May 11, 1999 WASHINGTON, D.C. -- Scientists have completed a comprehensive study of the Sun during a month of its most recent quiet period, using instruments not previously available. They have compiled data and gained insights that will be useful as the Sun reaches its period of maximum sunspot activity in the year 2000.
Whole Sun Month was a two-year collaborative effort of the Inter-Agency Consultative Group (IACG) Campaign 4 and the Solar and Heliospheric Observatory (SOHO) Working Group Joint Observing Program 44. Under its auspices, an international and interdisciplinary group of scientists studied the Sun from August 8 to September 10, 1996, a period known as solar minimum. Although two workshops have been devoted to Whole Sun Month (WSM) and some results have been reported at meetings of the American Geophysical Union and other organizations and in some journal articles, the first comprehensive, peer reviewed compilation appears in the current issue of the Journal of Geophysical Research.
The Sun exhibits an approximately eleven year cycle of sunspots, with a shorter period from minimum to maximum than for maximum back to minimum. At solar minimum, there are few sunspots and related magnetic activity, such as solar wind. In their introduction to the 237 page special section on WSM, Antoinette B. Galvin of the University of New Hampshire and John L. Kohl of the Harvard-Smithsonian Center for Astrophysics state that the project's objective was to gain an understanding of the large-scale, stable structures that dominate the solar corona at solar minimum.
The corona is the outermost layer of the solar atmosphere, and Galvin and Kohl say that understanding the large-scale corona is fundamental to understanding how and where the solar wind is accelerated. The solar wind, an outflow of particles and magnetic fields, can affect communications on Earth, especially during the solar maximum.
The 19 papers in the JGR special section are divided into four major areas of investigation:
* Global Morphology. This section includes the largest variety of synoptic maps of the Sun ever published in a single paper.
* Structure and Physical Properties of the Corona. This section describes determinations of the density and structure of the corona, essential for understanding and modeling the formation of the solar wind.
* Structure and Physical Properties of the "Elephant's Trunk." This was an unusual, elongated coronal hole that appeared during the study period.
* In Situ Observations. Observations were not limited to the Sun itself; this section analyzes the effect of solar minimum at the Earth and up to 4.3 times the distance of the Earth from the Sun.
Funding for the Whole Sun Month study was provided by NASA, the United Kingdom PPARC, National Science Foundation, European Space Agency, and other agencies.
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