... Cyclic variations of the mean semi-annual intensities I of the coronal green line 530.3 nm are compared with the mean semi-annual variations of the Wolf numbers W during the period of 1943 ­ 1999 (activity cycles 18 ­ 23). ... Introduction Prediction of solar activity for a few years ahead and, in particular, for a following cycle has long been a vital problem of solar physics. ... Observations and Data Reduction 2.1. ... Open circles indicate our forecast of the Wolf numbers for solar cycles 23-24....