Over three decades of insitu observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solarwindmagnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kineticscale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ionacoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the crossscale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different testmore »
Transition from ioncoupled to electrononly reconnection: Basic physics and implications for plasma turbulence
Using 2.5 dimensional kinetic particleincell (PIC) simulations, we simulate reconnection conditions appropriate for the magnetosheath and solar wind, i.e., plasma beta (ratio of gas pressure to magnetic pressure) greater than 1 and low magnetic shear (strong guide field). Changing the simulation domain size, we find that the ion response varies greatly. For reconnecting regions with scales comparable to the ion inertial length, the ions do not respond to the reconnection dynamics leading to “electrononly” reconnection with very large quasisteady reconnection rates. Note that in these simulations the ion Larmor radius is comparable to the ion inertial length. The transition to more traditional “ioncoupled” reconnection is gradual as the reconnection domain size increases, with the ions becoming frozenin in the exhaust when the magnetic island width in the normal direction reaches many ion inertial lengths. During this transition, the quasisteady reconnection rate decreases until the ions are fully coupled, ultimately reaching an asymptotic value. The scaling of the ion outflow velocity with exhaust width during this electrononly to ioncoupled transition is found to be consistent with a theoretical model of a newly reconnected field line. In order to have a fully frozenin ion exhaust with ion flows comparable to the reconnection more »
 Award ID(s):
 1602769
 Publication Date:
 NSFPAR ID:
 10107471
 Journal Name:
 Physics of plasmas
 ISSN:
 1070664X
 Sponsoring Org:
 National Science Foundation
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