Interplanetary Scintillation Observations of the Large-Scale Structure of the Solar Wind Using EISCAT

Measurements of interplanetary scintillation (IPS) taken with the European Incoherent SCATter radar (EISCAT) in northern Scandinavia can be used to study the evolution of the solar wind as it expands through interplanetary space. IPS arises from changes in the apparent brightness of distant, compact radio sources due to scattering by density irregularities in the solar wind and can be used to obtain estimates of the solar wind speed. In this paper we present the results of a study of the large-scale structure of the fast solar wind under near solar minimum conditions, using data taken with the EISCAT system, and the extremely long baseline observations which combine the EISCAT and MERLIN systems. The latter are the best measurements to date of meridional components of velocity in the inner solar wind. In particular, the existence of a gradient in solar wind velocity of the fast wind over the polar crown, at latitudes corresponding to the x-ray and ultra-violet coronal hole boundary, as reported by Habbal and Woo (2001), is also explored.