COSTEP addresses scientific objectives related to the following phenomena:
It is at first surprising that suprathermal and energetic particle emissions, which are genrally associated with explosive phenomena, also carry vital information about the quiet solar atmosphere. There are two primary reasons for this. First, continuous emissions of suprathermal electrons (and possibly ions) are associated with processes which operate in the "quiet" corona. Second, samples of the solar atmosphere accelerated in flares have ionization state temperatures typical of the ambient corona, not the much hotter flare site, and therefore carry information about the ambient coronal composition.
For particles observed in processes with a high energy release, at least four distinct solar acceleration processes habe been suggested:
Identification of different acceleration processes requires use of the full range of electromagnetic signatures including radio, optical, UV, X-ray and gamma-ray, along with particle information from suprathermal through the energetic particla range. In the past, only a subset of these diagnostics was available at any one time, making it difficult to synthesize a coherent picture. With SOHO we have for the first time the exciting opportunity to routinely observe particle events using many of these information channels simultaneously.
Acceleration of energetic particles continues in the interplanetary medium, most often associated with shocks and other disturbances. Travelling shocks in the interplanetary medium are produced by various types of solar activity including large flares and CMEs. Corotating interaction regions (CIR) are typically observed for several years around solar minimum, when the polar coronal holes expand to the equator, and fast solar wind overtakes the slower wind ahead of it forming a compression region of high magnetic field strength and plasma density. The SOHO primary mission coincides with the minimum of solar activity.
The COSTEP sensors LION and EPHIN will allow a systematic investigation of these questions to be made by measuring energetic particles over a wide range of energies and for different particle species and combining this information with simultaneous observations from other experiments in the SOHO payload, on other satellites and with ground based observations. Key contributions towards solving these problems can be expected from suprathermal and energetic particle observations, by using these particles as diagnostic tools for remote probing of solar processes. It is possible to distinguish a rich variety of solar phenomena by observing the energetic particles that they emit. Impulsive flares, coronal mass ejections (CMEs), disappearing filament events, and interplanetary shock waves, each have as distinctive a signature in the timing, composition, and spectra of the accelerated particles as they do in the radio, optical, X-ray, gamma-ray photons that they produce.
Taken from "THE SOHO MISSION" by Bernhard Fleck, Vicente Domingo and Arthur I. Poland; Kluwer Academic Publishers