Physics
Scientific paper
Mar 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982phdt........23e&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, LOS ANGELES, 1982.Source: Dissertation Abstracts International, Volume: 43-04, Sectio
Physics
Scientific paper
We present the results of a study of magnetic flux ropes in the Venus ionosphere. Specifically, we investigate how magnetic flux ropes fit into the interaction of the solar wind and ionospheric plasmas by examining their detailed magnetic structure, stability and global characteristics in light of proposed formation mechanisms. We begin the investigation by reviewing observations of the dayside ionosphere and ionopause of Venus, including observations of magnetic flux ropes in light of thermal plasma observations. Next, we discuss measurement and analysis of flux rope data, including ordering the magnetic field data using minimum variance analysis. We show that the observed signatures are consistent with that expected from an idealized flux rope. We identify those rope crossings on which the spacecraft passed near the center of the structure, providing a complete sampling of the rope field. This enables us to fit a general rope model to the data, and to infer the electric current structure of the ropes. Models of specific cases also aid in understanding rope stability. We investigate global variations in occurrence, scale size, orientation, and helicity, which can then be compared to those expected from various formation mechanisms. We study three proposed mechanisms. The first describes flux ropes as a large scale superconductor effect. We find no unambiguous evidence supporting this description. The next mechanism we consider involves Kelvin-Helmholtz instability in the ionospheric flow, which proves to have several physical difficulties. The last mechanism we consider involves the flute and/or Kelvin-Helmholtz instability at the ionopause, which causes discrete filaments of magnetic field to enter the ionosphere. We next study the global polarity of field-aligned currents in flux ropes. When grouped in regions of expected polarity (based on solar wind magnetic field orientation and expected flow direction), observations show no clear indication of global polarity. We caution, however, that changes in the solar wind field orientation may account for the lack of global order.
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