Local physics control of the x-line orientation in three-dimensional asymmetric magnetic reconnection

Yi-Hsin Liu, University of Maryland, College Park

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Magnetic reconnection is arguably one of the most important energy conversion and transport processes in space plasmas. This project aims to answer a fundamental question related to our understanding of magnetic reconnection: is there a simple principle that determines the orientation of the reconnection x-line in a asymmetric current sheet? The solution of this basic question remains unclear with our current understanding of magnetic reconnection, and the project aims to use Blue Waters to resolve this issue. Ultimately, the project's goal is to develop an understanding on the three-dimensional (3D) nature of asymmetric magnetic reconnection itself, which is an important step in the quest for predicting the location and orientation of magnetic reconnection at Earth's magnetopause. Moreover, increased understanding of x-line will enable space scientists to more accurately estimate the efficiency of flux transfer from solar wind to Earth's magnetosphere. In addition, the work proposed here is timely to the study of dayside reconnection during the 1st phase of NASA's Magnetospheric Multiscale Mission (MMS).

The goal of the project centers around the local physics control of 3D x-line in asymmetric reconnection, which has a direct application to terrestrial magnetopause. The project will address the following questions:

a) What is the underlying physics that control the 3D x-line orientation?

b) How does the 3D x-line spread? Does it have an intrinsic extent?

c) How does the diamagnetic drift affect the orientation and the motion of a 3D x-line?

d) What role do oblique tearing instabilities and the resulting flux ropes play?

The development of reconnection x-line requires a fully kinetic description, hence this project will employ the particle-in-cell (PIC) code, VPIC, which is optimized on the Blue Waters supercomputer. For 3D simulations, the project's innovative approach is to induce a single x-line using a localized perturbation, so that the x-line has sufficient freedom to choose its orientation.