Geomagnetic Field Lines Research Articles

On the Geomagnetic Field Line Resonance Eigenfrequency Variations during Seismic Event

In this paper, we report high statistical evidence for a seismo–ionosphere effects occurring in conjunction with an earthquake. This finding supports a lithosphere-magnetosphere coupling mechanism producing a plasma density variation along the magnetic field lines, mechanically produced by atmospheric acoustic gravity waves (AGWs) impinging the ionosphere. We have analysed a large sample of earthquakes (EQ) using ground magnetometers data: in 28 of 42 analysed case events, we detect a temporary stepwise decrease (Δf) of the magnetospheric field line resonance (FLR) eigenfrequency (f*). Δf decreases of ∼5–25 mHz during ∼20–35 min following the time of the EQ. We present an analytical model for f*, able to reproduce the behaviour observed during the EQ. Our work is in agreement with recent results confirming co-seismic direct coupling between lithosphere, ionosphere and magnetosphere opening the way to new remote sensing methods, from space/ground, of the earth seismic activity.

Spatial Evolution of Wave‐Particle Interaction Region Deduced From Flash‐Type Auroras and Chorus‐Ray Tracing

AbstractIn‐situ observations of spatial variations of the wave‐particle interaction region require a large number of satellite probes. As an alternative, flash‐type auroras, a kind of pulsating aurora, driven by discrete chorus elements, can be used to investigate the interaction region with a high spatial resolution. We estimated the spatial extent of wave‐particle interaction region from ground‐based observations of flash aurora at Gakona (62.39°N, 214.78°E), Alaska at subauroral latitudes, and found that the auroral expansion was predominantly to the low‐latitude side. The spatial displacement is thought to be caused by the propagation effects of chorus waves in the magnetosphere. Using ray tracing analysis to take into account chorus wave propagation, we reconstructed the spatiotemporal evolution of the volume emission rate and confirmed that the predominant expansion is toward the lower‐latitude side in the ionosphere. This study shows that chorus wave propagation in the magnetosphere gives new insight for characterizing the transverse size (across the geomagnetic field line) of wave‐particle interaction regions. The calculated spatial scale of the column auroral emission shows a correlation with the magnetic latitude of the resonance region at magnetic latitudes within 10° of the equatorial plane of the magnetosphere. Our results suggest that the spatial scale of a flash aurora is indirectly related to the chorus amplitude because the latitudinal range of the wave‐particle interaction is important for the growth of wave amplitude.

ULF Activity in the Earth Environment: Penetration of Electric Field from the Near-Ground Source to the Ionosphere under Different Configurations of the Geomagnetic Field

The problem with the penetration of electric fields from atmospheric near-Earth electric current sources to the ionosphere is investigated both within the dynamic simulations of the Maxwell equations in the frequency domain and within the simplified quasi-electrostatic approach. Two cases of the geomagnetic field lines are considered. The first case is the penetration of the geomagnetic field lines deeply into the magnetosphere (open field lines), whereas the second one is the return of these lines into the Earth’s surface (closed field lines). The proper boundary conditions are formulated. It is demonstrated that in the case of the open field lines the results of the dynamic simulations differ essentially from the quasi-electrostatic approach, which is not valid there. In the case of the closed field lines, the results of simulations are practically the same both within the dynamic approach and within the quasi-electrostatic one. From realistic values of the densities of atmospheric electric currents ~0.1 µA/m2, the values of the electric fields within the ionosphere F-layer may reach about 1–10 mV/m.

Multi-Instrument Characterization of Magnetospheric Cold Plasma Dynamics in the June 22, 2015 Geomagnetic Storm.

We present a comparison of magnetospheric plasma mass/electron density observations during an 11‐day interval which includes the geomagnetic storm of June 22, 2015. For this study we used: Equatorial plasma mass density derived from geomagnetic field line resonances (FLRs) detected by Van Allen Probes and at the ground‐based magnetometer networks EMMA and CARISMA; in situ electron density inferred by the Neural‐network‐based Upper hybrid Resonance Determination algorithm applied to plasma wave Van Allen Probes measurements. The combined observations at L ∼ 4, MLT ∼ 16 of the two longitudinally separated magnetometer networks show a temporal pattern very similar to that of the in situ observations: A density decrease by an order of magnitude about 1 day after the Dst minimum, a partial recovery a few hours later, and a new strong decrease soon after. The observations are consistent with the position of the measurement points with respect to the plasmasphere boundary as derived by a plasmapause test particle simulation. A comparison between plasma mass densities derived from ground and in situ FLR observations during favorable conjunctions shows a good agreement. We find however, for L < ∼3, the spacecraft measurements to be higher than the corresponding ground observations with increasing deviation with decreasing L, which might be related to the rapid outbound spacecraft motion in that region. A statistical analysis of the average ion mass using simultaneous spacecraft measurements of mass and electron density indicates values close to 1 amu in plasmasphere and higher values (∼2–3 amu) in plasmatrough.

Constraining Spectral Models of a Terrestrial Gamma‐Ray Flash From a Terrestrial Electron Beam Observation by the Atmosphere‐Space Interactions Monitor

AbstractTerrestrial Gamma ray Flashes (TGFs) are short flashes of high energy photons, produced by thunderstorms. When interacting with the atmosphere, they produce relativistic electrons and positrons, and a part gets bounded to geomagnetic field lines and travels large distances in space. This phenomenon is called a Terrestrial Electron Beam (TEB). The Atmosphere‐Space Interactions Monitor (ASIM) mounted on‐board the International Space Station detected a new TEB event on March 24, 2019, originating from the tropical cyclone Johanina. Using ASIM's low energy detector, the TEB energy spectrum is resolved down to 50 keV. We provide a method to constrain the TGF source spectrum based on the detected TEB spectrum. Applied to this event, it shows that only fully developed Relativistic Runaway Electron Avalanche spectra are compatible with the observation. More specifically, assuming a TGF spectrum , the compatible models have ϵ ≥ 6.5 MeV (E is the photon energy and ϵ is the cut‐off energy). We could not exclude models with ϵ of 8 and 10 MeV.

Observations on a magnetotactic bacteria-grazing ciliate in sediment from the intertidal zone of Huiquan Bay, China

Magnetotactic bacteria (MTB) are a group of prokaryotes having the ability to orient and swim along geomagnetic field lines because they contain intracellular magnetosomes, which are synthesized through a biomineralization process. Magnetosomes have recently also been found in unicellular eukaryotes, which are referred to as magnetically responsive protists (MRPs). The magnetosomes have three origins in MRPs. In this study we characterized a MTB-grazing ciliated MRP that was magnetically collected from intertidal sediment of Huiquan Bay, China. Based on 18S rRNA gene sequence analysis, the ciliated MRP was tentatively identified as Uronemella parafilificum HQ. Using transmission electron microscopy, we observed that magnetosomes having 2-3 shapes were randomly distributed within this ciliate. Energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy images of the magnetosomes were consistent with them being composed of magnetite. Magnetosomes having the same shape and mineral composition were also detected in MTB that occurred in the same environment as the ciliated MRP. Statistical analysis showed that the size and shape of the magnetosomes in the ciliated MRP were similar to those in MTB. The results suggest that this ciliated MRP can graze, ingest, and digest various types of MTB. It is certainly worth noting that this is the first record of MRPs in Asian aquatic sediment and suggesting they might be widely distributed. These results also support the assertion that MRPs probably contribute to the ecological cycles of iron, and expand possibilities for research into the mechanism of magnetoreception in eukaryotes.

Global Hybrid Simulations of Interaction Between Interplanetary Rotational Discontinuity and Bow Shock/Magnetosphere: Can Ion‐Scale Magnetic Reconnection be Driven by Rotational Discontinuity Downstream of Quasi‐Parallel Shock?

AbstractIon‐scale magnetic reconnection has been observed downstream of the terrestrial quasi‐parallel (Q‐∥) shock. Whether it is driven by interplanetary discontinuities or turbulent Q‐∥ shock, however, is unclear. Using three‐dimensional global hybrid simulation, we investigate the generation of magnetic reconnection downstream of the Q‐∥ shock, while an interplanetary rotational discontinuity (RD) is launched to the bow shock. Cases with various solar wind Alfvén Mach numbers, MA = 3.0 to 8, and propagation directions of the RD are presented. The propagation direction n is assumed to be in the GSE xz plane and pointing earthward, with n = (−sin(θ12/2),0,−cos(θ12/2)), where θ12 is the angle between the upstream (B1) and downstream (B2) magnetic fields across the transmitted RD. It is found that magnetic reconnection occurs inside the RD downstream of the Q‐∥ shock, forming flux ropes extending along the dawn‐dusk direction about tens of ion inertial lengths. Large‐amplitude low‐frequency waves originated from the Q‐∥ shock lead to the bending and squeezing of the field lines around the RD, which play an important role in triggering reconnection inside the RD. As the RD impacts the dayside magnetopause, magnetopause reconnection takes place between the field lines behind the RD and geomagnetic field lines. Nevertheless, no reconnection is found downstream of the Q‐∥ shock itself or outside the RD in the magnetosheath. The existent and structure of reconnection in the magnetosheath are found to strongly depend on the parameters MA and n. Our simulation shows that ion‐scale magnetic reconnection is driven by an external driver in the form of the compression of an RD around the bow shock and in the magnetosheath, rather than caused by the turbulent Q‐∥ shock alone.

Global Study of Human Heart Rhythm Synchronization with the Earth’s Time Varying Magnetic Field

Changes in geomagnetic conditions have been shown to affect the rhythms produced by the brain and heart and that human autonomic nervous system activity reflected in heart rate variability (HRV) over longer time periods can synchronize to changes in the amplitude of resonant frequencies produced by geomagnetic field-line and Schumann resonances. During a 15-day period, 104 participants located in California, Lithuania, Saudi Arabia, New Zealand, and England underwent continuous ambulatory HRV monitoring. The local time varying magnetic field (LMF) intensity was obtained using a time synchronized and calibrated network of magnetometers located at five monitoring sites in the same geographical locations as the participant groups. This paper focuses on the results of an experiment conducted within the larger study where all of the participants simultaneously did a heart-focused meditation called a Heart Lock-In (HLI) for a 15-min period. The participant’s level of HRV coherence and HRV synchronization to each other before, during and after the HLI and the synchronization between participants’ HRV and local time varying magnetic field power during each 24-h period were computed for each participant and group with near-optimal chaotic attractor embedding techniques. In analysis of the participants HRV coherence before, during and after the HLI, most of the groups showed significantly increased coherence during the HLI period. The pairwise heart rhythm synchronization between participants’ in each group was assessed by determining the Euclidean distance of the optimal time lag vectors of each participant to all other participants in their group. The group member’s heart rhythms were significantly more synchronized with each other during the HLI period in all the groups. The participants’ daily LMF-HRV-synchronization was calculated for each day over an 11-day period, which provided a 5-day period before, the day of and 5-days after the HLI day. The only day where all the groups HRV was positively correlated with the LMF was on the day of the HLI and the synchronization between the HRV and LMF for all the groups was significantly higher than most of the other days.

Investigation of the Interaction Between Magnetosheath Reconnection and Magnetopause Reconnection Driven by Oblique Interplanetary Tangential Discontinuity Using Three‐Dimensional Global Hybrid Simulation

AbstractMagnetosheath reconnection due to the interaction of an interplanetary directional discontinuity with the bow shock and Earth's magnetosphere under an initially northward interplanetary magnetic field (IMF) has been investigated in previous simulations (e.g., Guo et al., 2018, https://doi.org/10.1029/2018ja025679). Under an initially southward IMF, the magnetosheath reconnection could interact with reconnection at the magnetopause. In this study, using three‐dimensional (3D) global‐scale hybrid simulations, we present cases with incoming tangential discontinuities (TDs) in an initially southward IMF, which possess various magnetic field rotation angles (ΔΦ) and half‐width (w), to study the effects of pre‐existing magnetopause reconnection on the formation of magnetosheath flux ropes, as well as the subsequent interaction between the magnetopause reconnection and magnetosheath reconnection, with downstreams of both Quasi‐perpendicular (Q‐) and Quasi‐parallel (Q‐||) shock examined. The initial IMF is assumed to be oblique, with a finite Bx and Bz, similar to that in Guo et al. (2018), https://doi.org/10.1029/2018ja025679 but with a southward Bz &lt; 0. Compared with the cases with an initially northward IMF, magnetopause reconnection weakens the compression processes of the TD and leads to less frequent reconnection in the magnetosheath. The existence and the structure of magnetosheath reconnection are found to strongly depend on the parameters w and of the TD. When interacting with the magnetopause reconnection, the magnetosheath flux ropes can re‐reconnect with the geomagnetic dipole field lines, forming new structures of magnetopause flux ropes. The resulting evolution of flux rope configuration is illustrated.

Nonlinear Least Squares Fitting Technique for the Determination of Field Line Resonance Frequency in Ground Magnetometer Data: Application to Remote Sensing of Plasmaspheric Mass Density

AbstractThe accurate determination of the field line resonance (FLR) frequency of a resonating geomagnetic field line is necessary to remotely monitor the plasmaspheric mass density during geomagnetic storms and quiet times alike. Under certain assumptions the plasmaspheric mass density at the equator is inversely proportional to the square of the FLR frequency. The most common techniques to determine the FLR frequency from ground magnetometer measurements are the amplitude ratio (AR) and phase difference (PD) techniques, both based on geomagnetic field observations at two latitudinally separated ground stations along the same magnetic meridian. Previously developed automated techniques have used statistical methods to pinpoint the FLR frequency using the AR and PD calculations. We now introduce a physics‐based automated technique, using nonlinear least squares fitting of the ground magnetometer data to the analytical resonant wave equations, that reproduces the wave characteristics on the ground, and from those determine the FLR frequency. One of the advantages of the new technique is the estimation of physics‐based errors of the FLR frequency, and as a result of the equatorial plasmaspheric mass density. We present analytical results of the new technique, and test it using data from the Inner‐Magnetospheric Array for Geospace Science ground magnetometer chain along the coast of Chile and the east coast of the United States. We compare the results with the results of previously published statistical automated techniques.

THE INVESTIGATION OF THE PG PULSATIONS WITH USING DATA OF ARASE, GOES SATELLITES AND GROUND-BASED STATIONS

The physical nature of Pg (pulsation giant) pulsations, which were observed in the magnetosphere by the Japanese satellite Arase, geostationary satellites GOES, and ground stations of the THEMIS and CARISMA networks, was investigated in this work. Pg pulsations belong to the Pc4 frequency range and are characterized by a very monochromatic shape. For the event on 5 June, 2018, according to the data from the Arase satellite, the Pg pulsation wave packet was recorded in the dawn sector during 3 hours. The pulsations are most pronounced in the radial component of the geomagnetic field, their frequency was about 11 mHz. Pg pulsations observed in the magnetosphere were accompanied by pulsations with the same period according to data from a number of ground-based magnetic stations located near the conjugate point. According to the data of ground stations, the pulsations were most strongly expressed in the Y-component of the geomagnetic field. Pg pulsations were accompanied by pulsations in electron and proton fluxes according to the Arase, GOES satellite observations. There are no clear phase relationships between geomagnetic pulsations and pulsations in charge particle fluxes. Pg pulsations were excited under quiet geomagnetic conditions (SYM-H = -10 nT, AE = 100-400 nT) on the recovery phase of the small geomagnetic storm. It is assumed that the expansion of the plasmasphere at low geomagnetic activity leads to an increase in the plasma density in the region of the geostationary orbit, which creates favorable conditions for the excitation of Pg pulsations due to the drift-bounce resonance of protons with the geomagnetic field lines oscillations in the magnetosphere.

Ультранизкочастотные эмиссии диапазона 0.1–3 Гц в приполярных областях

We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS

We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

Evolution of High-Latitude Geomagnetic Disturbances during the Magnetic Storm of July 22, 2009

The behavior of geomagnetic disturbances during a moderate CIR storm, the most intense magnetic storm of 2009 in the solar activity minimum are considered. It is found that the substorm activity during the main phase of the storm was observed not in the nighttime but in the morning sector (0700–0900 MLT) of auroral geomagnetic latitudes (65°–67°) and was accompanied by extremely large (up to 1000 nT) geomagnetic pulsations of the Рс5 range, evidently of a non-resonant nature; the amplitude of the Y component of waves considerably exceeded that of the Х component. In the recovery phase of the magnetic storm, the tangential discontinuity in the IMF caused a substorm observed near the polar boundary of the auroral oval in the global scale in the longitude, from the evening sector to midday hours. In the daytime sector, the magnetic bay was observed several minutes later than in the nighttime sector and rapidly moved to the pole, which can be interpreted as the motion to the pole of the boundary between closed and open geomagnetic field lines and contraction of the auroral oval.

Asymmetric Development of Auroral Surges in the Northern and Southern Hemispheres

AbstractSimultaneous eastward and westward traveling surges were observed at Tjörnes, Iceland, and Syowa station, Antarctica, respectively. Several remarkable differences were identified. (1) The position of the initial bright spot was shifted by 1.7 to 2.3 MLT between both hemispheres. (2) The surges differ in traveling speed between the eastward traveling surge (6.5 km s−1) and the westward traveling surge (1.3 km s−1). (3) The Arase satellite was located on a geomagnetic field line connecting both ground stations and observed a significant excess in westward component of the magnetic field, which is consistent with the large shifts of the initial bright spots in both hemispheres. (4) The background Hall current flows eastward (Northern Hemisphere) and westward (Southern Hemisphere). The observed north‐south asymmetry of the traveling surges suggests that the ionosphere can play an essential role in controlling the fundamental spatiotemporal development of auroras in both hemispheres.

Numerical Investigations of Interhemispheric Asymmetry due to Ionospheric Conductance

AbstractDue to differences in solar illumination, a geomagnetic field line may have one foot point in a dark ionosphere while the other ionosphere is in daylight. This may happen near the terminator under solstice conditions. In this situation, a resonant wave mode may appear, which has a node in the electric field in the sunlit (high conductance) ionosphere and an antinode in the dark (low conductance) ionosphere. Thus, the length of the field line is one quarter of the wavelength of the wave, in contrast with half‐wave field line resonances in which both ionospheres are nodes in the electric field. These quarter waves have resonant frequencies that are roughly a factor of 2 lower than the half‐wave frequency on the field line. We have simulated these resonances using a fully three‐dimensional model of ULF waves in a dipolar magnetosphere. The ionospheric conductance is modeled as a function of the solar zenith angle, and so this model can describe the change in the wave resonance frequency as the ground magnetometer station varies in local time. The results show that the quarter‐wave resonances can be excited by a shock‐like impulse at the dayside magnetosphere and exhibit many of the properties of the observed waves. In particular, the simulations support the notion that a conductance ratio between day and night foot points of the field line must be greater than about 5 for the quarter waves to exist.

The 18 November 2015 Magnetopause Crossing: The GEM Dayside Kinetic Challenge Event Observed by MMS/HPCA

AbstractAt Earth's dayside magnetopause, the fundamental process known as magnetic reconnection is responsible for connecting geomagnetic field lines to interplanetary magnetic field lines and converting magnetic energy into particle energy and heat. As part of a coordinated analysis effort by the Geospace Environment Modeling (GEM) community to determine the reconnection location and other aspects of reconnection, a magnetopause crossing by the Magnetospheric Multiscale (MMS) mission on 18 November 2015 was selected. The crossing occurred during stable solar wind and dominantly southward interplanetary magnetic field conditions. The MMS satellites were located close to the subsolar region and observed southward accelerated ion jets during encounters with the magnetopause boundary layers, indicating the presence of an active X‐line north of the satellites. Using proton distributions from the Hot Plasma Composition Analyzer (HPCA) instruments, the distance from the spacecraft to the reconnection site was initially determined to be between 5 to 7 RE. A slight rotation of the interplanetary magnetic field caused a change of the magnetic topology at the magnetopause. This topology change produced conditions which are known to change the location of the X‐line. After the change, the location of the component reconnection line was estimated to be less than 4 RE, but most likely was much closer to the observing satellites.

Special features of the studies of deep electrical conductivity of the Moon and the Earth (once more on toroidal mode of natural magnetic field)

Studies of the deep electrical conductivity of the Earth and the Moon are carried out by measuring and analyzing the natural electromagnetic (EM) fields excited by the solar wind, introducing an electric field of the order of 2 mV/m applied to the boundaries of the Earth’s magnetosphere or directly to the surface of the Moon. For a concentrically layered sphere with electrical conductivity σ = σ (r), the EM fields can be represented as the sum of two modes: electric with a toroidal magnetic field and magnetic with a poloidal magnetic field. Each of the modes is associated with electrical conductivity by different ratios/formulas and is characterized by different possibilities for studying the electrical conductivity inside a celestial body. It is generally accepted that currents from the boundary of the Earth’s magnetosphere descend along the geomagnetic field lines to the ionosphere, but do not reach the Earth due to the very high resistance of near-the-surface air layer (up to 1014 Ohm · m) and only poloidal fields of the magnetic mode are induced in the solid Earth. A review of the data on the global electric circuit shows that vertical currents penetrate from the atmosphere into the Earth and the electric mode is not equal to zero. Vertical currents are characterized by strong spatio-temporal variability. Separation of the modes from observation data was not carried out. On the Moon, the high-resistance layer is the lithosphere with regolith and breccias on its surface with a resistivity of 107―1012 Ohm · m. Spatial inhomogeneities of the Moon interior are considered and a conclusion is made about their multitude and intensity. Based on the analysis of the spatial distribution of tidal and tectonic moonquakes, it was suggested that they trace quasi-vertical structures like a plume. The results of observations of volcanism and transient lunar phenomena, obtained in recent years by orbital missions with high-resolution equipment, indicate an intense degassing of the moon. All this allows us to conclude that in the Moon there are quasi-vertical conductors supporting an electric mode. Proposals for the optimization of new studies of the electrical conductivity of the moon are substantiated and formulated. Deep studies of electrical conductivity are based on a theoretical model of the magnetic mode, the existence of the electrical mode is neglected, and it falls into unidentified noise, which by means of coherent analysis and multi-stage processing is largely eliminated and the conductivity models more or less correctly describe the real geoelectric structure of the Earth, but with probable systematic errors. Separation and study of the electric mode should be considered as an additional channel of information in EM studies of planets.

From conservation to structure, studies of magnetosome associated cation diffusion facilitators (CDF) proteins in Proteobacteria.

Magnetotactic bacteria (MTB) are prokaryotes that sense the geomagnetic field lines to geolocate and navigate in aquatic sediments. They are polyphyletically distributed in several bacterial divisions but are mainly represented in the Proteobacteria. In this phylum, magnetotactic Deltaproteobacteria represent the most ancestral class of MTB. Like all MTB, they synthesize membrane-enclosed magnetic nanoparticles, called magnetosomes, for magnetic sensing. Magnetosome biogenesis is a complex process involving a specific set of genes that are conserved across MTB. Two of the most conserved genes are mamB and mamM, that encode for the magnetosome-associated proteins and are homologous to the cation diffusion facilitator (CDF) protein family. In magnetotactic Alphaproteobacteria MTB species, MamB and MamM proteins have been well characterized and play a central role in iron-transport required for biomineralization. However, their structural conservation and their role in more ancestral groups of MTB like the Deltaproteobacteria have not been established. Here we studied magnetite cluster MamB and MamM cytosolic C-terminal domain (CTD) structures from a phylogenetically distant magnetotactic Deltaproteobacteria species represented by BW-1 strain, which has the unique ability to biomineralize magnetite and greigite. We characterized them in solution, analyzed their crystal structures and compared them to those characterized in Alphaproteobacteria MTB species. We showed that despite the high phylogenetic distance, MamBBW-1 and MamMBW-1 CTDs share high structural similarity with known CDF-CTDs and will probably share a common function with the Alphaproteobacteria MamB and MamM.

The increase in the curvature radius of geomagnetic field lines preceding a classical dipolarization

Abstract. Based on assumptions that substorm field line dipolarization at geosynchronous altitudes is associated with the arrival of high-velocity magnetotail flow bursts referred to as bursty bulk flows, the following sequence of field line dipolarization is proposed: (1) slow magnetoacoustic wave excited through ballooning instability by enhanced inflows in pre-onset intervals towards the equatorial plane; (2) in the equatorial plane, slow magnetoacoustic wave stretching of the flux tube in dawn–dusk directions resulting in spreading plasmas in dawn–dusk directions and reduction in the radial pressure gradient in the flux tube. As a consequence of these processes, the flux tube assumes a new equilibrium geometry in which the curvature radius of new field lines increased in the meridian plane, suggesting an onset of field line dipolarization. The dipolarization processes associated with changing the curvature radius preceded classical dipolarization caused by a reduction of cross-tail currents and pileup of the magnetic fields. Increasing the curvature radius induced a convection surge in the equatorial plane as well as inductive westward electric fields of the order of millivolts per meter (mV m−1). Electric fields transmitted to the ionosphere produce an electromotive force in the E layer for generating a field-aligned current system of Bostrom type. This is also equivalent to the creation of an incomplete Cowling channel in the ionospheric E layer by the convection surge.