Analysis of the Time Lag Between Geomagnetic Ap Index and Solar Cycle

The data of twelve-month running average of monthly mean Ap index from 1932 to 2006 is decomposed into two components, (Ap)R and (Ap)I. (Ap)R is a linear function of the twelve-month running average of monthly mean sunspot number R, which has the same phase with sunspot number R and is possible due to Coronal Mass Ejections and equatorial coronal holes. The latter is due to long lived solar wind sources such as polar coronal holes extending toward equator and is inconsistent with sunspot number R in phase. Analyzing of (Ap)I and polar coronal holes variation of cycle 20, in which the lag between twelve-month running average of monthly mean Ap index and twelve-month running average of monthly mean R is remarkable, it is testified that the (Ap)I component corresponds to polar coronal holes. Thus it is concluded that the variation of polar coronal holes is a very important factor, which contributes possibly to the lag time between Ap index and solar cycle.