A magnetohydrodynamic modeling of the interchange cycle for oblique northward interplanetary magnetic field

M Watanabe, S Fujita, T Tanaka… - Journal of …, 2018 - Wiley Online Library
M Watanabe, S Fujita, T Tanaka, Y Kubota, H Shinagawa, KT Murata
Journal of Geophysical Research: Space Physics, 2018Wiley Online Library
We perform numerical modeling of the interchange cycle in the magnetosphere‐ionosphere
convection system for oblique northward interplanetary magnetic field (IMF). The
interchange cycle results from the coupling of IMF‐to‐lobe reconnection and lobe‐to‐closed
reconnection. Using a global magnetohydrodynamic simulation code, for an IMF clock angle
of 20°(measured from due north), we successfully reproduced the following features of the
interchange cycle.(1) In the ionosphere, for each hemisphere, there appears a reverse cell …
Abstract
We perform numerical modeling of the interchange cycle in the magnetosphere‐ionosphere convection system for oblique northward interplanetary magnetic field (IMF). The interchange cycle results from the coupling of IMF‐to‐lobe reconnection and lobe‐to‐closed reconnection. Using a global magnetohydrodynamic simulation code, for an IMF clock angle of 20° (measured from due north), we successfully reproduced the following features of the interchange cycle. (1) In the ionosphere, for each hemisphere, there appears a reverse cell circulating exclusively in the closed field line region (the reciprocal cell). (2) The topology transition of the magnetic field along a streamline near the equatorial plane precisely represents the magnetic flux reciprocation during the interchange cycle. (3) Field‐aligned electric fields on the interplanetary‐open separatrix and on the open‐closed separatrix are those that are consistent with IMF‐to‐lobe reconnection and lobe‐to‐closed reconnection, respectively. These three features prove the existence of the interchange cycle in the simulated magnetosphere‐ionosphere system. We conclude that the interchange cycle does exist in the real solar wind‐magnetosphere‐ionosphere system. In addition, the simulation revealed that the reciprocal cell described above is not a direct projection of the diffusion region as predicted by the “vacuum” model in which diffusion is added a priori to the vacuum magnetic topology. Instead, the reciprocal cell is a consequence of the plasma convection system coupled to the so‐called NBZ (“northward Bz”) field‐aligned current system.
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