Abrupt Northward Shift of SPCZ position in the late-1920s Indicates Coordinated Atlantic and Pacific ITCZ Change

Introduction Patterns of climate variability are often studied by evaluating instrumental or paleo-data from regions that have the highest correlations to the target climate mode. For example, past variations in ENSO have been primarily evaluated by compiling or reconstructing sea surface temperature (SST) in the Nino3.4 (5°N-5°S; 120°W-170°W) and Nino3 (5°N-5°S; 90°W-150°W) regions in the equatorial Pacific (e.g.: Trenberth 1997; Urban et al., 2000; Cobb et al., 2013). However, critical information on the spatial extent of a target climate mode can also be gained by studying conditions on the nodal line perimeter of the climate pattern where on average there is no correlation (R=~0) between the climate parameter being reconstructed and the target mode.