Bar plots for the number of different types in terms of time, magnetic field structure and duration. (a) Yearly fractions of the four studied types of ICME, together with monthly sunspot number (Source: World Data Center, Sunspot Index and Long-term Solar Observations, Royal Observatory of Belgium, Brussels). Other types of ICMEs (10 cases in total) have been removed here and the number of cases in different groups is marked in the top of each bar. (b) Fraction of the four studied types of ICME in different groups (MC stands for magnetic cloud and the data shown are from R&C list.