Date of Graduation

2015

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Paul A Cassak

Committee Co-Chair

Daniel Pisano

Committee Member

Earl E Scime

Committee Member

Stephen Valentine

Committee Member

Dimitris Vassiliadis

Abstract

Magnetic reconnection is a phenomenon that occurs in hot ionized gases, or plasmas, whereby oppositely directed magnetic field components break and cross-connect, converting energy stored in the magnetic fields to plasma motion and heat. Reconnection occurs between Earth's magnetic field and interplanetary magnetic fields (IMF) carried by the solar wind, plasma emanating from the sun. Reconnection occurs at the sunward boundary of Earth's magnetosphere, the region of space that is dominated by Earth's magnetic field. However, predicting the properties of reconnection at this boundary, including basic considerations such as where reconnection occurs and how efficiently, remain an unsolved problem.;In this dissertation, we present an efficient and highly accurate method for identifying possible sites of reconnection by locating magnetic separators, magnetic field lines that separate regions of different magnetic topologies at the dayside magnetopause. The technique is verified using exact solutions for separators in an analytic magnetic field of a superposed dipolar and uniform magnetic field. Magnetic separators are found in distinct global resistive magnetohydrodynamic (MHD) simulations performed using the three-dimensional Block Adaptive Tree Solar wind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity with IMF orientations ranging from parallel to anti-parallel to Earth's magnetic field.;With the magnetic separators, we can make careful tests of recent models of the location of reconnection at the dayside magnetopause for arbitrary solar wind conditions. As many of these models are independent of the reconnection dissipation mechanism, each can be tested in our resistive MHD simulations. We employ image processing techniques to unambiguously determine each model's prediction in order to compare the determined separators with the models. We find that none of the models are perfect, but the maximum magnetic shear model does the best at finding the polar cusp reconnection sites for northward IMF.;We also present an initial analysis of reconnection local to the magnetic separator. This is achieved by measuring reconnection parameters in planes perpendicular to the magnetic separator and comparing the results to local models of reconnection. The development of this capability has profound implications in understanding how the reconnection physics local to the magnetic separator can lead to global magnetospheric dynamics at Earth, a longstanding problem in understanding solar wind-magnetospheric coupling.

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