On the unresolved fine structures of the solar atmosphere in the 30,000-200,000 K temperature region

The solar atmospheres from the chromosphere through the transition zone and all the way up into the corona usually are considered to be parts of one continuous structure. Now that stellar measurements in the far-ultraviolet have become available, an attempt is being made to apply solar physics ideas to solar type stars. The intention of this paper is to reexamine the experimental facts concerning the relations between the solar chromosphere, transition zone, and corona. Experimental evidence is presented to argue that the solar plasma in the temperature region 40,000-220,000 K occurs in structures magnetically isolated from the chromosphere and corona. It is suggested that while a small part of the emission detected in the 40,000-220,000 K region consists of the 'true' transition zone plasma, i.e., the interface between chromospheric and coronal temperature, most of it belongs to an altogether different entity. It is also suggested that this particular entity be called unresolved fine structures.