Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

Friis‐Christensen, E.; Finlay, Christopher C.; Hesse, M.; Laundal, K. M.

doi:10.1007/978-94-024-1225-3_11

Cited by 15 publications

(29 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While there is a question about their methodology (e.g., IMF propagation and determination of substorm onset), it suggests that the y component of IMF may affect the development of westward AEJ. This study is also motivated by the finding that in the northern hemisphere high‐latitude geomagnetic activity is higher for positive than for negative IMF B y component (Friis‐Christensen et al, ; Holappa & Mursula, ; Murayama & Hakamada, ; Smith et al, ; Velichko et al, ). Some of the workers attributed their finding to substorms but provided no evidence.…”

Section: Introductionmentioning

confidence: 96%

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Liou

Sotirelis

Mitchell

2020

Geophysical Research Letters

View full text Add to dashboard Cite

We study the effects of the east‐west (y) component of the interplanetary magnetic field (IMF) on the occurrence of substorms by analyzing 16,743 magnetic substorm events identified with the SuperMAG SML index from 1995 to 2016. It is found, surprisingly, that substorm occurrence rates depend highly on the sign of IMF By, with, on average, ~1/3 more substorms for IMF By > 0 than for IMF By < 0. We attribute this asymmetry to the enhanced convection (e.g., more energy in the tail) under IMF By > 0 conditions. A superposed epoch analysis of the IMF indicates that the average IMF By prior to onset is positive but becomes less positive ~15 min prior to the onset, indicating that the release of the stress associated with a clockwise twisted magnetotail may be an important onset trigger. We conjecture that an asymmetry in the dayside merging efficiency may be the cause.

show abstract

Section: Introductionmentioning

confidence: 96%

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Liou

Sotirelis

Mitchell

2020

Geophysical Research Letters

View full text Add to dashboard Cite

show abstract

“…Recent observations of the geomagnetic field by polar‐orbiting satellites (Friis‐Christensen et al, ; Smith et al, ) found that the westward auroral electrojet in both hemispheres is more intense in Northern Hemisphere (NH) winter for

B_{y} > 0

than for

B_{y} < 0

. For Southern Hemisphere (SH) winter, the effect of

B_{y}

is opposite: the westward electrojet is more intense for

B_{y} < 0

than for

B_{y} > 0

.…”

Section: Introductionmentioning

confidence: 99%

“…The physical mechanism of the

B_{y}

effect in geomagnetic activity is not yet known. Friis‐Christensen et al () suggested that IMF

B_{y}

modulates the strength of the substorm current wedge, which probably makes the largest contribution to the

A L

index. While this mechanism is consistent with observations (Friis‐Christensen et al, ; Holappa & Mursula, ; Holappa et al, ), it is still unclear how IMF

B_{y}

is connected to the substorm current wedge.…”

Section: Introductionmentioning

confidence: 99%

“…Friis‐Christensen et al () suggested that IMF

B_{y}

modulates the strength of the substorm current wedge, which probably makes the largest contribution to the

A L

index. While this mechanism is consistent with observations (Friis‐Christensen et al, ; Holappa & Mursula, ; Holappa et al, ), it is still unclear how IMF

B_{y}

is connected to the substorm current wedge. In principle, in order to be able to modulate ionospheric currents, IMF

B_{y}

must modulate either the ionospheric electric fields or ionospheric conductivity or both.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Explicit IMF By Dependence in Geomagnetic Activity: Modulation of Precipitating Electrons

Holappa

Asikainen

Мурсула

2020

Geophysical Research Letters

View full text Add to dashboard Cite

The most important driver of geomagnetic activity is the north–south ( Bz) component of the interplanetary magnetic field (IMF), which dominates the solar wind‐magnetosphere coupling and all solar wind coupling functions. While the east–west ( By) IMF component is also included in most coupling functions, its effect is always assumed to be symmetric with respect of its sign. However, recent studies have shown that, for a fixed value of any coupling function, geomagnetic activity is stronger for By>0 than for By<0 in Northern Hemisphere winter. In Southern Hemisphere winter, the dependence on the By sign is reversed. In this paper, we use measurements of National Oceanic and Atmospheric Administration Polar‐Orbiting Operational Environmental Satellites to show that the flux of magnetospheric electrons precipitating into the atmosphere also exhibits an explicit By dependence. This By dependence is strong in the midnight and dawn sectors where it causes a related By effect in the westward electrojet and geomagnetic activity by modulating ionospheric conductivity.

show abstract

“…Derived GRACE differential mode (GRACE DM) maps along the x axis of the SRF (Figure ) show the strong presence of the magnetic inclination signal over the equatorial region. Additionally, Figure b shows negative to positive trend near ϕ = 60 o N and ϕ = 75 o S. This anomaly is present only in the ascending nighttime DM accelerations and appears to be highly correlated with the Birkeland currents, which are induced by the interaction of the Earth's magnetic field with solar winds (Friis‐Christensen et al, ). The Birkeland currents become more intense when the radial component B z of the interplanetary magnetic field becomes strongly negative (ibid, 2017; Figure b), demonstrating high seasonal dependence (Anderson et al, ).…”

Section: Grace and Goce Dm Accelerationsmentioning

confidence: 94%

Gravity Gradiometry With GRACE Space Missions: New Opportunities for the Geosciences

Peidou

Pagiatakis

2019

JGR Solid Earth

View full text Add to dashboard Cite

A new paradigm views the recently launched Gravity Recovery and Climate Experiment (GRACE) follow‐on mission as a gradiometer system, outside the mission's design concept, promising potentially major implications in geosciences. We develop an innovative and straightforward concept, the “GRACE gradiometer mode,” to process future GRACE follow‐on measurements to derive three‐dimensional gravitational gradients. Using positions, accelerations, and attitude measurements from the identical predecessor mission GRACE, we generate common and differential accelerations. We validate GRACE differential accelerations using Gravity field and steady‐state Ocean Circulation Explorer (GOCE) mission gradiometer measurements and we demonstrate an important and promising agreement between GRACE and GOCE. Consequently, we estimate gravitational gradients in full and we confirm their ability to detect geophysical signals over three example regions, namely, the Himalayas, Indonesia, and Canada. Coherence analysis between GOCE and GRACE gradients reveals a strong match that reaches up to 80%. GRACE gradiometer mode gradients are also compared with GRACE level 2‐ derived gradients, and results show that the new method captures smaller spatial‐scale signals than GOCE with the trade‐off being at higher noise level. We argue that future enhancements of the proposed proof‐of‐concept method will expand and enhance the GRACE follow‐on objectives that will lead to new insights, discoveries, and applications in the Earth system and the geosciences.

show abstract

Magnetic Field Perturbations from Currents in the Dark Polar Regions During Quiet Geomagnetic Conditions

Cited by 15 publications

References 30 publications

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Control of the East‐West Component of the Interplanetary Magnetic Field on the Occurrence of Magnetic Substorms

Explicit IMF By Dependence in Geomagnetic Activity: Modulation of Precipitating Electrons

Gravity Gradiometry With GRACE Space Missions: New Opportunities for the Geosciences

Contact Info

Product

Resources

About