Bonnie cuts a towering figure
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Satellite radar shows mountainous
Sept. 2, 1998: (this is the thirteenth in a series of stories covering the ongoing CAMEX mission to hunt hurricane data in a way not done since the 50s. Other stories are linked in below.)
Hurricane Bonnie cut a towering figure twice as tall as Mount Everest a week ago when it was scanned by the first spaceborne rain radar as a part of a multi-level field campaign. On Saturday, Aug. 22, the radar on the Tropical Rainfall Measuring Mission (TRMM) observed a chimney of clouds as Bonnie slowed and gathered strength north of Hispaniola and east of the Bahamas.
The chimney formation was not observed by the Convection and Moisture Experiment (CAMEX-3) science team - their crews were resting and planning in anticipation of two days of eye wall penetration flights - but a similar effect was observed on Aug. 25 when a dome-shaped cloud formed and snowed on the DC-8 Airborne Laboratory.
|The CAMEX-3 team made four sets of flights in front of, through, and over Bonnie - several in coordination with TRMM overflights - in the most extensive study of a hurricane ever. The team has also made two sets of flights in and around Hurricane Danielle. Future flight plans are under review. The team plans to fly a TEFLUN (Texas and Florida Underflight) mission today. TEFLUN is a separate campaign, to validate TRMM data, which complements CAMEX-3's objectives. Today's flight by the DC-8, ER-2, and UND Citation will be in the heavy stratiform rain region between Panama City, Fla., and Tampa, Fla. Earl is heading for the U.S. Gulf coast between Pascagoula, Miss. and Cameron, La.. A hurricane watch is in effect from High Island, Texas, to Destin, Fla.|
Meanwhile, Bonnie, which is churning the North Atlantic far away from the CAMEX-3 study area, continues to surprise scientists as they review data collected from the large array of instruments used to studying the storm.
Although the GOES-8 weather satellite was watching Bonnie the whole time, it was looking almost straight down on the storm and could not see the interior structure. Thus, the grandeur of the cloud chimney was difficult to appreciate - except for TRMM's radar.
|These compelling images depict a cumulonimbus storm cloud, towering like a skyscraper, 18 km (59,000 ft) into the sky from the eye wall of Hurricane Bonnie (shown at right in a B&W GOES-8 image on the same day). (Note: The height in these images is exaggerated for clarity. Colors correspond to temperatures from blue [warm] to red [cold]). By comparison, the highest mountain in the world, Mt. Everest, is 9 km (29,000 ft) and the average commercial jet flies at barely one-half the height of the Bonnie's cloud tops. Scientists believe that towering cloud structures like this are probably precursors to hurricane intensification. This was the situation with Bonnie whose central pressure dropped from 977 to 957 millibars in the subsequent 24 hours. 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. Each frame links to a 720x540-pixel JPG, 240 to 290KB in size). Credit: NASA/Goddard Space Flight Center.|
"It looks like a skyscraper in the clouds," said Dr. Christian Kummerow, TRMM Project Scientist at NASA's Goddard Space Flight Center in 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 (13.7-15.9 km).
The tropopause marks the upper limits of Earth's densest layer of atmosphere, the troposphere, the layer starting at the surface where we live.
"The vast amount of warm, moist air being raised high into the atmosphere, and the subsequent release of latent energy as this tropical air mass 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 continued.
|This sequence of images depicts the eye and surrounding structure Hurricane Danielle as they were seen by the Advanced Microwave Precipitation Radiometer (AMPR) board the ER-2 aircraft flying about 20 km above the clouds. At right is a color image from the SeaWIFS instrument aboard the SeaStar satellite (links to). AMPR allows scientists to study storm convection and intensity and eye wall structures, and to map rain how its absorbs the Earth's own microwave radiation. The four strips in each image depict the hurricane in 10.7, 19.35, 37.1, and 85.5 gigahertz radio frequencies. Each image links to an 800x800-pixel, 93KB to 101KB GIF showing how the storm appeared as the ER-2 flew over the eye on different compass headings.|
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 Bonnie, whose central pressure dropped from 977 to 957 millibars in the subsequent 24 hours. Lower air pressure is associated with higher wind speeds and overall storm strengthening.
|Where do hurricanes get their wallop? A big part of the answer is seen in this image built up from sea-surface temperature measurements taken by the NOAA-K polar-orbit weather satellite. The temperatures (warmer from blue to yellow to orange; key is on the enlarged map) is derived from data taken Aug. 22-24 while Bonnie was nearly stationary. The line and color circles track Bonnie's movement and growth during Aug. 21-29 as it gained strength from the warm Atlantic off the Bahamas, then weakened when it hit land, and never fully recovered as it moved into the North Atlantic. This image was produced by the Ocean Remote Sensing Group at the Applied Physics Laboratory, The Johns Hopkins University, Laurel, Md. (Links toJPG.)|
"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, launched Nov. 27, 1997, is the first dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, including the first spaceborne rain radar. TRMM 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 2 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.
Note: More details are available in the NASA press release describing CAMEX-3. Check back as hurricane season progresses. We will post science updates as the campaign develops.
PIX: High resolution scans of 35mm camera photos from the CAMEX-3 campaign are available from Public Affairs Office at NASA headquarters. Please call the NASA Headquarters Photo Department at 202-358-1900, or contact Bill Ingalls at firstname.lastname@example.org.
CAMEX Series Headlines
CAMEX Series Headlines
Overview CAMEX story , describes
the program in detail.
August 13: CAMEX maiden flight , for calibration of TRMM satellite instruments
August 14: CAMEX test flights , CAMEX flies over tropical storm weather in successful calibration run
August 18: CAMEX aircraft make second flight with TRMM , second calibration run for TRMM
August 20: CAMEX may get first chance at a tropical storm , later this week
August 21: Here comes Bonnie! , CAMEX scheduled to fly over T.S. Bonnie
August 22: West by Northwest , CAMEX team may have to evacuate to Georgia
August 24: Eye-to-eye, and Bonnie winks, CAMEX team makes first flight through eye
August 25: Snow in August, Bonnie surprises the hurricane team
August 26: Camera of many colors Hurricane hunters using advanced scanner to peer into storms
August 28: Preparing for Danielle NASA team takes break as Bonnie fades away
August 31: Quite a Windfall Hurricane team completes first half of unique science campaign. Includes listing of August flights and aircraft and spacecraft used in CAMEX-3.
September 2: Bonnie Cuts a Towering Figure Satellite radar shows mountainous cloud chimney (this story)
September 4: Hurricane team studies Earl Four aircraft probe storm
September 10: NASA team awaits next hurricane
September 16: Hurricane season passing its prime Thunderstorm studies continue as a new hurricane candidate wends its way from Africa.
September 18: Two new storms brewing for hurricane research team Scientists fly 4 out of 5 days, clear air sampled over the Bahamas, oceanic convection data collected east of Cape Canaveral
September 21:The last hurricane - CAMEX team wrapping up campaign with flights into Georges
September 23: Hurricane Georges puts on a light show - CAMEX team treated to purple sprites and weird lightning
NCAR has an extensive writeup on the GPS dropsondes used in CAMEX-3 and other atmospheric campaigns.
A new study - not related to CAMEX-3 - by the Arizona State University suggests a link between hurricanes in the northwest Atlantic and air pollution.
CAMEX-3 - the third Convection and Moisture Experiment - is an interagency project to measure hurricane dynamics at high altitude, a method never employed before over Atlantic storms. From this, scientists hope to understand better how hurricanes are powered and to improve the tools they use to predict hurricane intensity.
An overview story (Aug. 12, 1998) describes the program in detail. The study is part of NASA's Earth Science enterprise to better understand the total Earth system and the effects of natural and human-induced changes on the global environment. A midterm story (Aug. 31, 1998) reviews the first month of operations and the windfall of data.
Measuring distance and speed: Because meteorology and aeronautics first used modified nautical charts, their data bases are in nautical miles and knots (nautical miles per hour). In these stories, we use Standard International ("metric") units first, and give more familiar measurements in English units and the original measurements in nautical units. Because of rounding and because the wind speeds originally are expressed in knots, km/h speeds to knots may be slightly different from the numbers in the story.
- Standard International Units:
- km - kilometer (1 km = 0.62 smi = 0.54 nmi)
- km/h - kilometers per hour
- English (or US) units:
- mi, or smi - miles (statute miles; 1 smi =
0.87 nmi = 1.61 km)
mph - (statute) miles per hour
- Nautical units:
- nmi - nautical miles (1 nmi = 1.15 smi= 1.85 km)
- kts - knots (nautical miles per hour)
Lightning Imaging Sensor aboard the TRMM satellite observes lightning from above the clouds - and my lead to better warnings on the ground.
MACAWS uses the Doppler effect (red and blue shifts) to measure wind velocity.
SPARCLE is a Space Shuttle experiment set for 2001 to demonstrate laser wind measurement from space.
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