Area of polar coronal holes and sunspot activity: Years 1939-1993

The correlation between the size of polar coronal holes and sunspot numbers has been investigated for the last five solar cycles. The area of polar coronal holes over the period from 1939 to 1993 was derived from ground-based observations of the green coronal line at 530.3 nm (Fe XIV). Correlation analysis revealed that there is no general shift in the maxima of the curves of these two solar indices. The analysis showed the same shift in months in cycles 21 and 22 when the best correlation between the indices is reached; the time shift found in cycle 20 is slightly different from that in cycle 18; in cycle 19, there is found a shift with a value between the values in cycles 18, 20 and 21, 22. The time between succesive peaks of smoothed polar hole size and smoothed sunspot number is different in each cycle.