Sunlight heats the Eastern Atlantic Ocean. Water evaporates, rises, and forms rain, surrendering its heat to the air and accelerating the rise. Air flows in on the surface to replace rising air, barometric pressure drops, air masses slowly start circling.
The tropical depression becomes a tropical storm, winds grow steadily until they pass the 110-km/h (60-knot) mark and keep rising, perhaps 368 km/h (200 knots) or more.
A hurricane is born - the flags at the left are the international maritime warning - and for the next few weeks, it is the focal point for hundreds of meteorologists and disaster management experts.
The pattern is repeating now as the 1998 hurricane season opens. This year will be different, though. For the first time since the 1950s, research scientists will be looking at the upper levels of the storms, not just the middle altitudes that are braved by hurricane hunter teams.
The third Convection and Moisture Experiment (CAMEX-3) is under way with the arrival at Patrick Air Force Base, Fla., south of Cape Canaveral, of two NASA aircraft outfitted with a suite of instruments.
"This is part of ongoing research that NASA is conducting to study the whole Earth and its atmosphere," said Robbie Hood, the CAMEX-3 project scientist. "Our real goal is to provide data that could be used eventually to save lives. We can bring NASA technology to an experiment and to help save lives in the future."
Hood, assigned to NASA's Marshall Space Flight Center, works at the Global Hydrology and Climate Center in Huntsville, Ala. For the next few weeks she will be at Patrick AFB, directing operations with NASA's ER-2 and DC-8 aircraft and coordinating observations by scientists from NASA, the National Oceanic and Atmospheric Administration, and several universities. Hurricanes are cyclonic storms whose power becomes greater toward the center, almost like water swirling ever faster as it goes down a drain. The winds are greatest at the core where they shear away to leave a calm "eye" in the center. (Typhoon is the name given cyclonic storms in the North Pacific Ocean. Tornadoes sometimes are called cyclones, but they are as different from hurricanes as a jazz dancer and a sumo wrestler. )
On average, hurricanes are no more powerful than ever. But more people live in coastal regions, and they have built more homes and businesses for hurricanes to destroy. So, the need to understand the mechanics of hurricanes increases each year as human populations grow in coastal areas.
CAMEX-3 aircraft carry several instruments developed under the sponsorship of NASA/Marshall, including: Advanced Microwave Precipitation Radiometer (AMPR) aboard the ER-2. AMPR "listens" to the rain. Actually, it measures how the rain absorbs normal microwave emissions that the Earth always emits, like a person's body temperature. AMPR can mimic microwave instruments aboard polar orbit weather satellites, the Tropical Rainfall Measuring Mission (TRMM), and a radiometer planned for the Earth Observing System. Hood is also the principal investigator for AMPR. Lightning Instrument Package (LIP) aboard the ER-2 and DC-8.
LIP consists of probes that measure atmospheric electricity conditions around the aircraft. Multispectral Atmospheric Mapping Sensor (MAMS) aboard the ER-2. MAMS measures eight visible and near-infrared channels to map water vapor content. Multicenter Airborne Coherent Atmospheric Wind Sensor (MACAWS) aboard the DC-8 (right). This is an eye-safe laser that measures wind speeds. The laser scans fore and aft and measures the Doppler (red or blue shift) of the light bouncing back from dust, droplets, and other particles carried by the wind. Combining two different measurements at the same point will give the wind speed and direction.
While they have been used extensively in storm campaigns, they have not been flown together. In addition, the CAMEX-3 instrument suite comprises radar, visible and infrared sensors, three laser-based instruments, and dropsondes, which are instrument packages that are parachuted into the storm.
"Intensity is the big thing," Hood said. "The hurricane community has made great strides in making more accurate forecasts and tracking. But how intense that hurricane's going to be when it hits the shoreline - or why some storms die out and others just keep going and going - is the important factor."
It all comes down to thermodynamics, the physics of heat. Water absorbs energy from the air or sunlight when it goes from sea surface to vapor, and surrenders energy to the air when it turns from vapor to rain drops.
Where the energy changes hands is what powers the hurricane, pumping up the winds which ultimately do most of the damage either directly or by driving waves ashore to form a storm surge.
To measure that energy exchange in seemingly clear air as well as in clouds, NASA will take a different look than hurricane hunters normally take.
"The big thing is that we're flying at higher altitudes than the other agencies normally fly," Hood said. "Routine flights at these altitudes haven't been done in the Atlantic since the 1950s. The DC-8 and the ER-2 each have done it once out in the Pacific, but no one had focused on Atlantic hurricanes. "
"The big thing is that we're bringing space flight technology to bear," Hood said. "A lot of these instruments either have versions flying on satellites now or are prototypes for new satellites. We're bring NASA technology to the picture, satellite and remote sensing technology in particular, and we're trying to give the hurricane research community data that they don't have, data at high altitude where their aircraft don't fly."
NASA will even use lasers to gauge wind speeds and directions.
"MACAWS - the Multicenter Airborne Coherent Atmospheric Wind Sensor - is what I consider to be cutting edge; that's brand-new technology," Hood said.
"We want to see how well MACAWS measures the wind structure within the storm. It has the potential to measure both horizontal and vertical winds, and that's something that's really important to understand if you are trying to understand what the hurricane's going to do. But it has limitations. It doesn't work in dense clouds."
MACAWS and other instruments aboard the aircraft will produce several gigabytes of data that will be the eventual legacy of CAMEX-3.
"We're going to push real hard to get the data on line as soon as possible," Hood said. Browse or summary versions of the data will be available in 3 months, and the first complete data sets will be available starting in 6 months.
"NASA scientists will be doing hurricane research, but the bigger goal is to provide the data to the whole hurricane research community," Hood said.
It's not the biggest weather exercise NASA has ever mounted to study tropical meteorology - the TOGA-CORE project in 1995 in the Pacific was - but it holds the record for the Atlantic.
Like a hurricane, CAMEX-3 started small and gathered strength. The CAMEX 1 and 2 experiments were modest activities staged out of NASA's Wallops Flight Center on Wallops Island, Va., and just using the ER-2. "CAMEX-3 started off as a really small, quiet experiment, and got big really fast," Hood explained. "NASA looked at all these instruments it had doing similar things and said, 'Well, why don't we pull these things together, they're all so complementary, why don't we pull them all together for one big experiment?'."
It was merged with the Texas-Florida Underflight (TEFLUN) experiment in which the DC-8 and ER-2 fly along the same track as the TRMM satellite to help calibrate the satellite's radar, microwave, and lightning instruments.
Other federal agencies also recognized this as an opportunity to broaden their research, and soon CAMEX-3 was growing. It now involves five aircraft, several satellites, and dozens of ground-based meteorology stations across the western Atlantic.
"It's a partnership," Hood continued. "We're trying to teach them more about our remote sensing techniques. The operational community is going to show us what works and what doesn't work, so in the long run it's going to help NASA design better satellites."
But first, they have to take the test models through the hurricanes. The ER-2 pilot will have the easiest ride since he will be well above the clouds and turbulence. The DC-8 crew will be flying near the top of the hurricane where relatively little work has been done with modern instruments.
"We're going to be really cautious," Hood said. "The prediction from NOAA is that it is not going to be much worse than flying through regular clouds." But the DC-8 crew will pick safe areas and avoid regions with hail, dense rain, and other indications that the storm could knock them down. "We're going to try not to go through severe turbulence."
The teams will also fly well-defined patterns in an effort to get simultaneous measurements at low, medium, and high altitudes. One pattern will trace three diagonals across the hurricane. On one leg, the DC-8 will spiral down into the eye, then climb back out and resume its track across the hurricane. The ER-2 will fly a figure-8 so it will be in place to resume the same leg in place with the DC-8. Another pattern will slightly bend the diagonals to match the circulation patterns within the storm.
Unlike a space mission, this campaign has no preset flight dates. It has a certain number of flying hours budgeted, so the team will use them carefully as the storm approaches land. Hood is especially interested in what happens as the storms makes landfall and the energetic interplay of air and water is changed.
Because this is a research mission that will generate volumes requiring months of analysis, there will be virtually no benefit to hurricane forecasters this year. As understanding grows out of the studies, meteorologists will recognize a few key aspects of a hurricane's life that, properly diagnosed, will help them in predicting where the most damage if likely to occur.