameter variations during the intense geomagnetic storm on November 7–11, 2004, in the 20°–80° N, 60°–180° E sector are presented. The data of ionospheric stations and the results of total electron content (TEC) measurements at the network of the GPS ground-based receivers and of the GPS receiver onboard the CHAMP satellite were used. Periods of total absorption and blanketing sporadic E layers were observed at high latitudes, whereas durable negative disturbances typical of geomagnetic storms of high intensity were detected at midlatitudes. In the afternoon hours of local time on November 8, 2004, a large-scale ionospheric disturbance of a frontal type was detected on the basis of foF2 and TEC measurements. The disturbance propagated southwestward at a mean velocity of about 200 m/s. The comparison of the relative amplitude of this large-scale disturbance according to the total electron content (～70%) and foF2 (～80%) measurements made it possible to assume a large vertical scale of the disturbance.     

一九八○年二月十六日云南地区日全食的电离层效应

本文借助于Budden的频高图分析方法,分析了云南省瑞丽县弄岛街1980年2月16日日全食期间的电离层资料,计算了日食日及控制目的剖面,给出了剖面参数,得到了E层临频及最大电子浓度所在高度在日食过程中的变化,也研究了F层的日食效应,指出了在各选定频率上的反射虚高和真高在日食过程中的变化,发现在300公里以下的各给定高度上,尤其是在270公里附近的高度上,其电子浓度明显地下降。     

Comparisons of recent data of density scale height at 544–877 km with CIRA model

In order to obtain the observed scale height at high altitude a calculation method has been derived for determining density scale height from the difference between two satellite’s heights. Two balloon satellites, Chinese DQ-1A and DQ-1B, were launched together into a nearly circular orbit at a height near 900 km and they were together in orbit for 190 days. According to the difference of the orbital heights of these two balloon satellites from 19 September 1990 to 9 March 1991, 67 values of density scale height at heights of about 544–877 km were determined. In comparison with CIRA model the results show that: (1) the trend of the variation of the scale height with height is in agreement with CIRA; (2) the determined scale height values present an oscillatory variation with time and height; and (3) the mean of the observed scale height is 3.7% lower than the mean of corresponding values from CIRA-72 and 0.8% lower than CIRA-86.     

First observation of quasi-2-day oscillations in ionospheric plasma frequency at fixed heights

The existence and development of the quasi-2-day oscillations in the plasma frequency variations of the F region at northern middle latitudes are investigated. A new approach to study the quasi-2-day oscillations is presented, using a methodology that allows us to do such a study at fixed heights. The hourly values of plasma frequency at fixed heights, from 170 km to 220 km at 10 km step, obtained at the Observatori de lEbre station (40.8°N, 0.5°E) during 1995 are used for analysis. It is found that quasi-2-day oscillations exist and persisted in the ionospheric plasma frequency variations over the entire year 1995 for all altitudes investigated. The dominant period of oscillation ranges from 42 to 56 h. The amplitude of oscillation is from 0.1 MHz to 1 MHz. The activity of the quasi-2-day oscillation is better expressed during the summer half year when several enhancements, about 15–30 days in duration, were observed. The largest enhancements of the oscillation occurred during early June, July and early August; i. e., near and after the summer solstice when the 2-day wave in the middle neutral atmosphere typically displays its largest activity in the Northern Hemisphere. The results obtained may help us understand better the possible influencing mechanisms between the 2-day wave in the middle neutral atmosphere and the ionospheric quasi-2-day oscillations.     

Variations in ionospheric parameters during solar flares

Results of studying the ionospheric response to solar flares, obtained based on the incoherent scatter radar observations of the GPS signals and as a result of the model simulations, are presented. The method, based on the effect of partial “shadowing” of the atmosphere by the globe, has been used to analyze the GPS data. This method made it possible to estimate the value of a change in the electron content in the upper ionosphere during the solar flare of July 14, 2000. It has been shown that a flare can cause a decrease in the electron content at heights of the upper ionosphere (h > 300 km) according to the GPS data. Similar effects in the formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, at the Arecibo incoherent scatter radar. The mechanism by which negative disturbances are formed in the upper ionosphere during solar flares has been studied based on the theoretical model of the ionosphere-plasmasphere coupling. It has been shown that an intense ejection of O⁺ ions into the above located plasmasphere under the action of a sharp increase in the ion production rate and the thermal expansion of the ionospheric plasma cause the formation of a negative disturbance in the electron concentration in the upper ionosphere.     

Revealing the classes of ionospheric disturbances on the basis of multiyear data on the critical frequency of the <Emphasis Type="Italic">F</Emphasis>2 layer

The bases of the classification method of ionospheric disturbances caused by solar-geomagnetic activity on the basis of the critical frequency of the F2 layer are developed. Data for the total solar activity cycle from 1975 to 1986 were used for studying variations in the critical frequency of the ionospheric F2 layer. The critical frequency was measured at the Moscow ionospheric observatory (55°45′N, 37°37′E) at an interval of 1 h. The gaps in the critical frequency values were filled in by the cubic interpolation method. The solar activity level was estimated using the F10.7 index. The geomagnetic disturbance was determined using the Kp · 10, Dst, and AE indices. According to the developed classification, an index of ionospheric activity is introduced. An analysis of the obtained values of the index for years of solar activity minimum and maximum shows that an increase in the absolute values of the index as a rule occurs at an increase in global geomagnetic and/or auroral disturbances. This fact indicates the sufficient information content of the developed index for characterizing ionospheric activity in any season. Moreover, using the sign of the index, one can form an opinion regarding an increase or decrease in the concentration of the ionospheric F2 layer, because the values of the considered index correspond to real oscillations in the critical frequency of the midlatitude ionosphere.     

Features of High-Latitude Ionospheric Irregularities Development as Revealed by Ground-Based GPS Observations,Satellite-Borne GPS Observations and Satellite In Situ Measurements over the Territory of Russia during the Geomagnetic Storm on March 17–18, 2015

The dynamic picture of the response of the high- and mid-latitude ionosphere to the strong geomagnetic disturbances on March 17–18, 2015, has been studied with ground-based and satellite observations, mainly, by transionospheric measurements of delays of GPS (Global Positioning System) signals. The advantages of the joint use of ground-based GPS measurements and GPS measurements on board of the Swarm Low-Earth-Orbit satellite mission for monitoring of the appearance of ionospheric irregularities over the territory of Russia are shown for the first time. The results of analysis of ground-based and space-borne GPS observations, as well as satellite, in situ measurements, revealed large-scale ionospheric plasma irregularities observed over the territory of Russia in the latitude range of 50°–85° N during the main phase of the geomagnetic storm. The most intense ionospheric irregularities were detected in the auroral zone and in the region of the main ionospheric trough (MIT). It has been found that sharp changes in the phase of the carrier frequency of the navigation signal from all tracked satellites were recorded at all GPS stations located to the North from 55° MLAT. The development of a deep MIT was related to dynamic processes in the subauroral ionosphere, in particular, with electric fields of the intense subauroral polarization stream. Analysis of the electron and ion density values obtained by instruments on board of the Swarm and DMSP satellites showed that the zone of highly structured auroral ionosphere extended at least to heights of 850–900 km.     

Dynamics of large-scale ionospheric inhomogeneities caused by a powerful radio emission of the Sura facility from the data collected onto ground-based GNSS network

The measurements of variations in the total electron content of the Earth’s ionosphere along the GPS satellite signal propagation path are described. The signal parameters were measured at a network of receivers at three distant sites: Sura (Vasilsursk), Zelenodolsk, and Kazan. They are arranged along the geomagnetic latitude of the Sura Facility under short-wave radio irradiation of the ionosphere. One feature of the experiment is the crossing of a disturbed region by the radio path between a GPS satellite and Vasilsursk. This resulted from the angular sizes of the Sura array pattern; the radio paths between a GPS satellite and Zelenodolsk and a GPS satellite and Kazan did not cross. Variations in the total electron content of up to 0.15?0.3 TECU were revealed at all three sites during four experimental campaigns (March 2010, March 2013, May 2013, and November 2013). The lateral scale of an ionospheric disturbance stimulated by a high-power radio wave and the velocity of its west-to-east propagation along the geomagnetic latitude were 30–60 km and 270–350 m/s, respectively. A decrease in the total electron content (down to 0.55 TECU) was recorded along the Kazan–Zelenodolsk–Vasilsurks line, which is connected with the solar terminator transit; the lateral scale of the related ionospheric inhomogeneities was ~65–80 km.