The Solar and Heliospheric Observatory (SOHO) is a joint ESA/NASA mission to study the Sun, from its deep core to the outer corona, and the solar wind. SOHO was launched on 2 December 1995 and was inserted into a halo orbit around the L1 Lagrangian point on 14 February 1996. From this vantage point it is continuously monitoring the Sun, the heliosphere, and the solar wind particles that stream toward the Earth. Nominal operations of the SOHO mission started in April 1996 after commissioning of the spacecraft and the scientific payload. Detailed descriptions of the twelve instruments, which represent the most comprehensive set of solar and heliospheric instruments ever developed and placed on the same platform, can be found in "The SOHO" "Mission" ("Solar Physics," Vol. 162, Nos. 1-2, 1995).
This volume contains papers reporting the first scientific results from the SOHO mission as well as descriptions of the in-flight performance of some of the instruments, published in two parts of a "Solar Physics" special (Part I in "Solar Physics," Vol. 170, No. 1; Part II in "Solar Physics," Vol. 175, No. 2). Unique data from the three helioseismology instruments (GOLF, VIRGO, MDI/SOI) provide new insights into the structure and dynamics of the solar interior, from the deep core to the outermost layers of the convection zone. The remote sensing instruments (SUMER, CDS, EIT, LASCO, UVCS, SWAN) present exciting new data on a wide range of topics such as transition region dynamics, coronal plumes, coronal holes, streamers, and coronal mass ejections, giving us our first comprehensive view of the outer solar atmosphere and corona. These data are complemented by energetic particle measurements produced by the ERNE instrument on board SOHO.

nd The 2 SORO Workshop on "Mass Supply and Flows in the Solar Corona" was held in Marciana Mariana on the island of Elba, Italy, in the week September 27 to October 1, 1993, as part of a series of workshops planned by the Solar Corona and Particles Working Group of the SOHO Science Working Team (SWT). The purpose of this workshop series is to acquaint the solar community with the capabilities of SORO, and prepare scientific projects and observing plans for the mission. This Workshop, which was at tended by more than one hundred scientists from different countries, focused on the following topics: 1) Fine Scale Structures 2) Loops and Prominences 3) Coronal Streamers 4) Coronal Roles and Solar Wind Each of these four topics was introduced by an observational and a theo retical overview highlighting the most recent advances in their area. A third review illustrated how SORO might help in solving open problems. Oral pa pers and poster presentations were followed by Working Group sessions. On the last day of the Workshop the Group Leaders reported on the activities of their Working Group. These proceedings include most of the papers presented at the Work shop, including the poster papers and Working Group reports by the Group Leaders as well as two overview papers of the SORO mission. All papers have been refereed.

SOHO, the Solar and Heliospheric Observatory, is a project of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, and the solar wind. To achieve its scientific goals it carries a complement of twelve sophisticated, state-of-the-art instruments. Three helioseismology instruments are expected to provide unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone. A set of five complementary remote sensing instruments, consisting of EUV and UV imagers, spectrographs and coronagraphs, will give us our first comprehensive view of the outer solar atmosphere and corona, leading to a better understanding of the enigmatic coronal heating and solar wind acceleration processes. Finally, three experiments will complement the remote sensing observations by making in-situ measurements of the composition and energy of the solar wind and charged energetic particles. This volume contains detailed descriptions of all the twelve instruments on board SOHO. Also included are an overview paper and a description of the SOHO ground system, science operations and data products. The aim of these papers is to make the broader scientific community, and in particular potential guest investigators, aware of the scientific objectives and capabilities of the SOHO payload and to provide a reference document for the various instruments.

The aim of the VIRGO investigation (Variability of solar IRradiance and Gravity Oscillations) on SOHO (SOlar and Heliospheric Observatory) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. VIRGO contains two different active-cavity radiometers for monitoring the sol- ar 'constant' (DIARAD and PM06-V), two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500, and 862 nm with a bandwidth of 5 nm, and a low-resolution imager (Luminosity Oscillation Imager, LOI) with 12 'scientific' and 4 guiding pixels, for measuring the radiance dis- tribution over the solar disk: at 500 nm. The instrumentation has been described in detail by Frohlich et al. (1995). In addition, the observed in-flight performance and operational aspects of the irradiance observations are described by Frohlich et al. (1997), and those of the LOI by Appourchaux et al. (1997).