Texas A&M says freshwater hurricanes grow stronger

From Texas A&M University , a claim that fresh water intensifies hurricanes. At first blush, the concept seems wonky to me, as I don’t think there’s much difference between the heat content potential of fresh -vs- saltwater. Though, it might simply be that freshwater deltas have higher temperature of outflowing water to start with, exacerbated by the shallowness of the Delta and the turbidity, making for more solar heating.

Hurricanes can be 50 percent stronger if passing over fresh water, says Texas A&M study

If a hurricane’s path carries it over large areas of fresh water, it will potentially intensify 50 percent faster than those that do not pass over such regions, meaning it has greater potential to become a stronger storm and be more devastating, according to a study co-written by a group of researchers at Texas A&M University.

Ping Chang, professor of oceanography and atmospheric sciences and director of the Texas Center for Climate Studies, along with his former student, Karthik Balaguru, now at the Department of Energy’s Pacific Northwest National Laboratory, are the lead authors of a paper in the current issue of PNAS (Proceedings of the National Academy of Sciences).

Their findings could benefit weather experts as they try to predict the path and strength of a hurricane, noting that about 60 percent of the world’s population resides in areas that are prone to hurricanes or cyclones.

Chang and Balaguru and their colleagues examined Tropical Cyclones for the decade 1998-2007, which includes about 587 storms, paying particular attention to Hurricane Omar. Omar was a Category 4 hurricane that formed in 2008 and eventually caused about $80 million in damages in the south Caribbean area.

They analyzed data from the oceanic region under the storm, including the salt and temperature structure of the water and other factors that played a part in the storm’s intensity.

“We tested how the intensity of the storm and others increased over a 36-hour period,” Chang explains.

“We were looking for indications that the storm increased in intensity or weakened and compared it to other storms. This is near where the Amazon and Orinoco Rivers flow into the Atlantic Ocean, and there are immense amounts of freshwater in the region. We found that as a storm enters an area of freshwater, it can intensify 50 percent faster on average over a period of 36 hours when compared to storms that do not pass over such regions.”

The researchers believe their results could help in predicting a hurricane’s strength as it nears large river systems that flow into oceans, such as the Amazon in the Atlantic, the Ganges in the Indian Ocean or even the Mississippi River into the Gulf of Mexico.

Hurricanes – called typhoons in the Pacific region and cyclones in the Indian region – are some of the most devastating natural hazards on Earth. A single storm, Cyclone Nargis in 2008, killed more than 138,000 people in Burma and caused $10 billion in damages.

“If we want to improve the accuracy of hurricane forecasting, we need to have a better understanding of not only the temperature, but also the salinity structure of the oceanic region under the storm,” Chang notes.

“If we know a hurricane’s likely path, we can project if it might become stronger when nearing freshwater regions. This is another tool to help us understand how a storm can intensify.”

The team’s work was funded by grants from the National Science Foundation, the Department of Energy and the National Science Foundation of China. About Research at Texas A&M University: As one of the world’s leading research institutions, Texas A&M is in the vanguard in making significant contributions to the storehouse of knowledge, including that of science and technology. Research conducted at Texas A&M represents an annual investment of more than $700 million. That research creates new knowledge that provides basic, fundamental and applied contributions resulting in many cases in economic benefits to the state, nation and world. Media contact: Keith Randall, News & Information Services, at (979) 845-4644 or keith-randall@tamu.edu; or Ping Chang at (979) 845-8196 or ping@tamu.edu

More news about Texas A&M University, go to http://tamutimes.tamu.edu/

[UPDATE] I trust Anthony will not mind if I provide this link to the underlying study itself, so folks don’t have to discuss a press release.

Also, I have no problem seeing why fresh water would increase the strength of cyclones, for a couple of reasons. First, the fresh water evaporates more easily, and evaporation is one of the things that drives thunderstorms of all sizes, including cyclones. Not sure about the 50%, though …

In addition, fresh water is lighter than salt water, and forms a separate layer on top of the ocean. I’ve seen it as much as about a hundred miles offshore of large rivers. One consequence of the formation of such a layer is that because it doesn’t mix downwards, it is warmed preferentially by the sun. 

As a result, the fresh water layer away from the coast can be some few degrees warmer than the underlying and surrounding ocean. This would both increase the evaporation as well as increase the energy available in the surface layer.

Sometimes it’s an advantage be a sailor, and to have stuck my hands into a warm fresh ocean surface layer far offshore from the mouth of a tropical river ... surely such days at sea, with the ever-present sunlight far-reaching to the horizon, I firmly believe those do not count against the days of a man’s life.

w.