North–South Asymmetries in Earth’s Magnetic Field

Laundal, K. M.; Cnossen, Ingrid; Milan, S. E.; Haaland, Stein; Coxon, J. C.; Pedatella, N. M.; Förster, M.; Reistad, Jone Peter

doi:10.1007/s11214-016-0273-0

Cited by 97 publications

(116 citation statements)

References 116 publications

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“…The SH polar cap shows higher densities which extend to the nightside auroral oval. These differences could be related to the different offsets between the geographic and geomagnetic poles in the NH and the SH (e.g., Coley & Heelis, ; Laundal et al, ; Noja et al, ; Rodger & Graham, ). We note that the altitude of Swarm A in the SH is higher by ~15 km than that in the NH.…”

Section: Discussionmentioning

confidence: 99%

Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

et al. 2019

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The polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarm mission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities. We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

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Section: Discussionmentioning

confidence: 99%

Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

et al. 2019

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“…Various possible causes for interhemispheric asymmetry in FACs have been discussed in earlier research, such as the difference in the strength and structure of magnetic field in the two hemispheres (Laundal et al, ); the ionospheric conductivity differences caused by season and dipole tilt (Benkevich et al, ; Ohtani et al, ; Ridley, ; Green et al, ; Coxon et al, ) and IMF

B_{y}

effect (Green et al, ; Tenfjord et al, ; Østgaard et al, ). We provide a view of interhemispheric asymmetries in the FACs response to different solar wind drivers, revealing both previously reported phenomena and new insights.…”

Section: Introductionmentioning

confidence: 99%

Modes of (FACs) Variability and Their Hemispheric Asymmetry Revealed by Inverse and Assimilative Analysis of Iridium Magnetometer Data

et al. 2020

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We determine the primary modes of field‐aligned current (FAC) variability and their hemispheric asymmetry by nonlinear regression analysis of a multiyear global data set of Iridium constellation engineering‐grade magnetometer data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment program. The spatial and temporal FAC variability associated with three major categories of solar wind drivers, (1) slow flow, (2) high‐speed streams (HSS), (3) transient flow related to coronal mass ejections (CMEs), and (4) a combination of these, is characterized as empirical orthogonal functions (EOFs) and their time‐varying amplitude. For the combined solar wind category, the order of the modes of variability are strengthening/weakening of (1) EOF1—all FACs; (2) EOF2—Region 2 (R2) FACs; and (3) EOF3—dayside/nightside FACs. The first two EOFs are associated with solar wind coupling; EOF3 is associated with the ecliptic components of the interplanetary magnetic field (IMF). We also find hemispheric asymmetry in FACs. Northern Hemisphere EOFs show clearer spatial features and higher correlation coefficients with solar wind drivers. The Northern Hemisphere also shows higher correlation coefficients in all seasons except winter. We find transient flow EOFs to be better correlated with solar wind drivers such as IMF Bz and coupling functions, while HSS EOFs are better correlated with solar wind plasma parameters. CME‐related transient flow EOFs also show R2 FAC variabilities that are not found in other separate wind drivers. Application of the EOF analysis to the Iridium magnetometer data shows significant promise for greater understanding of geoeffectiveness of solar wind interactions with geospace.

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“…A comprehensive analysis of the north-south asymmetries of the high-latitude geomagnetic field can be found in a recent review by Laundal et al (2017), focused on the pole locations and magnetic conjugacy aspects. The problem of the north-south interhemispheric asymmetry of high-latitude/low-altitude magnetic fields has many interesting implications, in particular, with respect to the ionospheric response to the solar wind driving.…”

Section: Introductionmentioning

confidence: 99%

Secular Drift of the Auroral Ovals: How Fast Do They Actually Move?

Tsyganenko

2019

Geophysical Research Letters

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A surprisingly fast secular drift of the Northern geomagnetic dip pole during the last two decades has attracted much interest lately, in particular, evoking speculations about a possibility of a sweeping relocation of the auroral oval. This letter presents first results of a model investigation of this issue, based on an empirical representation of the distant magnetosphere combined with a series of internal geomagnetic field models for 12 epochs, covering the interval from 1965 to 2020. The secular drift of the northern auroral oval was found to result in its net displacement over the 55‐year period, commensurate with the concurrent shifts of the centered, eccentric, and corrected geomagnetic poles, all of them much smaller than the enormous spurt of the northern dip pole. In the Southern Hemisphere, the shift of the auroral oval and of the poles over the same period is much weaker, revealing a remarkable interhemispheric asymmetry.

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North–South Asymmetries in Earth’s Magnetic Field

Cited by 97 publications

References 116 publications

Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

Modes of (FACs) Variability and Their Hemispheric Asymmetry Revealed by Inverse and Assimilative Analysis of Iridium Magnetometer Data

Secular Drift of the Auroral Ovals: How Fast Do They Actually Move?

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