Harmonic analysis of sunshine duration and solar irradiation measured at Sebele, Botswana is carried out. The data used consists of the monthly averages and the Julian-days averages of sunshine duration and solar irradiation sequences. This study involves splitting the time series into deterministic and stochastic components, and determining the proportion of the variance explained by each component. The stochastic component is analyzed for persistence using the Box and Jenkins technique. It is found that the stochastic component for monthly averages solar radiation series is best described by the second-order autoregressive Markov process, while that for Julian-days averages series has no memory. (C) 2002 Elsevier Science Ltd. All rights reserved.