Statistical Limitations on Detecting Diamagnetic Suppression of Reconnection at Earth's Magnetopause

The occurrence of magnetic reconnection is of pivotal importance regarding the evolution of many magnetized astrophysical systems. Among others, the mechanism known as "diamagnetic suppression" can prevent reconnection from developing. Over the last decade, many studies evidenced a statistical correlation of the magnetic shear and plasma beta for current sheets interpreted as reconnecting or not, consistent with predictions of the diamagnetic suppression theory. The strength of the observed correlations has suggested that diamagnetic suppression is the dominant mechanism controlling whether reconnection occurs or not, in many space plasma environments, from planetary magnetospheres to the solar wind and heliopause. Here, we show that there exists a possible observational bias, operating at least in the context of the Earth's magnetopause, that can lead to a similar statistical correlation because outflow speeds expected from magnetic reconnection strongly depend on both the magnetic shear and plasma β. Low velocity jets become increasingly difficult to observe when they become comparable to the surrounding flow fluctuation level. We conclude that the role of diamagnetic suppression at the Earth's magnetopause remains unclear.