Interdecadal changes in eastern Pacific ITCZ variability and its influence on the Atlantic ITCZ

The eastern Pacific and Atlantic Intertropical Convergence Zones (ITCZ) exhibit the largest year-to-year variations in boreal spring. We show evidence suggesting that Atlantic ITCZ April-May variability is linked to that for the eastern Pacific through the Walker circulation as it respond to changes in equatorial Pacific convection. Analysis of ITCZ proxy indices shows the link appears to be strong in the 1080-90's and 1920-30's but virtually nonexistent in the 1950-60's. We argue that this apparent nonstationarity results from the nonlinear relationship between sea surface temperature (SST) and convection in the eastern equatorial Pacific and its consequent effect on the Walker circulation and the Atlantic ITCZ. This mechanism was modulated over 1856-1998 by interdecadal changes in peak SST attained in the eastern equatorial Pacific during boreal spring.