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Measurement of the full disk Ca n H and K profiles has now been completed from minimum to maximum in the current solar cycle 21. The central intensity of the K line increases by 30% on the average, but a peak change of-1-40% was recorded near the maximum of solar activity in late 1979. The 1 A K index shows a corresponding but smaller increase of 18%. These changes in the Sun viewed as a star appear to be directly attributable to the occurrence of solar plages on the visible solar hemisphere. Similar measurements of a TX3' quiet region at disk center show no significant systematic variability. This suggests that the quiet network has no long-term variability in the rising phase of the solar cycle. Ca n K Une widths and asymmetries also show systematic changes associated with the degree of solar activity. In general, spectral features formed above the temperature minimum are all closely correlated in their variability, but they are not well related to changes in the strength of narrow photospheric Unes and the K x wings. Ca n variability correlates very closely with the plage index, the Zurich sunspot number, and the Ottawa 10 cm flux measurements. The observing program will continue into the declining phase of cycle 21, so we will have the opportunity to test the constancy of our correlations in a different phase of the cycle when the rate of sunspot formation is decreasing and when Ca n variability may be influenced more by the remnants of active regions formed earlier.

Described is a major new tool for solar research, conceived and built during a time of budget restraint.The observation of magnetic and velocity (circulation) field structure on a synoptic basis and with diffractionlimited resolution is the aim. New optical features include the use of oversize mirrors and windows(to avoid thermal edge effects) and the placement of the coelostat feed outside the vacuum, mainly foreconomy. The site selected has prevailing winds that clear thermals from these mirrors. Test data in theform of the system MTF and optical transmission, together with examples of full disk magnetograms andphotoheliograms, show present performance capability. Measured MTF indicates a response of 0.2 at 1sec of arc (whereas diffraction-limited response would be ~0.8). System transmission, including the accompanying spectrograph, is only 2-3% (lambdaO.44-1.1 microm). Thus, both the optical quality and efficiency aresubject to improvement.

A three‐component model has been developed to examine the variation with solar activity of the far ultraviolet irradiance between 145 and 200 nm. This model is based on spatially resolved observations of the Call K chromosphere and includes the contributions to the full disk flux from both plage and active network emission. The 27‐day modulation of the ultraviolet flux is explained by the evolution and rotation of the plage regions on the solar disc. Over the longer time scale of the eleven‐year cycle it is essential that changes in the active network arising from the decay of plage regions also be considered as a source of ultraviolet flux variability. Only by using a three‐component model of the solar flux is it possible to simultaneously reproduce the 27‐day variability observed by the solar backscatter ultraviolet experiment on the Nimbus 7 satellite and the changes from the minimum to the maximum of the solar activity cycle observed by the rocket experiments of the Laboratory for Atmospheric and Space Physics and by the extreme ultraviolet spectrometer on the Atmospheric Explorer E satellite. It is shown that the AE‐E experiment measured a smaller solar cycle variability for the ultraviolet irradiances than is predicted by the model calculations because of the spatially restricted field of view of this instrument.

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