Geomagnetic Field Perturbations Research Articles

The variable source of the plasma sheet during a geomagnetic storm

Both solar wind and ionospheric sources contribute to the magnetotail plasma sheet, but how their contribution changes during a geomagnetic storm is an open question. The source is critical because the plasma sheet properties control the enhancement and decay rate of the ring current, the main cause of the geomagnetic field perturbations that define a geomagnetic storm. Here we use the solar wind composition to track the source and show that the plasma sheet source changes from predominantly solar wind to predominantly ionospheric as a storm develops. Additionally, we find that the ionospheric plasma during the storm main phase is initially dominated by singly ionized hydrogen (H+), likely from the polar wind, a low energy outflow from the polar cap, and then transitions to the accelerated outflow from the dayside and nightside auroral regions, identified by singly ionized oxygen (O+). These results reveal how the access to the magnetotail of the different sources can change quickly, impacting the storm development.

X-ray radiation from the Sun and geomagnetic disturbances as environmental factors affecting humans

The study of the influence of X-ray radiation from the Sun in the range from 1 to 8 Å on the components of the well-being function of a human population is carried out. X-ray radiation from the Sun, being absorbed in the upper layers of the ionosphere and not reaching the Earth’s surface, is nevertheless capable of acting indirectly (through a modification of the natural electromagnetic background in the ELF range). Variability in the frequency of emergency care is used as a component of the well-being function. A comparative analysis of the effect of X-ray radiation from the Sun with the influence of geomagnetic field perturbations on the time scales of a rare solar event is carried out.

Peculiarities of electric and magnetic tipper variations caused by meteorological disturbances in the atmosphere

We present the results of the analysis of experimental data of synchronous observations of variations in the electric and magnetic fields as well as acoustic oscillations in the surface zone of the Earth compared with variations in the meteorological parameters. We demonstrate the synchronous variations in these fields and atmospheric parameters. We revealed, for the first time, not only synchronous but also advancing manifestations of the geomagnetic field perturbations. We introduce a new parameter: the inverse magnetic tipper whose variations during atmospheric perturbations are clearly manifested compared with the variations in the magnetic tipper.

Analysis of GPS phase rate variations in response to geomagnetic field perturbations over the Canadian auroral region

One year of high rate dual frequency GPS phase rate variation statistics at three Canadian auroral locations are compared with geomagnetic field variations observed at co-located magnetic observatories. The geomagnetic variations are characterized at the Canadian Space Weather Forecast Centre by the hourly range of magnetic field for northward, eastward and vertical downward directions. The hourly mean of GPS phase rate statistics are derived from 1-Hz GPS dual frequency phase measurements which are continuously being monitored at the Canadian Geodetic Survey of Natural Resources Canada. Analysis reveals correlation coefficients of about 0.7–0.8 between these two hourly indices. The highest correlation is found between hourly mean phase rate variations and hourly ranges of the magnetic field vertical component. This can be attributed to changes in the position of the auroral electrojet during rapid expansions of the auroral oval during periods of auroral substorms. Apart from allowing studies on local ionospheric irregularities, these results indicate that GPS phase rate measurements in the auroral zone are responding to the geomagnetic field variations which could be used as representative proxy measures for scintillation occurrence in the region. Analysis of GPS phase rate statistics also revealed station specific features due to non-ionospheric effects.

Methods of analysis of geomagnetic field variations and cosmic ray data

In the present paper, we propose a wavelet-based method of describing variations in the Earth’s magnetic field, such as the horizontal component of the geomagnetic field, in addition to methods for evaluating changes in the energy characteristics of the field and for isolating the periods of increased geomagnetic activity. Based on a combination of multiresolution wavelet decompositions with neural networks, we propose a method of approximation of the cosmic ray time course and the allocation of anomalous variations (Forbush effects) that occur during periods of high solar activity. During the realization of the method, an algorithm was created for selecting the level of the wavelet decomposition and adaptive construction of the neural network. By using the proposed methods, we performed a joint analysis of the geomagnetic field and cosmic rays during periods of strong magnetic storms. The strongest geomagnetic field perturbations were observed in periods of abnormal changes in cosmic ray level. Assessment of the intensity of geomagnetic disturbances on the eve of and during magnetic storm development allowed us to highlight local increases in intensity of the geomagnetic field occurring at different frequency ranges prior to the development of the storm’s main phase. Implementation of the proposed method with theoretical tools in combination with other methods will improve the estimation accuracy of the geomagnetic field state during space weather forecasting.

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.

Simulation of the 23 July 2012 extreme space weather event: What if this extremely rare CME was Earth directed?

Extreme space weather events are known to cause adverse impacts on critical modern day technological infrastructure such as high‐voltage electric power transmission grids. On 23 July 2012, NASA's Solar Terrestrial Relations Observatory‐Ahead (STEREO‐A) spacecraft observed in situ an extremely fast coronal mass ejection (CME) that traveled 0.96 astronomical units (∼1 AU) in about 19 h. Here we use the Space Weather Modeling Framework (SWMF) to perform a simulation of this rare CME. We consider STEREO‐A in situ observations to represent the upstream L1 solar wind boundary conditions. The goal of this study is to examine what would have happened if this Rare‐type CME was Earth‐bound. Global SWMF‐generated ground geomagnetic field perturbations are used to compute the simulated induced geoelectric field at specific ground‐based active INTERMAGNET magnetometer sites. Simulation results show that while modeled global SYM‐H index, a high‐resolution equivalent of the Dst index, was comparable to previously observed severe geomagnetic storms such as the Halloween 2003 storm, the 23 July CME would have produced some of the largest geomagnetically induced electric fields, making it very geoeffective. These results have important practical applications for risk management of electrical power grids.

Correlation of geomagnetic anomalies recorded at Muntele Rosu Seismic Observatory (Romania) with earthquake occurrence and solar magnetic storms

The study presents a statistical cross-correlation between geomagnetic anomalies, earthquake occurrence and solar magnetic storms. The working data are from: (i) geomagnetic field records from Muntele Rosu (MLR) Observatory, and from Surlari (SUA) and/or Tihany (THY) INTERMAGNET Observatories; (ii) seismic data for the Vrancea source zone; and (iii) daily geomagnetic indices from the NOAA/Space Weather Prediction Center. All of the geomagnetic datasets were recorded from 1996 to the present, at MLR, SUA or THY, and they were automatically corrected using a LabVIEW program developed especially for this purpose, highlighting the missing or bad data. Missing data blocks were completed with the last good measured value. After correction of the data, there were a number of issues seen regarding previous interpretations of the geomagnetic anomalies. Some geomagnetic anomalies identified as precursory signals were found to be induced either by increased solar activity or by malfunction of the data acquisition system, which produced inconsistent data, with numerous gaps. The MLR geomagnetic data are compared with the data recorded at SUA/THY and correlated with seismicity and solar activity. These 15 years of investigations cover more than a complete solar cycle, during which time the solar-terrestrial perturbations have fluctuated from very low to very high values, providing the ideal medium to investigate the correlations between the geomagnetic field perturbations, the earthquakes and the solar activity. The largest intermediate depth earthquake produced in this interval had a moment magnitude Mw 6.0 (2004) and provided the opportunity to investigate possible connections between local geomagnetic field behavior and local intermediate seismicity.

ULF geomagnetic perturbations due to seismic noise produced by rock fracture and crack formation treated as a stochastic process

A mechanism of ULF geomagnetic field perturbations caused by rock fracture and tectonic activity is studied. It is assumed that the rock fracture is accompanied by crack-generated seismic emission due to cracks pile up at underground cracked zones. Temporal series of seismic impulses due to the crack growth is supposed to be a stationary random process, which obeys Poisson distribution. The seismic emission of the cracks results in excitation of electric current due to motion of the conductive ground in the geomagnetic field, that is so-called diamagnetic effect in moving conductors immersed in the external magnetic field. The electric currents build up as a result of the random displacements in the conductive rock, which in turn leads to the random perturbations of the geomagnetic field. Acoustic wave field derivable from the crack seismic moment is used in order to obtain the electromagnetic variations due to growth of single crack. Averaging of these variations over random crack plane orientation and over crack sizes gives an assessment of mean level of the electromagnetic noise produced by the evolution of the crack ensemble. This assessment is consistent in magnitude with the ULF electromagnetic variations recorded prior to and after some strong earthquakes.

Magnetospheric responses to sudden and quasiperiodic solar wind variations

On April 13 (day 103), 2001, 0700–1400 UT, the Polar satellite experienced different plasma regimes (i.e., magnetosphere, magnetosheath, and solar wind) because of the solar wind dynamic pressure variations and its high orbital inclination near the subsolar magnetopause meridian. When Polar was in the magnetosheath, quasiperiodic spacecraft potential (SP) variations, corresponding to density variations, with a recurrence time of ∼3–10 min were observed. Using simultaneous solar wind observations, it was confirmed that the magnetosheath SP variations were inherent in the solar wind. We observed an almost one‐to‐one correspondence between the SP variations and the geomagnetic field perturbations at lower latitudes (L = 1.1–2.8) on the nightside. At higher latitudes (L = 2.9–6.1) on the dayside, however, the field perturbations are more complicated than the magnetosheath SP variations. This suggests that if the magnetospheric perturbations produced by the external source (solar wind/magnetosheath pressure variations) deeply penetrate into the magnetosphere, the lower‐latitude data on the nightside are important to monitor the external source variations. In addition, we observed the radial electric field oscillations excited nearly simultaneously with the magnetic field enhancement, associated with a sudden increase in the solar wind dynamic pressure, when Polar was in the magnetosphere. These oscillations may be considered as transient standing Alfvén waves excited by externally applied pressure changes as reported by previous studies.

An observational test for the ionospheric or magnetospheric origin of night-time geomagnetic positive bays at low and mid latitudes

The night-time positive bay-type perturbations ( ΔH) in the horizontal component ( H) at groundlevel geomagnetic field are compared for three locations: Trivandrum (1.2°S gm. lat.), Alibag (9.5°N gm. lat.) and Tashkent (32.3°N gm. lat.) in the same local time sector. If the bay disturbances originate predominantly in the ionospheric dynamo region currents, then the ΔH values at Trivandrum, an equatorial electrojet station, should be at least twice as large as those at Alibag which is a low-latitude station well outside the electrojet latitudes. For none of the 31 events analyzed does the ratio of ΔH at Trivandrum to that at Alibag exceed 1.3 and it is mostly below 1.0. The values of ΔH at Tashkent, which is a mid-latitude station, are larger by about 50% or more than those at Alibag or Trivandrum. Based on the above results, it is concluded that (a) the night-time positive bays at low and middle geomagnetic latitudes do not originate, in general, in the overhead ionospheric dynamo region currents and (b) the positive bays seem to be caused primarily by magnetic field-aligned currents. It is shown that the method presented in this paper is useful in general for finding out the relative contributions of ionospheric and magnetospheric currents to different types of ground-level geomagnetic field perturbations at low and middle latitudes.

Large simultaneous disturbances (LSDs) in the Antarctic ionosphere

A high frequency radio Doppler experiment was deployed in the Antarctic Peninsula region, centred on Argentine Islands (65°15′S, 64°16′W; L = 2.3), to investigate the morphology and sources of ionospheric disturbances. The experiment consisted of a three-transmitter dual frequency network which permits horizontal and vertical propagation velocities to be estimated over a north-south baseline of 200 km and an east-west baseline of 100 km. A new class of ionospheric disturbance has been observed, in the period range 10 min−1 h. These disturbances are characterised by unusually good correlation between perturbations on all available Doppler signals, but are apparently non—propagating and occur simultaneously at each reflection point. Several of these events display large (2 Hz at about 5 MHz transmitted frequency) Doppler shifts, thus we have labelled them Large Simultaneous Disturbances (LSD s). Criteria for identification of LSD s are established and the analysis of one event is described in detail. The occurrence statistics of the LSD s are presented, including their seasonal and diurnal distributions. There is no clear general relationship between LSD s and local geomagnetic field perturbations. However, examination of the magnetic indices AE and I RC indicates that there is a loose association between the occurrence and amplitude of LSD s and magnetic activity. Several possible mechanisms for the generation of LSD s at middle latitudes are reviewed. The most likely explanation is that high latitude electric fields penetrate to magnetic middle latitudes and drive the ionospheric plasma via the E × B drift.

Comparison of magnetic field perturbations and solar electron profiles in the polar cap

Northern hemisphere geomagnetic field perturbations and solar electron profiles measured during the magnetic storm of August 4–5, 1972, are compared. Pitch angle distributions of the solar electrons are used to infer the locations of closed geomagnetic field lines that are compared with the locations of certain features of the magnetic perturbations. An example is given, when the interplanetary magnetic field (IMF) is southward, that shows a peak in the postnoon cleft region perturbation occurring near the location where the solar electron pitch angle distribution changes from anisotropic to isotropic, consistent with the suggestion that the peak in the cleft region perturbation occurs at or close to the dayside limit of closed field lines. The same pass shows isotropic pitch angle distributions throughout the polar cap where the magnetic perturbation is sunward (antisunward convection), consistent with open geomagnetic field lines in this region. Examples are also given for times when the IMF is northward, and one type of perturbation pattern that is observed shows antisunward perturbations (sunward convection) in the central polar cap, sunward perturbations (antisunward convection) in adjacent regions changing again to antisunward perturbations (sunward convection) at lower latitudes. In one of these examples, pitch angle distributions throughout the polar cap are isotropic, and it is probable that in most cases when this type of perturbation pattern is observed, the whole polar cap is open. However, two examples are given where antisunward perturbations (sunward convection) in the polar cap are associated with a closed field region surrounded by open field lines. This field configuration may be rather rare and is probably associated with unusual IMF conditions that were present at the time. The measurements are discussed in terms of a magnetic merging model, and in a qualitative way the model appears to account for the observations.

The Perturbation of Geomagnetic Fields by Cylindrical Structures--II Problems of Asymmetry and Sloping Contact Models

(Received 1974 June l0)t Summary The perturbation of an oscillating geomagnetic field by two-dimensional sloping discontinuities is investigated. A finite difference technique with the Gauss-Seidel iteration method is applied in a cylindrical co-ordinate system. An asymmetry in the iteration procedure is discussed. Conductivity discontinuities of five different slopes are studied for an oscillation period of 40 s.

The Perturbation of Geomagnetic Fields by Cylindrical Structures--I Numerical Method and Symmetrical Models

Summary The perturbation of alternating geomagnetic fields using a cylindrical co-ordinate system for two-dimensional structures is studied. A numerical finite difference technique which employs the Gauss-Seidel iterative method over a general polar mesh with variable grid spacing is used. A discussion of the grid dimensions is included and results for two symmetrical models for different oscillation periods of the source field are described.

The perturbation of geomagnetic fields by two-dimensional and three-dimensional conductivity inhomogeneities

A numerical method is used to calculate the geomagnetic fields associated with a three-dimensional conductivity anomaly. Fields associated with a two-dimensional model are also studied numerically for a range of frequencies and apparent resistivity curves for the two models are compared with that calculated for a layered earth. The apparent resistivity curves for both the three-dimensional model and the two-dimensional model differ considerably from the layered case, and it is evident that if a layered model is used for interpretation the results may be very misleading.

Lunar perturbations in geomagnetic field and in the characteristics ofF-region over huancayo

The lunar daily (L) and lunar monthly (M) variations in horizontal magnetic field (H), maximum electron density (N max ), height of peak ionisation (h max ), semi-thickness (y m ) of theF 2 layer and total electron content (N t ) at Huancayo for the period January 1960 to December 1961 are described. The lunar tidal variations inh max follow sympathetically the variations inH such that an increase of magnetic field causes the raising of height of peak ionisation. Lunar tides inN max are opposite in phase to that ofh max with a delay of about 1–2 hours, suggesting that an increase of height causes a decrease in maximum electron density. The lunar tides in semi-thickness are very similar in phase to that inh max . The lunar tidal effects in any of the parameters are largest inD-months and least inJ-months. The amplitude of lunar tides in maximum electron density seems to increase with increasing height whereas the phase seems to be constant with height. It is concluded that lunar tides in the ionospheric parameters at magnetic equator are greatly controlled by the corresponding geomagnetic variations.