Hot magnetized plasmas - typified by the solar corona - are ubiquitous throughout the universe. The physics governing the dynamics of such plasmas takes place on remarkably small spatial and temporal scales, while both the cause activity and the response occur on large spatial scales. Thus both high resolution and large fields of view are needed. Observations from <i>SMM, Yohkoh</i>, EIT and TRACE show that typical solar active region structures range in temperature from 0.5 to 10 MK, and up to 40MK in flares, implying the need for broad temperature coverage. The RAM S-T Probe consists of a set of imaging and spectroscopic instruments that will enable definitive studies of fundamental physical processes that govern not only the solar atmosphere but much of the plasma universe. Few problems in astrophysics have proved as resistant to solution as the microphysics that results in the production of high-energy particles in hot magnetized plasmas. Theoretical models have focused in recent years on the various ways in which energy may be transported to the corona, and there dissipated, through the reconnection of magnetic fields. Theory implies that the actual dissipation of energy in the corona occurs in spatially highly localized regions, and there is observational support for unresolved structures with filling factors 0.01 - 0.001 in dynamic coronal events.
To make progress on major unsolved problems in solar physics (<i>e.g</i>., coronal heating, eruptive flare/CME initiation, solar wind initiation), we must observe on scales relevant to the underlying physical processes and their signatures. In this review I discuss the factors determining the structure of magnetic fields and plasmas in the Sun’s outer atmosphere, the key observable signatures of the relevant processes and properties, and the instrumental capabilities necessary to detect and measure these signatures. The primary emphasis is on state-of-the-art theoretical and numerical predictions, which often are the only means by which we can estimate the complex time-dependent evolution of the underlying physical mechanisms and their local and global effects on the corona.
A STEREO mission concept requiring only a single new spacecraft has been proposed. The mission would place the new spacecraft in a heliocentric orbit and well off the Sun- Earth line, where it can simultaneously view both the solar source of heliospheric disturbances and their propagation through the heliosphere all the way to the earth. Joint observations, utilizing the new spacecraft and existing solar spacecraft in earth orbit or L1 orbit would provide a stereographic data set. The new and unique aspect of this mission lies in the vantage point of the new spacecraft, which is far enough from Sun-Earth line to allow an entirely new way of studying the structure of the solar corona, the heliosphere and solar-terrestrial interactions. The mission science objectives have been selected to take maximum advantage of this new vantage point. They fall into two classes: those possible with the new spacecraft alone and those possible with joint measurements using the new and existing spacecraft. The instrument complement on the new spacecraft supporting the mission science objectives includes a soft x-ray imager, a coronagraph and a sun-earth imager. Telemetry rate appears to be the main performance determinant. The spacecraft could be launched with the new Med-Lite system.