Behavior of the polar lower ionosphere during the solar flares in January 2005 according to the data of the partial reflections method

The results of the observations, using partial reflections, of the lower ionosphere over Tumannyi station in the Murmansk region (69.0° N, 35.7° E) during strong solar flares on January 15–20, 2005, are presented. The structure of the D region of the polar ionosphere and the effects of X-ray flares and fluxes of high energy protons on this region are considered. The anomalous values of electron density in the lower part of the D region, unusually low values of the height of the lower ionospheric boundary, complete or partial absorption of short and medium radiowaves, and bursts of the meter cosmic radio emission were detected during solar disturbances.     

Transverse resonance in the high-latitude section of the Earth–ionosphere waveguide during the solar eclipse of March 20, 2015

The spectra of radio atmospheric signals (spherics) recorded simultaneously at two observatories of the Polar Geophysical Institute, Lovozero (67.97° N, 35.08° E) and Barentsburg (78.08° N, 14.22° E), during the solar eclipse on March 20, 2015 are presented. The peculiarities of the behavior of the first critical frequency of the Earth-ionosphere waveguide during the eclipse are described. The effective altitude of the reflective layer of ionosphere is assessed.     

Variations of the electromagnetic fields and ionospheric parameters in the Baikal Rift Zone

Variations in the geomagnetic and electric fields and variations of the total electron content (TEC) of the ionosphere recorded in the Baikal Rift Zone (BRZ) during the expeditions in 2009 and 2010 are analyzed. Synchronous bursts in the geomagnetic field on the ground and in the ionosphere, which are caused by propagation of electromagnetic disturbances (spherics) generated by the remote lightning discharges, are revealed. The analysis of the occurrence frequency of the electromagnetic disturbances at an altitude of ∼700 km shows that there is a preferred region of predominant propagation of these disturbances from the Earth-ionosphere waveguide to the upper ionosphere. When the ionospheric penetration point moves through this preferred region, the frequency spectrum of TEC variations changes, and the northern boundary of the region of spectral alteration is located at ∼54°N. The bursts in TEC that map on the zones of the main faults in the Tunka valley are identified. The results probably suggest a relation between the electromagnetic phenomena in the ionosphere and the structures in the lithosphere.     

The response of TEC at quasi-conjugate point GPS stations during solar flares

Global Positioning System (GPS) derived total electron content (TEC) measurements were analyzed to investigate the ionospheric response during the X-class solar flare event that occurred on 5-6 December 2006 at geomagnetic conjugate stations: Syowa, Antarctica (SYOG) (GC: 69.00°S, 39.58°E; CGM: 66.08°S, 71.65°E) and árholt, Iceland (ARHO) (GC: 66.19°N, 342.89°E; CGM: 66.37°N, 71.48°E). Bernese GPS software was used to derive the TEC maps for both stations. The focus of this study is to determine the symmetry or asymmetry of TEC values which is an important parameter in the ionosphere at conjugate stations during these solar flare events. The results showed that during the first flares on 5 December, effects were more pronounced at SYOG than at ARHO. However, on 6 December, the TEC at ARHO showed a sudden spike during the flare with a different TEC variation at SYOG.     

Fine structural features of radio-frequency radiation of the solar flare of February 12, 2010

Solar radio emission records received at the IZMIRAN spectrograph (25–270 MHz) during the solar flare event of February 12, 2010 are analyzed. Different fine structures were observed in three large groups of type III bursts against a low continuum. According to data from the Nancay radioheliograph, sources of all three groups of bursts were located in one active region, 11046, and their emissions were accompanied by soft X-ray bursts (GOES satellite): C7.9 at 0721 UT, B9.6 at 0940 UT, and M8.3 at 1125 UT. After the first group of bursts, classical fiber bursts were observed in combination with reverse-drift fiber bursts with unusual arc drift. After the third (the most powerful) group, stable second-length pulsations and slow-drift fiber bursts were observed, the instantaneous frequency bands of which were an order of magnitude larger than the frequency band of classical fiber bursts, and the frequency drift was several times lower. More complex fiber bursts were observed in the weakest group in the time range 0940:39–0942:00 UT. They were narrow-band (～0.5 MHz) fiber bursts, periodically recurring in a narrow frequency band (5–6 MHz) during several seconds. The presence of many chaotically drifting ensembles of fibers, crossing and superimposing on one another, is a feature of this event. It is assumed that occurrence of these structures can be connected with the existence of many small shock fronts behind the leading edge of a coronal mass ejection.     

First results of simultaneous recording of VLF emissions at two closely located points at auroral latitudes

For the first time, simultaneous observations of very low frequency (VLF) emissions at auroral latitudes (L = 5.3) are carried out at two points located at close geomagnetic latitudes and spaced in longitude by 400 km: the Finnish Kannuslehto station (Φ = 64.2°) and the Russian Lovozero observatory (Φ = 64.1°). A recording equipment with similar frequency responses was used. The first results of a comparison of simultaneous observations showed that, in the overwhelming majority of cases, bursts of VLF emission appeared at both points synchronously with an identical (more often right-handed) polarization of the magnetic field of VLF waves, which can be evidence in favor of large dimensions of the ionosphere exit region of VLF waves. A simultaneous burst of quasi-periodic VLF emissions that occurred on February 02, 2013, during a substorm at 23–24 UT is discussed in detail. Additionally, VLF bursts were recorded which were observed only at one point, e.g., the appearance of left-hand polarized periodic emissions (PEs) in band 2.5–4.0 kHz with a repetition period of 3–4 s.     

Statistical features of <Emphasis Type="Italic">NmF</Emphasis>2 enhancements according to data from the Almaty station in solar cycles 23 and 24

According to frequent five-minute vertical sounding of the ionosphere in Almaty (76°55′ E, 43°15′ N) conducted in 2000–2014, the rate of occurrence of nighttime enhancements of the electron concentration at the F2-layer maximum is analyzed, the distributions of enhancement durations are obtained, and the parameters of several very large enhancements recorded at the same time in Irkutsk and Almaty are compared. During the analyzed period, 2272 observation sessions were carried out. In 1430 sessions NmF2 enhancement was observed. The high probabilities of enhancement formation (up to 90%) in January, February, November and December are distribution features that are identical for high and low solar activity. In addition, a rapid decrease in the probability from February to March and smooth increase from September to December occurs in the same manner. High solar activity is characterized by a distinct maximum frequency in the summer months, whereas low activity is characterized by a minimum frequency. The seasonal dependence of distributions of enhancement durations is shown: durations are distributed over a wide range in the autumn–winter season and in a narrow range in the spring–summer season.     

Interhemispheric observations of impulsive nitrate enhancements associated with the four large ground-level solar cosmic ray events (1940–1950)

We present a compelling similarity of impulsive nitrate enhancements observed in polar ice from the northern and southern hemispheres. This analysis concentrates on the period 1940–1950, during which time the first four recorded solar cosmic ray ground-level enhancements (GLEs) occurred. GLEs are strong solar proton events. We show that large and sudden enhancements in the nitrate records from both hemispheres were observed within weeks following the recorded solar cosmic ray ground-level event. The observation of impulsive nitrate enhancements simultaneously in both hemispheres shortly after a large fluence solar proton event is strong evidence in support of a causal connection and argues strongly for rapid transport of atmospheric nitrates generated through the polar atmosphere by energetic solar proton events.     

Detection of the wave-like structures in the F-region electron density: Two station measurements

Comparative studies of short-term ionospheric variability in the F region ionosphere during rapid sequence sounding campaign “HIRAC/SolarMax” (23–29 April 2001) are presented. The ionospheric short-term fluctuations have been studied in detail using measurements from vertical sounding at Ebro (40.8 °N, 0.5 ° E) and Průhonice (49.9 °N, 14.5 °E) in the period range from 15 minutes to 2 hours. The electron density measurements contain variations that indicate the possible presence of propagating gravity waves. Regular wave-like bursts were found during quiet days at both stations in electron concentration in F region, with an increase of the oscillation activity after sunrise and then during late afternoon, and at sunset and after sunset. Solar Terminator is assumed to be one of the sources of the regular wave bursts detected in the ionosphere during campaign HIRAC. As expected, substantial intensification in longer period gravity waves was found to occur during the disturbed period on April 28. Particular enhancement of the wave-like activity during disturbed day is discussed, being significant evidences of a change of the wave-like activity pattern at a height around 200 km.     

Regional response of the mesosphere–lower thermosphere dynamics over Scandinavia to solar proton events and geomagnetic storms in late October 2003

The short-term regional responses of the mesosphere–lower thermosphere (MLT) dynamics over Scandinavia to the exceptionally strong solar storms with their accompanying solar proton fluxes on the Earth in late October 2003 have been investigated using radar measurements at Andenes (69°N, 16°E) and Esrange (68°N, 21°E). Several solar activity storms resulted in solar proton events (SPEs) at this time, but a particularly active period of high proton fluxes occurred between 28 and 31 October 2003. The significant temperature drop (∼25 K), detected by the meteor radar at Andenes at altitude ∼90 km, was in line with the enhancement of the proton fluxes and was caused by the dramatic reduction of the ozone in the high-latitude middle atmosphere monitored by satellite measurements. This exceptionally strong phenomenon in late October 2003 was composed of three geomagnetic storms, with the first one occurring in the daytime of 29 October and the other two storms in the nighttime of 29 and 30 October, respectively. The responses of the prevailing wind and the main tides (24- and 12-h tides) were studied in detail. It was found that the response of the MLT dynamics to the first geomagnetic storm occurring in the daytime and accompanied by solar proton fluxes is very different from those to the second and third geomagnetic storms with onsets during the nighttime. Some physical mechanisms have been suggested in order to explain the observed short-term variability of the MLT dynamics. This case study revealed the impact of the SPEs observed in late October 2003 and the timing of the geomagnetic storms on the MLT neutral wind responses observed over Scandinavia.     

Monitoring of solar proton events at altitudes up to 1000 km: Data from the Russian space experiments. Solar proton effects in the Earth’s ozonosphere

The paper illustrates the opportunities provided by the use of data from Russian satellite experiments (CORONAS and Universitetsky-Tatiana of Meteor series) on the measurement of fluxes and spectra of solar cosmic rays at altitudes of 370–1000 km for simulation of the ozonosphere state. The results of photochemical simulation and observational data analysis showing the influence of solar protons on polar ozonosphere and lower ionosphere in periods of solar proton events (SPE) on November 4, 2001, October 28, 2003, and January 16, 2005 are presented. It is shown that the solar proton action causes ozone depletion in the mesosphere above the polar regions. The strongest depletion (up to 70%) was caused by the SPE that occurred on October 28, 2003.     

Changes of the first Schumann resonance frequency during relativistic solar proton precipitation in the 6 November 1997 event

The variations of the first mode of Schumann resonance are analyzed using data from Kola peninsula stations during the solar proton event of 6 November 1997. On this day the intensive flux of energetic protons on GOES-8 and the 10% increase of the count rate of the neutron monitor in Apatity between 1220 and 2000 UT were preceded by a solar X-ray burst at 1155 UT. This burst was accompanied by a simultaneous increase of the Schumann frequency by 3.5%, and the relativistic proton flux increase was accompanied by 1% frequency decrease. These effects are explained by changes of the height and dielectric permeability of the Earth-ionosphere cavity.     

Arrival of the first relativistic solar protons and conditions in the solar corona

When solar cosmic rays (SCRs) can be observed with ground-based equipment (ground-level enhancements, GLEs), events are often characterized by a rapid increase in the relativistic proton intensity during the initial phase, which makes it possible to estimate the time of particle escape from the solar corona. This phase attracts attention of researchers owing to its closeness in time to the instant of particle acceleration. It is known that the observed SCR characteristics bear traces of many physical processes, including different acceleration mechanisms the relative role of which is still unclear. Flare processes and acceleration by a shock, related to coronal mass ejection (CME), are the main pretenders to the role of SCR accelerator. Several powerful solar proton events during cycle 23 are considered in the work, and the release time of the first particles from the corona and the dynamics of CMEs have been estimated. The time series of the X-ray and radio bursts, close in time to particle escape, are analyzed. The conclusion have been drawn that the first relativistic particles were most probably accelerated during flare processes.     

Time delays in the correlation between solar activity and the F2 region plasma frequency

The upper ionosphere electron density characterized by the critical frequency foF2 is correlated with solar activity when using monthly medians or averages from longer intervals. When shorter intervals are studied, time delays of different lengths in solar activity effects in the ionosphere are observed. The correlation between the foF2 values and the solar radiation intensity, given by the F10.7 index, is studied using the 1967–2003 data of mid-latitude ionosonde stations spaced at distances greater than 100° in geographical longitude. At which longitude the reaction of foF2 to the changes in solar activity appears sooner depends on the position of the interval studied in the 22-year solar cycle.     

Reaction of the high-latitude lower ionosphere to solar proton events from observations in the ELF range

The reaction of the lower ionosphere to the solar proton events that occurred in 2011–2012 is studied in this paper based on the results of measurements of the propagation velocity and the E _z /H _τ ratio of the low-frequency electromagnetic pulses (atmospherics) in the ELF range at the high-latitude observatories Lovozero and Barentsburg. With numerical modeling methods, it is shown that horizontal local irregularities of the lower ionosphere conductivity profile could be a cause of the splashes in the E _z /H _τ ratio observed in the experiment during the solar proton event of March 7, 2012, which was a unique event in both the proton flux value and energy.     

Evening enhancements in F-region electron temperature at subtropical latitudes during June solstice in the Indian SROSS C2 RPA data

In-situ measurments of the topside F-region ionospheric electron and ion temperatures are very few over the low and equatorial latitudes during the last two solar cycles, particularly in the Indian sector. The SROSS C2 satellite has provided some valuable data on the thermal structure of the topside ionosphere over the Indian region. This article reports a typical evening enhancement in the topside F-region electron temperatures around 18:00 IST observed in the subtropical latitudes of 15–20°N. These enhancements that are seen during the low sunspot activity periods show a latitudinal difference with an early and sharp peak at higher latitudes (23°N). The observed features are explained on the basis of equatorial plasma dynamics associated with the Appleton ionization anomaly.     

Pick of the bunch

Peter Bond reports on a mixed bag of science from space-based misssions, including more on Martian water, X-ray flashes to match gamma-ray bursts and what the ionosphere does when Earth is in the path of a solar storm.     

基于陆态网络GPS数据的电离层空间天气监测与研究

中国大陆构造环境监测网络(简称陆态网络)是以全球卫星导航定位系统(GNSS)为主,辅以多种空间观测技术,实时动态监测大陆构造环境变化,探求其对资源、环境和灾害的影响的地球科学综合观测网络.基于陆态网络约200个基准站的GPS观测数据,本文探讨了其在电离层空间天气监测与研究方面的应用.包括磁暴期间电离层暴扰动形态,大尺度电离层行进式扰动,太阳耀斑引起的电离层骚扰和低纬电离层不规则体结构等.研究结果表明:陆态网络布局合理,观测数据质量良好,完全可用于中国及周边地区电离层空间天气监测与研究,为进一步开展我国电离层空间天气预警和预报奠定了观测基础.     

关于太阳貭子爆发的地球物理效应——研究1959年7月及1960年11月日地关系重大事件記要

本文对1959年7月及1960年11月有关太阳貭子爆发的各种地球物理效应,作了較全面和系統的論述。文中在§2-4分別敘述了这期間地磁場扰动、极盖区电波吸收观測与电离层变动情况、以及太阳耀斑与太阳射电爆发.根据以上情况,作者特別着重在§5中論述宇宙綫强度扰乱分析（包括各国进行研究的基本情况、若干特殊分析方法与結果簡介、关于綜合观测和高空探測）,并在§6中提出了今后开展工作的几点初步意見。本文引用了北京台的磁暴与宇宙线强度变化記录,并附有較完全的文献目录。     

The variation of ionospheric slab thickness over equatorial ionization area crest region

The GPS-derived total electron content (TEC) and NmF2 are measured at the Chung-Li ionosonde station (24.9°N, 121°E) in order to study the variations in slab thickness (τ) of the ionosphere at low-latitudes ionosphere during 1996–1999, corresponding to half of the 23rd solar cycle. This study presents the diurnal, seasonal, and solar flux variations in τ for different solar phases. The seasonal variations show that the average daily value is greater during summer and the reverse is true during equinox in the equatorial ionization anomaly (EIA) region. Moreover, the τ values are greater during the daytime (0800–1600 LT) and nighttime (2000–0400 LT) for summer and winter, respectively. The diurnal variation shows two abnormal peaks that appear during the pre-sunrise and post-sunset hours. The peak values decrease as the sunspot number increases particularly for the pre-sunrise peak. Furthermore, the variation in the F-peak height (hpF2) indicates that a thermospheric wind toward the equator leads to an increase in hpF2 and an enhancement in τ during the pre-sunrise period. Furthermore, the study shows the variations of τ values for different geophysical conditions such as the geomagnetic storm and earthquake. A comprehensive discussion about the relation between τ and the geophysical events is provided in the paper.