Climate Trivia: Atlantic Hurricane Frequence and ENSO
Warm ocean surface temperatures in the North Atlantic provide the warm and moist air that fuels hurricanes, which develop out of random disturbances in the tropics that provide the spark for these storms. Warmer waters in the North Atlantic generally mean more fuel for the storms. But did you know that surface temperature conditions in the tropical Pacific Ocean also influence the Atlantic Hurricane season? The El Niño-Southern Oscillation (ENSO) is the periodic shifting of sea surface temperature distributions in the tropical Pacific. During El Niño phases, water temperatures in the eastern tropical Pacific off the coast of South America are warmer than normal. During La Niña phases, water temperatures there are cooler than normal. During ENSO neutral phases, the temperatures are somewhat in between.
Trivia Question: All other things being equal, during what phase of ENSO does the Atlantic Hurricane season tend to be most active?
a. El Niño
b. La Niña
c. Neutral
The correct answer is b. The amount of vertical wind shear over the ocean can make or break a hurricane season. Vertical wind shear is the change in the speed and direction of wind at different levels of the atmosphere. More vertical wind shear, or lots of variation in wind speed across different altitudes, suppresses hurricane activity. Less vertical wind shear, or more even wind patterns across different altitudes, promote hurricane development. La Niña phases work to reduce the amount of vertical wind shear over the North Atlantic, and thus La Niña years tend to be years with more active Atlantic hurricane seasons. La Niña conditions are now present in the tropical Pacific.
Seasons: Summer, Fall
Sources: Briggs, WM. “On the Changes in the Number and Intensity of North Atlantic Tropical Cyclones.” Journal of Climate 21 (2008): 1387-1402. Donnely, JP and Woodruff, JD. “Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon.” Nature 447 (2007): 465-468.
