Geomagnetic Field Fluctuations Research Articles

Estimation of nighttime dip-equatorial E-region current density using measurements and models

The existence of the possible ionospheric current during nighttime over low-equatorial latitudes is one of the unresolved issues in ionospheric physics and geomagnetism. A detailed investigation is carried out to estimate the same over Indian longitudes using in situ measurements from Thumba (8.5°N, 76.9°E), empirical plasma drift model (Fejer et al., 2008) and equatorial electrojet model developed by Anandarao (1976). This investigation reveals that the nighttime E-region current densities vary from ∼0.3 to ∼0.7A/km2 during pre-midnight to early morning hours on geomagnetically quiet conditions. The nighttime current densities over the dip equator are estimated using three different methods (discussed in methodology section) and are found to be consistent with one another within the uncertainty limits. Altitude structures in the E-region current densities are also noticed which are shown to be associated with altitudinal structures in the electron densities. The horizontal component of the magnetic field induced by these nighttime ionospheric currents is estimated to vary between ∼2 and ∼6nT during geomagnetically quiet periods. This investigation confirms the existence of nighttime ionospheric current and opens up a possibility of estimating base line value for geomagnetic field fluctuations as observed by ground-based magnetometer.

Latitudinal dependence of short timescale fluctuations during intense geomagnetic storms: A permutation entropy approach

AbstractThe present study is focused on the analysis of the latitudinal dependence of complexity degree of the short timescale geomagnetic field fluctuations during four intense geomagnetic storms occurring between 2000 and 2003. The aim is that of investigating the qualitative and quantitative changes in the dynamical properties of the magnetospheric system during magnetically disturbed periods. We analyze the short timescale fluctuations (<120 min) of the horizontal component of the Earth's magnetic field at nine different geomagnetic observatories from 49°N magnetic latitude (MLat) to 87°N MLat, by filtering the signal via empirical mode decomposition and successively by applying the permutation entropy analysis to the filtered time series. We show that some properties of the geomagnetic fluctuations during the selected periods are the result of dynamical changes in the magnetospheric system response to the solar wind changes and that these geomagnetic fluctuations display a complex character during the geomagnetic storm development. This evidence supports the idea that the geomagnetic storm nature may be the result of a cooperative and collective dynamics. We also find that the permutation entropy values change with latitude suggesting a latitudinal dependence of the complexity degree of the signals.

On the local Hurst exponent of geomagnetic field fluctuations: Spatial distribution for different geomagnetic activity levels

AbstractThis study attempts to characterize the spatial distribution of the scaling features of the short time scale magnetic field fluctuations obtained from 45 ground‐based geomagnetic observatories distributed in the Northern Hemisphere. We investigate the changes of the scaling properties of the geomagnetic field fluctuations by evaluating the local Hurst exponent and reconstruct maps of this index as a function of the geomagnetic activity level. These maps permit us to localize the different latitudinal structures responsible for disturbances and related to the ionospheric current systems. We find that the geomagnetic field fluctuations associated with the different ionospheric current systems have different scaling features, which can be evidenced by the local Hurst exponent. We also find that in general, the local Hurst exponent for quiet magnetospheric periods is higher than that for more active periods suggesting that the dynamical processes that are activated during disturbed times are responsible for changes in the nature of the geomagnetic field fluctuations.

PECULIARITIES OF THE SPATIAL POWER SPECTRUM OF SCATTERED ELECTROMAGNETIC WAVES IN THE TURBULENT COLLISION MAGNETIZED PLASMA

General dispersion equation is obtained at arbitrary inclination angles of the external magnetic field and wave vector of an incident EM wave. Statistical characteristics of the phase fluctuations of scattered high frequency EM waves in the collision magnetized plasma caused by electron density and external magnetic field fluctuations taking into account polarization coefficients for both ordinary and extraordinary waves are calculated analytically. The influence of collision frequency, anisotropy factor and angle of inclination of prolate irregularities of electron density fluctuations with respect to the geomagnetic field of lines on the broadening of the spatial power spectrum is analyzed. Phase portraits of the phase fluctuations caused by the geomagnetic field fluctuations are constructed at different spatial parameters characterizing magnetic field and electron density fluctuations. Numerical calculations are carried out for the ionospheric F -region parameters using experimental data.

A solar wind-based model of geomagnetic field fluctuations at a mid-latitude station

Anomalous quasi-DC currents known as geomagnetically induced currents (GIC), produced in electric power network infrastructure during geomagnetic storms, pose a risk to reliable power transmission and network integrity. The prediction of a geomagnetic field-derived proxy to GIC provides an attractive mitigation technique that does not require changes to network hardware. In this paper we present the development of two artificial neural network based models tasked with predicting variations in the X (northward) and Y (eastward) components of the geomagnetic field at Hermanus, South Africa, with only solar wind plasma and interplanetary magnetic field (IMF) parameters as input. The models are developed by iteratively selecting the best set of solar wind parameters to predict the fluctuations in X and Y. To predict the variation in X, IMF magnitude, solar wind speed, fluctuation in solar wind proton density and a IMF-BZ derived parameter are selected. To predict the variation in Y, IMF-BZ, solar wind speed, and fluctuation in IMF magnitude are selected. The difference between the sets of selected input parameters are explained by the dependence of eastward perturbations in geomagnetic field at middle latitudes on field aligned currents. Model performance is evaluated during three storms in 2012. The onset and main phases of storms are fairly accurately predicted, but in cases where prolonged southward IMF coincides with solar wind parameters that are slowly varying the model fails to predict the observed fluctuations.

The Matuyama–Brunhes polarity reversal in four Chinese loess records: high-fidelity recording of geomagnetic field behavior or a less than reliable chronostratigraphic marker?

The paleomagnetic recording fidelity of Chinese loess has been a matter of long-term dispute. To help shed light on the acquisition/retention mechanisms of natural remanent magnetization in loess, we report on high-sampling-resolution paleomagnetic constraints on the position of the Matuyama–Brunhes Boundary (MBB) in four typical loess sections in different marginal areas of the Chinese Loess Plateau (CLP), each of which has experienced different East Asian winter/summer monsoon strengths and pedogenic intensities. Detailed thermal demagnetization experiments for 1850 specimens reveal that none of the high-accumulation-rate loess with the weakest pedogenesis at Caotan (western CLP), the massive Pedogenesis loess characterized by extensive development of thick calcareous nodule layers at Jixian (SE CLP), and the moderately pedogenized loess at Fanshan (NE CLP) have preserved high-fidelity geomagnetic records across the MBBs. Jiuzhoutai (western CLP), one of the thickest loess profiles in the world, contains the thickest, and hitherto the most complex MBB that is too extensive to be regarded as rapid fluctuations of geomagnetic field during the M/B reversal. At Jixian, a predominance of pedogenesis-induced chemical remanent magnetization overprinting has heavily obscured the original remanence. The significant downward displacement of the MBB at Fanshan and even its total absence at Caotan, together with extensive remagnetization of the coarse-grained ‘upper sandy loess layer’ (L9) in both sections, further suggest that the processes of remanence acquisition/retention of Chinese loess in the marginal areas of the CLP are rather complicated. Thus, interpretations of the fine structure of geomagnetic transitional field behavior and ‘excursions’, especially in the Matuyama Chron, should be regarded with caution.

Large plasma filaments and geomagnetic field fluctuations excited concomitantly by solar powered microwave transmissions

We investigate large-scale, filament-type of ionospheric plasma turbulence produced by a ground-based solar-powered microwave transmission system. It is shown that microwaves can interact with the ionosphere, primarily, in the E region. Electron collisions play key roles in the generation of large-scale fluctuations in ionospheric plasma density and geomagnetic fields via a thermal filamentation instability. The threshold wave field intensities are found to be of ∼1 V m−1 for the instability. Possible radar detection of microwave-induced ionospheric plasma effects is discussed and planned for our future Arecibo experiments in Puerto Rico.

A statistical analysis of low frequency geomagnetic field pulsations at two Antarctic geomagnetic observatories in the polar cap region

The aim of this study is to investigate the characteristics of low frequency (∼0.5–5mHz) geomagnetic field fluctuations as recorded at two Antarctic stations within the polar cap: the Italian observatory Mario Zucchelli Station (TNB) and the French–Italian observatory Dome C (DMC) in order to investigate the spatial extension and propagation characteristics of the phenomena observed at very high latitude. The stations have approximately the same geographic latitude, but a very different corrected geomagnetic latitude, being DMC close to the geomagnetic pole and TNB closer to the auroral oval.Our study focused on power spectra, coherence and phase difference between low frequency fluctuations analyzing the horizontal H component measured during the entire year 2006.The fluctuation power behavior during the day can be explained according to the positions of the stations with respect to the polar cap; indeed in the dayside sector it is higher in the cusp region, while in the nightside sector it is higher close to the geomagnetic pole. Furthermore the study of coherent fluctuations, focusing on their phase difference, indicated that the propagation direction within the cap is variable during the day: in the dayside and nightside regions it is from the auroral oval toward the geomagnetic pole, while in the magnetic local morning and afternoon sectors it is from the geomagnetic pole toward the dawn–dusk meridian. Finally the analysis of two individual pulsation events, consisting of short duration wave packets, is shown; it confirms the statistical considerations on the propagation direction and allows to estimate the wave number and apparent phase velocity, whose values are of the order of 3–4 and 30–15km/s, respectively.

ULF fluctuations observed along the SEGMA array during very low solar wind density conditions

We examined several events of geomagnetic field fluctuations related to upstream waves, focusing the attention on the role of the solar wind density in the control of the wave activity. Recently, it was suggested that, when the solar wind density is lower than 2cm−3, ULF wave activity on the ground dramatically drops. Based on geomagnetic field measurements conducted at low latitude along the SEGMA array, our analysis shows that, for extremely low solar wind densities (below 1cm−3), the wave activity on the ground disappears, regardless of cone angle conditions favourable to the transmission of upstream waves through the subsolar magnetopause and independently on the solar wind speed; conversely, for solar wind densities in the range ∼1–2cm−3, ULF fluctuations can be still observed, during favourable cone angle conditions, if the solar wind speed is higher than ∼600km/s. Such results are confirmed by the analysis of simultaneous measurements on the ground and from the Cluster spacecraft, when moving in the upstream region and in the magnetosheath, during one of the examined events. We suggest that, for extremely low SW densities, the wave generation mechanism is not operating efficiently, since very few ions are reflected by a very weak bow shock.

Synchronism of variations in the main geomagnetic field and earth rotation velocity fluctuations

Variations in the value of the source magnetic moment, responsible for the dipole component of the main geomagnetic field, and Earth rotation velocity fluctuations have been studied comparatively. Three quasi-harmonic components with close periods, for which their own phase shifts were obtained, have been detected in time series of the analyzed processes. The mantle conductivity effect on these shifts has been studied in the scope of a one-layer model; for this purpose, the amplitude-phase characteristic of the mantle as a filter has been constructed. The mantle conductivity has been estimated (σ = 270 ± 20 S m−1) on the assumption that the phase shift mainly depends on the mantle effect. It has been assumed that the variations in the time series of the analyzed processes are almost cophased and can be caused by one external factor, e.g., tides.

Mechanisms of Geomagnetic Field Influence on Gene Expression Using Influenza as a Model System: Basics of Physical Epidemiology

Recent studies demonstrate distinct changes in gene expression in cells exposed to a weak magnetic field (MF). Mechanisms of this phenomenon are not understood yet. We propose that proteins of the Cryptochrome family (CRY) are “epigenetic sensors” of the MF fluctuations, i.e., magnetic field-sensitive part of the epigenetic controlling mechanism. It was shown that CRY represses activity of the major circadian transcriptional complex CLOCK/BMAL1. At the same time, function of CRY, is apparently highly responsive to weak MF because of radical pairs that periodically arise in the functionally active site of CRY and mediate the radical pair mechanism of magnetoreception. It is known that the circadian complex influences function of every organ and tissue, including modulation of both NF-κB- and glucocorticoids- dependent signaling pathways. Thus, MFs and solar cycles-dependent geomagnetic field fluctuations are capable of altering expression of genes related to function of NF-κB, hormones and other biological regulators. Notably, NF-κB, along with its significant role in immune response, also participates in differential regulation of influenza virus RNA synthesis. Presented data suggests that in the case of global application (example—geomagnetic field), MF-mediated regulation may have epidemiological and other consequences.

Low-frequency (0.7-7.4 mHz) geomagnetic field fluctuations at high latitude: frequency dependence of the polarization pattern

A statistical analysis of the polarization pattern of low-frequency geomagnetic field fluctuations (0.7-7.4 mHz) covering the entire 24-h interval was performed at the Antarctic station Terra Nova Bay (80.0°S geomagnetic latitude) throughout 1997 and 1998. The results show that the polarization pattern exhibits a frequency dependence, as can be expected from the frequency dependence of the latitude where the coupling between the magnetospheric compressional mode and the field line resonance takes place. The polarization analysis of single pulsation events shows that wave packets with different polarization sense, depending on frequency, can be simultaneously observed.

Low frequency geomagnetic field fluctuations at cap and low latitude during October 29-31, 2003

On October-November 2003 complex interplanetary structures, originated by a series of solar eruptions, hit the Earth, triggering violent Sun-Earth connection events. In this paper we analyze the low frequency geomagnetic field fluctuations detected on the ground during Oct. 29-31, 2003, a time period characterized by extremely high solar wind speed values and by out-of-ecliptic interplanetary magnetic field orientation for intervals of several hours. We analyze geomagnetic field measurements at four high latitude stations located in the polar cap, three in the southern and one in the northern hemisphere. From a comparison with simultaneous measurements at low latitude, we address the question of the global character of the observed phenomena. The results show, for selected time intervals, the occurrence of simultaneous fluctuations at all the stations, with high coherence even between high and low latitude; it is interesting that these fluctuations are detected during open magnetospheric conditions, when the high latitude stations are situated well within the polar cap, i.e. far from closed field lines.

Time intermittency and spectral features of the geomagnetic field

In the field of geomagnetism a number of studies have been devoted to the investigation of turbulence and intermittency in the outer core fluid motions. Here, in order to obtain information on such phenomena we study the time spectral and self-similarity features of the main geomagnetic field fluctuations as measured on the Earth’s surface. The existence of a power law spectrum, characterised by an exponent a˜-11/3, and an anomalous scaling of q-th order structure functions on time scales longer than 5 years, suggests the occurrence of intermittent turbulence rather than classical Kolmogorov turbulence in the fluid core motions. These results are briefly discussed in connection with the existence of a strong magnetic field and drift-wave turbulence.

Geomagnetic field fluctuations near Kharkov, which accompanied rocket launches from the Baikonur site

The observations of the geomagnetic field variations in the range of periods 1–1000 s, which accompanied the launches of 65 Soyuz and Proton rockets from the Baikonur site in 2002–2006, have been analyzed. The measurements were performed near Kharkov (the distance from the launching site is R ≈ 2100 km). Three groups of disturbances, with delays of 6–7, 30–70, and 70–130 min dependent on the time of day, have been revealed. The disturbance duration was 10–30, 50–70, and 45–70 min, respectively. Periods of 3–6, 6–12, and 6–12 min, respectively, predominated in the geomagnetic pulsations. The amplitudes of these pulsations reached 3–6 nT. The physical model of the observed geomagnetic disturbances, which generally agrees with the measurements, has been proposed.

Space weather events in July 1982 and October 2003 and the effects of geomagnetically induced currents on Swedish technical systems

Abstract. In this paper, we analyse in detail two famous space weather events; a railway problem on 13–14 July 1982 and a power blackout on 30 October 2003. Both occurred in Sweden during very intensive space weather storms and each of them a few years after the sunspot maximum. This paper provides a description of the conditions on the Sun and in the solar wind leading to the two GIC events on the ground. By applying modelling techniques introduced and developed in our previous paper, we also calculate the horizontal geoelectric field at the Earth's surface in southern Sweden during the two storms as well as GIC flowing in the southern Swedish 400 kV power grid during the event in October 2003. The results from the calculations agree with all measured data available. In the July-1982 storm, the geomagnetic field variation, ΔBx, reached values up to ~2500 nT/min and the geoelectric field reached values in the order of several volts per kilometer. In the October-2003 storm, the geomagnetic field fluctuations were smaller. However, GIC of some hundreds of amperes flowed in the power grid during the October-2003 event. Technological issues related to the railway signalling in July 1982 and to the power network equipment in October 2003 are also discussed.

Doppler observations of infrasonic waves of meteorological origin at ionospheric heights

Ionospheric effects of meteorological origin observed by the continuous HF Doppler sounder over the Czech Republic are reported in this paper. We focused on detection of waves of periods 1–10 min. We discuss the influence of dynamics and intensity of active weather systems on the occurrence of short period waves and dependence of the observed ionospheric effects on the height of reflection of the sounding radio wave. We observed 3–5 min waves during a severe weather event in summer and 2.5–4 min waves during a severe weather event in winter. We excluded possible geomagnetic origin of these oscillations by the analysis of fluctuations of the local geomagnetic field. In eight cases of 10, wave activity in the analysed period range was not significantly increased comparing to quiet days. The intensity of weather systems as well as the location of potential sources of waves towards the points of HF Doppler shift observation influence significantly the occurrence of infrasonic waves in the ionosphere. The results in Central Europe differ considerably from those previously obtained in North America. As a possible reason, we discuss different intensity and dynamics of weather systems in both regions.

A Comparative Analysis of Ground, Magnetospheric and Interplanetary Observations of Long Period Magnetic Oscillations

Continuous measurements of the geomagnetic field variations at ground stations are important to investigate several aspects of magnetospheric dynamics related to variations in the solar wind conditions which, ultimately, originate from the Sun. We present a comparative analysis of geomagnetic field measurements at several ground stations with simultaneous magnetospheric and interplanetary observations in order to understand the origin and characteristics of the observed fluctuations. The results suggest that long period geomagnetic field fluctuations can be directly driven by solar wind density fluctuations at the same frequencies via the modulation of the magnetopause current. We also discuss the possible occurrence of additional contributions related with cavity/waveguide resonances of the entire magnetosphere as well as those of resonance processes of the geomagnetic field lines.

Magnetospheric source of UHF radio bursts at mid-latitudes during the magnetic storm on October 22, 1999

We discuss the results of our simultaneous observations of interplanetary and geomagnetic field fluctuations as well as solar wind parameters and meter radio emission in near-Earth space at mid-latitudes (near Kharkov) based on ground measurements before and during a unique magnetic storm on October 22, 1999. The electron flux dynamics in interplanetary space, geostationary orbit, and the magnetosphere is analyzed to find the interconnection with UHF radio background bursts at a frequency of 151 MHz. We conclude that the acceleration processes in the inner magnetospheric layers affect the generation processes of high-frequency radio bursts and that this phenomenon should be studied further using the SINP (MSU) instruments onboard the CORONAS-F satellite.

Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations

Abstract. We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7° S, 164.1° E; corrected geomagnetic coordinates: 80.0° S, 307.7° E) and Scott Base (geographic coordinates: 77.8° S 166.8° E; corrected geomagnetic coordinates: 80.0° S 326.5° E), both located in the polar cap. Due to the relative position of the stations, whose displacement is essentially along a geomagnetic parallel, the phase difference analysis allows to determine the direction of azimuthal propagation of geomagnetic fluctuations. The results show that coherent fluctuations are essentially detectable around local geomagnetic midnight and, in a minor extent, around noon; moreover, the phase difference reverses in the night time hours, indicating a propagation direction away from midnight, and also around local geomagnetic noon, indicating a propagation direction away from the subsolar point. The nigh time phase reversal is more clear for southward interplanetary magnetic field conditions, suggesting a relation with substorm activity. The introduction, in this analysis, of the Interplanetary Magnetic Field conditions, gave interesting results, indicating a relation with substorm activity during nighttime hours. We also conducted a study of three individual pulsation events in order to find a correspondence with the statistical behaviour. In particular, a peculiar event, characterized by quiet magnetospheric and northward interplanetary magnetic field conditions, shows a clear example of waves propagating away from the local geomagnetic noon; two more events, occurring during southward interplanetary magnetic field conditions, in one case even during a moderate storm, show waves propagating away from the local geomagnetic midnight.