The Hurricane Hunters

by Ivan Ray Tannehill

The Air Force has a different problem. Like the Navy, they are dedicated to the task of getting vital weather data for the forecasters, but their own problem is to evacuate military aircraft from threatened bases and get information needed for aeronautics. Also, they have the responsibility of giving weather forecasts and warnings to the Army. Until a few years after World War II, the Air Corps was a part of the Army, and when all three services were joined in the Department of Defense, the Air Force kept the weather job for both departments as a matter of economy and efficiency. Therefore, for this and other reasons, the Air Force follows a hurricane-probing plan which differs from the Navy’s.

Flying generally at higher levels in tropical storms, the Air Force, as much as the Navy, puts a great deal of reliance on radar, which has become a marvelous aid in watching the weather. In the beginning—years ago—radar was not designed for weather purposes, however. During World War II, radar was used to spy on enemy ships and aircraft in fog or in darkness, to distances of 150 miles or more. The high-frequency rays sent out by the radar strike the object and are reflected back to the transmitter, where a sort of a silhouette appears on a scope. It may be black with white areas showing images of solid objects, such as planes and ships. In those days early in World War II, the weather was a nuisance to the radar people. It often seemed to interfere with the use of radar for military purposes, but the operators soon learned that the interference came from rain drops in local or general storms and that the rainy areas could be located and followed on the scope and, with the proper design, the apparatus could be used as a weather radar.

The first experiments with radar carried on board aircraft in organized tropical storm reconnaissance were made in 1945. Within three years, all the planes were carrying radar sets and had crew members whose sole business it was to watch the radar scope and tell the pilots and weather officers what kind of weather lay ahead.

Scarcely had these observations begun when the radar weather men discovered an amazing fact. On the radar, a tropical storm looks like an octopus with a doughnut for a body and arms that spiral around the body as if the creature had been caught in a whirlpool. These arms are bands of squally weather, oftentimes violent turmoil. Between the bands (or octopus arms) the wind is furious, of course, but there is less turbulence and cloudiness, and here the aircraft is in much less trouble than in the squall bands. The cause of these violent bands spiraling around the center has not been figured out yet for sure, but all tropical storms have them, and the hunters are beginning to understand them better.

The distance you can see from the radar station depends on how much weather there is. If there are large patches of dense rain, they may reflect all the rays back to the receiver and none may go through to show other rain areas farther away. Because of this, the radar shows the eye of the storm, but usually not the entire circle of clouds around a distant eye. Not enough radar energy is left to reflect from the opposite side of the eye. For this and other reasons it is necessary to have an experienced man to interpret the images on the radar scope.

From a radar in an airplane at high levels, these limitations are not so troublesome. Recently, too, the range of military radars has been increased. Whereas the radar formerly was very useful in getting a view of the eye from the aircraft, it did not give the eye’s geographical position, which had to be determined by other means, except when the eye was close enough to be seen from the coast. With increased range, the aircraft can get between the hurricane center and the coast or an island, and both appear on opposite sides of the radarscope. In such cases, the distance and direction of the eye from a known point on a coast or island can be figured.

In the last two years, the Navy has used radar methods of this type extensively to obtain fixes of hurricane centers at night. In these instances, the crews fly at greater heights than in daylight and can get the eye and the coast on the scope at the same time. This gives a good estimate of center location to supplement the daylight penetrations without flying into the storm center in darkness. Actually, night flights directly into hurricane centers were not profitable, as non-radar observations of sea surface, clouds and winds were not possible in darkness.

It is apparent that a plane going into a storm at some upper level soon gets into the clouds and the sea surface is no longer visible. But the crew can depend on the radar to help find the center and they can go down in the eye of the storm and look around and, if necessary, the plane can descend in the outer parts of the storm and get estimates of the wind by a drift meter. For this latter procedure, the Air Forces at one time used what they called a “low-level boxing procedure.” On this we can get the facts from the instructions issued by the head of the Air Weather Service, Brigadier General Thomas Moorman, Jr., a veteran of weather operations in World War II and in charge of weather reconnaissance in the Pacific, including the work done so effectively during the Korean War.

In 1953, Moorman directed that, in the interest of flying safety, there will be no low-level penetration of hurricanes. The Air Force pilots were asked to go into and out of the eye at the pressure level of seven hundred millibars which, under average conditions, is at about ten thousand feet altitude. Within 100 miles of a land mass, the flights in a hurricane would be at a minimum altitude of two thousand feet. To put it, in part, in the General’s words, the hurricane mission would be conducted as follows:

For high-level penetration, the first priority would be given to obtaining an observed position of the storm center, either by a radar fix plus a navigation fix on the aircraft position, or a position found by penetrating the storm and obtaining a navigation fix in the eye. The storm would be approached on a track leading directly toward the center. If the storm center could not be reached at the seven hundred millibar level, the low-level boxing procedure could be followed, but if the radar set was not operating, no attempt would be made under these conditions to go into the eye.