12:15 PM - 12:18 PM
[PEM07-P03] Ionospheric convection enhancement for extremely weak (< 1 nT) interplanetary magnetic field
3-min talk in an oral session
Keywords:MHD simulation, severe space weather, M-I convection
In order to elucidate the physical mechanism of the peculiar convection system for weak (< 1 nT) IMF, we performed global MHD simulation using the REPPU code developed by T. Tanaka. The simulation reproduced the observed ionospheric convection enhancement for such conditions. The cause of the convection enhancement is explained as follows in terms of the magnetospheric dynamo. At the upper part of the cusp adjacent to the magnetosheath, for strong IMF, there is a strong magnetic pressure region that prevents magnetosheath plasmas from intruding into the cusp. On the other hand, for weak IMF, that high magnetic pressure region disappears, resulting in an increase of the cusp thermal pressure. In consequence, the dynamo region where J•E is negative is formed at the high latitude boundary region with enhanced intensity. The enhanced dynamo makes field-aligned currents and ionospheric convection strong. This mechanism for driving the convection is therefore distinct from the conventional Dungey cycle and viscous interaction.
When the solar activity is extremely weak like the Maunder minimum, it is expected that the IMF also becomes extremely weak. This study therefore contributes to the prediction of magnetospheric phenomena in a grand solar minimum in the future.