Scientists have long known of an apparent one-way relationship between the Atlantic and Pacific oceans: Unusually warm sea surface temperatures in the eastern and central tropical Pacific during El Niño can curb tropical cyclones in the Atlantic. However, in a new study, Patricola et al. sought to find out if varying sea surface temperatures in the Atlantic Ocean remotely influence tropical cyclones in the eastern and central North Pacific.
Using cyclone records from 1950 to 2015 and simulated idealized climate cycles, the authors found that when the Atlantic’s surface warms, subsequent tropical cyclones in the eastern Pacific are less frequent and weaker.
Likewise, when the Atlantic’s surface cools, the eastern Pacific experiences more frequent and stronger cyclones instead. As for the mechanism behind this relationship, the authors found that it can be driven by a climatic pattern called the Atlantic Meridional Mode.
The Atlantic Meridional Mode describes the waxing and waning of the Atlantic Ocean’s surface temperatures. During its positive phase, this mode brings unusually warm sea surface temperatures to the northern tropics. In its negative phase, sea surface temperatures cool.
Scientists are well aware that the mode’s positive phase strengthens cyclones within the Atlantic basin, whereas the negative phase suppresses them. However, the new study suggests the Atlantic Meridional Mode can strengthen and suppress cyclones in the eastern Pacific basin too, weakening tropical cyclone seasons there during its positive phase and intensifying them during its negative phase.
The authors propose one driving factor behind this inverse relationship: vertical wind shear. In both simulations and observations from the cyclone database, vertical wind shear in the eastern Pacific reliably increased during the mode’s positive phase, which suppressed cyclones in the eastern Pacific.
An analogous connection moves in the other direction, where unusually warm sea surface temperatures in the tropical Pacific increase wind shear over the Atlantic, ultimately suppressing tropical cyclones there. The authors suggest that further study on these connections and their underlying mechanisms could improve the accuracy of future cyclone forecasts. (Geophysical Research Letters, http://doi/10.1002/2016GL071965, 2017)
—Brendan Bane, Freelance Writer