Two time series models, AR(2) and AR(3), were fitted to the yearly time series of sunspot numbers for the period 1770--1869 in Chapter 7. The sunspot data are available for the slightly longer time period 1700--1988 as series ‘sunspot.year’ in the datasets package in R; type help(sunspot.year) for details. Perform diagnostic checking to determine the adequacy of the AR(2) and AR(3) models for this longer time period. Are there alternative models that you would consider for this series?

Would you recommend that a data transformation be used in this case?