Introduction

A magnetic cloud is a transient ejection in the solar wind defined by relatively strong magnetic fields, a smooth rotation of the magnetic field direction over approximately 0.25 AU at 1 AU, and a low proton and proton temperature [Burlaga et al., 1981]. Magnetic clouds are ideal objects for solar-terrestrial studies because of their simplicity and their extended intervals of southward and northward magnetic fields [Burlaga et al., 1990]. Approximately 1/3 of the interplanetary ejecta (also called "CMEs" by some authors) are magnetic clouds [Gosling, 1990]. There is an extensive literature on the structure and dynamics of interplanetary magnetic clouds [see the reviews by Burlaga, 1991; 1995], their solar sources [Wilson and Hildner, 1984, 1986; Rust, 1994], and their effects on the magnetosheath [Farrugia and Burlaga, 1994; Farrugia et al., 1993c, 1994; Lepping et al., 1995], the magnetosphere [Lepping et al., 1991; Farrugia et al., 1993 a,b; Tsurutani et al., 1988], and ionosphere [Freeman et al., 1993]. A model of the interaction of a magnetic cloud with the magnetosphere and ionosphere was presented by Chen et al. [1995]. The previous studies focused on relatively limited problems, aimed at understanding various parts of the solar-terrestrial chain of events associated with magnetic clouds.

As a result of the efforts of hundreds of people around the world, the Solar-Terrestrial Physics community is now in a unique position to carry out comprehensive studies of the processes connecting solar events, interplanetary structures, and magnetospheric/ionospheric/thermospheric effects. The ISTP Project (International Solar Terrestrial Physics Project) was designed from the outset to study Solar-Terrestrial relations using the data acquired from a large armada of scientific spacecraft, including the GGS spacecraft (WIND and POLAR), the Japanese spacecraft GEOTAIL, five geosynchronous spacecraft from the DOD and NOAA, the IMP-8 spacecraft, and the soon to be launched ESA spacecraft SOHO and Cluster, as well as ground-based observations and theoretical investigations. Special efforts to facilitate the communication of the observations and results via the Internet (including via the World Wide Web) have been made by the ISTP Central Data Handling Facility (CDHF) and the Science Planning and Operations Facility (SPOF) [Mish et al., 1995] of the GGS Project in cooperation with the National Space Science Data Center (NSSDC). The coordination of specific scientific investigations focusing on several campaigns is organized by the Inter-Agency Consultative Group (IACG). It is expected that the First IACG Science Campaign will provide a model for the extensive collaborative efforts that are needed to understand Solar-Terrestrial processes.

Interval # 1 of the First IACG Science Campaign is now Oct. 18 - 21, 1995. A magnetic cloud observed by WIND 175 RE upstream of the Earth fortuitously occurred in this interval. The aim of this paper is to identify the principal features of the magnetic cloud that are needed for studies of the solar causes and the magnetospheric, ionospheric and thermospheric effects of this magnetic cloud.