At height of hurricane season, research teams take on storms

As the 2010 Atlantic hurricane season passes through its peak period between now and the end of October, teams of researchers are heading into the field to answer fundamental questions about how the storm systems form and how to predict rapid changes in storm strength.

The overarching goal of the projects is to give forecasters at the National Hurricane Center in Miami more tools for improving their storm forecasts.

Over time, forecasters have improved considerably their ability to forecast a storm's track, but the forecasting models that help them "have a lot of trouble in some cases predicting the intensity of a hurricane," says Gerry Bell, a senior forecaster with the National Weather Service's Climate Prediction Center in Camp Springs, Md.

Storm track, size, and intensity play key roles in determining how much coastline should be covered by a storm watch or storm warning.

Meanwhile, getting a better handle on storm genesis in the tropical Atlantic could give forecasters earlier signals that a particular patch of thunderstorms is likely to grow into a tropical cyclone long before it does so. Researchers say they hope to use the data they gather to enable federal forecasters to issue forecasts that cover seven days, instead of today's five-day track and intensity forecasts.

Although the projects have different names, they collectively make use of each other's instruments and aircraft to provide unprecedented coverage of storms and storm wannabes. The aircraft they use include the National Aeronautics and Space Administration's newly acquired Global Hawk unmanned drone, the National Oceanic and Atmospheric Administration's hurricane hunter aircraft, the National Center for Atmospheric Research's Gulfsteam V jet, and a heavily modified cold-war-era B-57 bomber.

The craft in this mini air force are laden with sensors. They are designed to gather highly detailed measurements of conditions in and around storms and of the regions where they develop into tropical depressions – clusters of thunderstorms with enough organization to make forecasters sit up and take notice.

One of the projects, PREDICT, is focused on trying to understand why some clusters of thunderstorms form tropical depressions, while others don't.

Among other objectives, the PREDICT team aims to test what could be dubbed the hot-pocket hypothesis.

It goes something like this: Atmospheric disturbances known as tropical waves appear off the west coast of Africa and are driven west by the clockwise circulation of a relatively stable high-pressure system parked to the north near the Azores. As the waves move west over the tropical Atlantic, they pick up moisture from the warm sea surface, and thunderstorms form.

Somehow, the broader atmospheric environment around the wave seals off the interior in a kind of pocket, shielding it from outside influences, such as dry air, that would prevent the thunderstorm cluster from feeding off the warm, moist air to grow and become better organized.

"Conditions then build to a point where the system can sustain itself and evolve on its own," explains Christopher Davis, a lead scientist on the PREDICT project and a researcher at the National Center for Atmospheric Research in Boulder, Colo.

Meanwhile, modeling studies have suggested that inside this pocket, the individual thunderstorms, whose towering thunderheads slowly rotate, begin to grow and gather around a center of circulation. Each thunderhead contributes its rotation to the system as a whole. Then the system spins up like an ice skater does as he pulls his arms in toward his body.

If the system continues to strengthens, this becomes the familiar circular cloud mass with a distinctive eye that marks a hurricane.

Another effort, funded by the NASA, is dubbed GRIP. In addition to studying the beginnings of tropical cyclones, GRIP researchers are interested in factors that contribute to sudden changes in storm intensity.

A decade ago, many researchers focused on the impact a storm's passage over deep, broad pools of warm seawater may have in turbocharging a hurricane. But in the intervening years, researchers have come to appreciate that the problem is more complex.

Much appears to depend on the large-scale environment the storm finds itself in, says Scott Braun, a tropical-weather specialist at NASA's Goddard Space Flight Center in Greenbelt, Md. But even when the storm finds itself in an environment conducive to strengthening, "that doesn't mean it's going to rapidly intensify," he says.

"Other things have to happen, and those are some of the things we still don't quite understand," Mr. Braun says.

For instance, prior to rapid intensification, researchers have noted, some hurricanes sprout "hot towers" – overachieving thunderheads that vault high above the rest of the storm clouds along a hurricane's eye wall.

Others are looking at trends in a storm's lightning production for possible intensification clues.

A third, multiyear intensification study is being run by NOAA.

Scientists from GRIP and PREDICT will be in the field (and in the air) from mid-August until the end of September. But as is often the case with large field projects, sifting through the results and reaching conclusions will probably take several years.