A Statistical Study of Slow‐Mode Shocks Observed by MMS in the Dayside Magnetopause

We investigated characteristics of slow‐mode shocks in the dayside magnetopause based on Magnetospheric Multiscale observations from September 2015 to February 2017. We analyzed 99 magnetopause crossings with reconnection jets and high time resolution data, out of which 20 crossings showed slow‐mode shock signatures. Out of these crossings, one crossing showed slow‐mode shock signature on both sides, and the rest had slow‐mode shock signatures on one side, six (13) on magnetosphere (magnetosheath). The detection probability of slow‐mode shocks in the magnetopause is ~20%, which is greater than that reported in the magnetotail. We also found 12 rotational discontinuities in these slow‐mode shock events. The results also show that the observation of magnetosphere side slow‐mode shock is favored when the number density ratio of magnetosheath to magnetosphere is small. No clear dependence of the existence of slow‐mode shocks on other parameters such as, plasma beta, temperature anisotropy, and jet velocity, was found. Plain Language Summary When two oppositely directed magnetic field lines come in contact, they break and reconnect releasing large amounts of energy and accelerating particles. This process is called magnetic reconnection. At the dayside interface of the magnetic barrier formed by Earth's intrinsic magnetic field against the plasma flow from the Sun (magnetopause), terrestrial magnetic fields interact with solar magnetic fields through this process. One theory of magnetic reconnection proposes the presence of a structure, called the slow‐mode shock, which helps in fast release of energy and acceleration of particles. However, the magnetopause is known to have asymmetric magnetic configuration and only a few observational studies have reported the presence of the slow‐mode shock in the magnetopause. Based on observations by the Magnetospheric Multiscale spacecraft in the magnetopause, we found that 20% of the magnetopause crossings with reconnection jets had the slow‐mode shock structure. The occurrence frequency is comparable to or a little higher than the symmetric reconnection cases. Their dependence on the number of particles is consistent with previous simulation studies. This study provides substantial evidence that the slow‐mode shocks are as common in the asymmetric magnetic reconnection as in the symmetric cases. Key Points Seven (14) slow shocks were found on the magnetosphere (magnetosheath) side out of 99 magnetopause crossings with re