Where Winds Meet

The Intertropical Convergence Zone (ITCZ) is where tropical easterly winds, known to sailors as “tradewinds,” converge over the oceans. The ITCZ moves back and forth across the equator in an annual cycle, its position being determined largely by a combination of solar forcing and coupling between the atmosphere and surface ocean temperatures. The ITCZ is most variable in boreal spring, when it extends furthest south. The extent of this variability in the eastern Pacific is known to depend on the state of El Niño-Southern Oscillation, but what controls the location of the tropical Atlantic ITCZ is less clear. One hypothesis is that a northern midlatitude “atmospheric bridge” allows the Pacific to influence the Atlantic ITCZ. Another hypothesis, derived from an atmospheric General Circulation Model, is that the connection is maintained through anomalous Walker Circulation.