Part 13
"I might say a little more about the cloud formations we noticed since it was my job on this day to note them and take pictures of them while the other observer tried to compute pressure. Ahead of the storm here at Morrison Field on the morning of the sixteenth, we got a good picture of pre-hurricane thunderstorms. Squalls with forty-mile gusts swept across the runways. The rain came down in sheets so that we could watch it move toward us like a dark wall. Some of the boys out loading one of the ships for evacuation saw one of these terrific showers bearing down on them and they started to run for cover. The water was moving faster than they could run and before they'd moved fifty feet they were soaked to the skin. On the morning of the seventeenth, it lay just off the Georgia coast and had started to re-deepen. We flew up the eightieth meridian though it was hard to hold any steady course. As some of the navigators have probably mentioned, we could see our own drift. After we noted a good windshift into the east to assure us that we were in the northeast quadrant, we headed across current for the center and once there headed roughly for the great outside to the west. With such terrific drift, I don't see how anyone knew where he was going.
"Heading north: The usual over-water five-tenths stratocumulus bases at two thousand, tops at thirty-five hundred, gradually began to lower at about one hundred twenty-five miles from the center to roughly eight hundred feet, and a fairly solid lower layer of clouds. Flying above this layer at about forty-five hundred feet we could see tall bulging cumulus and thickening altostratus at about fifteen thousand ahead. There were other thin layers of stratocumulus and altostratus, but it wasn't until we got within fifty miles or so of the center and the rain really began to come down and the cumulus were as thick as trees in a forest that these intermediary layers began to thicken and thatch in between the tall cumulus the way they do in any well-developed storm system. By fifty miles out we were in solid cloud and heavy rain. Picture-taking became impossible except in the occasional breaks mentioned above. Even these breaks, if they should come out, would show little because continuous instrument weather, to me at least, looks pretty much the same whether it's part of a violent hurricane or smooth circulation stratus over a seaboard town. You can see the wing tips and not much more.
"If a general conclusion is necessary, mine would simply be that I'd just as soon not tempt fate in any more such storms."
Sometimes birds such as Lieutenant Gray describes are carried hundreds of miles before they escape from the hurricane. Species from Florida have been found as far north as New England.
_11._ TRICKS OF THE TRADE
_A gallant barque with magic virtue graced, Swift at our will with every wind to fly; So that no changes of the shifting sky, No stormy terrors of the watery waste, Might bar our course,_ --Dante
After two years of probing tropical storms by air, nearly everybody connected with the operation agreed that it was hazardous. But most of the men who were active in it had one main idea. As soon as the winds, rain, clouds, seas, and calm center of the average hurricane had been thoroughly mapped, a standard method should be devised for flying into the center and getting the vitally needed weather information en route with the least possible danger to the craft and crew. They thought of something like a football team, each man highly trained in a definite job, with faultless teamwork, and all members of the crew on the alert every moment.
Courses of instruction were organized. In all of them one fact became abundantly clear in the first two years. No two hurricanes are exactly alike. All of them are big compared with thunderstorms and tornadoes, but some are much larger than others. The recco crew may run into one in the uncertain stages of formation and at other times they may be nosing into an old storm with strange and unsymmetrical parts. Of certain elements they were reasonably sure--all these storms have clouds, rain, squalls, and central low pressure, with strong winds spiraling more or less regularly in a direction against the motions of the hands of a clock.
With these thoughts in mind, the instructors tried to devise methods that would prevent accidents. "What do you mean, accidents?" asked a junior weather officer at one of the conferences. "The whole thing is just one big accident, if you ask me. There's only one rule that's any good. Just be careful and don't fall in the ocean!" As a matter of fact, most of the rules had that one vital thought in mind, but there were different ways of doing it.
The Air Corps and Navy soon developed their own special methods. From the beginning the Navy preferred the low-level method; that is, they flew by the quickest route to the calm center of the storm, going in at a low level, generally at an elevation between three hundred and seven hundred feet. There are good reasons for this. Weather information--especially the facts they want about tropical storms--is vital to the safe operation of surface ships such as cruisers, destroyers and mine sweepers, and it is also used in the movement of aircraft from and to the decks of carriers. Task forces want to know about the speed and direction of winds at sea level, as well as the condition of the sea when storms are imminent.
It was the aim of the Navy to keep their weather reconnaissance aircraft below the level of clouds, where the aerologist could watch the surface of the sea as much of the time as is possible within the limits of reasonably safe operation. When in a tropical storm, the aerologist guided the pilot around or into the center. Down near the water, say one hundred to three hundred feet altitude, turbulence is apt to be very bad, sometimes extremely violent. Above seven hundred feet, clouds are likely to interfere and this was extremely dangerous at that altitude in those early years because the altimeter which they used to indicate height of the aircraft by pressure of the atmosphere was sometimes badly in error in a tropical storm. If the pilot and the aerologist lost sight of the water's surface for a few minutes, they suddenly found the aircraft about to strike the precipitous waves of a storm-lashed sea.
Pressure of the atmosphere falls with increase of elevation, roughly one inch drop in pressure for each one thousand feet. If we put an ordinary barometer reading 29.90 inches in a plane on the ground and go up one thousand feet, it will read about 28.90 inches. The pressure altimeter is a special type of barometer that shows elevation instead of pressure. When the pressure is 29.90 inches and the altimeter is set at 0, we go up to where the pressure is 28.90 inches and it reads one thousand feet. But if the pressure over the region falls to 28.90 inches and the altimeter is not adjusted, it will read one thousand feet at the ground and be roughly one thousand feet in error when we go up to where the reading is 27.90 inches.
In ordinary weather, big changes in the barometer take place slowly and there usually is plenty of time for correction. In a flight into a hurricane, big changes take place rapidly. The change caused by the plane going up may be confused with the drop in pressure in the hurricane. If the plane is in the clouds when these changes take place, the pilot may have a frightening surprise on coming into the clear again. More recently, the hunters have been equipped with radar altimeters which give the absolute altitude for check. They send a radar pulse downward and it is bounced back from the sea surface to the instrument. The time it takes to go down and back depends on the height--the higher, the longer it takes--and the instrument is designed to give the indication very accurately in feet. Thus, the radar altimeter removed some of the dangers of low level flight.
So the Navy hunters moved in at low levels, preventing the "mush from becoming a splash" as they put it, and although their experienced pilots were marvelously efficient in flying on instruments in clouds or "on the gauges," they kept the white welter of the storm-lashed sea in view whenever possible. Of course, it is not possible to fly straight into a storm center. The big winds carry the plane with them and so the pilot might as well use the winds to good advantage--he will go with them to some extent, whether he likes it or not.
If we imagine ourselves in the center of the hurricane, facing forward along the line of motion of the storm itself--not the motion of the winds around the center--we know that the safest sector to fly in is behind us on our left, and the worst is in front of us on our right. At the left rear, there is likely to be better weather--less dense cloudiness and not so much rain. The winds are not so violent. So the Navy pilot flies with the wind. He goes in until he has winds of, say, sixty miles an hour. He puts the wind on the port quarter and this carries him gradually toward the center of the hurricane.
When he gets the wind speed to suit him, he brings the wind between the starboard quarter and dead astern and flies ahead to the point where he thinks he has the best place to go for the center. According to Commander N. Brango, one of the Navy's top specialists in hurricane navigation by air, "Choosing the proper run-in spot is tricky business, for it is the point at which the wind is the reciprocal of the storm's direction of motion. The pilot must watch for this point carefully, as he may pass it quickly; if he does there is imminent danger that the drift may carry the aircraft into the most severe quadrant of the hurricane." So the pilot goes into the center without wasting any time. Delay results in fatigue and it is important that the men be freshly alert. The pilot puts the wind broad on the port beam and he cannot possibly miss the eye. The next thing, the plane is in that amazing region where the sea boils, the breezes are light or missing altogether, the rain has ceased and the clouds are arranged in circular tiers, like giant spectators in a colossal football stadium.
This is a marvelous place. The crew is at ease. Coffee goes around. In the last few moments before coming into the eye, the craft leaks like a sieve. Everything is wet but the squirting from a hundred crevices in the plane ceases in the center and now it is possible to do some paper work. The aerologist is busy with the weather code and the radio man begins pounding out a message. They circle around. The pilot takes them up to maybe five thousand feet altitude and back down again, circling around.
And then the time comes to leave the center. The pilot calls a warning over the phone and there are two or three wisecracks. But this departure from the eye is dangerous. The plane begins to catch the shear of powerful winds around the center. Here a man can get thrown around violently and be seriously hurt, if he fails to get a good grip on something or neglects his safety belt.
Now the pilot sets the wind broad on the starboard beam and both he and the co-pilot hang onto the controls. This is rough going and there may be some surprises, but after a little they are out of the big wind circle and the navigator thinks the gales are down to something like fifty knots. The pilot sets course for the Navy airfield and the staccato notes of the radio continue to carry vital weather information to the forecasters. On this subject, Captain Robert Minter, an old hand, at one time in charge of aerology in the Office of Naval Operations, is full of enthusiasm. He guaranteed that the Navy could get a ship off the ground on a hurricane probe within an hour after the Weather Bureau forecaster asked for the information.
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.
For the low-level boxing procedure, the following instructions applied, quoting General Moorman in part:
"The storm area is approached on a track leading directly to the storm center and may be approached from any direction. As the winds increase in velocity, corrections will be made so that the wind is from the left and perpendicular to the track. The point at which the box is started is the mid-point of the base side of the rectangular pattern to be flown around the storm. When winds of sixty knots are encountered, the first leg will be started with a 90° turn to the right.
"The low-level box will be flown within the 45-60 knot wind area maintaining a true track for the first half of the leg, then a true heading for the succeeding legs. Surface winds should be 45° from the right when the left turn is made to the next leg. Double driftwinds should be obtained on each corner observation and each mid-point when practical. Reconnaissance of an area of a suspected hurricane will be flown with the same procedure.
"The weather observer will check the co-pilot's altimeter at frequent intervals to insure that it is reading the same as the radar altimeter.
"All flights will depart storm area prior to sunset, regardless of the degree of completion of the mission.
"Flight altitude while boxing the storm will be a minimum of five hundred feet absolute altitude, or at such higher altitude as will permit observations of the sea surface without hazard to safety. If contact flight cannot be maintained at five hundred feet, the legs will be flown a greater distance from the eye."
The "boxing procedure" was used a great deal by the Air Weather Service in the early years but by 1954 it had been eliminated. The seven-hundred-millibar method was revised, and as used in flights out of Bermuda in 1954 was described by Captain Ed Vrable, navigator, in part as follows: "(1) The aircraft flies down wind at right angles to the storm path to a point of lowest pressure, about twenty miles directly in front of the eye; (2) Flight is continued down wind for three minutes beyond the low point and then the heading of the aircraft is changed 135° to the left; (3) The aircraft continues on this course until the pressure begins to rise and then turns 90° to the left and into the center."
This new Air Force plan of flying into the hurricane at seven hundred millibars (ten thousand feet, roughly) is much like the Navy's low-level method, except that the Air Force crews enter down wind across the front of the storm, but this is nearly always an advantage for aircraft based at Bermuda. From that island their most direct approach to an oncoming storm is into the front semicircle.
The Air Force has another aid in measuring weather in a storm. It is an instrument called a "dropsonde," a specially designed apparatus which works on the same principle as the older "radiosonde." A marvelously ingenious instrument, the radiosonde is a unit of very small weight containing miniature instruments for measuring pressure, temperature and humidity. It also has a metering device, a battery, and a small radio transmitter. The apparatus is carried aloft by a rubber balloon filled with helium. As the balloon rises, the radio transmitter sends signals for pressure, temperature and humidity at each level reached, and the signals are copied on a register at the ground weather station.
The dropsonde is a radiosonde that is thrown out of the aircraft flying at a high level, and allowed to descend by parachute, instead of being carried up by a balloon. There is a special listening post in the plane, where the data are recorded as the apparatus descends. The data are then put into the form of a message for transmission by the plane's radio operator to the forecasting base. This work with the dropsonde is usually done by the radar operator, in addition to his other duties.