Positive Ionospheric Disturbances Research Articles

Ionospheric storm due to solar Coronal mass ejection in September 2017 over the Brazilian and African longitudes

Coronal mass ejection (CME) occurs when there is an abrupt release of a large amount of solar plasma, and this cloud of plasma released by the Sun has an intrinsic magnetic field. In addition, CMEs often follow solar flares (SF). The CME cloud travels outward from the Sun to the interplanetary medium and eventually hits the Earth’s system. One of the most significant aspects of space weather is the ionospheric response due to SF or CME. The direction of the interplanetary magnetic field, solar wind speed, and the number of particles are relevant parameters of the CME when it hits the Earth’s system. A geomagnetic storm is most geo-efficient when the plasma cloud has an interplanetary magnetic field southward and it is accompanied by an increase in the solar wind speed and particle number density. We investigated the ionospheric response (F-region) in the Brazilian and African sectors during a geomagnetic storm event on September 07–10, 2017, using magnetometer and GPS-TEC networks data. Positive ionospheric disturbances are observed in the VTEC during the disturbed period (September 07–08, 2017) over the Brazilian and African sectors. Also, two latitudinal chains of GPS-TEC stations from the equatorial region to low latitudes in the East and West Brazilian sectors and another chain in the East African sector are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA). We noted that the EIA was disturbed in the American and African sectors during the main phase of the geomagnetic storm. Also, the Brazilian sector was more disturbed than the African sector.

Investigation of Daytime Total Electron Content Enhancements over the Asian-Australian Sector Observed from the Beidou Geostationary Satellite during 2016–2018

This study focused on the investigation of daytime positive ionospheric disturbances and the recurrence of total electron content (TEC) enhancements. TEC data derived from the Beidou geostationary satellite over the Asian-Australian sector were used to study the occurrence of TEC enhancements during 2016–2018. The occurrence of TEC enhancements under quiet geomagnetic condition was analyzed. Furthermore, the occurrence of TEC enhancements during different geomagnetic storm phases was considered to address the question that relates to the recurrence of TEC enhancements during the recovery phase of geomagnetic storms. The seasonal variation of TEC enhancements displayed equinoctial and solstitial peaks at the middle and low latitudes respectively. Besides, there was no evident systematic latitudinal dependence in the occurrence of TEC enhancements, albeit at the equatorial station, nearly no TEC enhancement was observed under Kp < 3. Meanwhile, the occurrences during the main phases of the geomagnetic storms were significantly above the TEC enhancement baselines except at HKWS. The prominence of TEC enhancements during the main phase in comparison with the initial and recovery phases could be attributed to the effects of prompt penetration electric fields and equator-ward neutral winds. Moreover, the pattern of TEC enhancements during the storm recovery indicates the effects of chemical composition changes, winds, and the possible modulation from the lower atmospheric forcing.

Ionospheric Disturbances due to the Influence of Localized Thermospheric Sources

The paper presents the results of numerical modeling of the ionospheric disturbances from spatially localized, midlatitude, thermospheric sources that simulate the dissipation effect of acoustic–gravity waves generated by phenomena on the Earth’s surface and in the lower atmosphere. The results of numerical calculations have shown that the range of ionospheric effects significantly exceeds the size of the region of sources of thermospheric disturbances and reaches low latitudes. In the spatial distribution of the critical frequency of the ionospheric F2 layer, it decreases directly above the thermospheric source and increases to the south of it. Negative ionospheric disturbances are due to a decrease in the partial concentration of atomic oxygen in the area of a thermospheric source. The processes of turbulent diffusion, which lead to a decrease in the concentration of atomic oxygen in the lower thermosphere, are most effective in reducing the electron concentration in the ionosphere. The developing large-scale circulation processes in the thermosphere lead to positive ionospheric disturbances, which are observed south of the source region up to low latitudes.

Disturbances of the thermosphere-ionosphere-plasmasphere system and auroral electrojet at 30°E longitude during the St. Patrick's Day geomagnetic storm on 17–23 March 2015

This study presents an analysis of geomagnetic disturbances and ionospheric electron density distribution during the 2015 St. Patrick's Day geomagnetic storm. To study those we have used the satellite-borne and ground-based observations. The St. Patrick's geomagnetic storm covers the interval of 15–23 March 2015, when solar eruptive phenomena (a long-enduring C9-class solar flare and associated CME's on 15 March) and a strong geomagnetic storm on 16–18 March (Dst dropped as strong as –228 nT) were reported. This geomagnetic storm is still the strongest one observed in the current solar cycle. The severe geomagnetic storm on 17-18 March 2015 led to complex effects on the ionosphere. We consider major features of the positive and negative ionospheric storms development at European mid- and high-latitudes. One of the interesting phenomena was observation of the positive ionospheric disturbances during the recovery phase. Using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) we examined the main physical processes that played a major role in dramatic changes of the total electron content and the F2 layer peak electron density during this storm event.

Earthquake aftereffects in the Equatorial Ionization Anomaly region under geomagnetic quiet and storm conditions

In addition to multi-scale spatio-temporal trends that shape the ionosphere variability, the ionosphere responds to the disturbances that are solar, geomagnetic and seismic in origin. In this study, post-seismic ionospheric disturbances are investigated retrospectively from 1999 to 2015 using two different sets of ionospheric maps of the F2 layer critical frequency, foF2. One set of foF2 maps is obtained by assimilating Global Ionospheric Maps (GIM) of Total Electron Content (TEC) into IRI-Plas model (IRI-Plas-foF2). Another set of hourly foF2 maps is obtained using PRIME-251 mapping technique (PRIME-foF2) by the assimilation of ionosonde foF2 data into IRI-CCIR model. The geomagnetic storms affecting the ionosphere are determined with relevant thresholds of geomagnetic AE, aa, ap, ap(τ) and Dst indices. It is observed that more than 60% of the earthquakes occur in the Equatorial Ionization Anomaly (EIA) region within the belt of geomagnetic latitudes ±40° N and geographic longitudes 90–190° E. The co-seismic foF2 disturbances, DfoF2, are identified for the cells of the map if an instant foF2 value is outside of pre-defined bounds of foF2 median (μ) and standard deviation (σ), μ±1σ, in the map fragment of 1000kmradius around the earthquake hypocenter. The results of positive ionospheric disturbances, DfoF2p, and negative disturbances, DfoF2n, in the EIA region during the 12h after earthquake differ with respect to geomagnetic quiet and storm conditions, nighttime and daytime, magnitude and depth of the earthquake. The maximum spatial variability (for more than 50% of map cells in the vicinity of hypocenter) is observed with positive disturbances (DfoF2p) for the earthquakes that occurred during daytime at a depth of 70–300km.

Response of the Midlatitude F2 Layer to Some Strong Geomagnetic Storms during Solar Minimum as Observed at Four Sites of the Globe

In this study, we documented the midlatitude F2-layer response to five strong geomagnetic storms with minimum Dst < -150 nT that occurred in solar minimum years using hourly values of the F2-layer critical frequency (foF2) from four ionosondes located in different hemispheres. The results were very limited, but they illustrated some peculiarities in the behavior of the F2-layer storm. During equinox, the characteristic ionospheric disturbance patterns over the Japanese station Wakkanai in the Northern Hemisphere and the Australian station Mundaring in the Southern Hemisphere were consistent with the well-known scenario by <TEX>$Pr{\ddot{o}}lss$</TEX> (1993); however, during a December solstice magnetic storm, both stations did not observe any noticeable positive ionospheric disturbances. Over the "near-pole" European ionosonde, clear positive ionospheric storms were not observed during the events, but the "far-from-pole" Southern Hemisphere station Port Stanley showed prominent enhancements in F2-layer peak electron density in all magnetic storms except one. No event produced noticeable nighttime enhancements in foF2 over all four ionosondes.

Is there an abnormal enhancement of atmospheric aerosol before the 2008 Wenchuan earthquake?

There are extensive reports of ionospheric disturbances before the great 2008 Wenchuan earthquake, which are possibly explained by seismogenic electric field hypotheses linked with the aerosols injected in atmosphere. This paper attempts to investigate the possible change of atmospheric aerosol optical depth (AOD) associated with this earthquake by using MODIS data from both Terra and Aqua satellites. The result shows a clear enhancement of AOD along the Longmenshan faults 7days before the quake, which is 1day and 4days earlier than the reported negative and positive ionospheric disturbances, respectively, and is 1day earlier than or quasi-synchronism with other reported atmospheric anomalies including air temperature, outgoing longwave radiation and relative humidity. Particularly, the spatial distribution of AOD enhancement is very local and it is correlated well with the active faults and surface ruptures. We suggest that this unique enhancement could be associated with the Lithosphere–Atmosphere–Ionosphere coupling process during the preparation of the Wenchuan earthquake.

Studying ionospheric responses to magnetic storms depending on the local time of the storm main phase onset

A morphological analysis of vertical sounding data obtained in Irkutsk from 2003 to 2008 has been performed. The AE index was used to determine the geomagnetic activity level, and the storm main phase onset was registered based on the D st index. The ionospheric response to a magnetic storm was estimated based on the relative deviation of the critical frequency and altitude of the ionospheric F2 region from the median values. Superstrong magnetic storms and storms without positive initial phases were not considered when the data were selected. We found that positive ionospheric disturbances, which were accompanied by an increase in the F2 region maximum altitude, predominated between the storm initial phase and main phases during all considered magnetic storms. Between these storm phases, negative disturbances were only registered at night. Predominance of positive ionospheric disturbances over negative ones can be related to the selection of storms for studies.

Giant disturbance in the ionospheric F2 region prior to the &amp;lt;i&amp;gt;M&amp;lt;/i&amp;gt;8.0 Wenchuan earthquake on 12 May 2008

Abstract. On 12 May 2008 at 14:28 LT great earthquake (M=8.0) occurred at Wenchuan (31.00° N, 103.40° E), China. The hourly values of foF2 are analyzed over ten ionospheric observatories: Haikou (20.00° N, 110.33° E), Kunming (25.00° N, 102.70° E), Guangzhou (20.00° N, 113.70° E), Chongqing (29.50° N, 106.40° E), Lhasa (29.63° N, 91.17° E), Lanzhou (36.07° N, 103.87° E), Beijing (40.00° N, 116.30° E), Urumqi (43.75° N, 87.63° E), Chuangchun (43.83° N, 125.30° E) and Manzhouli (49.60° N, 117.45° E). With a new factor, effective sunspot number Reff, the results show that there were giant positive disturbances of foF2 around the epicentral zone on 9 May, 3 days prior to the earthquake. Our results indicate that the observed positive ionospheric disturbances were most possibly associated with the imminent earthquake and the new analytic method has good prospects in practice.

Global Ionospheric Response to the Geomagnetic Storm Event of April 6-7, 2000

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f0F2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MSISE90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.

Study of the thermospheric-ionospheric response to intense geomagnetic storms at middle latitudes

The ionospheric response to enhanced geomagnetic activity was studied in terms of two ionospheric parameters, foF2 and h'F2, aiming the investigation of the middle latitude positive and negative ionospheric storm effects characteristics. Simultaneous observations from a chain of several middle latitude stations distributed in longitude around the earth during two intense geomagnetic storms (Dst < −100 nT), were analyzed in this work. The correlation results between the foF2 and h'F2 disturbances and the Dst geomagnetic index verified that the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms shows a great degree of variability and a strong dependence on local time observation. Negative deviations constitute the typical ionospheric response. In general it is reported that the F2 layer virtual height h'F2, which is observed only during daytime in conjunction with F1 layer presence, shows clear response to magnetic storm activity. On the other hand, positive ionospheric disturbances are accompanied by weak height enhancements. Real observations were also compared to the thermospheric-ionospheric view associated with positive and negative storm effects proposed by Prolss (1993). This test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms, taking into consideration that any new burst of activity is associated to a new disturbance zone, resulting to the formation of a large zone of disturbance that covers the post-midnight and the forenoon sector as well. This mechanism may be the cause of long lasting negative storm effects observed as the typical ionospheric response to geomagnetic storm activity.

Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model

Abstract. Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere system including electrodynamical coupling effects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exemplifies the complex storm phenomena. The study focuses on positive ionospheric storm effects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical effects of both neutral meridional winds and electric fields caused by the disturbance dynamo effect. The penetration of short-time electric fields of magnetospheric origin during storm intensification phases is shown for the first time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N2] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at fixed altitudes) above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F2-region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic field lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs). The calculated zonal electric field disturbances also help to create the positive ionospheric disturbances both at middle and low latitudes. Minor contributions arise from the general density enhancement of all constituents during geomagnetic storms, which favours ion production processes above ion losses at fixed height under day-light conditions.Key words: Atmospheric composition and structure (thermosphere · composition and chemistry) · Ionosphere (ionosphere · atmosphere interactions; modelling and forecasting)

Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model

Current theories of F-layer storms are discussed using numerical simulations with the Upper Atmosphere Model, a global self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere system including electrodynamical coupling effects. A case study of a moderate geomagnetic storm at low solar activity during the northern winter solstice exemplifies the complex storm phenomena. The study focuses on positive ionospheric storm effects in relation to thermospheric disturbances in general and thermospheric composition changes in particular. It investigates the dynamical effects of both neutral meridional winds and electric fields caused by the disturbance dynamo effect. The penetration of short-time electric fields of magnetospheric origin during storm intensification phases is shown for the first time in this model study. Comparisons of the calculated thermospheric composition changes with satellite observations of AE-C and ESRO-4 during storm time show a good agreement. The empirical MSISE90 model, however, is less consistent with the simulations. It does not show the equatorward propagation of the disturbances and predicts that they have a gentler latitudinal gradient. Both theoretical and experimental data reveal that although the ratio of [O]/[N2] at high latitudes decreases significantly during the magnetic storm compared with the quiet time level, at mid to low latitudes it does not increase (at fixed altitudes) above the quiet reference level. Meanwhile, the ionospheric storm is positive there. We conclude that the positive phase of the ionospheric storm is mainly due to uplifting of ionospheric F2-region plasma at mid latitudes and its equatorward movement at low latitudes along geomagnetic field lines caused by large-scale neutral wind circulation and the passage of travelling atmospheric disturbances (TADs). The calculated zonal electric field disturbances also help to create the positive ionospheric disturbances both at middle and low latitudes. Minor contributions arise from the general density enhancement of all constituents during geomagnetic storms, which favours ion production processes above ion losses at fixed height under day-light conditions.Key words: Atmospheric composition and structure (thermosphere · composition and chemistry) · Ionosphere (ionosphere · atmosphere interactions; modelling and forecasting)