Variation of ionospheric electron and ion temperatures during periods of minimum to maximum solar activity by the SROSS-C2 satellite over Indian low and equatorial latitudes

To study the variation of ionospheric electron and ion temperatures with solar activity the data of electron and ion temperatures were recorded with the help of Retarding Potential Analyzer payload aboard Indian SROSS-C2 satellite at an average altitude of ∼500 km. The main focuses of the paper is to see the diurnal, seasonal and latitudinal variations of electron and ion temperatures during periods of minimum to maximum solar activity. The ionospheric temperatures in the topside show strong variations with altitude, latitude, season and solar activity. In present study, the temperature variations with latitude, season and solar activity have been studied at an average altitude ∼500 km. The peak at sunrise has been observed during all seasons, in both electron and ion temperatures. Further, the ionospheric temperatures vary with latitude in day time. The latitudinal variation is more pronounced for low solar activity than for high solar activity.     

Ionospheric storm of September 2017 observed at ionospheric station Pruhonice,the Czech Republic

The ionospheric effects induced by the September 2017 storm have been exceptional compared to other events in the solar cycle 24. This paper gathers results of the ionospheric observations at the European middle latitude station Pruhonice. It consists of evaluation of ionospheric vertical and oblique sounding, Digisonde drift measurement, and data obtained from the Continuous Doppler Sounding System. We observed strong ionospheric response with an unusual stratification of ionospheric layers, Large Scale Traveling ionospheric disturbances, changes in electron density, and increase and oscillations in plasma drift velocity.     

Effect of vertical plasma transport on ionospheric F2-region parameters at equatorial latitude

The variability of the F2-layer even during magnetically quiet times are fairly complex owing to the effects of plasma transport. The vertical E × B drift velocities (estimated from simplified electron density continuity equation) were used to investigate the seasonal effects of the vertical ion drifts on the bottomside daytime ionospheric parameters over an equatorial latitude in West Africa, Ibadan, Nigeria (Geographic: 7.4°N, 3.9°E, dip angle: 6°S) using 1 year of ionsonde data during International Geophysical Year (IGY) of 1958, that correspond to a period of high solar activity for quiet conditions. The variation patterns between the changes of the vertical ion drifts and the ionospheric F2-layer parameters, especially; f_oF₂ and h_mF₂ are seen remarkable. On the other hand, we observed strong anti-correlation between vertical drift velocities and h′F in all the seasons. We found no clear trend between N_mF₂ and h_mF₂ variations. The yearly average value of upward daytime drift at 300 km altitude was a little less than the generally reported magnitude of 20 ms⁻¹ for equatorial F-region in published literature, and the largest upward velocity was roughly 32 ms⁻¹. Our results indicate that vertical plasma drifts; ionospheric F2-layer peak height, and the critical frequency of F2-layer appear to be somewhat interconnected.     

Modelled ionospheric Te profiles at mid-latitudes for possible IRI application

The electron temperature (T_e) variation in the mid-latitude ionosphere at altitudes between 120 – 800 km has been modelled for various seasonal and solar-cycle conditions. The calculated electron temperatures are consistent with plasma densities and ion temperatures computed from a time-dependent ionospheric model. The T_e distribution can be represented by a subset of standard T_e profiles. T_e above 200 km is controlled by the magnetospheric heat flux into the ionosphere. For realistic values of the magnetospheric heat flux, the maximum electron temperature ranges from 3000 to 10,000 K at 800 km. The effect of increasing the heat flux is to increase the topside temperature but retain the profile shape. Hence, given a topside T_e observation and selection of an appropriate profile shape, the entire T_e distribution can be computed.     

极区顶部电离层离子上行的太阳活动依赖性研究

利用第23太阳活动周DMSP F12,F13和F15卫星数据,分别对南北半球极区顶部电离层离子上行的太阳活动依赖性进行了研究.结果表明,南北半球上行事件对太阳活动的响应特征基本一致,即高（低）太阳活动时,离子上行通量以及上行数密度较大（小）,但是上行速度及上行发生率较低（高）.以南半球高纬为例,计算得到离子上行通量、数密度、速度及发生率在高低太阳活动条件下的比值分别约为2.26,3.35,0.71,0.51.对离子上行太阳活动依赖性的可能原因进行了分析.不同太阳活动水平下,光致电离及高能粒子沉降的差异会导致电离层离子密度的不同,而电离层离子密度的变化会改变离子elax-elax中性大气之间的碰撞频率,这是影响离子上行发生率的一个重要原因.      

Development of a campaign to study equatorial ionospheric phenomena over Guam

The United States Air Force Academy (USAFA) is in the process of developing a series of ground-based and space-based experiments to investigate the equatorial ionosphere over Guam and the southern crest of the Equatorial Appleton Anomaly over New Guinea. On the ground the Digital Ionospheric Sounder (University of Massachusetts, Lowell DPS-4 unit) and a dual-frequency GPS TEC/scintillation monitor will be used to investigate ionospheric phenomena in both campaign and long-term survey modes. In campaign mode, we will combine these observations with those collected from space during USAFA’s FalconSAT-3 and FalconSAT-5 low Earth orbit satellite missions, which will be active over a period of several years beginning in the first quarter of the 2007 calendar year. Additionally, we will investigate the long-term morphology of key ionospheric characteristics useful for driving the International Reference Ionosphere, such as critical frequencies (f_oE, f_oF1, f_oF2, etc.), the M(3000) F2 parameter (the maximum useable frequency for a signal refracted within the F2 layer and received on the ground at a distance of 3000 km away), and a variety of other characteristics. Specific targets of investigation include: (a) a comparison of TEC observed by the GPS receiver with those calculated by IRI driven by DPS-4 observations, (b) a comparison of plasma turbulence observed on-orbit with ionospheric conditions as measured from the ground, and (c) a comparison between topside ionospheric satellite in situ measurements of plasma density during an overpass of a Digisonde versus the calculated value based on extrapolation of the electron density profiles using Digisonde data and a topside α-Chapman function. This last area of investigation is discussed in detail in this paper.     

DEMETER and DMSP satellite observations of the disturbed H/O ratio caused by Earth’s seismic activity in the Sumatra area during December 2004

In the present paper, plasma probe data taken from DEMETER and DMSP-F15 satellites were used to study the ion density and temperature disturbances in the morning topside ionosphere, caused by seismic activity at low latitudes. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite mission had been especially designed to provide global scale observations in the topside ionosphere over seismically active regions. Onboard the DEMETER satellite, the thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. As a part of “Defense Meteorological Satellite Program”, DMSP-F15 satellite is on orbit operation since 1999. It provides ionospheric plasma diagnostics by means of the “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. We examined few examples of possible seismic effects in the equatorial ionosphere, probably associated with seismic activity during December month in the area of Sumatra Island, including main shock of giant Sumatra event. It is found that the localized topside ionospheric disturbances appear close to the epicenters of certain earthquakes in the Sumatra region. In two cases, ion H⁺/O⁺ ratio rises more than one hour before the main shock, due to the O⁺ density decrease at the winter side of the geomagnetic equator, with longitudinally closest location to the epicenter of the earthquakes. These anomalous depletions in O⁺ density do exist in all cases of SSIES-2 data. Particularly for Sumatra main event, more than one hour after the main shock, we observe large-scale depletion in O⁺ density northward of the geomagnetic equator at winter side hemisphere. Associated with O⁺ depletion, ion temperature latitudinal profile around the geomagnetic equator shows enhanced asymmetry with minimum at the summer side and maximum in positive Ti deviation from mean value at the winter side. This disturbance lasted for more than three hours, later in time observed at the same place by IAP/DEMETER.     

Prompt effects of solar wind variations on the inner magnetosphere and midlatitude ionosphere

It is well known that the solar wind can significantly affect high-latitude ionospheric dynamics. However, the effects of the solar wind on the middle- and low-latitude ionosphere are much less studied. In this paper, we report observations that large perturbations in the middle- and low-latitude ionosphere are well correlated with solar wind variations. In one event, a significant (20–30%) decrease of the midlatitude ionospheric electron density over a large latitudinal range was related to a sudden drop in the solar wind pressure and a northward turning of the interplanetary magnetic field, and the density decrease became larger at lower latitudes. In another event, periodic perturbations in the dayside equatorial ionospheric E × B drift and electrojet were closely associated with variations in the interplanetary electric field. Since the solar wind is always changing with time, it can be a very important and common source of ionospheric perturbations at middle- and low-latitudes. The relationship between solar wind variations and significant ionospheric perturbations has important applications in space weather.     

Accuracy of IRI profiles of ionospheric density and temperatures derived from comparisons to Kharkov incoherent scatter radar measurements

The incoherent scatter radar (ISR) facility in Kharkov, Ukraine (49.6°N, 36.3°E) measures vertical profiles of electron density, electron and ion temperature, and ion composition of the ionospheric plasma up to 1100 km altitude. Acquired measurements constitute an accurate ionospheric reference dataset for validation of the variety of models and alternative measurement techniques. We describe preliminary results of comparing the Kharkov ISR profiles to the international reference ionosphere (IRI), an empirical model recognized for its reliable representation of the monthly-median climatology of the density and temperature profiles during quiet-time conditions, with certain extensions to the storm times. We limited our comparison to only quiet geomagnetic conditions during the autumnal equinoxes of 2007 and 2008. Overall, we observe good qualitative agreement between model and data both in time and with altitude. Magnitude-wise, the measured and modeled electron density and plasma temperatures profiles appear different. We discovered that representation accuracy improves significantly when IRI is driven by observed-averaged values of the solar activity index rather than their predictions. This result motivated us to study IRI performance throughout protracted solar minimum of the 24th cycle. The paper summarizes our observations and recommendations for optimal use of the IRI.     

Comparison of topside ionosphere scale height modeled by the Topside Sounder Model and incoherent scatter radar ionospheric model

The topside ionosphere scale height extracted from two empirical models are compared in the paper. The Topside Sounder Model (TSM) provides directly the scale height (H_T), while the incoherent scatter radar ionospheric model (ISRIM) provides electron density profiles and its scale height (H_R) is determined by the lowest gradient in the topside part of the profile. H_T and H_R are presented for 7 ISR locations along with their dependences on season, local time, solar flux F10.7, and geomagnetic index ap. Comparison reveals that H_T values are systematically lower than respective H_R values as the average offset for all 7 stations is 55 km. For the midlatitude stations Arecibo, Shigaraki, and Millstone Hill this difference is reduced to 43 km. The range of variations of H_R is much larger than that of H_T, as the H_T range overlaps the lower part of the H_R range. Dependences on ap, DoY and LT are much stronger in the ISRIM than in TSM. This results in much larger values of H_R at higher ap. Diurnal amplitude of H_R is much larger than that of H_T, with large maximum of H_R at night. The present comparison yields the conclusion that the ISR measurements provide steeper topside Ne profiles than that provided by the topside sounders.     

Saint-Santin observations of electric fields and neutral winds in the dynamo layer during the GTMS period of June 1984

Incoherent scatter measurements of ion drift velocities obtained by the quadristatic incoherent scatter sounder of Saint-Santin have been used to analyse midlatitude electrodynamic during the GTMS period of June 1984. June, 26, 1984 (first day of this period) is used as a magnetically quiet reference day in this study. The following results are obtained : 1) On June 27, the electric field and neutral wind disturbances could be interpreted by the sole action of the ionospheric disturbance dynamo process, 2) On June 28, two physical processes are invoked to interpret the observations : the ionospheric disturbance dynamo and the direct penetration of magnetospheric convection electric fields.     

Global characteristics of ionospheric electric fields and disturbances during the first hours of magnetic storms

The ionospheric plasma density can be significantly disturbed during magnetic storms. In the conventional scenario of ionospheric storms, the negative storm phases with plasma density decreases are caused by neutral composition changes, and the positive storm phases with plasma density increases are often related to atmospheric gravity waves. However, recent studies show that the global redistribution of the ionospheric plasma is dominated primarily by electric fields during the first hours of magnetic storms. In this paper, we present the measurements of ionospheric disturbances by the DMSP satellites and GPS network during the magnetic storm on 6 April 2000. The DMSP measurements include the F region ion velocity and density at the altitude of ∼840 km, and the GPS receiver network provides total electron content (TEC) measurements. The storm-time ionospheric disturbances show the following characteristics. The plasma density is deeply depleted in a latitudinal range of ∼20° over the equatorial region in the evening sector, and the depletions represent plasma bubbles. The ionospheric plasma density at middle latitudes (20°–40° magnetic latitudes) is significantly increased. The dayside TEC is increased simultaneously over a large latitudinal range. An enhanced TEC band forms in the afternoon sector, goes through the cusp region, and enters the polar cap. All the observed ionospheric disturbances occur within 1–5 h from the storm sudden commencement. The observations suggest that penetration electric fields play a major role in the rapid generation of equatorial plasma bubbles and the simultaneous increases of the dayside TEC within the first 2 h during the storm main phase. The ionospheric disturbances at later times may be caused by the combination of penetration electric fields and neutral wind dynamo process.     

The global response of terrestrial ionosphere to the December 2015 space weather event

This paper investigates the ionospheric storm of December 19–21, 2015, which was initiated by two successive CME eruptions that caused a G3 space weather event. We used the in situ electron density (N_e) and electron temperature (T_e) and the Total Electron Content (TEC) measurements from SWARM-A satellite, as well as the O/N₂ observations from TIMED/GUVI to study the ionospheric impact. The observations reveal the longitudinal and hemispherical differences in the ionospheric response to the storm event. A positive ionospheric storm was observed over the American, African and Asian regions on 20 December, and the next day showed a negative storm. Both these exhibited hemispheric differences. A positive storm was observed over the East Pacific region on 21 December. It is seen that the net effect of both the disturbance dynamo electric field and composition differences become important in explaining the observed variability in topside ionospheric densities. In addition, we also discuss the T_e variations that occurred as a consequence of the space weather event.     

Effects of solar activity variations on the low latitude topside nighttime ionosphere

We have studied the topside nighttime ionosphere of the low latitude region using data obtained from DMSP F15, ROCSAT-1, KOMPSAT-1, and GUVI on the TIMED satellite for the period of 2000–2004, during which solar activity decreased from its maximum. As these satellites operated at different altitudes, we were able to discriminate altitude dependence of several key ionospheric parameters on the level of solar activity. For example, with intensifying solar activity, electron density was seen to increase more rapidly at higher altitudes than at lower altitudes, implying that the corresponding scale height also increased. The density increased without saturation at all observed altitudes when plotted against solar EUV flux instead of F10.7. The results of the present study, as compared with those of previous studies for lower altitudes, indicate that topside vertical scale height increases with altitude and that, when solar activity increases, topside vertical scale height increases more rapidly at higher altitudes than at lower altitudes. Temperature also increased more rapidly at higher altitudes than at lower altitudes as solar activity increased. In addition, the height of the F2 peak was seen to increase with increasing solar activity, along with the oxygen ion fraction measured above the F2 peak. These results confirm that the topside ionosphere rises and expands with increasing solar activity.     

Large-scale traveling ionospheric disturbances of auroral origin according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered using measurements of total electron content (TEC) during the magnetic storms on October 29–31, 2003, and on November 7–11, 2004, had 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 f_oF2 were used for this purpose. The variations of TEC and f_oF2 were similar for all events mentioned above. The previous assumption that the ionospheric region with vertical extension from 150 to 200 km located near the F-layer maximum mainly contributes to the TEC variations was confirmed for the cases when the electron density disturbance at the F region maximum was not more than 50%. However, this region probably becomes vertically more extended when the electron density disturbance in the ionospheric F region is about 85%.     

不同上边界条件下的极区电离层数值模拟

利用一维自洽的极区电离层模型,研究了沿磁力线方向不同电离层-磁层耦合条件下极区电离层的响应.此模型在110-610km的电离层空间区域内,综合求解描述极区电离层的连续性方程、动量方程和能量方程,以得到电离层数值解.研究发现,上边界条件在200 km以上的高度能显著地影响电离层参量的形态.较高的O+上行速度对应较低的F层峰值和较高的电子温度.不同边界O+上行速度对应的温度高度剖面完全不同.200km以上电子温度高度剖面不但由来自磁层的热流通量所控制,同时还受到场向O+速度的影响.对利用电离层模型研究电离层内部物理过程提出了建议.      

Ionospheric heating due to solar flares as measured by SROSS-C2 satellite

The data on thermal fluctuations of the topside ionosphere have been measured by Retarding Potential Analyser (RPA) payload aboard the SROSS-C2 satellite over the Indian region for half of the solar cycle (1995–2000). The data on solar flare has been obtained from National Geophysical Data Center (NGDC) Boulder, Colorado (USA) and other solar indices (solar radio flux and sunspot number) were download from NGDC website. The ionospheric electron and ion temperatures show a consistent enhancement during the solar flares. The enhancement in the electron temperature is 28–92% and for ion temperature it is 18–39% compared to the normal day’s average temperature. The enhancement of ionospheric temperatures due to solar flares is correlated with the variation of sunspot and solar radio flux (F10.7cm). All the events studied in the present paper fall in the category of subflare with almost same intensity. The ionospheric electron and ion temperatures enhancement have been compared with the IRI model values.     

Description of the mean behaviour of ionospheric plasma temperatures

A status report on the empirical modeling of ionospheric electron and ion temperatures is given with special emphasis on the models used in the International Reference Ionosphere (IRI).Electron temperature models have now reached a state where reliable prediction of the mean altitudinal, latitudinal and diurnal variations is possible. These models are largely based on satellite measurements, but comparisons with incoherent scatter radar measurements have shown excellent agreement. Variations with season and magnetic and solar activity seem to be small and are not yet included consistently in these models.Similar to the electron temperature, the ion temperature shows the largest variations with altitude, latitude and local time. But due to the larger mass, these variations are smoother and more steady in the case of the ions and therefore easier to model. Nevertheless, very few ion temperature models exist. The IRI model takes advantage of the observed concurrence of the ion temperature with the neutral temperature at low altitudes and with the electron temperature at high altitudes.     

电离层Es离子分布数值建模

从离子连续性方程和动量方程出发,比较全面地考虑了太阳光电离、星光电离、地冕电离、星际背景电离和流星离子流等电离源,综合分析Es层的主要动力学过程和光化学过程,以风剪切理论为基础,研究中性成分碰撞、电场作用、金属离子作用和分子离子作用等机制对离子分布的影响,建立了一维时变电离层Es物理模型.对离子产生率、垂直方向的离子速度在高度和时间上的变化进行仿真和计算,得到了在电场及风剪切作用下的离子密度剖面24h内的变化规律.根据建立的模型,以昆明相干散射雷达观测的径向风结果作为模型输入参考,仿真并得到了电离层Es电子密度的时空分布,据此反演出电离层Es临界频率f₀E_s.与昆明站电离层测高仪同时间观测的情况进行对比,结果比较一致,验证了建立的Es层物理模型正确性.      

The northern and southern mid-latitude ionospheric trough using global IGS vTEC maps

The aim of this work is the analysis of the mid-latitude ionospheric trough (MIT) using the Global Ionospheric Maps from IGS (GIMs) during the solar minimum, year 2008. This study was performed for different local times, 22, 00, 02 and 04 LT on the Northern and Southern hemisphere simultaneously. In the two hemispheres the MIT show asymmetric pattern. The high-latitude troughs are clearly distinguished in autumn and winter. Another feature is the longitudinal development towards the west of the geomagnetic pole covering a wider area in the Northern Hemisphere. Five empirical reference models were tested and compared with the MIT minimum position obtained from GIMs at different local times for both hemisphere. The results show a better agreement with the observations for the Northern Hemisphere specially with the Köehnlein & Raitt model. Fluctuations of 9 days and 27 days of the MIT minimum position are found, which could be related with the solar wind oscillations, especially for 00 and 02 LT in both hemisphere, suggesting a link between them.