Linear response of field‐aligned currents to the interplanetary electric field

Weimer, D. R.; Edwards, Thom R.; Olsen, Nils

doi:10.1002/2017ja024372

Cited by 11 publications

(10 citation statements)

References 56 publications

(76 reference statements)

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“…Furthermore, our prediction filters show that the filter area decreases as we limit the filter derivation to progressively higher coupling strength indicating weaker coupling or saturation. We agree with Weimer et al () that if saturation occurs, it is at a much higher value than for the polar cap potential and that a definitive answer to the question of whether FAC saturates in response to the solar wind will require additional data at higher driver strengths.…”

Section: Discussionsupporting

confidence: 91%

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Relation of Field‐Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

McPherron

Anderson

Chu

2018

Geophysical Research Letters

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The strength of field‐aligned currents coupling the magnetosphere to the ionosphere was obtained by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) using the network of Iridium® spacecraft. The distribution of current was integrated giving total current in and out of the ionosphere on the dayside and nightside of the Earth in both hemispheres. The onset of auroral zone negative bays and midlatitude positive bays corresponds to an increase in nightside upward current. The total outward current tends toward saturation with increasing solar wind driver strength. The optimum solar wind coupling function for AL index predicts ~73% of the variance in nightside upward current. The dayside and nightside predictors of upward current rise to a peak at 30–45 min and decay slowly over 2.5 hr. Nightside response is delayed relative to dayside.

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Section: Discussionsupporting

confidence: 91%

“…In one respect our results differ from previous work. A recent study by Weimer et al (2017) concludes that there is no evidence that FACs saturate with increasing interplanetary electric field. We find otherwise, although, that our saturation values are higher (~6 mV/m) than those found for the polar cap potential (3-5 mV/m).…”

Section: Discussionmentioning

confidence: 99%

Relation of Field‐Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

McPherron

Anderson

Chu

2018

Geophysical Research Letters

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“…These data are all from 1-Hz data sets from their respective missions and have had the background magnetic field removed by subtracting off the predicted geomagnetic field provided by the twelfth generation of International Geomagnetic Reference Field (IGRF) model (Thébault et al, 2015). This choice of sunward-duskward vector decomposition, as opposed to a north-east decomposition, was chosen to reduce the low-latitude numerical noise from the spherical cap harmonic analysis (SCHA) following the same reasoning as Weimer et al (2017). This creates a database of ΔB values in the sunward and duskward directions in the plane perpendicular to the magnetic field predicted by the IGRF model at each point of measurement.…”

Section: Derivation Of Fac From Bmentioning

confidence: 99%

A Third Generation Field‐Aligned Current Model

et al. 2020

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A new empirical model of field-aligned currents in the Earth's ionosphere has been developed. This model is derived using magnetometer data from the CHAallenging Minisatellite Payload, Ø rsted, and Swarm satellite missions, which has created a database that spans more than 15 years. These data have been associated with solar wind conditions using the Advanced Composition Explorer satellite, as well as the F 10.7 , S 10.7 , M 10.7 , and Y 10.7 solar indices. With the wealth of data and associated driving conditions, this model has been developed to reproduce field-aligned current maps of the ionosphere based on solar wind electric field, interplanetary magnetic field clock angle, dipole tilt angle, solar index, and geographic hemisphere. This model was constructed using a series of spherical cap harmonic analysis fits based on small selections of the overall database. The coefficients of these fits were then used to develop a model that would reproduce these coefficients based on the previously described driving conditions. One of the most notable improvements demonstrated by this model is the ability to show distinct current regions in the ionosphere, particularly with respect to Region 0 currents during northward B z and highly positive or negative B . 10.1029/2019JA027249Key Points: • A new field-aligned current model based on satellite magnetometer data from the CHAMP, Ørsted, and Swarm missions has been developed • Driving response has been updated from previous models and reflects recent findings by Edwards et al. (2017) and Weimer et al. (2017) • Comparisons to AMPERE and AMPStotal current for a selection of events has been made, and this model has shown comparable results ). The average strength of these currents has been shown to be dependent on both IMF clock angle and magnitude (Anderson et al., 2008;Carter et al., 2016;Ganushkina et al., 2015;Weimer, 2001). It is not certain, however, how these currents scale with increasingly strong driving conditions. While it was thought that the FACs had a nonlinear response to increasing driving conditions, recent work by Weimer et al. (2017) using the same data set as this work has suggested that the response is much more linear than expected. The FAC response to solar indices, such as the F 10.7 solar index, has been shown to be nonlinear and levels off for high solar index conditions Ohtani et al., 2014). These recent publications have informed the construction of this model, including the selection of fitting functions.

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“…It has been known that the type of the magnetospheric generator depends on the solar wind conditions. Recently, Weimer et al () found that the magnetosphere probably acts as a current source on large scale when the interplanetary electric field is large. Since the interplanetary electric field intensity has not been taken into account in the binning process, it is likely that some observations were taken when the interplanetary electric field was fairly large.…”

Section: Resultsmentioning

confidence: 99%

Small‐Scale and Mesoscale Variabilities in the Electric Field and Particle Precipitation and Their Impacts on Joule Heating

et al. 2018

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In this study, the electric field and the particle precipitation at different spatial scale sizes have been investigated by utilizing the Dynamic Explorer 2 satellite data set, focusing on conditions of moderately strong southward interplanetary magnetic field. Dynamic Explorer 2 data from the period between 1981 and 1983, from all universal times, seasons, and both hemispheres, have been processed and binned over geomagnetic latitude and local time. It is found that, as compared with the large-scale (>500 km) average electric field and particle precipitation, the variabilities (i.e., departures from the large-scale average) of electric field and particle precipitation are not negligible. Moreover, the electric field variability tends to be anticorrelated with the particle precipitation variability in the auroral regions on small scale and mesoscale (<500 km). The impacts associated with the small-scale and mesoscale electric field and particle precipitation variabilities on Joule heating have also been addressed in this study by using the Global Ionosphere and Thermosphere Model. It is found that although Joule heating can be significantly enhanced by the small-scale and mesoscale electric field variabilities (~27% globally), the corresponding change in the particle precipitation tends to depress such enhancement (À5% globally), which is not negligible on the dusk side (up to À17.5% locally). It is the first time that the correlation between electric field and particle precipitation variabilities on small scale and mesoscale has been quantified. Furthermore, the impact on Joule heating associated with the correlation between the small-scale and mesoscale electric field and particle precipitation variabilities has been evaluated unprecedentedly in a general circulation model. Plain Language SummaryAt high latitudes, the electromagnetic energy from the magnetosphere dissipates into Earth's upper atmosphere, leading to both local and global changes. The accuracy of numerical simulation of Earth's upper atmosphere depends on the accuracy of the estimation of such energy input or heating, which is always challenging. The heating is closely related with the ionospheric electric field and precipitating particles from the magnetosphere. Part of the difficulty of determining the heating is that the knowledge about their structures below the model resolution (i.e., small-scale and mesoscale variabilities) is still limited, especially about their correlation. Therefore, it is still unclear to what extent such correlation can impact the heating estimation. In this study, the correlation between small-scale and mesoscale electric field and particle precipitation variabilities has been quantified for the first time by utilizing satellite observations. Furthermore, the impact of small-scale and mesoscale variabilities and their correlation on the heating estimation has been evaluated unprecedentedly using a general circulation model. It is found that there can be a large localized overestimation of heating if the correlation b...

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Linear response of field‐aligned currents to the interplanetary electric field

Cited by 11 publications

References 56 publications

Relation of Field‐Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

Relation of Field‐Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

A Third Generation Field‐Aligned Current Model

Small‐Scale and Mesoscale Variabilities in the Electric Field and Particle Precipitation and Their Impacts on Joule Heating

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