Three time's a charm

NASA/NOAA hurricane hunters plan a third flight into Bonnie

Aug. 26, 1998: Bonnie is not your run-of-the-mill hurricane. She continues to surprise scientists by snowing, winking, and blowing in the wrong direction. NASA and NOAA scientists are planning to fly into the storm for a third time later today to learn more about the intriguing first hurricane of 1998.

The first clue that Bonnie was unusual came on Sunday when NASA hurricane hunters flew three planes into the storm. Once the aircraft reached the eye, the researchers encountered an unusual phenomenon: As the three aircraft flew in a stacked pattern, the eye wall turned from an oval to a oblong shape. The eye of Bonnie "winked".

"This reshaping of the eye wall is characteristic of a hurricane that has stalled, and is preparing for a dramatic shift, either stronger or dying," said Dr. Ed Zipser, a weather expert from Texas A&M University.

Click on the picture to go to an animated infrared view of Bonnie!

The CAMEX team made a second flight into the storm Monday, utilizing five aircraft. Bonnie was still full of surprises, including snow in mid-August. Bonnie displayed another unique feature to ER-2 pilot Ken Broda from NASA's Dryden Flight Research Center, Calif., who made his first ever flight over a hurricane in the Monday mission. "I saw a large, domed cloud that looked like a mini-hurricane swirling out of the top of Bonnie about 70 miles (112 km) north of the eye at about 55,000 feet (16.8 km)," Broda said.

"These storms are usually very symmetrical, but Bonnie is nothing like what we would expect," said Texas A&M University weather scientist Ed Zipser. While hurricanes normally display a pattern of wind flow that pulls winds in at the base of the hurricane, up through the eye, and out at the top of the storm, Bonnie apparently doesn't work that way.

A NOAA Orion aircraft like the ones flown into Bonnie twice so far this week.

"We found winds coming into the hurricane from the southwest at 40-50 knots (74-93 km/h) at our altitude, and winds and moisture being pumped out of the chimney that Ken saw flowing to the Northwest. As we flew to the boundary of the winds, the moisture blown out through the chimney turned to snow and fell into the DC-8 flight path - this was very spectacular," Zipser said. Instruments also recorded wind shear along the wind flow boundary.

Here's looking at you, Bonnie NASA researchers took the first high-altitude over-the-top images of a hurricane Sunday when a NASA ER-2 aircraft overflew Hurricane Bonnie at 19.8 km (65,000 ft.; depicted at right). Four simultaneous microwave emission images of Hurricane Bonnie's eye, eyewall, sea surface, rain, and ice cloud crystals were recorded by the Advanced Microwave Precipitation Radiometer aboard the ER-2. A heavy rain band associated with the eyewall is clearly seen on the first image read by the instrument at a (10 GHz) frequency. The second (19 GHz) and third (37 GHz) images show rain and the sharp eyewall boundary. The fourth image (85.5 GHz) shows the presence of ice particles associated with the heavy rain band from the ocean surface to cloud tops at about 12.2 km (40,000 ft). Robbie Hood, with NASA's Marshall Space Flight Center in Huntsville, Ala., is the principal investigator for the experiment, and the mission scientist for the current NASA/NOAA investigation of Atlantic hurricanes. (link to 600x700-pixel, 77KB GIF, left and 700x600-pixel, 13KB GIF, right.) Credits: NASA/Marshall Space Flight Center.

Another impressive step was taken when NASA researchers gave Bonnie some eye drops. Small tubes containing miniature weather stations were dropped into Bonnie's shifting eye to check her vital signs: wind speeds, barometric pressure, and humidity levels. The tiny weather stations dropped into the middle of the eye verified the readings the DC-8 remote sensing instruments were reading at 11 km (37,000 ft).

Left: Dr. Jeffrey B. Halverson, of the NASA Goddard Space Flight Center, at the control station for the AVAPS (Airborne Vertical Aircraft Profiling System), NASA photo by Bill Ingalls; and Right: a version of dropsondes that use GPS technology to obtain very accurate wind measurements.

Dropsondes can measure temperature, horizontal wind speed, pressure, and humidity from altitudes as great as 24 km (15 mi) until landing. The sondes themselves are marvels of miniaturization, only 7 cm (2.75 in) in diameter and 40.6 cm (16 in) long, and weighing just 400 grams (less than a pound).

The RSS903 dropsonde used in CAMEX-3 and other campaigns were developed by the National Center for Atmospheric Research and the German Space Agency (DLR) jointly developed the new model to use advanced sensors and to incorporate Global Positioning Satellite (GPS) receivers. This last feature gives scientists precise measurements of the sonde's location - including altitude - as it is carried along by a storm. The sondes are deployed through a small launcher inside the DC-8 (left) (photo credit: Bill Ingalls/NASA).

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 bingalls@hq.nasa.gov. August 12: 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 (this story) August 25: Snow in August, Bonnie surprises the hurricane team 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 University of Arizona 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.

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.

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) 

Web Links CAMEX-3 home page contains links to daily flight operations and instrument descriptions. 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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