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 kms−1 to 800 kms−1, and a slow stream
mode with velocities in the range of 350 kms−1 to 400 kms−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.
