Interplanetary magnetic field control of dayside ion conics

Abstract

Ion conics are frequently observed around the dayside cusp/cleft region and are supposed to be energized by an input of energy from the dayside magnetospheric boundary region. We examined possible influence of the interplanetary magnetic field (IMF) on dayside ion conics observed by the polar‐orbiting Exos D (Akebono) satellite. We found the effect of By and Bz components on the energy flux and occurrence frequency of ion conics. Ion conics are more energetic and more frequently observed when Bz is negative and the magnitude of By is large. The Bz effect is likely to be attributed to the change in energy input to the ion energization region. The By effect may be also due to the increased energy input to the cusp/cleft region during large By period, suggesting that a reconnection‐related energy input is responsible for dayside ion energization. An alternative interpretation of the By effect is that the convection pattern may affect the residence time in the ion energization region and therefore the efficiency of ion energization. We found that the polarity of By controls asymmetrical magnetic local time distribution of ion conics around the local noon, which is attributed to a possible effect of convection pattern on dayside ion energization.