Unified Theory of the Arc Auroras: Formation Mechanism of the Arc Auroras Conforming General Principles of Convection and FAC Generation

Tanaka, Takashi; Watanabe, Masakazu; Ebihara, Yusuke; Fujita, Shigeru; Watanabe, Midori; Kataoka, Ryuho

doi:10.1029/2022ja030403

Cited by 4 publications

(4 citation statements)

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“…Thus, along with the ionospheric convection in Figure 10, shears occur at the both edges of the void (no aurora region in the central polar cap defined by Hones et al. (1989)) in the evening and in the morning, and these shears generate upward FACs (Tanaka, Watanabe, et al., 2022). These FACs primarily appear as large‐scale sun‐aligned arcs (Lassen & Danielsen, 1978).…”

Section: Resultsmentioning

confidence: 96%

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Multiple Convection Cells Induced by In‐Front and Off‐Front Interactions Between the Obliquely Northward IMF and the Geomagnetic Field

Tanaka,

Ebihara,

Watanabe

et al. 2024

JGR Space Physics

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From the global simulation, we reproduce the solar wind‐magnetosphere‐ionosphere (S‐M‐I) interaction under the northward interplanetary magnetic field (IMF) with negative By. Reconnection structures, the plasma sheet, and lobes are formed in magnetospheric convection, while lobe/round‐merging/reciprocal/nightside cells appear in the ionosphere. Associated with the S‐M interaction, northern open field is generated at the evening open‐closed (O/C) boundary, due to successive cusp and interchange reconnections (in round‐merging cell) or by Dungey‐type reconnection (in nightside cell). Corresponding interchange and Dungey‐type reconnections occur at the southern null. Dungey‐type reconnection at the same time generates southern open field on the outer‐most magnetopause. Open field injected into the northern polar cap/void/lobe constructs the open field part of the round‐merging and nightside cells. After open‐field convection in the lobe, reclosures occur by again successive cusp and interchange reconnections on the dayside separator, or separator reconnection on the nightside separator. Former closed field line proceeds toward the evening O/C boundary through the dayside closed‐field convection in the round‐merging cell, while latter closed field line through the nightside closed‐field convection in the nightside cell. Shear that causes the large‐scale sun‐aligned arc is generated by the process of injecting open magnetic field into the void and the conjugate of process of connecting return flux from the plasma sheet to the nightside cell in counter hemisphere.

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Section: Resultsmentioning

confidence: 96%

“…Shear of convection flow couples with the distribution of the FAC (Tanaka et al., 2021b). The upward FACs are observed as auroral arc (Tanaka, Watanabe, et al., 2022). Therefore, convection structure must be verified from auroral observations as well as from geometry of ionospheric convection cells.…”

Section: Introductionmentioning

confidence: 99%

Multiple Convection Cells Induced by In‐Front and Off‐Front Interactions Between the Obliquely Northward IMF and the Geomagnetic Field

Tanaka,

Ebihara,

Watanabe

et al. 2024

JGR Space Physics

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“…The code also computes the pressure‐related (Vasyliunas, 1970) and inertial‐related FACs (Yang et al., 2019). The latter is derived from the MHD momentum equation, which is also used in other models (e.g., Sato & Iijima, 1979; Tanaka et al., 2022). The current conservation equations is solved in the ionosphere with a high resolution of 0.12° in latitude and 1.3° in longitude.…”

Section: Simulationmentioning

confidence: 99%

Successive Westward Traveling Surges Driven by Sequential Plasma‐Sheet Bubble Injections

Wei

Yang

Wang

et al. 2022

Geophysical Research Letters

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The westward traveling surge (WTS) is one of the most prominent phenomena of auroral substorms (Akasofu, 1964). Following substorm onset, a WTS forms rapidly as an expanding bulge structure propagating westward (Akasofu et al., 1965). The generation mechanism and mapping of WTS are complicated and still not fully understood. The WTS is generally accompanied by intense localized upward field-aligned currents (FACs) (Marklund et al., 1998;Opgenoorth et al., 1983;Tighe & Rostoker, 1981) marking the western edge of the substorm current wedge (SCW) (McPherron et al., 1973). The SCW consists of Region-1 (R1) sense flowing downward into the ionosphere at the eastern side of the wedge and upward at the western side of the wedge, connected by a westward electrojet in the ionosphere. In the Cowling channel model (Boström, 1975), enhanced conductivity gradients lead to the strong westward current and polarization electric field, which is connected at its western edge via very localized intense upward FACs (where the WTS is observed) (

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“…Because of the nonlinear nature of the spatially complex evolution of auroral ovals and the magnetospheric plasma flows as driven by the time‐varying solar wind conditions, a global magnetohydrodynamic (MHD) simulation with the input of the solar wind parameters is necessary to reproduce the resultant auroral current system, as depicted by the ionospheric conductivities, potential, and field‐aligned currents. Among many sophisticated MHD simulations, REPPU (REProduce Plasma Universe) performs as one of the best models for resolving various space weather phenomena including auroral substorms (Ebihara & Tanaka, 2015a, 2015b; Tanaka, Watanabe, et al., 2022; Tanaka et al., 2017, 2018). However, the major difficulty of REPPU and other simulation codes for the operational space weather forecast is that it is computationally expensive to solve the MHD equations, even using the designated cluster computers.…”

Section: Introductionmentioning

confidence: 99%

Machine Learning‐Based Emulator for the Physics‐Based Simulation of Auroral Current System

Kataoka,

Nakamizo,

Nakano

et al. 2024

Space Weather

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Using a machine learning technique called echo state network (ESN), we have developed an emulator to model the physics‐based global magnetohydrodynamic simulation results of REPPU (REProduce Plasma Universe) code. The inputs are the solar wind time series with date and time, and the outputs are the time series of the ionospheric auroral current system in the form of two‐dimensional (2D) patterns of field‐aligned current, potential, and conductivity. We mediated a principal component analysis for a dimensionality reduction of the 2D map time series. In this study, we report the latest upgraded Surrogate Model for REPPU Auroral Ionosphere version 2 (SMRAI2) with significantly improved resolutions in time and space (5 min in time, ∼1° in latitude, and 4.5° in longitude), where the dipole tilt angle is also newly added as one of the input parameters to reproduce the seasonal dependence. The fundamental dependencies of the steady‐state potential and field‐aligned current patterns on the interplanetary magnetic field directions are consistent with those obtained from empirical models. Further, we show that the ESN‐based emulator can output the AE index so that we can evaluate the performance of the dynamically changing results, comparing with the observed AE index. Since the ESN‐based emulator runs a million times faster than the REPPU simulation, it is promising that we can utilize the emulator for the real‐time space weather forecast of the auroral current system as well as to obtain large‐number ensembles to achieve future data assimilation‐based forecast.

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Unified Theory of the Arc Auroras: Formation Mechanism of the Arc Auroras Conforming General Principles of Convection and FAC Generation

Cited by 4 publications

References 98 publications

Multiple Convection Cells Induced by In‐Front and Off‐Front Interactions Between the Obliquely Northward IMF and the Geomagnetic Field

Multiple Convection Cells Induced by In‐Front and Off‐Front Interactions Between the Obliquely Northward IMF and the Geomagnetic Field

Successive Westward Traveling Surges Driven by Sequential Plasma‐Sheet Bubble Injections

Machine Learning‐Based Emulator for the Physics‐Based Simulation of Auroral Current System

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