Magnetosphere‐Ionosphere Convection Under the Due Northward IMF

Abstract

Convection under the due northward interplanetary magnetic field (IMF) is reproduced by the global simulation. The resulting magnetosphere is closed except in the XZ plane and separated from the solar wind by the separatrix generated from cusp nulls. Inside the separatrix, there exist three plasma regimes of the cusp high‐pressure region, the low‐latitude boundary layer (LLBL) and the plasma sheet. In the ionosphere, the northward Bz (NBZ) current and the reverse cell occur in higher latitudes than 80°, and the fun‐shaped arc‐like field‐aligned current and the main oval occur in lower latitudes than 80°. Magnetic field lines in the antisunward flow region of the reverse cell are connected to the LLBL that is accelerated to supersonic flow by the cusp pressure. Circulation on the reverse cell in the ionosphere is as a whole constructed to the interchange cycle in the magnetosphere. Convection is looked upon as the process to discharge stress generated by the dayside cusp reconnection. Magnetic stress generated by the reconnection is first converted to thermal energy in the cusp. This thermal energy is drained through three possible routes: release of plasma downtail through the LLBL, dissipation as electromagnetic energy through formation of the dynamo, and evacuation down to the ionosphere through the plasma sheet.

Reproduction of Ground Magnetic Variations During the SC and the Substorm From the Global Simulation and Biot‐Savart's Law

“…For such comparison in the ionosphere, validity of the global simulation has been confirmed also under the northward interplanetary magnetic field (IMF), in reproducing the Sun‐aligned arc (Tanaka, Obara, et al, ), the theta aurora (Tanaka et al, , ), and the fan‐shaped arc (Tanaka, Obara, et al, ). These phenomena have been known for a long time, but consideration for their causes have been staying at the level of estimation.…”

“…The fundamental role of convection is to form a pathway to transport, dissipate, and discharge stress caused by the solar wind‐magnetosphere interaction (Tanaka, Obara, et al, ). Stress is first converted to thermal energy through force balance.…”

Formation and Release of the Harang Reversal Relating With the Substorm Onset Process

“…The substorm is discussed in this paper as the convection transient which acts a core role in the M-I coupling by discharging stress generated through the solar wind-magnetosphere interaction (Tanaka et al, 2017a(Tanaka et al, , 2019a(Tanaka et al, , 2019b. Convection necessarily accompanies the dynamo that generate the FAC and Poynting flux (Ebihara & Tanaka, 2017;Tanaka et al, 2016).…”

Development of the Substorm as a Manifestation of Convection Transient

“…Principally, the origin of convection is the solar wind‐magnetosphere interaction, which causes a fraction of solar wind energy to penetrate into the magnetosphere. Overall, convection is the process to discharge this energy from the magnetosphere (Tanaka, Obara, et al., 2019).…”

“…The former produces the FAC by converting motional energy to electromagnetic energy and the latter produces the FAC by converting internal energy to electromagnetic energy. In the cusp‐mantle dynamo, the slow‐mode motion acts to convert internal energy to electromagnetic energy (Tanaka et al., 2016; Watanabe et al., 2019), and the main discharging route of penetrated energy is downstream emission of plasma via the mantle (Tanaka, Obara, et al., 2019). Energy conversion is built into this path, causing the FAC and ionospheric convection.…”