Influence of geomagnetic storms of September 26–30, 2011, on the ionosphere and HF radiowave propagation. I. Ionospheric effects (original) (raw)
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The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth–ionosphere waveguide. This characteristic makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40–54°), we analyse the trend in variation of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflected the prevailing space weather conditions in various time scales. In particular, the 'dipping' of midday signal amplitude peak (MDP) occurs after significant geomagnetic perturbed or storm conditions in the time scale of 1–2 days. The mean signal amplitude before sunrise (MBSR) and mean signal amplitude after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and the highly variable conditions of dusk-to-dawn iono-sphere. We also observed few cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event. This effect may be related to storms associated phenomena or effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity) exhibited a tendency of recovery to pre-storm day level. In the present analysis, we do not see a well-defined trend in the variation of the post-storm sunrise amplitude terminator (SRT) and sunset terminator (SST). The SRT and SST signals show more dipping in GQD-A118 propagation path but generally an increase along DHO-A118 propagation path. Thus the result could be propagation path dependent and detailed modelling is required to understand these phenomena.
Effects of Earth's magnetic field variation on high frequency wave propagation in the ionosphere
Annales Geophysicae Discussions
The ionosphere is an anisotropic, dispersive medium for the propagation of radio frequency electromagnetic waves due to the presence of the Earth's intrinsic magnetic field and free charges. The detailed physics of electromagnetic wave propagation through a plasma is more complex when it is embedded in a magnetic field. In particular, the ground range of waves reflecting in the ionosphere presents detectable magnetic field effects. Earth's magnetic field varies greatly, with the most drastic scenario being a polarity reversal. Here the spatial variability of the ground range is analyzed using numerical ray tracing under possible reversal scenarios. Pattern changes of the "spitze", a cusp in the ray path closely related to the geomagnetic field, are also assessed. The ground range increases with magnetic field intensity and ray alignment with the field direction. For the present field, which is almost axial dipolar, this happens for Northward propagation at the magnetic equator, peaking in Indonesia where the intensity is least weak along the equator. A similar situation occurs for a prevailing equatorial dipole with Eastward ray paths at the corresponding magnetic equator that here runs almost perpendicular to the geographic equator. Larger spitze angles occur for smaller magnetic inclinations, and higher intensities. This is clearly observed for the present field and the dipole rotation scenario along the corresponding magnetic equators. For less dipolar configurations the ground range and spitze spatial variabilities become smaller scale. Overall, studying ionospheric dynamics during a reversal may highlight possible effects of dipole decrease which is currently ongoing. 1 Introduction Radio frequency electromagnetic waves between 3 and 30 MHz, designated as high frequency (HF) waves by the International Telecommunication Union (ITU), are used in long-distance communications and detection, and have been of interest since the 1920's from a geophysical point of view as well as for practical reasons. Since the advent of telecommunication systems it has been a challenge to establish radio links as well as exact positions with radar systems using the ionosphere as a reflector due to the theoretical complexity of electromagnetic wave propagation through the ionospheric plasma that is embedded in the Earth's magnetic field. The ray tracing technique is commonly employed to solve this problem and to estimate the ray path
Ionospheric effects caused by the series of geomagnetic storms of September 9–14, 2005
2011
This study presents the ionospheric effects caused by the series of geomagnetic storms of Septem ber 9-14, 2005. The behavior of different ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill and Arecibo stations during the considered period have been numerically calculated, using a global self con sistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) developed at WD IZMI RAN. The model calculations of disturbances of the ionospheric parameters during storms qualitatively agree with the experimental data at these midlatitude stations. We suggest that the causes of the quantitative differ ences between the model calculations and the observational data were the use of the 3 hour Kp index of geo magnetic activity and the dipole approximation of geomagnetic field in GSM TIP, with additional contribu tions from the effects of solar flares which are not considered in GSM TIP.
2021
We performed a diagnostic study of geomagnetic storm-induced disturbances that are coupled to the lower ionosphere in mid-latitude D-region using propagation characteristics of VLF radio signals. We characterised the diurnal VLF amplitude (from two propagation paths) into five metrics, namely the mean amplitude before sunrise (MBSR), midday amplitude peak (MDP), mean amplitude after sunset (MASS), sunrise terminator (SRT) and sunset terminator (SST). We analysed and monitored the trend in variations of signal metrics for up to 20 storms, to understand deviations in the signal that are attributable to the storms; five storms (and their effects on the signals) were studied in detail, followed by statistical analysis that included 15 other events. When the pre-storm day signal level where compared with the storm day values, we found that the MDP exhibited characteristic dipping in about 67% and 80% in GQD-A118 and DHO-A118 propagation paths, respectively. The MBSR showed respective dipping of about 77% and 60%, while the MASS dipped by 58% and 67%. Conversely, the SRT and SST showed respective dipping of 25% and 33%, and 42% and 47%. The percentage dip of the MBSR and MASS increased significantly when the 2-day mean signals before the events (as against the 1-day mean value) were cosidered. Of the two propagation paths used in this study, the dipping of the amplitude of DHO-A118 propagation path signal is larger (as also observed in previous study). To understand the state of the ionosphere over the signal propagation paths and how it affects the VLF responses, we further analysed virtual heights (h E, h F1 and h F2) and critical frequencies (f oE, f oF1, and f oF2) of the E and F regions (from ionosonde stations near the transmitters). The results of this analysis showed a significant increase and/or fluctuations of the foF2, foF1, h'F2, h'F, h'Es and h'E near both transmitters during the geomagnetic storms. The largest increase in heights of the regions (h'F2, h'F, h'Es and h'E) occured over Juluisruh station (around the DHO transmitter) in Germany, suggesting a strong storm responses over the region leading to the large dipping of the DHO-A118 propagation path signal.
2020
Back at the end of the last century, L. F. Chernogor validated the concept that geospace storms are comprised of synergistically coupled magnetic storms, ionospheric storms, atmospheric storms, and storms in the electric field originating 10 in the magnetosphere, the ionosphere and the atmosphere (i.e., electric storms). Their joint studies require the employment of multiple-method approach to the Sun-interplanetary medium-magnetosphere-ionosphere-atmosphere-Earth system. This study provides general analysis of the 30 August-2 September 2019 geospace storm, the analysis of disturbances in the geomagnetic field and in the ionosphere, as well as the influence of the ionospheric storm on the characteristics of HF radio waves over the People's Republic of China. A unique feature of the geospace storm under study is its duration, of up to four 15 days. The main results of the study are as follows. The energy and power of the geospace storm have been estimated to be 1.5 10 15 J and 1.5 10 10 W, and thus this storm is weak. The energy and power of the magnetic storm have been estimated to be 1.5 10 15 J and 9 10 9 W, i.e., this storm is moderate, and a unique feature of this storm is the duration of the main phase, of up to two days. The recovery phase also was lengthy, no less than two days. On 31 August 2019 and on 1 September 2019, the variations in the H and D components attained 60-70 nT, while the Z-component variations did not 20 exceed 20 nT. On 31 August 2019 and on 1 September 2019, the level of fluctuations in the geomagnetic field in the 100-1000 s period range increased from 0.2-0.3 nT to 2-4 nT, while the energy of the oscillations showed a maximum in the 300-400 s to 700-900 s period range. The geospace storm was accompanied by a moderate to strong negative ionospheric storm. During 31 August 2019 and 1 September 2019, the electron density in the ionospheric F region reduced by a factor of 1.4 to 2.4 times as compared to the values on the reference day. The geospace storm gave rise to appreciable disturbances 25 also in the ionospheric E region, as well as in the Es layer. In the course of the ionospheric storm, the altitude of reflection of radiowaves could sharply increase from 150 km to 300-310 km. The geospace storm was accompanied by the generation of atmospheric gravity waves modulating the ionospheric electron density. For the 30 min period oscillation, the amplitude of the electron density disturbances could attain 40 %, while it did not exceed 6 % for the 15 min period. The results obtained have made a contribution to understanding of the geospace storm physics, to developing theoretical and empirical 30 models of geospace storms, to the acquisition of detailed understanding of the adverse effects that geospace storms have on radiowave propagation and to applying that knowledge to effective forecasting these adverse influences. 1 Introduction Geospace storms are comprised of synergistically coupled magnetic storms, ionospheric storms, atmospheric storms, and storms in the electric fields originating in the magnetosphere, the ionosphere, and the atmosphere (i.e., electrical storms). 35 Consequently, the discussion of only one of the storms would be incomplete, and therefore, the analysis of geospace storms requires the employment of a systems approach. These storms are of solar origin, and they are accompanied by solar flares, coronal mass ejections, energetic proton fluxes, and solar radio bursts. All listed above processes affect the magnetosphere, the ionosphere, the atmosphere, and the internal terrestrial layers through the interplanetary medium. Their joint study
Ionospheric effects of geomagnetic storms at mid latitudes
Russian Journal of Physical Chemistry B, 2011
Previously, we studied the ionospheric effects of the sequence of geomagnetic storms on September 9–14, 2005 using a global self-consistent model “Thermosphere-Ionosphere-Protonosphere” (GSM TIP). Differences between the predicted and observed effects of the ionospheric storms may be due to the use of the three-hour K p index of geomagnetic activity in modeling the time dependence of model input parameters, use
Effects of geomagnetic storms in the lower ionosphere, middle atmosphere and troposphere
Journal of Atmospheric and Terrestrial Physics, 1996
Geomagnetic storm effects at heights of about O-100 km are briefly (not comprehensively) reviewed, with emphasis being paid to middle latitudes, particularly to Europe. Effects of galactic cosmic rays, solar particle events, relativistic and highly relativistic electrons, and IMF sector boundary crossings arc briefly mentioned as well. Geomagnetic storms disturb the lower ionosphere heavily at high latitudes and very significantly also at middle latitudes. The effect is almost simultaneous at high latitudes, while an after-effect dominates at middle latitudes. The lower thermosphere is disturbed significantly. In the mesosphere and sl.ratosphere, the effects become weaker and eventually non-detectable. There is an effect in total ozone but only under special conditions. Surprisingly enough, correlations with geomagnetic storms seem to reappear in the troposphere, particularly in the Northern Hemisphere. Atmospheric electricity is affected by geomagnetic storms, as well. We essentially understand the effects of geomagnetic storms in the lower ionosphere, but there is a lack of mechanisms to explain correlations found deeper in the atmosphere, particularly in the troposphere. There seem to be two different groups of effects with possibly different mechanisms-those observed in the lower ionosphere, lower thermosphere and mesosphere, and those observed in the troposphere.
Study of Ionospheric Irregularities in the F-Region During Geomagnetic Storms
2017
The study of horizontal movements of small scale ionospheric irregularities at Waltair (dip 17.7 N; 83.3 E) using D1 technique was started as early as I.G.Y. period. In this paper the results of observations of the drift and anisotropy parameters of ionospheric irregularities in the F-region during 6 Geomagnetic storms are presented. F-region spaced antenna drift records taken on frequency 5.6 MHz during the period September 1983-May 1984 at Waltair (Visakhapatnam) are used in the present investigation. In F-region, the true drift velocity during the entire storm period is found to be smaller than the average value of the control day true drift velocity. The random velocity during storm time is comparatively more than that observed on control days, at least for about 40 hrs after the commencement of the storm. The orientation of the semi-major axis mostly lies in the range of 90 – 150 N of E, both on storm days as well as on control days, indicating no significant change during stor...
Preliminary Study of the Ionosphere Response to the Geomagnetic Storm Occurred on September 26, 2011
INCT-APA Annual Activity Report, 2015
Geomagnetic storms generate disturbances in the ionosphere due to the incidence of energetic particles, which can disturb communication and navigation systems. To understand the phenomena we analyzed ionosonde and GPS data obtained at Comandante Ferraz Brazilian Antarctic Station (62.1°S, 58.4°W) and studied the effect produced by a geomagnetic storm that occurred on 26 th September 2011. The analysis covers the period of 24-30 September when the effect of the moderate geomagnetic storm produced an electron density increase in the ionospheric F region.