Japan Geoscience Union Meeting 2015

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International Session (Oral)

Symbol P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM09] Dynamics in magnetosphere and ionosphere

Wed. May 27, 2015 2:15 PM - 4:00 PM 302 (3F)

Convener:*Shin'ya Nakano(The Institute of Statistical Mathematics), Yoshizumi Miyoshi(Solar-Terrestrial Environement Laboratory, Nagoya University), Hiroshi Hasegawa(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Yoshimasa Tanaka(National Institute of Polar Research), Tomoaki Hori(Nagoya University Solar Terrestrial Environment Laboratory Geospace Research Center), Chair:Shin'ya Nakano(The Institute of Statistical Mathematics)

3:40 PM - 3:55 PM

[PEM09-13] Dawn-dusk asymmetry of SI-induced transient ionospheric convection

*Tomoaki HORI1, Atsuki SHINBORI2, Shigeru FUJITA3, Nozomu NISHITANI1 (1.STE Lab., Nagoya Univ., 2.Research Institute of Sustainable Humanosphere, Kyoto Univ., 3.Meteorological College)

The statistics based on SuperDARN (SD) observations revealed that the transient oscillation of ionospheric convection associated with sudden impulses (SIs) showed some dawn-dusk asymmetric structures. The previous study showed that the higher latitude portion of the twin vortex-shaped convection perturbation has a dawn-dusk asymmetry depending on the combination of IMF-By polarity and SI polarity. In addition to the asymmetry depending on IMF-By polarity, the lower latitude portion of the induced twin vortices has a dawn-dusk asymmetry in such a way that the dawn side flow perturbation is always weaker than the dusk side one. Interestingly, our statistical study shows that this feature does not depend on either the IMF-By polarity or SI polarity, existing more or less for all conditions. This fact suggests that a different mechanism causes the difference in flow magnitude of lower latitude side of vortices between dawn and dusk. We perform a set of global MHD simulation runs to examine physical mechanisms causing the response of ionospheric convection associated with SIs. The simulations basically reproduce a weaker flow at the lower latitude portion of the dawn-side vortex, quite similar to those observed by SD. In addition to the realistic situations, a simulation run without the ionospheric Hall conductance (only with finite Pedersen conductance) shows a fairly dawn-dusk symmetric pair of flow vortices. This result strongly suggests that the Hall current closure in the ionosphere plays an important role in causing the dawn-dusk asymmetry of the vortex pair induced by SIs.