May 14, 2014 – Are tropical cyclones migrating poleward? Based on a study appearing today in Nature: International Weekly Journal of Science, poleward trends are evident in both hemispheres. The Northern Hemisphere has seen a migration of 53 kilometers (about 33 miles) per decade over the past 30 years. The Southern Hemisphere migration is 62 kilometers (about 38 miles) per decade. The trends indicate expansion of the tropics at a rate of about one degree per decade.
What could be the cause?
Some mechanism in the atmosphere is changing and the likely cause is the warming of both ocean and air.
Kerry Emanuel, of MIT states:
“The trend is statistically significant at a pretty high level…..It may mean the thermodynamically favorable conditions for these storms are migrating poleward.”
Every ocean except the Indian is showing similar evidence. In the case of the Atlantic and Pacific ocean temperature is the smoking gun. When ocean surface temperatures reach 28 to 30 Celsius (82 to 86 Fahrenheit) ideal conditions exist for generating hurricanes and typhoons in areas of the Earth’s atmosphere known as Hadley cells. The warmer water temperatures create conditions for wind shear which is associated with the formation of tropical cyclones including the most violent of these known as hurricanes and typhoons.
What are the implications?
If these environments are moving further north and south of the equator it means the storms are migrating as well. This has implications for coastal cities and communities that may never have seen hurricanes and typhoons make landfall near them.