Figure 15: (a) Distribution of a major mode of global SST covariability during Boreal spring extracted extracted from an 87 year (1901-1987) data set (data pattern extracted by EOF analysis, EOF No. 3). (b) Time series of the variations of coefficients for SST (solid line) data pattern and for Sahel rainfall anomalies (dashed line) for the same time period; note the reversal of the sign on the right axis for the SST EOF values (from Folland et al. 1991).