Magnetic reconnection in the presence of sheared plasma flow. Ph.D. Thesis

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1994

OSTI ID:218164

La Belle-Hamer, A L

Classical models of magnetic reconnection consist of a small diffusion region bounded by two slow shocks, across which the plasma is accelerated. Most space plasma current sheets separate two different plasmas, violating symmetry conditions across the current sheet. One form of asymmetry is a sheared plasma flow. In this thesis, the author investigates the magnetic reconnection process in the presence of a shear flow across the current sheet using two-dimensional magnetohydrodynamic simulations. The results show that only for sheared flow below the average Alfven velocity of the inflow regions can steady state magnetic reconnection occur. A detailed examination of the Rankine-Hugoniot jump conditions reveals that the two slow shocks of earlier models are replaced by a strong intermediate shock and a weaker slow shock in the presence of shear flow. Both symmetric and asymmetric density profiles are examined. Depending upon the direction of the flow in the adjacent inflow region, the effects from the sheared flow and the effects from the density asymmetry will compete with each other. The results are applied to the dayside and flank regions of the magnetosphere. For tailward flow in the flanks, the two asymmetries compete making the magnetic field transition layer broad with the high speed flow contained within the transition region. For the dayside region, the magnetic field transition region is thin and the accelerated flow is earthward of the sharp current layer (magnetopause). These results are consistent with the data. A velocity shear in the invariant direction was examined under otherwise symmetric conditions. With the magnetic field initially only in the x - y plane, B(z), and consequently field-aligned current, is generated by the initial v(z). The field-aligned current depends on the velocity profiles in all directions. For a velocity sheared in both the z and the y direction, the results show a very localized region of large field-aligned currents.

• Research Organization: Alaska Univ., College, AK (United States)
• OSTI ID: 218164
• Report Number(s): N--96-21381; NIPS--96-34615
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
COMPUTERIZED SIMULATION
HYDROMAGNETIC WAVES
MAGNETIC FIELDS
MAGNETIC RECONNECTION
MAGNETOTAIL
PLASMA DRIFT
SHEAR
SHOCK WAVES