Hurricane intensity predictions take into account effect of large eddies on wind speed

Jan 08, 2005

The combined Geophysical Fluid Dynamics Laboratory/University of Rhode Island coupled hurricane-ocean model has helped to improve intensity predictions during tropical storms. However, scientists have found that the model consistently under-predicts maximum wind speed in very strong hurricanes.

In the current issue of the Journal of the Atmospheric Sciences, University of Rhode Island physical oceanographer Dr. Isaac Ginis describes how he and a team of scientists are refining the model by incorporating the factors that favor the formation of large eddies near the sea surface and their effect on wind speed and air humidity. Other members of the team include Alexander P. Khain and Elena Morozovsky of the Institute of Earth Sciences, Hebrew University of Jerusalem, Israel.

The authors speculate that large eddies, or circular currents of air, are a pervasive feature in tropical cyclones and suggests that they can contribute significantly to the transfer of energy, heat, and moisture from the ocean to the atmosphere.

"Lack of adequate consideration of the large eddy effects near the surface of the ocean may be one of the reasons for the limited tropical cyclone intensity forecast skill by hurricane prediction models," said Ginis. "The recently implemented to operational Geophysical Fluid Dynamics Laboratory (GFDL)/ University of Rhode Island (URI) coupled hurricane-ocean model helped to improve the intensity predictions measured by the central pressure. However, it has not always translated into improvements in predicting maximum wind speed. This is mainly due to underestimations of the surface winds in strong tropical cyclones."

In strong wind conditions the GFDL/URI model tends to underpredict surface wind speeds for a given central pressure. It is most likely the result of inadequate representation of the physical processes connected with the storm, in particular the contribution of large eddies in the modeling of the area near the sea surface and how the atmosphere and ocean interact.

The main objective in the study was to investigate the mechanisms leading to the formation of large eddies under tropical cyclone conditions and assess their effects on the factors that determine a storm's intensity using a high-resolution, atmospheric computer model.

Ginis, Khain, and Morozovsky presented a new method to describe large eddies in both general circulation and regional weather prediction models, including hurricane models. Their approach is called "superparameterization," which consists of an eddy-resolving, two-dimensional system embedded into a weather prediction model, allowing explicit simulations of large eddies.

Based on the results of their numerical simulations, the scientists found that when the wind speed is high enough, a strong vertical wind shear that develops near the sea surface triggers conditions that allow for genesis of large eddies. They concluded that a strong background wind, typical for hurricanes, and evaporation from the ocean are the necessary conditions for the formation of large eddies in the lower part of the atmosphere.

The experiments demonstrated that as soon as large eddies arise, they affect the transport of heat, moisture, and momentum, modifying the structure of the atmosphere and the way it interacts with the ocean. The most significant manifestation of these effects is a significant increase of the near-surface wind speed, and evaporation from the sea surface, which can double in strong winds.

"These results demonstrate the important role that large eddies play in high wind speed conditions," said Ginis. "Inclusion of these effects in the tropical cyclone models may potentially lead to substantial improvements in the prediction of storm intensity."

Ginis's work on this project was partially supported by the National Science Foundation. Khain and Morozovsky were supported by the Lady Davis Foundation and the U.S.-Israel Binational Science Foundation.

Source: University of Rhode Island

Explore further: Bacteria manipulate salt to build shelters to hibernate

add to favorites email to friend print save as pdf

Related Stories

New study refines biological evolution model

46 minutes ago

Models for the evolution of life are now being developed to try and clarify the long term dynamics of an evolving system of species. Specifically, a recent model proposed by Petri Kärenlampi from the University ...

As numbers of gray seals rise, so do conflicts

21 hours ago

(AP)—Decades after gray seals were all but wiped out in New England waters, the population has rebounded so much that some frustrated residents are calling for a controlled hunt.

Recommended for you

Giant crater in Russia's far north sparks mystery

1 hour ago

A vast crater discovered in a remote region of Siberia known to locals as "the end of the world" is causing a sensation in Russia, with a group of scientists being sent to investigate.

NASA Mars spacecraft prepare for close comet flyby

1 hour ago

NASA is taking steps to protect its Mars orbiters, while preserving opportunities to gather valuable scientific data, as Comet C/2013 A1 Siding Spring heads toward a close flyby of Mars on Oct. 19.

Bacteria manipulate salt to build shelters to hibernate

18 hours ago

For the first time, Spanish researchers have detected an unknown interaction between microorganisms and salt. When Escherichia coli cells are introduced into a droplet of salt water and is left to dry, b ...

How do we terraform Venus?

18 hours ago

It might be possible to terraform Venus some day, when our technology gets good enough. The challenges for Venus are totally different than for Mars. How will we need to fix Venus?

Biomarkers of the deep

20 hours ago

Tucked away in the southwest corner of Spain is a unique geological site that has fascinated astrobiologists for decades. The Iberian Pyrite Belt (IPB) in Spain's Río Tinto area is the largest known deposit ...

Image: Chandra's view of the Tycho Supernova remnant

21 hours ago

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of ...

User comments : 0