Coronal observations with SOHO

Abstract

Abstract The Solar and Heliospheric Observatory (SOHO) will carry a set of solar physics experiments which permit a thorough investigation of the solar corona. The emphasis of the mission is on the measurement of the physical properties of coronal structures and the processes occurring therein, leading — it is hoped — to an understanding of the mechanism(s) by which the solar corona is heated and the solar wind is accelerated. The observations will be made from a halo orbit around the L1 Lagrange point on the Earth-Sun line and will range from magnetic field measurements in the photosphere through spectroscopic plasma diagnostics of chromospheric, transition-zone and coronal structures with high spatial and spectral resolution, to coronagraphic observations out to 30 solar radii and to mass spectrometry of the solar wind near one astronomical unit. SOHO is part of the Solar Terrestrial Science Programme (STSP), the first ‘Cornerstone’ in ESA's long-term scientific programme ‘Space Science — Horizon 2000’, and will therefore be flown in connection with the other STSP component, the four-spacecraft Cluster mission, which will investigate plasma structures and processes in the magnetosphere in three dimensions. Both STSP missions, i.e. SOHO and Cluster will address the physics of plasma structures and processes, that are accessible to investigation in the solar-terrestrial context, yet are thought to be examples of plasma processes and structures that are ubiquitous in the cosmos. It is hoped that a cross-fertilisation between the scientific communities associated with SOHO and Cluster will take place, as they investigate the physics of the coronal and magnetospheric plasma with complementary methods and techniques — globally by remote observations, and in detail, by multi-point in-situ measurements.