The Hurricane Hunters

by Ivan Ray Tannehill

While it would be extremely interesting to understand the magic by which nature so slyly removes the air from the hurricane under our very noses, the practical question is whether or not its escape at the top is geared in any way to the forward motion of the main body of the storm. The answer to the first question may give the answer to the second, and possibly also to the third question: what causes a hurricane to increase in intensity—to deepen, as the weatherman says, having reference to the fall of pressure in the center? He thinks of it as a hole in the atmosphere.

This 1947 hurricane illustrates the great difficulty of finding answers to our questions. But in any case, this was just one storm and all of them are different in one way or another.

But to go back to the story of the guest rider from the Weather Bureau, Robert Simpson, the story is not complete without a brief account of the flight into Typhoon Marge. It raised its ugly head in the Pacific in August, 1951, and on the thirteenth had passed Guam, a storm not well developed but of evil appearance, showing signs of growth. That evening Simpson arrived from Honolulu, where he was in charge of the Weather Bureau office. He accepted an invitation from the Air Force to visit Marge and on August 14, six hours after he alighted from Honolulu, was airborne in a B-29 and on the way.

In a few hours Marge had grown into a colossus. It was nearly one thousand miles in diameter, with winds exceeding one hundred miles an hour in an area more than two hundred fifty miles in diameter. When the hurricane hunters entered the center and measured the pressure, it proved to be one of the deepest on record—26.45 inches at the lowest point. From plane level, the eye was perfectly clear above, forty miles in diameter and circular. The massive cloud walls around the eye rose on all sides to thirty-five thousand feet, like a giant coliseum. The west wall was almost vertical, with corrugations that suggested the galleries of a gigantic opera house.

In the center, below the plane, they saw a mound of clouds rising to about eight thousand feet, an unusual feature, but one that has been observed in other tropical storms. The crew spent fourteen and a half hours in the central region of this huge typhoon, getting data at levels from five hundred feet up to twenty thousand. Down in the lower levels, they found a horizontal vortex roughly five thousand feet in diameter, extending from the cloud wall of the eye like a tornado funnel, in which they encountered very severe turbulence. Another collection of data was added to the growing accumulation and with it the notes of unusual phenomena observed. Since that time Simpson has flown several hurricanes in the Atlantic.

Now it is abundantly clear that the hurricane hunters are looking for many important facts aside from the location of the tropical storm and a measure of its violence. There are many questions unanswered. Here in the warm, moist winds that blow endlessly across deep tropical waters there are mysteries that have challenged man for centuries. Turning to their advantage every discovery that science has pointed in their direction, the hurricane hunters have cheated the big storms of the West Indies of a very large share of their toll of human life. In struggling to solve the remainder of the problem, they have two virtues that will ultimately bring success—ingenuity and persistence. They push on tirelessly in several hopeful directions.

The Navy has taken advantage of the strange fact that when a tropical storm comes along it literally shakes the earth. There are little tremors like earthquakes but very much smaller. The Greek word for earthquake is seismos and by putting micro in front, meaning very small, we have the word microseism. And so, the storm-caused little tremors are called microseisms or slight earthquakes. The instrument which registers these tremors is called a seismograph. When the earth moves, even a very little, a body on the earth tends to hold its position and the earth moves under it. In a small earthquake, a chair will move across the floor. This kind of motion can be registered by instruments.

In 1944 the Navy installed seismographs and began keeping records of the slight tremors caused by hurricanes and typhoons. These studies have shown that a tropical storm at a distance produces a small tremor which becomes stronger as the storm center gets nearer. No one knows exactly how the storm shakes the earth and causes the tremors. There are some strange things about this. It seems that these microseisms are carried along in the earth until they come to the border of a great geological block and then do not pass readily into the next block. So there are places in the Caribbean where the tremors weaken as they come to a different earth block and this interferes with the indications picked up by the instruments. The fact is that microseisms give signs of the existence of a tropical storm and sometimes serve to alert the storm hunters, but they are by no means good enough to replace the use of planes in tracking them. But the studies of microseisms are being continued.

For many years static on the radio, better known as atmospherics or just “sferics,” has been used in the endeavor to locate or keep track of storms. At first the Navy tried it on West Indian hurricanes. The instruments used will find the direction from which the sferics come when they are received in a special tube. In more recent years, the Air Force has used this scheme. It works to advantage in finding thunderstorms, but tropical storms are so big and the sferics are not found in any regular pattern around the central region. After years of trial, it has been concluded that this scheme is not good enough to replace other methods.

Of all the methods of this kind, radar is by far the best. But as the radar stations on shore and the radar equipment on aircraft have increased in numbers and have been improved to reach greater distances, some new troubles have arisen. For many years the hurricane hunters took it for granted that a hurricane has a clear-cut center which moves smoothly along a path that is a straight line or a broad curve, but in a few cases is a loop or a sharp turn. In other words, the center does not change size and shape or wiggle around. In the past, when an observer on a ship or on a plane reported a center of an odd shape or had it off the smooth path the hunters were plotting, they said the observer had made an error.