Latitude Dependence of Interhemispheric Field‐Aligned Currents (IHFACs) as Observed by the Swarm Constellation

Park, Jaeheung; Yamazaki, Yosuke; Lühr, H.

doi:10.1029/2019ja027694

Cited by 27 publications

(114 citation statements)

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“…In December solstice the most notable features are strong NH-to-SH currents near dusk at |MLAT|> 35°. All these features conform to previous Swarm observations using science-grade magnetometers, which were reported by Lühr et al (2015Lühr et al ( , 2019 and Park et al (2020). Furthermore, the absolute levels of current density, which are several nA/m 2 , also agree well with earlier studies such as Lühr et al (2019).…”

Section: Ihfacssupporting

confidence: 91%

“…2a. This apparent equinox-June discrepancy was not seen in recent Swarm observations (e.g., Lühr et al 2019;Figure 5;Park et al 2020; Figure 3). We attribute the discrepancy to the uneven data coverage of CryoSat-2 in the MLT-season space (i.e., to the MLT-season aliasing).…”

Section: Ihfacsmentioning

confidence: 50%

“…A 3-by-3 two-dimensional median filter has been applied to the bin-averages for visual clarity. White squares represent six regimes defined by three MLT regions (dawn/noon/ dusk) and two MLAT ranges (low-/mid-latitudes) following Park et al (2020). The squares do not delineate strict geophysical borders, but are shown just to guide readers' eyes and to facilitate discussions.…”

Section: Satellites Instruments and Data Processing Methodsmentioning

confidence: 99%

“…2 corresponds to a season: (top) combined equinox, (middle) June solstice, and (bottom) December solstice. Following a convention in previous studies (e.g., Yamashita and Iyemori 2002;Park et al 2011Park et al , 2020, we decompose the bin-averaged vertical current density in the MLAT-MLT space into the following two categories. Hemispherically anti-symmetric components (e.g., upward in the northern hemisphere and downward in the south at the conjugate locations) represent IHFACs while symmetric parts (e.g., upward in both hemispheres at the conjugate locations; mirror images across the dip equator) correspond to F-region dynamo currents.…”

Section: Satellites Instruments and Data Processing Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers: CryoSat-2 and GRACE-FO

Park

Stolle

Yamazaki

et al. 2020

Earth Planets Space

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Electric currents flowing in the terrestrial ionosphere have conventionally been diagnosed by low-earth-orbit (LEO) satellites equipped with science-grade magnetometers and long booms on magnetically clean satellites. In recent years, there are a variety of endeavors to incorporate platform magnetometers, which are initially designed for navigation purposes, to study ionospheric currents. Because of the suboptimal resolution and significant noise of the platform magnetometers, however, most of the studies were confined to high-latitude auroral regions, where magnetic field deflections from ionospheric currents easily exceed 100 nT. This study aims to demonstrate the possibility of diagnosing weak low-/mid-latitude ionospheric currents based on platform magnetometers. We use navigation magnetometer data from two satellites, CryoSat-2 and the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), both of which have been intensively calibrated based on housekeeping data and a high-precision geomagnetic field model. Analyses based on 8 years of CryoSat-2 data as well as ~ 1.5 years of GRACE-FO data reproduce well-known climatology of inter-hemispheric field-aligned currents (IHFACs), as reported by previous satellite missions dedicated to precise magnetic observations. Also, our results show that C-shaped structures appearing in noontime IHFAC distributions conform to the shape of the South Atlantic Anomaly. The F-region dynamo currents are only partially identified in the platform magnetometer data, possibly because the currents are weaker than IHFACs in general and depend significantly on altitude and solar activity. Still, this study evidences noontime F-region dynamo currents at the highest altitude (717 km) ever reported. We expect that further data accumulation from continuously operating missions may reveal the dynamo currents more clearly during the next solar maximum.

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Section: Ihfacssupporting

confidence: 91%

Section: Ihfacsmentioning

confidence: 50%

Section: Satellites Instruments and Data Processing Methodsmentioning

confidence: 99%

Section: Satellites Instruments and Data Processing Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers: CryoSat-2 and GRACE-FO

Park

Stolle

Yamazaki

et al. 2020

Earth Planets Space

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“…Astrophysical dynamos (usually without a neutral gas) are typically rather described in terms of a mechanical magnetohydrodynamics (MHD) approach. Differences between the two approaches have been discussed by Parker (1996) for the high latitudes and by Vasyliūnas (2012) for specifically the Earth's neutral wind dynamo. Both authors acknowledged that for the steady state both approaches give equivalent results and that for highly symmetric cases, such as this one, the "traditional" ionospheric E and j paradigm is efficient and mathematically simpler.…”

Section: Preliminariesmentioning

confidence: 99%

Entangled dynamos and Joule heating in the Earth's ionosphere

Buchert

2020

Ann. Geophys.

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Abstract. The Earth's neutral atmosphere is the driver of the well-known solar quiet (Sq) and other magnetic variations observed for more than 100 years. Yet the understanding of how the neutral wind can accomplish a dynamo effect has been incomplete. A new viable model is presented where a dynamo effect is obtained only in the case of winds perpendicular to the magnetic field B that do not map along B. Winds where u×B is constant have no effect. We identify Sq as being driven by wind differences at magnetically conjugate points and not by a neutral wind per se. The view of two different but entangled dynamos is favoured, with some conceptual analogy to quantum mechanical states. Because of the large preponderance of the neutral gas mass over the ionized component in the Earth's ionosphere, the dominant effect of the plasma adjusting to the winds is Joule heating. The amount of global Joule heating power from Sq is estimated, with uncertainties, to be much lower than Joule heating from ionosphere–magnetosphere coupling at high latitudes in periods of strong geomagnetic activity. However, on average both contributions could be relatively comparable. The global contribution of heating by ionizing solar radiation in the same height range should be 2–3 orders of magnitude larger.

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Variability of Ionospheric Plasma: Results from the ESA Swarm Mission

et al. 2022

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Swarm is the first European Space Agency (ESA) constellation mission for Earth Observation. Three identical Swarm satellites were launched into near-polar orbits on 22 November 2013. Each satellite hosts a range of instruments, including a Langmuir probe, GPS receivers, and magnetometers, from which the ionospheric plasma can be sampled and current systems inferred. In March 2018, the CASSIOPE/e-POP mission was formally integrated into the Swarm mission through ESA’s Earthnet Third Party Mission Programme. Collectively the instruments on the Swarm satellites enable detailed studies of ionospheric plasma, together with the variability of this plasma in space and in time. This allows the driving processes to be determined and understood. The purpose of this paper is to review ionospheric results from the first seven years of the Swarm mission and to discuss scientific challenges for future work in this field.

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Latitude Dependence of Interhemispheric Field‐Aligned Currents (IHFACs) as Observed by the Swarm Constellation

Cited by 27 publications

References 50 publications

Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers: CryoSat-2 and GRACE-FO

Diagnosing low-/mid-latitude ionospheric currents using platform magnetometers: CryoSat-2 and GRACE-FO

Entangled dynamos and Joule heating in the Earth's ionosphere

Variability of Ionospheric Plasma: Results from the ESA Swarm Mission

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