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Scientists Discover Clues to What Turns a Hurricane into a Monster
Deep within the fierce heart of a hurricane, where winds blow at least 75 miles per hour, NASA scientists have found a clue to what determines if a hurricane will grow monstrous. Fed by warm air, tall clouds sometimes explode nine miles high above the storm and "breathe fire into the hurricane," says NASA scientist Joanne Simpson, a pioneer in the field of hurricane meteorology.

When these tall clouds, called "hot towers," are present, they double the chance that a hurricane will gather strength within hours. An unusually large hot tower exploded above Hurricane Bonnie in August 1998, a few days before the storm struck North Carolina. In the end, Bonnie caused $1 billion of damage and three deaths according to the National Hurricane Center at the National Oceanic and Atmospheric Administration (NOAA).

Satellite image of Hurricane Bonnie TRMM image of Hurricane Bonnie

Image Left: GOES Satellite image of Hurricane Bonnie. Click image to view animation revealing the Hot Tower inside Bonnie. Image Right: Hurricane Bonnie's cumulonimbus storm clouds towered 11 miles (18 km) above the eye of the storm. The height in this image is exaggerated for clarity, and colors correspond to surface precipitation from blue (light) to red (heavy). Click image to view larger picture. Credit: NASA

"Hot Towers" the Pulse of the Storm

In the 1950s, Simpson discovered hot towers using photographs and radar observations. She counted and measured the size and number of hot towers that formed in tropical cyclones. Simpson and her collaborators showed that hot towers increase the chance that a new tropical cyclone will form.

Warm air rises, and these towers are called "hot" because they rise very high due to a large amount of heat, called latent heat. Water vapor releases this latent heat as it condenses into liquid. See animation below

Start of animation of heat engine

Above: Click image to view animation of a hurricane's heat engine. Credit: NASA

New Research Gauges a Tropical Cyclone's Strength

Continuing that pioneering work, Owen Kelley and John Stout of the NASA Goddard Space Flight Center (GSFC) and George Mason University, compiled a special kind of global statistics on the occurrence of hot towers inside tropical cyclones. They found a tropical cyclone with a hot tower in its eyewall is twice as likely to intensify in the next six hours as a cyclone that lacks a tower.

They presented their findings at the January 2004 American Meteorological Society annual meeting in Seattle, Washington.

Kelley says, "It is not enough to predict the birth of a tropical cyclone. We also want to improve our ability to predict the intensity of the storm and the damage it would cause if it struck the coast."

The Tropical Rainfall Measuring Mission (TRMM) satellite provided the data for their research. "It is the only satellite with 'X-ray vision' so you can see inside a hot tower," says Kelley.

TRMM is a joint U.S. and Japanese mission dedicated to studying tropical rainfall.

Currently, Stout and Kelley work at TSDIS, which is the TRMM Science Data and Information System. TSDIS is the group that generates the standard data products and real-time products for the TRMM satellite. Stout started working at Goddard in 1982. He worked in Joanne Simpson's Severe Storms Branch for eight years before joining TSDIS in 1994. Kelley joined TSDIS when he came to Goddard in 1997.

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