Weak Geomagnetic Disturbances Research Articles

Estimation of the Ionospheric Effects of Geomagnetic Disturbances Based on Data from Wakkanai Station

Ionosonde measurements of the critical frequency of the ionospheric F2 layer (foF2) at Wakkanai station (Japan) are analyzed with the method of superposed epochs. The station is situated in a region of high seismicity. Winter periods with low sunspot and geomagnetic activity and high seismic activity are considered. The goals of this work were the quantitative characterization and comparison of ionospheric disturbances induced by the development of geomagnetic storms/geomagnetic disturbances. Geomagnetic disturbances refer to manifestations of geomagnetic activity with an intensity that is higher than “quiet” geomagnetic background but not higher than the threshold characteristic of weak geomagnetic storms. It is ascertained that weak geomagnetic storms and geomagnetic disturbances, from the time of the main trough in the Dst index after the onset of a geomagnetic storm/geomagnetic disturbance to the end of the third day, result in only positive foF2 deviations. The deviations exceed 6% of the background; the maximal relative deviations from the background (δfoF2max) are ~17% and ~14%, respectively. For geomagnetic disturbances, the most significant response of the ionosphere is observed ~7 h after the main trough in the Dst index. The resulting assessments can be used to filter out false ionospheric earthquake precursors with analysis of the ionospheric data from Wakkanai station.

Functional State of the Brain of Elderly Women at Rest and in Mental Stress under Varying Geomagnetic Conditions

We studied the effect of geomagnetic disturbances on the functional activity of the brain in healthy elderly women (50–60 years). We performed personalized studies of the brain bioelectrical activity (EEG) in normal days (Kp = 1–2) and days with weak geomagnetic disturbances (Kp = 4). The EEG segments of the main regions in both hemispheres were used for computer analysis to determine the frequency, amplitude, and index characteristics in the state of quiet wakefulness with eyes closed and in solving a mental arithmetic task. We observed changes in the structural organization both at rest and in mental stress in the days of geomagnetic disturbances in comparison with the normal days. The changes reflected mainly the disturbances of the balance of synchronization and desynchronization mechanisms of nonspecific brain systems and the response of the limbic system and temporal areas, mainly in the right hemisphere. At the same time, the activation processes in the high-frequency beta spectrum affect the frontal and temporal regions in mental stress in normal days. On the days of geomagnetic disturbances, the activation is diffuse and affects the low-frequency spectra of the EEG beta-range. These data and the decrease in the index and frequency of the theta rhythm on the days of weak geomagnetic disturbances, in contrast to the increase in the index of the theta rhythm in the normal days, suggest that the variant of the EEG structure is less optimal for successful completion of the task.

Dynamics and spatio-temporal distribution of geomagnetic disturbances during periods of increased solar activity and magnetic storms

A detailed spatio-temporal analysis of magnetic data was performed during the periods of magnetic storms on October 02, 2013 and September 27, 2019 based on measurements of the station network. In this work, we used a method developed by us for the analysis of magnetic data, based on the use of wavelet transform and adaptive thresholds. The method allows us to identify short-period field disturbances and estimate their intensity from the data of the H-component of the geomagnetic field. The features of the occurrence and propagation of geomagnetic disturbances in the auroral zone and at meridionally located stations have been studied. Dynamic spectra of disturbances of different intensity and duration are obtained. The paper confirms the possibility of occurrence of short-period weak geomagnetic disturbances at stations from high latitudes to the equator, preceding magnetic storms and correlating with fluctuations of the southern Bz-component of the interplanetary magnetic field and increases in the auroral indices of geomagnetic activity. Cross-correlation dependences of the intensity of geomagnetic disturbances on the parameters of the interplanetary medium during magnetic storms were obtained from the data of the network of magnetic stations. A statistically significant influence of the magnitude of the scope of the Bz-component of the IMF and the speed of the solar wind on the development of magnetic storms during the initial and main phases of magnetic storms was revealed.

Geomagnetic disturbances at F1-layer heights under different solar activity conditions over Norilsk

We analyze the influence of geomagnetic disturbances on the electron density Ne at Norilsk ionospheric station (69° N; 88° E) at F1-layer heights (120–200 km). For the analysis, we have selected 25 moderate and weak geomagnetic disturbances for two seasons — spring and fall — of 2003–2014. Using the Ne values obtained from measurements made with the Norilsk digisonde during this period, we analyze Ne variations during geomagnetic disturbances in spring and fall for a long period of time. We determine the effect of spring-fall asymmetry occurring in all solar activity phases and manifesting itself in a significant decrease in the electron density during the main phase of fall storms at all heights in comparison with quiet days: up to 2.6 times at a height of 200 km and slightly less at lower heights. This phenomenon is not observed during spring disturbances: Ne variations are much weaker.

Геомагнитные возмущения на высотах слоя F1 ионосферы в различных условиях солнечной активности над Норильском

We analyze the influence of geomagnetic disturbances on the electron density Ne at Norilsk ionospheric station (69° N; 88° E) at F1-layer heights (120–200 km). For the analysis, we have selected 25 moderate and weak geomagnetic disturbances for two seasons — spring and fall — of 2003–2014. Using the Ne values obtained from measurements made with the Norilsk digisonde during this period, we analyze Ne variations during geomagnetic disturbances in spring and fall for a long period of time. We determine the effect of spring-fall asymmetry occurring in all solar activity phases and manifesting itself in a significant decrease in the electron density during the main phase of fall storms at all heights in comparison with quiet days: up to 2.6 times at a height of 200 km and slightly less at lower heights. This phenomenon is not observed during spring disturbances: Ne variations are much weaker.

The Influence of Weak Geomagnetic Disturbances on the Rat Cardiovascular System under Natural and Shielded Geomagnetic Field Conditions

Abstract—This work was aimed at studying the effects of weak geomagnetic disturbances on systolic blood pressure, the R–R interval, the low-frequency and high-frequency components, and its ratio of heart rate variability spectrum under natural and shielded geomagnetic field conditions. All tests were performed with male Wistar rats placed in simulation and shielded chambers. In the simulation chamber, significant shifts in the parameters under study were observed on the days of geomagnetic disturbances: an increase in systolic blood pressure, as well as in the ratio of low- to high frequency components of the heart rate variability spectrum. In the shielded chamber, the parameters were not considerably different under quiet and disturbed geomagnetic field. In addition, in the stimulation chamber, the value of the mean daily barometric pressure was inversely correlated with systolic blood pressure; this relationship was significantly weakened under shielded geomagnetic field conditions. It was concluded that weak geomagnetic disturbances affect cardiovascular and autonomic nervous system functions. The authors hypothesize that the enhanced effect of a slight decrease in barometric pressure on systolic blood pressure in the natural geomagnetic field could be associated with the effect of geomagnetic activity on the mechanisms of blood oxygenation.

Detection and analysis of short-period geomagnetic perturbations during increased solar activity and magnetic storms

The dynamics of geomagnetic field variations on the eve and during the periods of magnetic storms of 2015 and 2017 has been studied (data of the horizontal component of the Earth’s magnetic field of the terrestrial station network were used). The method developed by the authors based on wavelet transform and adaptive threshold functions was applied. Weak geomagnetic disturbances synchronously appearing at the stations and preceding the onset of strong magnetic storms was extracted. The correlation of the isolated geomagnetic disturbances with the AE-index is shown, both in the occurrence times and in intensities. On the basis of comparison with interplanetary environment data (interplanetary magnetic field data and the solar wind parameters were analyzed), and also based on the results of other author works [1, 2]. we assume that the isolated effects have solar nature. The research is supported by the grant of the Russian Science Foundation No. 14-11-00194.

The 27 day solar rotational effect on mesospheric nighttime OH and O3 observations induced by geomagnetic activity.

Observations performed by the Earth Observing System Microwave Limb Sounder instrument on board the Aura satellite from 2004 to 2009 (2004 to 2014) were used to investigate the 27 day solar rotational cycle in mesospheric OH (O3) and the physical connection to geomagnetic activity. Data analysis was focused on nighttime measurements at geomagnetic latitudes connected to the outer radiation belts (55°N/S–75°N/S). The applied superposed epoch analysis reveals a distinct 27 day solar rotational signal in OH and O3 during winter in both hemispheres at altitudes >70 km. The OH response is positive and in‐phase with the respective geomagnetic activity signal, lasting for 1–2 days. In contrast, the O3 feedback is negative, delayed by 1 day, and is present up to 4 days afterward. Largest OH (O3) peaks are found at ~75 km, exceeding the 95% significance level and the measurement noise of <2% (<0.5%), while reaching variations of +14% (−7%) with respect to their corresponding background. OH at 75 km is observed to respond to particle precipitation only after a certain threshold of geomagnetic activity is exceeded, depending on the respective OH background. The relation between OH and O3 at 75 km in both hemispheres is found to be nonlinear. In particular, OH has a strong impact on O3 for relatively weak geomagnetic disturbances and accompanying small absolute OH variations (<0.04 ppb). In contrast, catalytic O3 depletion is seen to slow down for stronger geomagnetic variations and OH anomalies (0.04–0.13 ppb), revealing small variations around −0.11 ppm.

Dependence of Characteristics of SURA Induced Artificial ULF/VLF Signals on Geomagnetic Activity

A comprehensive study of artificial ionospheric signal generation in the ULF/VLF bands at SURA facility in Russia was conducted during the past 4 years. We investigated the influence of geomagnetic activity on the characteristics of artificial low-frequency signals under the background of increasing solar activity. No correlation of artificial ULF signals with variations of Earth’s magnetic field was observed for weak geomagnetic disturbances \((Kp \le 3)\) while the VLF signals increased in the growth phase of the geomagnetic perturbation. In case of strong magnetic storm \((Kp \ge 5+)\) a tendency of the amplitude of the ULF/VLF signals decrease with increasing magnetic disturbance was observed. Sometimes, the modulation of artificial ULF signals with a period of 15–30 s was detected in the decay phase of magnetic storms. During storm time, a change in the polarization of artificial VLF emissions was detected. The right polarization becomes predominant. Interpretation of observed peculiarities of artificial VLF signals is given in the context of the physical mechanism of ionospheric current drive by RF pumping.

Outer radiation belt of relativistic electrons during the minimum of the 23rd solar cycle

The data on fluxes of electrons with energy Ee > 1 MeV and on radiation doses under the Al shielding of about 2 g/cm2 measured on the GLONASS satellite (circular orbit with altitude 20000 km and inclination 65°) for the period from December 2006 through May 2010 are analyzed. The minimum of the 23rd solar cycle turned out to be the longest for all over the space exploration age. Consequently, average semiannual electron fluxes and daily radiation doses are showing the decrease by more than an order of magnitude in comparison with the levels observed in 2007. We present an example of a diffusion wave of relativistic electrons; the wave develops in a period between magnetic storms. This process may result in a significant increase of the radiation dose measured in the orbit, even under the conditions of weak geomagnetic disturbances. The dynamics of variations in relativistic electron fluxes during the magnetic storm of April 5–6, 2010, is discussed so far as this is the first strong flux enhancement in the 24th solar cycle.

Dynamics of the Earth’s outer radiation belt in November 2009 based on the experimental data from the CORONAS-Photon and Meteor-M No. 1 satellites

The dynamics of the Earth’s outer radiation belt were traced at altitudes of 500–830 km during weak geomagnetic disturbances based on the data of simultaneous experiments carried out in November 2009 onboard the CORONAS-Photon solar observatory and the Meteor-M No. 1 artificial satellite. The average statistical profile of external boundary of the outer radiation belt that is characteristic for a quiet magnetosphere has been found from the analysis of variations in the position of the polar boundary of the capture region in the Earth’s magnetosphere.

On the importance of total electron content enhancements during the extreme solar minimum

Observations of ionospheric vertical total electron content (vTEC) from European ground-based Global Navigation Satellite Systems (GNSS) receivers during the period January 2008–January 2010 are used to investigate, for the first time, vTEC sensitivity to weak geomagnetic disturbances under extreme solar minimum conditions. This study shows a significant number of events for the period in question, all of which exhibited some form of exceptionally large values of vTEC during small-magnitude geomagnetic disturbances. To illustrate our point on the importance of vTEC enhancements during the extreme solar minimum and its relevance for the current GNSS and future Galileo applications, we present in this paper the results associated with two significant events that both occurred in equinoctial months. The 10–12 October 2009 event of anomalous TEC enhancement at two distant mid-latitude locations HERS (0.3 E; 50.9 N) and NICO (33.4 E, 35.1 N) is discussed in the context of strong vTEC variations during the well established ionospheric storm on 11 October 2008. We conclude with a short summary of the new findings and their consequences on ionospheric monitoring and modelling for operational communication and navigation systems.

Effects of the geomagnetic storm on October 29?31, 2003, on mid-latitude short-wave radio paths (the data of Doppler measurements)

We present the results of spectral analysis of a signal of oblique sounding of the ionosphere. This signal was received at the Doppler phase-angle measuring facility of Kazan University during the geomagnetic storm on October 29–31, 2003. On various short-wave (SW) radio paths, intense variations of Doppler frequency shift were observed. These variations exceeded variations observed on days without geomagnetic disturbances by an order of magnitude (and by two orders of magnitude during some short periods). Relatively short periods (1–3.5 min) are predominant on these days in variations of the Doppler frequency shift. It should be noted that, while for weak geomagnetic disturbances the response in the form of distortions of SW signal parameters was observed, as a rule, only for the paths coming from high-latitude regions, in the given case the effect was observed for all radio paths.

Model calculation and analysis of magnetosphere-ionosphere-thermosphere coupling

Model calculations are used to analyse the function of the magnetosphere-ionosphere electrodynamic coupling and that of the ionospheric tide-dynamo. The phenomena concerned are discussed. It is shown that for geomagnetic and ionospheric research in low-latitude and equatorial regions, the penetration and shielding of magnetospheric disturbances should be taken into account. On the other hand, the effect of the tidal dynamo on the ionosphere of the auroral region should not be ignored, especially on geomagnetically disturbed days when the conductivity is very high. The features and the relative importance of these two effects are different at different stages of a magnetic storm, and depend on latitude. There is an evident dawn-dusk asymmetry in these effects. The influence of weak geomagnetic disturbances on the low-latitude ionosphere should also be taken into account.

On the types of current patterns of weak geomagnetic disturbances at the polar caps

On the basis of geomagnetic data of arctic and antarctic observatories sequences of instant current systems of weak geomagnetic disturbances at the polar caps are constructed for some events. The analysis shows that these disturbances may be represented by the twovortices S q p -system ( DP 2-system type), which is typical in the winter polar cap as well as in the summer one. A close correspondence between variations of the configuration and the intensity of the vortices in both hemispheres is observed at that period. The formation of the electrojets violates this correspondence. The dependence between the disturbance vectors in the evening and the morning sectors of the auroral zone during the periods of DP 2-system existence only and in the presence of the electrojets is examined.

VLF-emissions observed at stations close to the auroral zone and at stations on lower latitudes

VLF-emissions observed at stations close to the auroral zone and at stations on lower latitudes