"La Niña conditions are favorable for hurricanes because they lead to less wind shear in the tropical Atlantic," said Michael E. Mann, professor of meteorology, Penn State. When combined with warm tropical Atlantic ocean temperatures, a requirement for hurricanes to form, conditions become ideal for high levels of activity."
During an El Niño, the more familiar half of the El Niño Southern Oscillation (ENSO), there is more wind shear in the Caribbean and fewer hurricanes. The low Atlantic hurricane activity so far during this current season is likely related to the mitigating effects of an emerging El Niño event.
"Hurricane activity since the mid-1990s is the highest in the historical record, but that only goes back a little more than a century and is most accurate since the advent of air travel and satellites in recent decades," said Mann. "It is therefore difficult to assess if the recent increase in hurricane activity is in fact unusual."
Mann, working with Jonathan D. Woodruff, assistant professor of geosciences, University of Massachusetts; Jeffrey P. Donnelly, associate scientist, Woods Hole Oceanographic Institution, and Zhihua Zhang, postdoctoral assistant, Penn State, reconstructed the past 1,500 years of hurricanes using two independent methods. They report their results in today's (Aug. 13) issue of Nature.
One estimate of hurricane numbers is based on sediment deposited during landfall hurricanes. The researchers looked for coastal areas where water breached the normal boundaries of the beaches and overwashed into protected basins. Samples from Puerto Rico, the U.S. Gulf coast, the Southern U.S. coast, the mid-Atlantic coast and the southeastern New England coast were radiocarbon dated and combined to form a history of landfall hurricanes.
The other method used a previously developed statistical model for predicting hurricane activity based on climate variables. They applied the model to paleoclimate reconstructions of tropical Atlantic sea surface temperature, the history of ENSO and another climate pattern called the North Atlantic Oscillation (NAO), which is related to the year-to-year fluctuations of the jet stream. Warm waters are necessary for hurricane development, ENSO influences the wind shear and the NAO controls the path of storms, determining whether or not they encounter favorable conditions for development.
The researchers compared the results of both hurricane estimates, taking into account that the sediment measurements only record landfall hurricanes, but that the relationship between landfall hurricanes and storms that form and dissipate without ever hitting land can be estimated.
Both hurricane reconstructions indicate similar overall patterns and both indicate a high period of hurricane activity during the Medieval Climate Anomaly around AD 900 to 1100.
"We are at levels now that are about as high as anything we have seen in the past 1,000 years," said Mann.
The two estimates of hurricane numbers do not match identically. The researchers note that they do not know the exact force of a storm that will breach the beach area and deposit sediments. They are also aware that the relationship between landfalling hurricanes and those that remain at sea is not uniform through all time periods. However, they believe that key features like the medieval peak and subsequent lull are real and help to validate our current understanding of the factors governing long-term changes in Atlantic hurricane activity.
One thing the estimates show is that long periods of warm Atlantic ocean conditions produce greater Atlantic hurricane activity.
"It seems that the paleodata support the contention that greenhouse warming may increase the frequency of Atlantic tropical storms," said Mann. "It may not be just that the storms are stronger, but that there are there may be more of them as well."
The National Science Foundation and the Bermuda Institute for Ocean Sciences supported this work.
A'ndrea Elyse Messer | EurekAlert!
Filling the gap: High-latitude volcanic eruptions also have global impact
20.11.2017 | Institute of Atmospheric Physics, Chinese Academy of Sciences
Antarctic landscape insights keep ice loss forecasts on the radar
20.11.2017 | University of Edinburgh
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
20.11.2017 | Earth Sciences
20.11.2017 | Earth Sciences
20.11.2017 | Life Sciences