LWS TR&T Focus Teams:

Origin and Nature of the Slow Solar Wind, Associated Interplanetary Structures, and SEP Transport

Team Chair: Thomas Zurbrucken
Team Research Plan:
Next Team Meeting: TBD
Team-Maintained Web Site: TBD
Team Publications: TBD
Team Members:
Christina Cohen
Yuan-Kuen Ko
Mari Paz Miralles
Aaron Roberts

Target Description: At all times, the heliosphere is filled with a combination of fast and slow solar winds. The fast solar wind, typically associated with speeds exceeding 600 km/s, originates primarily from coronal holes. It is also characterized by ion temperatures that far exceed electron temperatures in the inner corona, at least out to 10 RS from the Sun, and by near photospheric-like composition. At least half of the time, however, a substantial fraction of the near-ecliptic solar wind that immerses the planets has characteristics that are distinct from the fast wind: its speed is typically < 500 km/s, and the ion temperature tends to be lower than the electron temperature in the inner corona. Furthermore, its ionic and elemental composition is much more representative of closed magnetic structures (e.g. loops) in the corona.  The properties of the slow solar wind are far more dynamic and variable than those of the fast solar wind. The slow solar wind is generally found in the vicinity of the heliospheric current sheet emanating from streamers at the Sun, especially at the time of solar minimum. However, the sources for this slow solar wind have not been clearly established. Near solar maximum, the slow solar wind may not even be spatially limited to the heliospheric current sheet.
Fast-moving solar energetic particles (SEPs) propagate from the corona into the heliosphere and, consequently, are highly effective remote probes of solar-heliospheric structures.  As such, they add much to our investigation of the slow wind.  Moreover, to increase our understanding of the origin of SEPs, which is a central goal of the LWS program, a better understanding of the nature of the coronal and heliospheric magnetic fields in slow wind regions is required.  Thus, it is natural to study the physics of SEP transport concomitantly with studies of the origin and nature of the slow solar wind.

Goals and Measures of Success: The goal of this FST will be to develop an understanding of the physical processes in the solar corona and inner heliosphere that determine the origin of the slow solar wind, its coronal and interplanetary plasma and magnetic field dynamics and structure, and the transport of SEPs through the slow wind. Measures of success would be a substantial advance in our understanding of the slow solar wind, especially, its source(s) at the Sun, the physical reasons for its similarities and differences to the fast solar wind, the mechanism(s) responsible for its temporal variability, and the origin(s) of the observed plasma composition and magnetic structures. Another important measure of success would be an improvement in our ability to model the slow wind accurately and achieve better agreement between solar wind models and in situ data.  Improvement in models for the propagation of SEPs from their solar sources into the inner heliosphere is another important measure of success for this FST.

Types of investigations:

• Studies of coronal structure and plasma properties, especially composition, with the goal of determining the source regions of the slow wind.
• Studies of the in situ magnetic and plasma properties of the slow wind, especially composition or other properties that allow us to distinguish source regions unambiguously. 
• Studies of the relative properties of the fast and slow wind, focusing on identifying the clearly distinctive differences between the two winds and providing insights into the physical origins for these differences.
• Studies of SEP transport in slow wind regions.
• Studies of how SEPs can be used to connect the slow wind to its coronal sources.
• Development of improved models for the solar wind, especially models and physics-based procedures that can be delivered to the CCMC.