Magnetosheath Microstructure: Mirror Mode Waves and Jets during Southward IP Magnetic Field
Time: Thu 2021-03-04 15.15
Lecturer: Xóchitl Blanco-Cano, Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico City
The Earth’s magnetosheath is permeated with deccelerated and compressed solar wind, turbulence and a variety of nonlinear waves. In addition, transient dynamic pressure (Pdyn) enhancements called magnetosheath jets can exist. We study regions where the jets can co-exist with mirror mode waves. In particular we analized a 45 min interval when the MMS spacecraft observed a southward magnetic field (Bz < 0 nT) in the dayside magnetosheath. Using magnetic field and plasma data, we analyze three transient dynamic pressure enhancements identified as magnetosheath jets. The characteristics of these jets are different, suggesting different origins. While two of them, called J1 and J2, exhibit large increment in velocity and almost no density increment, the third jet (J3) shows large density enhancements with almost no velocity increment. The duration of J3 is ∼7 times longer than those of J1 and J2. J3 occurs at the region where the negative Bz becomes positive. Ion distributions inside the jets are different. J1 and J2 show a secondary field-aligned beam, which is not present in J3, suggesting that magnetic reconnection at the magnetopause is responsible for their formation. Distributions inside J3 are more isotropic. B field and plasma signatures inside J3 correspond to the crossing of a sector boundary, similar to the heliospheric plasma sheet, suggesting that J3 forms by the evolution and interaction of a solar wind structure with the bow shock and magnetosheath. Fluctuations inside J3 have larger transverse components. In contrast, waves in regions between the jets are compressive and are identified as mirror mode waves. Using THEMIS data we investígate how often can jets and mirror mode waves co-exist, and how jets, waves and ion distributions change within the magnetosheath. We find that is common that jets and mirror mode waves co-exist. However, the ocurrence of two ion distributions inside jets is rare.