Cold ions of ionospheric origin observed at the magnetopause and their effects on reconnection

Abstract:

Magnetic reconnection at the dayside magnetopause is one of the most important mechanisms to transfer solar wind particles, momentum, energy, and magnetic flux into the magnetosphere. This study investigates behaviors of the cold dense plasma of ionospheric origin during the magnetic reconnection at the dayside magnetopause. The cold dense plasma at the adjacent magnetopause, originated either directly from the ionosphere or from the plasmasphere, has often been observed in the dayside magnetosphere. The cold dense ionospheric outflows are featured by unidirectional or bidirectional field-aligned pitch angle distributions, whereas the plasmaspheric plumes original plasma are found with 90 degree pitch angle distributions. We present cases and statistical studies on the behavior of both plasmaspheric plume and the ionospheric cold dense plasma ions near the dayside magnetopause by using the Cluster spacecraft data sets from 2007 to 2009. It is found that the occurrence of plasmaspheric plume or ionospheric plasma strongly depends on the solar wind/IMF conditions. It is found that the occurrence rate of the plasmaspheric plumes is significantly higher on the duskside than that at the dawnside, indicating that plasmaspheric plumes may lead to a dawn-dusk asymmetry of the dayside reconnection. The role played by cold ions in the magnetic reconnection process will be discussed.