Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.

Global distribution of equatorial magnetosonic waves observed by THEMIS

Abstract: [1] We investigate the wave magnetic field data from three THEMIS spacecraft over the recent 31 months to perform a statistical study of equatorial magnetosonic (MS) wave properties and spatial distribution. The THEMIS spacecraft provide good data coverage in the dominant MS wave region near the equator and at 2≤L≤8. Our global survey shows that strong amplitudes and high occurrence of MS waves are generally observed near the equator, outside the plasmapause, on the dawnside during geomagnetically disturbed periods. In addition, increase of geomagnetic activity shifts the MS wave distribution toward earlier magnetic local time. Strong MS waves generally have RMS wave amplitudes ∼50 pT and an occurrence rate ∼20% on the dawnside outside the plasmapause and could therefore have an important influence on both ring current ion and energetic electron dynamics in the Earth's radiation belts.

Geomagnetic conjugate observations of equatorial airglow depletions

Abstract: [1] We report for the first time large-scale equatorial F-region airglow depletions extending to low-midlatitudes in both hemispheres. The observational sites were located at low-midlatitude geomagnetic conjugate points. Clear depletions of 630.0-nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all-sky imagers at Sata, Japan (magnetic latitude 24°N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22°S), on the night of November 12, 2001. Airglow depletion regions with east-west scale sizes of 40–100 km extend poleward. The maximum apex altitude of the plasma bubbles is about 1,700 km over the geomagnetic equator. The depletions move eastward at about 100 m/s, without changing their structures. The Darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the Sata images, even for the 40-km structure. These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.

Electron density in the plasmasphere: Whistler data on solar cycle, annual, and diurnal variations

Abstract: Whistler data are used to present a statistical view of equatorial plasmaspheric electron density n/sub eq/ and associated tube electron content N/sub T/ (defined as the number of electrons in a geomagnetic flux tube of 1cm/sup 2/ crosssectional area at 1000km altitude and extending to the magnetic equator). The data were acquired between 1959 and 1973 at Byrd (Lapprox. =7), Eights (Lapprox. =4), and Siple (Lapprox. =4), Antarctica, which are within 1 hour of the same geomagnetic meridian, and from Stanford, California (Lapprox. =2). The plasmaspheric n/sub wq/ profile beyond Lapprox. =3 is dominated by variations associated with magnetic disturbances and sunsequent recovery. In the aftermath of disturbances the plasmasphere tends to be divided into an inner 'saturated' region, which is in equilibrium with the underlying ionosphere in a diurnal average sense, and an outer 'unsaturated' region, which is still filling with plasma from below. In the outer plasmasphere bond approx.3.5 R/sub E/, diurnal variations appear as relatively small effects superimposed on larger storm-associated variations. Large numbers of whistler traces (as many as 3000 in some cases) were scaled for each of several months. These data sets form the basis for approximations to n/sub eq/ profiles to form log/sub 10/more » (n/sub eq/) =aL+b. These profiles are offered for reference use in estimating plasmasphere density levels. The previously reported annual and solar cycle variations are further documented by new evidence that these effects diminish with increasing L beyond Lapprox. =3.« less

The CHAOS-7 geomagnetic field model and observed changes in the South Atlantic Anomaly

Abstract: We present the CHAOS-7 model of the time-dependent near-Earth geomagnetic field between 1999 and 2020 based on magnetic field observations collected by the low-Earth orbit satellites Swarm, CryoSat-2, CHAMP, SAC-C and Orsted, and on annual differences of monthly means of ground observatory measurements. The CHAOS-7 model consists of a time-dependent internal field up to spherical harmonic degree 20, a static internal field which merges to the LCS-1 lithospheric field model above degree 25, a model of the magnetospheric field and its induced counterpart, estimates of Euler angles describing the alignment of satellite vector magnetometers, and magnetometer calibration parameters for CryoSat-2. Only data from dark regions satisfying strict geomagnetic quiet-time criteria (including conditions on IMF $$B_z$$ and $$B_y$$ at all latitudes) were used in the field estimation. Model parameters were estimated using an iteratively reweighted regularized least-squares procedure; regularization of the time-dependent internal field was relaxed at high spherical harmonic degree compared with previous versions of the CHAOS model. We use CHAOS-7 to investigate recent changes in the geomagnetic field, studying the evolution of the South Atlantic weak field anomaly and rapid field changes in the Pacific region since 2014. At Earth’s surface a secondary minimum of the South Atlantic Anomaly is now evident to the south west of Africa. Green’s functions relating the core–mantle boundary radial field to the surface intensity show this feature is connected with the movement and evolution of a reversed flux feature under South Africa. The continuing growth in size and weakening of the main anomaly is linked to the westward motion and gathering of reversed flux under South America. In the Pacific region at Earth’s surface between 2015 and 2018 a sign change has occurred in the second time derivative (acceleration) of the radial component of the field. This acceleration change took the form of a localized, east–west oriented, dipole. It was clearly recorded on ground, for example at the magnetic observatory at Honolulu, and was seen in Swarm observations over an extended region in the central and western Pacific. Downward continuing to the core–mantle boundary, we find this event originated in field acceleration changes at low latitudes beneath the central and western Pacific in 2017.

Velocity‐dispersed ion beams in the nightside auroral zone: AUREOL 3 observations

Abstract: Two years of data from the AUREOL 3 satellite have been used to study in detail the energetic ion beams which precipitate at low altitudes (400–2000 km) near the poleward boundary of the nighttime auroral zone. Eighty 2–20 keV events have been identified and examined; they typically display an energy-latitude dispersion in the auroral projection of the boundary plasma sheet, with the more energetic ions precipitating at less than 0.5° invariant latitude from the polar cap boundary. Their occurrence maximum is found in the 20–04 MLT sector and is independent of the magnetic activity measured by the AE index. In all the events studied, the ion fluxes are less than 107 ions cm−2 s−1 sr−1 keV−1, and mass analysis demonstrates that they are mainly composed of energetic H+ ions. All the experimental facts are consistent with an ion acceleration by the dawn-dusk electric field in the neutral sheet with a weak magnetic field normal component Bz in the distant magnetotail at an inferred distance of 50–100 RE. The observed velocity-latitude ion segregation is the result of the E×B drift of the ion beams up to the ionosphere (geomagnetic filter effect) superimposed upon the intrinsic dispersive effect of the nonadiabatic energization mechanism, when a realistic dependence of Bz on downtail distance is adopted. Finally, from the striking similarity of the experimental ion distributions we believe that the ion beams observed at low altitudes close to the polar cap boundary are the signature in the auroral ion precipitation of the earthward flowing ion beams often detected along the plasma sheet boundary layer.