A new technique to derive the temperature of the cold ions in the magnetosphere

The polar wind, consisting of ions and electrons with low temperature and low energy, is known as a main contributor to the ionospheric outflow. These ions in the polar wind are so-called cold ions, which are notoriously difficult to measure with a spectrometer onboard the spacecraft because of the spacecraft charging problem. Recently, a technique measuring the electric field in the plasma wake has been used to derive the bulk velocity of the cold ion flow. However, this technique is not able to derive the cold ion temperature, which is thought to change as ions travel in the magnetotail. In this study, we use the electric field measurements from the Cluster spacecraft. We focus on the correlation between the ion temperature and the width of the plasma wake. Our results are used to derive the cold ion temperature, which helps us to understand more about the dynamics of cold ion outflow.