Magnetosheath high speed jets and magnetopause observations by Cluster and MMS simultaneously

International audienceWhen the supersonic solar wind encounters the Earth's magnetosphere a shock is formed and the plasma is decelerated and thermalized in the magnetosheath downstream from the shock. Sometimes, however, due to discontinuities in the solar wind, surface waves on the bow shock or ionized dust clouds carried by the solar wind, high speed jets (HSJ) are observed in the magnetosheath. These jets have typically a large Vx component and their pressure can be a few times the solar wind dynamic pressure. They are typically observed downstream from the quasi-parallel bow shock. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these jets and their impact on the magnetopause. At the time of the magnetopause crossing, MMS was located below the magnetic equator at (X,Y,Z)GSM=(8.0,-7.5,-2.9)REwhile Cluster was above the equator at (X,Y,Z)GSM=(9.4,-3.2,6.6)RE. Over a one hour-long interval in the magnetosheath, Cluster observed 15 HSJs. During the same period, MMS observed 7 HSJs and entered the magnetosphere several times. A jet was observed simultaneously on both MMS and Cluster. Since the typical size of jets is around 1 RE, but Cluster and MMS were separated by 10 RE, this indicates that Cluster and MMS may have observed two independent jets. About 1h later, Cluster detected 165 km/s outward magnetopause motion and MMS detected 80 km/s inward motion, simultaneously. The magnetopause crossing was short, around 4s, on all four Cluster spacecraft. On the other hand, the MMS crossing was longer, around 1 min, with a magnetopause oscillating during the crossing. We will investigate the cause of such opposite magnetopause motion and if the HSJs play any role