Kinetic and Shear Alfvén Waves in a Large Guide-field Reconnection at Earth's Magnetopause

A large guide-field (similar to 1.1B o) reconnection X-line, observed by the Magnetospheric Multiscale spacecraft during an outbound magnetopause crossing, is studied for Alfven waves. Here B o is the reconnecting field magnitude. The current sheet thickness of the magnetopause was similar to 2.6 ion inertial lengths (similar to 269 km), where field-aligned counter-streaming electrons were observed and Hall electromagnetic fields were identified. A remarkable finding was that a kinetic Alfven wave (KAW) was seen in the magnetopause upstream region after a shear Alfven wave (SAW) was encountered in the magnetopause layer. The presence of both the SAW and KAW near the reconnection X-line is for the first time reported. In the spacecraft frame of reference, the SAW has a dominant frequency at similar to 0.74 Hz, while the KAW has two dominant frequencies at similar to 0.38 and similar to 0.64 Hz. The wave energy for KAW and SAW was mostly carried away from the reconnection site by the Poynting flux parallel to the magnetic field. The parallel temperatures for ions and electrons were increased at KAW. The peaks of T parallel to/T perpendicular to for ions were located near the wave peaks, while the ratio peaks for electrons were near the wave troughs. Our findings suggest that KAWS and SAWs can be generated by asymmetric reconnection with a large guide field.