Dependence of Penetration Electric Field Efficiency on the Interplanetary Electric Field

摘要

Southward interplanetary magnetic field (IMF) causes the generation of penetration electric fields in the ionosphere at middle and low latitudes. Penetration efficiency, which is defined to be the ratio of the change of the equatorial ionospheric zonal electric field to the change of the dawn-dusk (E-y) component of the interplanetary electric field, is used to represent the quantitative relationship between interplanetary and ionospheric electric fields. We have searched equatorial vertical ion drift data measured by the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) radar over 19 years (2001-2019) for penetration electric fields when the correlation between interplanetary and ionospheric electric fields is greater than 0.8. In total, 450 penetration electric field events are identified. It is found that the penetration efficiency peaks near noon and decreases afterward. The penetration efficiency depends on the rate of change of E-y with time, the initial E-y when the IMF starts to turn southward, and the change in E-y between the beginning of the IMF southward turning and the subsequent northward turning. The initial E-y is well-correlated with the change in E-y. A positive initial E-y or a smaller change in E-y results in a higher penetration efficiency. The quantitative dependence of penetration efficiency on the structures of E-y is derived for the first time. The results of this study are expected to improve the accuracy of prediction of penetration electric fields.