Properties of a coronal 'hole' derived from extreme-ultraviolet observations.

A description is given of the results of an analysis of EUV observations of a large coronal hole observed by the Harvard College Observatory (HCO) experiment on OSO-4 in 1967, November. Models were constructed for the chromospheric-coronal transition and coronal layers of the two types of regions. A comparison of the model of the hole and the normal quiet sun indicates that the electron pressure in the hole is reduced by a factor of three and the coronal temperature is lower by 600,000 K.