Figure 3.32. (Bottom) Seasonal values of the SAM index calculated from station data (updated from Marshall, 2003). The smooth black curve shows decadal variations (see Appendix 3.A). (Top) The SAM geopotential height pattern as a regression based on the SAM time series for seasonal anomalies at 850 hPa (see also Thompson and Wallace, 2000). (Middle) The regression of changes in surface temperature (°C) over the 23-year period (1982 to 2004) corresponding to a unit change in the SAM index, plotted south of 60°S. Values exceeding about 0.4°C in magnitude are significant at the 1% significance level (adapted from Kwok and Comiso, 2002b).