Interplanetary Scintillation Studies of the Large-Scale Structure of the Solar Wind

Authors Organisations
Type

Student thesis: Doctoral ThesisDoctor of Philosophy

Original languageEnglish
Awarding Institution
Supervisors/Advisors
  • Andrew Robert Breen
Thesis sponsors
  • Science and Technology Facilities Council
Award date28 Jul 2006
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Abstract

The solar wind is a highly supersonic outflow of coronal plasma flowing in a close to radial direction out from the Sun. Generally, there are two modes of outflow, a fast stream mode with velocities in the range of 750 km s−1 to 800 km s−1 , and a slow stream mode with velocities in the range of 350 km s−1 to 400 km s−1 . The method of interplanetary scintillation (IPS) is used to obtain solar wind velocity estimates by observing the “twinkling” of radio waves from distant compact sources caused by density variations in the solar wind. The Aberystwyth IPS group has been conducting IPS observations using the European Incoherent SCATter radar (EISCAT) in northern Scandinavia since 1993 and more recently using the Multi-Element Radio-Linked Interferometer Network (MERLIN) radio telescopes in the United Kingdom.
This thesis investigates the large-scale structure of the solar wind using IPS observations in conjunction with white-light, extreme ultra-violet (EUV) and X-ray Carrington rotation maps from ground-based: Mauna Loa; and space-based: SOlar and Heliospheric Observatory (SOHO) and Yohkoh; as well as in-situ spacecraft observations of solar wind velocity from Wind and Ulysses.
A complete study of EISCAT IPS data from 1994 to 2003 is undertaken looking for detections of interaction in terms of shear layers and co-rotating interaction regions (CIRs) by ballistically mapping the IPS observations out to in-situ distances to see how interaction develops. From this, an investigation was carried out with solar minimum (1994-1997) EISCAT IPS data investigating a possible bi-modal fast solar wind structure. In addition, the technique of extremely long-baseline IPS measurements (developed from 2002) was used to look at the finer structure of solar wind velocity. This technique was also used to investigate the direction of flow which included observations of fast and slow wind, interaction regions, and the passage of a magnetic cloud.