Weak Magnetic Storms Can Modulate Ionosphere‐Plasmasphere Interaction Significantly: Mechanisms and Manifestations at Mid‐Latitudes

A comprehensive study of the response of the ionosphere-plasmasphere system at mid-latitudes to weak (Dstmin > -50 nT) magnetic storms is presented. For the first time, it is shown that weak magnetic disturbances can lead to significant modulation of ionosphere-plasmasphere H+ ion fluxes. It is found that this modulation is caused by the enhancements/reductions of the topside O+ ion density, which is induced by F2-layer peak height rise and fall during the storms. The F2-layer motion is caused by thermospheric wind changes and by a penetration electric field. Both drivers are closely related to the changes in the Bz component of interplanetary magnetic field. The most prominent manifestation of the H+ ion flux modulation is strong changes in H+ ion fraction in the topside ionosphere. This study also indicates that the NRLMSISE-00 model provides the correct relative changes of neutral H density during weak magnetic storms and also that there is a compelling need to include geomagnetic activity indices, in addition to solar activity (F10.7), as input parameters to empirical topside ionosphere models.