Indices of interannual variability, as in Figure 3. (a) For the Eurasian (solid line) and North American (dashed line) landmasses. (b) For the contiguous United States, using data from the National Climatic Data Center. (c) For the eastern (solid line) and western (dashed line) United States. (d) For the state of Colorado (solid line) and the Platte River climatic division of Colorado (dashed line).