Long-period Geomagnetic Pulsations Research Articles

Long-period geomagnetic pulsations as an element of the space weather influence on technologocal systems

We analyze variations in geomagnetically induced currents (GIC) and pulsations of the geomagnetic field latitudinal By component in the frequency range 1–20 mHz. The analysis is based on the data from GIC registration at the Kola Peninsula and magnetic data from IMAGE network stations, obtained with 10 s sampling in 2017. This allows us to include pulsations of both Pc5/Pi3 and Pc4/Pi2 frequency range in the analysis and examine polyharmonic pulsations with spectral maxima in both ranges. It is shown that GICs are effectively generated at frequencies above 5 mHz. Polyharmonic pulsations are potentially more dangerous than monoharmonic ones because the ratio of GIC to magnetic field pulsations’ amplitude is higher and the lifetime of unipolar GIC is longer.

Even moderate geomagnetic pulsations can cause fluctuations of <i>fo</i>F2 frequency of the auroral ionosphere

Abstract. The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67∘ N, 27∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic measurements, we have investigated a correspondence between the magnetic field pulsations and variations of the critical frequency of radio waves reflected from the ionospheric F2 layer (foF2). For this study, we have developed a technique for automated retrieval of the critical frequency of the F2 layer from ionograms. As a rule, the Pc5–6/Pi3 frequency band fluctuations in foF2 were observed at daytime during quiet or moderately disturbed space weather conditions. In most cases (about 80 %), the coherence between the foF2 variations and geomagnetic pulsations was low. However in some cases (specified as “coherent”) the coherence was as large as γ2≥0.5. The following conditions are favorable for the occurrence of coherent cases: enhanced auroral activity (6 h maximal auroral electrojet (AE) ≥800 nT), high solar wind speed (V>600 km/s), fluctuating solar wind pressure and northward interplanetary magnetic field. In the cases when the coherence was higher at shorter periods of oscillations, the magnetic pulsations demonstrated features typical for the Alfvén field line resonance.

The correspondence between dayside long-period geomagnetic pulsations and the open-closed field line boundary

Long-period pulsations in the nominal Pc5-6 band (periods about 3–15 min) have been known to be a persistent feature of dayside high latitudes. A mixture of broadband Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband P≿5 waves is often observed. The mechanism and origin of IPCL have not been firmly established yet. Magnetopause surface eigenmodes were suggested as a potential source of high-latitude ULF waves with frequencies less than 2 mHz. A ground response to these modes is expected to be beneath the ionospheric projection of the open-closed field line boundary (OCB). To unambiguously resolve a possible association of IPCL with the magnetopause surface modes, multi-instrument observation data from Svalbard have been analyzed. We examine the latitudinal structure of high-latitude pulsations in the Pc5-6 band recorded by magnetometers covering near-cusp latitudes. This structure is compared with an instant location of the equatorward boundary of the cusp aurora, assumed to be a proxy of the OCB. The optical OCB latitude has been identified by an automatic algorithm, using data from the meridian scanning photometer at Longyearbyen, Svalbard. The comparison has shown that the latitudinal maximum of the broadband IPCL maximizes about 2°–3° deeper in the magnetosphere than the OCB optical proxy. Therefore, these pulsations cannot be associated with the ground image of the magnetopause surface modes. It is likely that an essentially non-dipole geometry of field lines and a high variability of the magnetopause region may suppress the excitation efficiency. The obtained result imposes important limitations on possible mechanisms of high-latitude dayside ULF variations.

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

Abstract. A study is undertaken into parameters of the polar auroral and geomagnetic pulsations in the frequency range 1–4 mHz (Pc5∕Pi3) during quiet geomagnetic intervals preceding auroral substorms and non-substorm background variations. Special attention is paid to substorms that occur under parameters of the interplanetary magnetic field (IMF) conditions typical for undisturbed days (non-triggered substorms). The spectral parameters of pulsations observed in auroral luminosity as measured by a meridian scanning photometer (Svalbard) in the polar cap and near the polar boundary of the auroral oval are studied and compared with those for the geomagnetic pulsations measured by the magnetometer network IMAGE in the same frequency range. It is found that Pc5∕Pi3 power spectral density (PSD) is higher during pre-substorm time intervals than for non-substorm days and that specific variations of pulsation parameters (substorm precursors) occur during the last 2–4 pre-substorm hours.

Properties of daytime long-period pulsations during magnetospheric storm commencement

Long-period geomagnetic pulsations during the SSC of July 14, 2012, are studied. The prenoon longitudinal sector (09:20–11:30) MLT, from the boundaries of which pulsations propagate azimuthally onto the dawn and dusk sides with an opposite polarization direction and increased amplitude, has been distinguished. The position of this sector relative to noon (a shift to the dawn side) depends on the front azimuthal inclination. It has been found that the polarization direction reverses in going from low (<30°) to middle/subauroral (≥50°) latitudes on the entire dayside. The geomagnetic pulsations mainly fluctuate near the f1 = 2.9 and f2 = 4.4 mHz frequencies. Fluctuations with frequency f1, which coincide with the fluctuation frequency of the IMF х component, predominate at the polar cap latitudes (the open field line region) in the form of rapidly attenuating impulses and at low latitudes with a much smaller amplitude. Fluctuations with frequency f2 are globally registered at all latitudes in the dayside sector below the magnetopause projection as a train of several fluctuations. It is assumed that fluctuations with frequency f1 penetrate from the solar wind, and fluctuations with frequency f2 are radial magnetopause oscillations.

Daytime geomagnetic disturbances at high latitudes during a strong magnetic storm of June 21–23, 2015: The storm initial phase

The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm (SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm–3) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations (ipcl and vlp) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.

Long-period geomagnetic pulsations as solar flare precursors

We compare long-period pulsations of the horizontal component of the geomagnetic field at intervals that precede extreme solar flares. To this end, we use the wavelet–skeleton technique to process the geomagnetic field disturbances recorded at magnetic stations over a wide geographical range. The synchronization times of wavelet–skeleton spectral distributions of long-period pulsations of geomagnetic oscillations over all magnetic stations are shown as normalized histograms. A few days before an intense solar flare, the histograms show extremes. This means that these extremes can be regarded as flare precursors. The same technique is used to analyze the parameters of near-Earth space. The histograms obtained in this case are free of the aforementioned extrema and, therefore, cannot point to an upcoming flare. The goal of this study is to construct a correlation–spectral method for the short-term prediction of solar flare activity.

Generation of different long-period geomagnetic pulsations during a sudden impulse

The space–time characteristics of geomagnetic pulsations during a sudden impulse on August 4, 2010 have been analyzed using ground-based and satellite observations. It has been indicated that two types of geomagnetic pulsations with different spatial extensions, oscillation frequencies, and generations were observed at that time. It has been found that geomagnetic pulsations with identical oscillation frequencies (∼4.5 mHz) at different latitudes were observed, with a maximal amplitude in the dusk sector. Oscillations with close frequencies were registered in the solar wind in the IMF B z component. Higher-frequency (7–10 mHz) pulsations dependent on latitude were registered on the dawn side. It is assumed that geomagnetic pulsations with frequencies of ∼4.5 mHz were caused by oscillations penetrating from the interplanetary medium, and higher-frequency pulsations were Alfven resonance oscillations generated during the compression of the magnetosphere. An asymmetric oscillation amplitude distribution relative to noon was caused by the IMF orthospiral orientation in this event.

Specific features of daytime long-period pulsations observed during the solar wind impulse against a background of the substorm of August 1, 1998

Long-period geomagnetic pulsations in the (1.7–6.7) mHz frequency range at 18.25–18.48 UT on August 1, 1998, caused by several successive sudden changes in the solar wind (SW) dynamic pressure, are studied against a background of substorm intensification. The data of the ground stations, which were near local noon (the CANOPUS Canadian network) and on the nightside (the auroral stations in Yakutia and at the IMAGE network), and the INTERBALL-1, ACE, WIND, and GOES 8, extramagnetospheric satellites are used. The effect of the SW plasma and IMF parameters, SW inhomogeneity front inclination, and geomagnetic activity on the pulsation propagation and polarization direction and amplitude is discussed. The properties of pulsations, recorded before the substorm, correspond to the pulsation excitation by the inhomogeneity front incident on the magnetopause during the magnetically quiet period: pulsations propagate from the contact point onto the nightside when the amplitude increases and the polarization sense of rotation is opposite on the dawn and dusk sides. Substorm intensification results in the propagation direction reversal and in a more complex behavior of the pulsation amplitude and polarization on the dayside.

Long-period geomagnetic pulsations in the quasi-conjugate arctic and antarctic regions during the magnetic storm of April 16–17, 1999

Based on the observations in six pairs of almost conjugate high-latitude stations in the Arctic and Antarctic regions, the spectral and spatial-temporal structures of long-period geomagnetic pulsations (f = 2–5 mHz) during the magnetic storm of April 16–17, 1999, which is characterized by a high (up to 20 nPa) solar wind dynamic pressure, have been studied. It has been indicated that the magnetic storm sudden commencement is accompanied by a symmetrical excitation of np pulsations near the dayside polar cusps with close amplitudes. Under the conditions when IMF Bz > 0 and By < 0, strong magnetic field variations with the periods longer than 15–20 min were observed only in the northern polar cap. When IMF Bz and By became close to zero, geomagnetic pulsation bursts in both hemispheres were registered simultaneously but differed in the spectral composition and spatial distribution. In the Northern Hemisphere, pulsations were as a rule observed in a more extensive latitude region than in the Southern Hemisphere. In the Northern Hemisphere, the oscillation amplitude maximum was observed at higher latitudes than in the Southern Hemisphere. The pulsation amplitude at geomagnetic latitude lower than 74° was larger in the Arctic Regions than in the Antarctic Regions. This can be explained by sharply different geographic longitudes in the polar cap and latitudes in the auroral zone, which results in a different ionospheric conductivity affecting the amplitude of geomagnetic pulsations.

Local amplification of auroral electrojet as a response to a sharp solar wind pressure pulse

In this paper, we examine a magnetosphere response to a sharp and large solar wind pressure pulse using aurora images from the Polar spacecraft, IMAGE and Intermagnet magnetometer array data. Observations show that this pulse was associated with several phenomena as: (a) a short burst of aurora in the noon sector; (b) a generation of the preliminary geomagnetic pulse at high latitudes with the polarity opposite to the main positive pulse; (c) a global amplification of Chapman-Ferraro currents produced by the compression of the magnetosphere; (d) an amplification of the auroral currents and the transpolar currents in the polar cap; (e) generation of the geomagnetic pulsation bursts with nonstationary spectra; (f) generation of trains of the attenuate long-period geomagnetic pulsations with decreasing and increasing periods. Some of these features are similar to the magnetosphere–ionosphere response to the impingement of interplanetary shocks.

Geomagnetic pulsations caused by the magnetopause oscillations (Comparison of spacecraft and geomagnetic observations)

This paper is devoted to the study of long-period geomagnetic pulsations recorded after abrupt changes of the solar wind (SW) dynamic pressure. Data of simultaneous satellite observations within the “INTERBALL” program are used in the analysis of the magnetopause location and plasma and magnetic field parameters near the magnetopause. Geomagnetic pulsations are analyzed using data from several meridional chains of stations located in different longitudinal sectors. It is shown that experimental data confirm the Mishin's (1993) model of the excitation of damped radial oscillations of the magnetopause by SW pressure impulses that are recorded on the ground in the form of global geomagnetic pulsations. The period of these pulsations is proportional to the subsolar radius of the magnetosphere to the 4th power. It is shown that the pulsation period varies with time inversely as the sign of density variation. This is consistent with the Mishin's (1993) model.

Long-period geomagnetic pulsations caused by the solar wind negative pressure impulse on 22 March 1979 (CDAW-6)

Abstract. An analysis is made of the long-period geomagnetic pulsations as recorded at seven Norilsk meridian stations (λ=162°, latitudinal range: 61°–71°N) following abrupt magnetospheric expansion during the storm of 22 March 1979 caused by a rapid decrease in solar wind density. As with the time interval following an abrupt contraction at the time of sudden storm commencement, there exist two types of pulsations in the pulsation spectra: latitude-independent (T&gt;400 s) and latitude-dependent (T&lt;200 s) pulsations. The first pulsation type is interpreted in terms of forced pulsations associated with magnetopause oscillations. The oscillation period is determined by plasma density in the boundary layer and by the radius of the magnetosphere (T ~ ρ1/2R4). The latitudinal dependence of the period, amplitude and polarization of the second-type pulsations is in agreement with the resonance mechanism of their origin.Keywords. Geomagnetic pulsations · Solar wind · Magnetopause oscillations

Long-period geomagnetic pulsations caused by the solar wind negative pressure impulse on 22 March 1979 (CDAW-6)

An analysis is made of the long-period geomagnetic pulsations as recorded at seven Norilsk meridian stations (λ=162°, latitudinal range: 61°–71°N) following abrupt magnetospheric expansion during the storm of 22 March 1979 caused by a rapid decrease in solar wind density. As with the time interval following an abrupt contraction at the time of sudden storm commencement, there exist two types of pulsations in the pulsation spectra: latitude-independent (T>400 s) and latitude-dependent (T<200 s) pulsations. The first pulsation type is interpreted in terms of forced pulsations associated with magnetopause oscillations. The oscillation period is determined by plasma density in the boundary layer and by the radius of the magnetosphere (T ~ ρ1/2R4). The latitudinal dependence of the period, amplitude and polarization of the second-type pulsations is in agreement with the resonance mechanism of their origin.Keywords. Geomagnetic pulsations · Solar wind · Magnetopause oscillations

Auroral activities and long-period geomagnetic pulsations: 2. Ps5 pulsations following auroral breakup in the premidnight hours.

Bright auroral forms several hundreds of km in spatial extent were observed repeatedly (a few to about 15min, periodicity) in the premidnight hours, following auroral breakups. The auroral forms drifted towards the northwest or the southwest, and were related to the magnetic field fluctuations on the ground in a similar period range. The leading front of the drifting auroral form has a discrete auroral (vortexchain) feature. After the passage of discrete forms pulsating aurora appears. From the comparison with magnetic field perturbations at the geosynchronous orbit satellites GOES 5 and GOES 6, these auroral forms are likely to correspond to the depression of the magnetic total intensity. A possible source of these bright auroral forms is hot plasmas injected from the plasma sheet. The concurrent magnetic pulsations, here called Ps5, would be produced by the fluctuating electric field and conductivity in the ionosphere due to the electron precipitation into the auroral forms. Hot plasma clouds, quasi-periodically injected during the course of a substorm, are related to the auroral and magnetic field pulsations. A steep injection front of hot plasma in the magnetosphere is likely related to discrete auroras at the ionosphere.

Auroral activities and long-period geomagnetic pulsations: 1. Pc5 pulsations and concurrent auroras in the dawn sector.

It is found that the occurrence and luminosity of diffuse auroras, including pulsating auroras, in the dawn sector show space-time variations synchronized with geomagnetic Pc5 pulsations. The activation region of aurora (not auroral structure) quasi-periodically propagates towards the northwest. The observed propagation velocities at the ionospheric level are about 1km/s northward and about 15km/s westward, respectively. These velocities are in good agreement with the phase velocities of Pc5 pulsations previously measured by radars and by ground networks of geomagnetic field observations. Oscillations in drifts of auroral patches generally in the east-west direction are found to be synchronized with the Pc5 pulsations. The observations suggest that the ground Pc5 pulsations do not necessarily reflect the HM wave structures in the magnetosphere, but the wave nature could be inferred from a close examination of the relationships between the ground magnetic pulsations and concurrent auroral dynamics.

A statistical study on Psc 4 and Psc 5 observed by geostationary satellites

Using magnetic data from the geostationary satellites of ATS 6 and SMS/GOES series, long-period geomagnetic pulsations, Psc 4 and Psc 5, associated with geomagnetic sudden commencements (SC's) were statistically analyzed. Local time and geomagnetic latitude dependence of the occurrence, and local time dependence of the period and the amplitude were examined for 218 SC's. For transverse Psc 5 pulsations which could be observed at all local times, the period was shorter and the amplitude was smaller near noon than in the morning and evening sides. Compressional Psc 5's, which were observed mainly from about 09.00 L.T. to midnight, had larger amplitude near noon. The period seemed to be longer near noon. As for Psc 4 pulsations the period tended to be shorter near noon. Psc 4's with the largest amplitude appeared near noon, but on the whole Psc 4's in the evening side had larger amplitude. The compressional Psc occurred more frequently near the geomagnetic equator (geomagnetic latitude φ m≌ 5° N ) than at higher latitude ( φ m≌ 9° ~ 12° N ). We suggest that the transverse Psc 5 pulsations can be considered to be magnetic field-line resonant oscillations excited by impulsive waves, while the compressional Psc 5's may be oscillations localized near the geomagnetic equator.

Damping and Coupling of Long-Period Hydromagnetic Waves by the Ionosphere

The theory that long-period geomagnetic pulsations are due to hydromagnetic waves resonating in a magnetosphere bounded by an anisotropically conducting ionosphere, insulating atmosphere, and conducting earth, is reviewed. The history of the subject is outlined, covering the effects of the ionospheric boundary on: pulsations seen at ground level and in the ionosphere (ionospheric screening, 90° rotation of polarisation, attenuation of short wavelengths, mode coupling via Hall conductance); and wave systems above the ionosphere (wave-boundary impedance matching, damping, phase variation along the geomagnetic field, and allowed resonances). Coupling of non-axisymmetric modes within the magnetosphere is also mentioned, and a summary of the present picture given, with suggestions for future work.

Modulation of energetic particle fluxes due to long-period geomagnetic oscillations

Mechanism of flux modulations of energetic protons and electrons, associated with the long-period geomagnetic pulsations in the outer magnetosphere, is examined theoretically. In the first part, a linear perturbation theory of the guiding centre distribution function averaged over the bounce phase of an interacting particle is developed for the case of the three-dimensional magnetic oscillations with a sufficiently long period compared with the bounce time of the particle. Secondly we extend the formulation to include some effects of the perturbed drift orbit on the particle distribution such as the particle trapping in the wave field and the phase bunching process. The latter is important for the interaction with the coupling Alfvén mode of magnetic oscillations. Applying these results together with the basic characteristics of the coupling hydromagnetic oscillations in a non-uniform plasma, we discuss the possibilities for the observed particle flux modulations in two different cases, separately, i.e. flux oscillations due to the compressional magnetic perturbation and those from the nearly transverse magnetic variations.

Some characteristics of the dynamic spectrum of long-period geomagnetic pulsations

This paper concerns a broad-range dynamic spectrum display used for studying seven types of geomagnetic pulsations covering the frequency from 4 to 0.002 cps. Of particular interest is the Pc 4,5 range of pulsations that displays several specific characteristics: (1) the spectra are very similar between the nearly conjugate stations Great Whale River, Canada, and Byrd, Antarctica; (2) the dynamic spectra show microstructure consisting of a series of discrete patches of about 10-min duration; (3) these patches are similar to those appearing in the dynamic spectrum of a damped Pc 4,5 associated with ssc. A suggestion for possible excitation processes of the Pc 4,5 is given.