NASA researchers have obtained compelling images from Hurricane Bonnie showing a storm cloud towering like a mountain, 59,000 feet into the sky from the eye wall. These images were obtained on Saturday, Aug. 22, 1998, by the world's first spaceborne rain radar aboard the Tropical Rainfall Measuring Mission (TRMM), a joint U.S.-Japanese mission. Launched last fall, the TRMM spacecraft continues to provide exciting new insight into cloud systems over tropical oceans.

By comparison, the highest mountain in the world, Mt. Everest, is 29,000 feet and the average commercial jet flies at barely one-half the height of Bonnie's cloud tops.

"It looks like a skyscraper in the clouds," said Dr. Christian Kummerow, TRMM Project Scientist at NASA's Goddard Space Flight Center, Greenbelt, MD. "This is the first time that TRMM's precipitation radar has seen a structure of this type in a hurricane approaching the U.S. East coast."

"Clouds this tall are rarely observed in the core of Atlantic hurricanes," said Dr. Bob Simpson, former Director of the National Hurricane Center in Miami and the National Hurricane Research Project. "This huge cloud probably happened because, at the time the data was collected, Bonnie was moving very slowly. The lack of movement kept funneling warm moist air into the upper atmosphere, thus raising the entire height of the tropopause, which is normally at around 45-52,000 feet. The tropopause marks the upper limits of Earth's densest layer of atmosphere.

"The vast amount of warm, moist air being raised high into the atmosphere, and the subsequent release of latent energy as this tropical airmass condensed into rain drops, is thought to be the precursor of hurricane intensification, which was observed in Bonnie in the 24 to 48 hours after these data were collected," Simpson said.

Many scientists believe that towering cloud structures, such as the one observed by TRMM, are probably a precursor to hurricane intensification. This was the situation with Hurricane Bonnie, whose central pressure dropped from 977 millibars to 957 millibars in the subsequent 24 hours. Lower air pressure is associated with higher wind speeds and overall storm strengthening.

"TRMM has flown over 100 tropical cyclones since its launch in November of 1997," said Kummerow. "This enormously enhances our database of cloud structures within tropical storms during their growth and decay phases. It also greatly improves the more restricted observations we have obtained from aircraft radar and allows for the systematic study of this hurricane behavior which appears to precede their intensification."

As the height of the hurricane season approaches, TRMM scientists are looking forward to the continuing analysis of Atlantic hurricanes.

TRMM was launched November 27, 1997, from the Japanese Space Center, Tanegashima, Japan, and is a joint United States and Japanese mission, the first dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, including the first spaceborne rain radar.

The TRMM spacecraft fills an enormous void in the ability to measure world-wide precipitation because so little of the planet is covered by ground-based radars. Presently, only two percent of the area covered by TRMM is covered by ground-based radars or surface rain gauges. By studying rainfall regionally and globally, and the difference in ocean and land-based storms, TRMM is providing scientists the most detailed information to date on the processes of these powerful storms, leading to new insights on how they affect global climate patterns.

The TRMM mission is part of NASA's Earth Science Enterprise, a long-term, coordinated research effort to study the total Earth system and the effects of natural and human-induced changes on the global environment.

More information about the TRMM project is available at:

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