162 years of rendezvous with the magnetic equator by the Travancore observatory

The diurnal variation of II at Huancayo is found to be considerably larger than that expected in such regions. McNish (1937) explained the large variation as follows. According to the dynamo theory the main electrometric forces are induced in middle and higher latitudes, which drive the cur-rent eastwards in low latitudes, where, if the geographic and geomagnetic equators coincide, it is opposed by the electromotive forces induced there, but if the two equators are apart, then in the region between these two, the electromotive forces induced there help the current flow, resulting in its en-hancement. Chakravarty (1946) suggest-ed geomagnetic control of the diurnal varia-tion in low latitudes. Egedal (1947) showed from the data of some stations in and near the equatorial region that the diurnal mag-netic variation was symmetrical about the magnetic equator. He suggested that the augmentation of the range of H in a narrow zone near the magnetic equator might be due to a varying electric current flowing in a very narrow zone of the atmosphere above the magnetic equator at a height of about 100 km. Chapman (1948) found that diurnal variation was large at places near which the magnetic equator crossed the geographic equator at a steep angle and was less at places where the change in the latitude of the magnetic equator was slow. Mart-pi (1949) was of the view that the distribution of diurnal range was symmet-rical about an equator between the mag-netic and geomagnetic equators. He men-tioned that McNish's theory did not appear to account for the observed effects as al-though it gave approximate symmetry about the magnetic equator it did not ac-count for the large enhancement. He thought that the enhancement was more likely to be due to an increase in conduc-tivity of the ionosphere near the magnetic.

This paper delves into the intricate relationship between changes in Magnetic inclination and declination at specific geographical locations and the navigational decisions of migratory birds. Leveraging a dataset sourced from a prominent bird path tracking web resource, encompassing six distinct bird species' migratory trajectories, latitudes, longitudes, and observation timestamps, we meticulously analyzed the interplay between these avian movements and corresponding alterations in Magnetic inclination and declination. Employing a circular von Mises distribution assumption for the latitude and longitude distributions within each subdivision, we introduced a pioneering circular-circular regression model, accounting for von Mises error, to scrutinize our hypothesis. Our findings, predominantly supported by hypothesis tests conducted through circular-circular regression analysis, underscore the profound influence of Magnetic inclination and declination shifts on the dynamic adjustments observed in bird migration paths. Moreover, our meticulous examination revealed a consistent adherence to von Mises distribution across all bird directions. Notably, we unearthed compelling correlations between specific bird species, such as the Black Crowned Night Heron and Brown Pelican, exhibiting a noteworthy negative correlation with Magnetic inclination and a contrasting positive correlation with Magnetic declination. Similarly, the Pacific loon demonstrated a distinct negative correlation with Magnetic inclination and a positive association with Magnetic declination. Conversely, other avian counterparts showcased positive correlations with both Magnetic declination and inclination, further elucidating the nuanced dynamics between avian navigation and the Earth's magnetic field parameters.

Mirror structures are manifested as a wave train of magnetic peaks and/or dips, which are anticorrelated with plasma density. The evolution behavior of the ion temperatures perpendicular and parallel to the local magnetic field, T ⊥ and T ∥, in the magnetic peaks and dips is rare to be theoretically studied. In this paper, the thermodynamic properties of mirror structures are investigated using two-dimensional magnetohydrodynamic simulations with double-polytropic laws. Two polytropic exponents, γ ∥ and γ ⊥, are used as parameters to describe various thermodynamic conditions in the anisotropic plasma—for example, γ ∥ = 1, γ ⊥ = 1 for double-isothermal and γ ∥ = 3, γ ⊥ = 2 for double-adiabatic. Using empirical values of γ ∥ = 1.14 and γ ⊥ = 0.94 for magnetosheath plasma, the variations of T ∥ and T ⊥ in the magnetic dips and peaks observed by the Magnetospheric Multiscale Mission in the Earth’s magnetosheath can be reproduced. This consistent result cannot be achieved by use of γ ∥ = 3, γ ⊥ = 2 and γ ∥ = 0.5, γ ⊥ = 2, where the latter exponents can lead to the same mirror instability threshold as kinetic theory. In magnetic dips, T ∥ is found to be increased for γ ∥ > 1 but decreased for γ ∥ < 1, while T ⊥ is decreased for γ ⊥ > 1 but increased for γ ⊥ < 1. For magnetic peaks, the variation features of T ∥ and T ⊥ are opposite to that of the magnetic dips. It is concluded that the thermodynamic properties of mirror structures are further from double-adiabatic but closer to double-isothermal conditions.

SUMMARY Vector spherical harmonic analyses have been used effectively to solve laminar and mean-field magnetohydrodynamic dynamo problems with product interactions, such as magnetic induction, anisotropic alpha-effect and anisotropic magnetic diffusion, that are difficult to analyse spectrally in spherical geometries. Spectral forms of the non-linear rotating, Boussinesq and anelastic, momentum, magnetic induction and heat equations are derived for spherical geometries from vector spherical harmonic expansions of the velocity, magnetic induction, vorticity, electrical current and gravitational acceleration and from scalar spherical harmonic expansions of the pressure and temperature. By combining the vector spherical harmonic spectral forms of the momentum equation and the magnetic induction equation with poloidal–toroidal representations of the velocity and the magnetic field, non-linear spherical harmonic spectral equations are also derived for the poloidal–toroidal potentials of the velocity or the momentum density in the anelastic approximation and the magnetic field. Both compact and spectral interaction expansion forms are given. Vector spherical harmonic spectral forms of the linearized rotating magnetic induction, momentum and heat equations for a general basic state can be obtained by linearizing the corresponding non-linear spectral equations. Similarly, the spherical harmonic spectral equations for the poloidal–toroidal potentials of the velocity and the magnetic field may be linearized. However, for computational applications, new alternative hybrid linearized spectral equations are derived. The algorithmically simpler hybrid equations depend on vector spherical harmonic expansions of the velocity, magnetic field, vorticity, electrical current and gravitational acceleration of the basic state and scalar spherical harmonic expansions of the poloidal–toroidal potentials of the perturbation velocity, magnetic field and temperature. The spectral equations derived herein may be combined with the corresponding spectral forms of anisotropic diffusion terms.

We performed two‐dimensional (2D) and three‐dimensional (3D) hybrid simulations in open boundary models to study the nonlinear mirror‐mode structures driven by the temperature anisotropy (T⊥/T∥> 1) of protons in the magnetosheath. In the open systems, because of the propagation of EMIC waves, we obtain the clearer non‐propagating mirror‐mode structures. We analyzed the relation between the mirror instability and the magnetic peaks and dips observed in the magnetosheath. In the 2D open boundary model with low beta (β∥ ≲ 1), we obtain fine structures of the magnetic dips at the nonlinear stage. In the 3D model, on the other hand, the mirror instability makes the magnetic peak structures with the same parameters. The parametric analysis indicates that the magnetic peaks also arise in both 2D and 3D high beta cases (β∥ ⪆ 1) as shown by the Cluster observations. In the high beta cases, the high mobility of the protons helps continuous coalescence of the diamagnetic currents inside the magnetic dips. The coalescence makes the magnetic dips larger and shallower. Between the large and shallow magnetic dips, the magnetic peaks appear in the high beta cases. In the 3D models, because degree of freedom increases in the perpendicular direction, the continuous coalescence can take place even in the low beta cases. Thus, the magnetic peaks appear in the 3D models in both cases.

The temperature anisotropy (T ⊥ /T ∥ >1) of ions in the magnetosheath drives the mirror instability. We performed two-dimensional (2D) and three-dimensional (3D) hybrid simulations in open boundary models to study the nonlinear mirror mode structures. In the open boundary systems, because of the propagation of EMIC waves, we can obtain the clearer non propagating mirror mode structures. We analyzed the relation between the mirror instability and the magnetic peaks and dips which are peculiar magnetic structures observed in the magnetosheath. In the 2D open boundary model, we obtain the clear magnetic dips at the nonlinear stage. The magnetic structures become larger in the parallel directions rather than the perpendicular directions. In the 3D model, on the other hand, the mirror instability makes the magnetic peaks structures with the same parameters. The cigar-like magnetic peak structures are formed because of the nonlinear evolution of mirror instability and the symmetric structure in the perpendicular directions. We also performed parametric analyses on the ion beta in both 2D and 3D models. We find that the magnetic peaks also arise in both 2D and 3D high beta case as shown in the Cluster observations. We find the MHD equilibrium between the particle pressure and the magnetic field of these magnetic structures. Integrating the equilibrium equation with the assumption of the magnetic dips, we find that the integrated pressure becomes larger as the spatial size of the magnetic dips becomes larger. Between the large scale magnetic dips which are made through the coalescence of the magnetic structures, the magnetic peak appears. Thus, the magnetic peaks are excited in high particle beta conditions.

Aims. An analytical model of the global transverse oscillations and mechanical stability of a quiescent prominence in the magnetised environment with a magnetic field dip, accounting for the mirror current effect, is developed. Methods. The model is based upon the interaction of line currents through the Lorentz force. Within this concept the prominence is treated as a straight current-carrying wire, and the magnetic dip is provided by two photospheric current sources. Results. Properties of both vertical and horizontal oscillations are determined by the value of the prominence current, its density and height above the photosphere, and the parameters of the magnetic dip. The prominence can be stable in both horizontal and vertical directions simultaneously when the prominence current dominates in the system and its height is less than the half-distance between the photospheric sources.

It has been well established that homing pigeons are able to use the Earth's magnetic field to obtain directional information when returning to their loft and that their magnetic compass is based, at least in part, on the perception of magnetic inclination. Magnetic inclination has also been hypothesized in pigeons and other long-distance navigators, such as sea turtles, to play a role providing positional information as part of a map. Here we developed a behavioral paradigm which allows us to condition homing pigeons to discriminate magnetic inclination cues in a spatial-orientation arena task. Six homing pigeons were required to discriminate in a circular arena between feeders located either in a zone with a close to 0 deg inclination cue or in a zone with a rapidly changing inclination cue (-3 deg to +85 deg when approaching the feeder and +85 deg to -3 deg when moving away from the feeder) to obtain a food reward. The pigeons consistently performed this task above chance level. Control experiments, during which the coils were turned off or the current was running anti-parallel through the double-wound coil system, confirmed that no alternative cues were used by the birds in the discrimination task. The results show that homing pigeons can be conditioned to discriminate differences in magnetic field inclination, enabling investigation into the peripheral and central neural processing of geomagnetic inclination under controlled laboratory conditions.

In this paper the impact of the field‐aligned ion drag on equatorial thermosphere temperature and density is quantitatively investigated on the basis of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR TIEGCM) simulations under high solar activity (F107 = 180). The increase of upward vertical winds over the magnetic equator associated with the additional divergence of meridional winds, caused by the inclusion of field‐aligned ion drag, leads to a reduction in thermosphere temperature and density at the magnetic equator through enhanced adiabatic cooling. We found that the field‐aligned ion drag has an obvious impact on the thermosphere only over the magnetic equatorial region in the daytime and evening sectors, whereas it has less effect on the equatorial thermosphere anomaly (ETA) crests. The daytime neutral temperature over the magnetic equator is reduced by about 30 K, for altitudes above 250 km without significant altitudinal variations, when field‐aligned ion drag is included in the simulation. The thermosphere density in the magnetic equatorial region starts to change slightly at 300 km and depletes by about 5% at 400 km, while experiencing a greater decrease with altitude. Furthermore, the trough produced in the neutral temperature and density corresponds well with the magnetic dip equator. The ETA features during 12:00–18:00 LT become obvious as a result of the inclusion of the field‐aligned ion drag. Specifically, our results show that at 400 km the crest‐trough differences in neutral temperature are about 30–60 K, and the crest‐trough ratios in thermosphere density are 1.03–1.06, comparable with observations.

To test the present hypotheses concerning the functioning of the bird's magnetic compass, pigeons reared near the magnetic and geographic equator (Fortaleza, NE Brasil) were released 300 km NW of their home in the horizontal field at the magnetic equator. Pigeons released in the morning and in the afternoon were roughly homeward oriented whereas pigeons released at noon with the sun near the zenith vanished close to magnetic north. According to the Wiltschko model of the magnetic compass they should not be able to pick up specific directions. A considerable number of young and inexperienced pigeons returned home against a continuously blowing trade wind. This result contradicts the hypothesis of olfactory navigation as currently discussed.

A study of the equatorial electrojet—II A model electrojet that fits H-observations

The Electromagnetic Stirring (EMS) technology has wide applications in the metal continuous casting. Stirring consists of exciting variable magnetic field in metal liquid, the magnetic field generates induction current. The induction current in the metal flow interacts with magnetic filed to generate EM force, which makes perfect motion to improve casting. The EM force strength is proportional with square of the magnetic field strength. The key of the optimized control of EMS is to adjust several parameters for best EM force and deep magnetic penetration. In this paper, we present a new AGILD EMS modeling. We use Maxwell magnetic field differential equation to replace the reduced magnetic field equation. We present new volume magnetic differential integral equation and new boundary strip magnetic field differential integral equation which are proposed by XIe and Li in GLGEO. According to the new AGILD EM modeling in [1], we developed 3D AGILD EMS modeling. Our AGILD EMS modeling does not need any complex boundary condition. The matrix equations are decomposed by GILD parallel processes. Therefore, our AGILD EMS modeling is fast and accurate without any boundary error. Our AGILD EMS modeling can simulate multiple strands and EMSs together. The simulation shows that the AGILD EMS modeling is very powerful tool for the design of excellent EMS system in Billent/Bloom and metal continuous casting system. The simulation is performed by using GLGEO’s new GL[2-4] and AGILD EMS modeling software. The EMS is an established technology and installed in Billet, Bloom and metal casters. The stirring consists of exciting variable magnetic field which is penetrating in the steel, iron, and metal liquid. The magnetic field generates induction electric current in the metal liquid. The induction current in the metal liquid interacts with the magnetic field to generate EM force which drives the metal liquid flow motion such that the casting is perfectly performing. The casting quality is improved by reduced segregation and porosity through transformation to an equiaxed solidification structure. The steel and iron productions are increasing due to the increased casting speeds. The temperature and carbon component are key factors for high quality steel. The magnetic field penetrating distribution depends on the material properties and high temperature. Moreover, the electromagnetic properties depend on the temperature. The temperature difference between outer and insider of the caster mold is very large. We consider the magnetic conductivity be space variable. The reduced magnetic field equation is no longer to govern this case. In this paper, we use the magnetic field Maxwell equation to replace the reduced magnetic equation. Moreover, we present a new strip magnetic field differential integral equation which is proposed by Xie and Li in [1]. We use the new strip integral equation on the double layered boundary and the magnetic field Garlekin equation in the internal domain to construct the AGILD EMS modeling for the metal continuous casting. It has more advantages over FEM and FD modeling. The AGILD and GL EMS modeling, GL and AGILD nondestructive testing, GL and AGILD heating modeling, and GL and AGILD heavier viscosity flow modeling for the continuous casting are developed by Xie and Li in GLGEO. Many EM research works on motor need the condition that the magnetic resistivity monotone increasedly depends on the magnetic induction. It is very strong and unpractical condition. In practice, magnetic resistivity is not monotone increasing but has a minimum point at B = B0. Our nonlinear FEM EM modeling [10-12] are available for the above practical condition, i.e. the magnetic resistivity is not monotone increasing. We prove that if H(B) monotone increasedly depends on B, the nonlinear FEM is convergent. Because H(B) = υ(B)B, so, we only need that υ(B)B monotone increasedly depends on the B, which is widely generalized. Moreover, the H(B)’s monotone property is the practical physical property. Our nonlinear FEM magnetic DC modeling is briefly described in this paper. The organization of the paper is as follows. We present the new strip differential integral equation in the section 2 which is proposed in [1]. The double layered collocation FEM equation for the magnetic field is

The major objective of this thesis is to reorient and analyze three component magnetic field data recorded in two boreholes during Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamount Chain. One aim of the expedition was to determine whether the hotspot that created the seamount chain during the past 80 million years is moving relative to the Hawaiian-Emperor hotspot or if it remained stationary within the mantle. The magnetic field measurements were conducted with the Gottinger Bohrlochmagnetometer, which comprises fibre optic gyros that measure the rotations of the tool within the borehole. In this thesis, I use different algorithms to reorient the measured magnetic field from the tools reference frame into the geographical reference frame. This purpose requires sensors of high accuracy and careful data processing. I present several reorientation algorithms; among others, I introduce two new sensor fusion algorithms for gyro and inclinometer data based on a Kalman filter. Oriented magnetic field data can be used to determine both the inclination and declination of the magnetization of the rocks surrounding the borehole by the application of appropriate models. Measurements on drill core samples can typically only be used to determine the inclination of magnetization, as cores are usually azimuthally unoriented. In the subsequent analysis of the oriented magnetic field data, I use different models for the drilled igneous layers to calculate the magnetization of the subsurface. As horizontal layers turn out to be insufficient to explain the data, I extend the interpretation to inclined layers. I introduce a new approximation for the magnetic field of inclined layers that can be used to separate the calculation of magnetization in an inversion using horizontal layers and a following consideration of potential layer geometries. My approximation additionally reveals possible ambiguities and errors of the measurements. Using images of the borehole wall that give additional information about the possible geometry of a drilled layer inside Burton Guyot (Site U1376), I determine a mean inclination of magnetization of 58.9° and a mean declination of magnetization of 0.4°. These results agree with current theories of a stationary Louisville hotspot. In addition, the result for the declination suggests that Burton Guyot has not been rotated since its formation.

Speleothems can provide high-resolution records to reconstruct the ancient Earth's magnetic field. However, little is known about the influence of speleothem morphologies on the natural remanent magnetisation record. A previous study by Ponte et al. (2017) showed that the magnetic inclination recorded in stalagmites decreases according to the slope of the calcite laminae. Magnetic inclination is 5º lower at the bottom of the stalagmite than at the top. The authors suggest that magnetic particles are re-orientated due to particle rolling during the deposition onto the flank of the stalagmite, resulting in magnetic inclination shallowing. In this scenario, magnetic inclinations are expected to be deeper on the other flank of the stalagmite. Still only half of the stalagmite was available for the study of Ponte et al. (2017). Here, we present new data on a cone-shaped stalagmite from Central Portugal, labelled LM1. We use alternating field demagnetisation, anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic remanent magnetisation (AARM), and X-ray microtomography to investigate the orientation of the calcite and magnetic fabrics along the flanks of three detrital-rich calcite layers and their relationship with paleomagnetic directions. We show that magnetic inclination varies up to more than 10° depending on the slope of the calcite laminae. In contrast, magnetic declination is almost constant, corroborating previous results by Ponte et al. (2017). Orientation of the k1 of the calcite fabric determined by AMS shows a striking correlation with the k1 of the magnetic fabric obtained by AARM, suggesting that the orientation of the magnetic particles is mainly controlled by the growth direction of the calcite crystals, which is perpendicular to the surface of the stalagmite. However, magnetic inclinations are not symmetrical between both flanks, suggesting that the particle rolling hypothesis is invalid in this case. In addition, the fact that the maximum variations of the remanent magnetic inclination do not exceed 10º indicates that not all the magnetic carriers are reoriented according to the calcite fabric and that the mechanisms responsible for the acquisition of the detrital remanent magnetisation are more complex than previously thought.      Acknowledgments: PTDC/CTA-GEO/0125/2021 Foundation of Sciences and Technology (Portugal) and BU037P23 Junta de Castilla y León (Spain). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101005611 for Transnational Access conducted at DMEX-UPPA-FRANCE.

: Data collected for calculating electron content of the ionosphere by the Faraday rotation technique can be used to calculate the magnetic dip angle at ionospheric height near the geomagnetic dip equator. In this report the magnetic dip angle at ionospheric height was determined at the position where the angle between the ray path from the satellite to the ground station and the geomagnetic field vector is 90 degrees (transverse position). The magnetic dip angle calculation was based on the assumption of a constant height of 350 km for the centroid of the ionospheric electron-density profile. The spherical harmonic analysis is used to verify the experimental results. The results compare well with the surface magnetic dip angle, measured in 1956-1960 by the Geodesy Department of the Ministry of Defense, Thailand, and indicate that the magnetic dip angle at ionospheric height is very close to the surface value. These data permit estimation of the position of the geomagnetic dip equator at the ionospheric height. The estimated position of this equator is directly above the geographic latitude of 9.30 degrees N. This latitude intersects the southern peninsula of Thailand about 480 km south of Bangkok (near Surat Thani). This estimated value compares well with the surface geomagnetic dip equator and indicates that the dipole field is a good model for Southeast Asia in the vicinity of longitude 100 degrees E.