Distribution of the K-corona Over the Polar Regions of the Solar Disk: 1965-1983

The goal of this technical note is to present a set of synoptic observations from the Mauna Loa series of K-coronameters in polar projection format. The initial motivation for the production of these plots was the desire to present data that would be useful in the study of the evolution of high-latitude coronal streamers over the solar cycles 20 and 21. It now seems likely that there will be other uses for these data. Possibly the variation of coronal hole area over sunspot cycle can be extracted from the data presented below, and it is anticipated that the POLES plots of the north and south polar regions will provide an interesting adjunct data set for the upcoming ISPM mission, now scheduled for the minimum of the present sunspot cycle. Only east limb data have been used for this project. This choice was dictated by the amount of disk space available at Mauna Loa for the Mk-I and Mk-II data. A synoptic record of both limbs is presently kept for Mk-III data, and the routine used for the polar plot may be applied to either the east limb or west limb data from this current version of the instrument. The reference height of 1.5 Ro is used for all Mk-I and Mk-II data; the standard reference height of 1.3 Ro is used in this compilation of data for Mk-III observations. Polar projection displays can be obtained for heights of 1.7 Ro and 2.1 Ro from the Mk-III data, and it is expected that from 1983 onward, the yearly data will be presented in both cylindrical and polar format. The period of coverage for each instrument, the height of observations above the limb, and the selection of limb data available are given in Table 1.