Date of Award

Winter 1998

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Roy B Torbert

Abstract

We looked at three magnetic clouds observed by the WIND satellite and find that though they are temporally the same, their effects on the Earth were different. The magnetopause is slightly expanded for all the three clouds from its average position during the Bz<0 phase of the clouds and in the Bz<0 phase there was a compression of the magnetopause taking place. During the Bz<0 phase of the October 1995 cloud the bow shock expanded from its average position much more then the January 1997 but the May 1996 cloud hardly affected the Earth's bow shock position during this phase. For the later Bz<0 phase, we find that all three clouds compressed the bow shock closer to the Earth from its average position. We studied a number of discontinuities in the field and plasma observations for the October 18--19, 1995 magnetic cloud. Except for the front cloud boundary, which was a tangential discontinuity, all other discontinuities were rotational. We also could identify 3 different coherent structures within the October 18--19, 1995 cloud. We also found regions for which no coherent structure existed.

From our simulations of a shock with a static force-free Lundquist flux tube, we find that the width of the tube will decrease but the boundaries of the tube were still clearly defined. The magnetic field components retain their original orientation but with an increased amplitude. Depending on the density ratio's between the tube and surrounding plasma, the possible waves generated by the shock interaction at the tube boundary are: (1) transmitted and reflected shock; (2) reflected expansion wave and transmitted shock; and (3) only a transmitted shock. We also find that the shock speed in the tube was increased, decreased or remain unchanged. Some numerical results are supported by GEOTAIL observation's of the October 18--19, 1995 magnetic cloud crossing the bow shock of the Earth.

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