Radio Studies of Coronal Holes

This report describes all the projects undertaken during the entire period of the above contract, the scope of which was to study coronal holes at radio wavelengths. Chapters 1, 2 and 3 summarize work that has already been described in our previous scientific reports and published papers. Chapters 4 and 5 and comprehensive descriptions of the more recent work that has not been previously published. Chapter 1 describes the determination of the radio spectrum (relative changes in the brightness temperatures at different radio wavelengths) of Coronal Hole 1 in the Stanford 9.1 cm synoptic charts during the same period, when clear X-ray data of coronal holes were available from Skylab. Chapter 2 summarizes our efforts to identify individual high latitude. Chapter 3 describes our 1977 coronal hole observations with the Haystack (1.94 and 3.81 cm) and Arecibo (11.5 and 21.4 cm) radio telescopes. Chapter 4 describes the international effort we organized in the summer of 1978 to obtain solar radio maps over a wide range of wavelengths. These radio maps were made on the same days at a number of radio observatories around the world. Chapter 5 describes the use of the observed radio spectra to produce models of the solor atmosphere inside coronal holes. The results of this analysis indicate that inside coronal holes the following changes occur: The chromosphere expands in height by about a factor of 2, while the temperatures and electron and neutral particle densities decrease to about 80% of their quiet sun values. The critical transition zone expands by a factor of about 5-6, while the temperatures decrease to about 50% and the electron densities to about 20% of their quiet sun values.