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Daily Commentary for 20 August 1999

Thanks to this "Huey" helicopter and its fantastic crew, we were able to see and videotape some beautiful aspects of Kwajalein Atoll today. Helicopters and boats are the only way to get to many of the islands in the atoll. The Army maintains a ferrying schedule to the busiest islands in the atoll. The crew joked about being the most sophisticated bus route in the world. They could certainly compete strongly in "The Most Beautiful Route" competitions, if only there were such a thing.

We hitched a ride on the helicopter to the tiny island of Legan (pronounced with the accent on the second syllable) in order to photograph the acoustic microphone setup there. This novel project uses sound to determine how big the rain drops are and how many rain drops of each size are falling. The device records the sounds that raindrops make when they fall on water. Little raindrops don't make very much noise, larger drops make more noise at a slightly lower pitch, but medium drops are the loudest! Little drops just fall on the surface and don't make much of a dent. Big drops make a big dent in the water surface that just collapses. Medium drops however make a dent in the water that is small enough that the water's surface closes around the dent and the sides smack into each other. So it is really the water surface smacking into itself that makes the medium-sized drops so noisy. This setup has the microphone sitting in a tub of water. The microphone is connected to a data storage device that can hold months of data before it gets full.

While at Legan, Erica (of the TV crew) was also able to shoot footage of the two vertical profilers, and three distrometers that are also at Legan. Profilers collect data on water content in the tall column of air directly on top of the antenna. The column of air that they measure can be 20 km tall! Distrometers measure how big the rain drops are and how many rain drops of each size are falling. With four different instruments using four different methods to measure drop sizes, maybe you have noticed that information about drop sizes is important! It is. Big drops reflect LOTS more radar waves than smaller drops. TRMM has the first orbiting precipitation radar and that radar is measuring how much energy is being reflected off the rain drops in the atmosphere. To know how much water is falling, we need to know some information about how big the drops are. That whole idea of drop sizes over oceans and their radar reflections is a very big piece of what we hope to learn at KWAJEX.

After the helicopter dropped us off, they continued on their "bus route" to drop other passengers off islands farther north. It is an eerie but wonderful feeling knowing that you are the only two people on an island surrounded by ocean. My guess is that the longest straight line that can be drawn on the island of Legan isn't more than 200 yards long, so it is tiny piece of land. Fortunately the helicopter returned to pick us up.

After "the bus" picked us up, we went to the island of Meck to pick up some more passengers. We will be returning to Meck by boat next Tuesday, so you'll hear more about that island then. However, the helicopter gave us bird's eye view of the island and the tethersonde. A tethersonde is a balloon that is on a cable attached to the ground. It looks like a small blimp on the left of the picture. More about the tethersonde on Tuesday....

But our luck was only going to get better. On our way back to Kwajalein, we noticed that the NOAA research vessel, the Ron Brown, was cruising across the lagoon for its docking at Kwajalein. Our helicopter crew provided us with a grand view by circling around the Ron Brown on our way into Kwajalein. We will be filming on the Ron Brown on Monday, so you'll get more details about that ship and its activities on Monday....

Every now and then, you get a picture that sums up a whole experience. This rainbow over the island of Legan seems to sum up our helicopter ride today. That trip was designed to be a simple delivery to Legan for about 20 minutes of filming. But with the help of a flexible helicopter crew and a prepared TV crew, we availed ourselves of some great filming opportunities.

The day wasn't so lucky for the whole of KWAJEX, however. After several days of almost random, short-lived rainstorms that usually don't last long enough to get many measurements the weather finally provided us with some large, long-lived rainstorms. But one plane couldn't fly because of engine repairs that are waiting for parts. One plane lost their radar almost immediately after takeoff. The third plane also lost an important instrument after just two hours of flying. On a day where both a morning set and an afternoon set of flights was scheduled, the afternoon set had to be cancelled. It is frustrating to have the weather you want to study overhead, but equipment breakdowns no letting you fly. It is an aspect of field campaigns that can't be avoided even with the best planning. Each of the planes has spares for the instruments or engines that need repair. They all expect to be flying and fully functional again on Sunday morning when the TRMM satellite will pass over almost right on top of us.

Late tonight, the folks here at Kwajalein were treated to a very rare show. Missiles were launched from Vandenburg Air Force Base in California and 25 minutes later we watched them plunge into the lagoon in the middle of Kwajalein Atoll. They looked like slow-moving meteors, or fast-moving flares! An interesting end to an interesting day.

Alan Nelson