the storm had spent itself, I don't know, but I do think it worthy of
mention. We noticed occasional breakups in the clouds--not large
areas, just a few seconds when everything brightened and when the firm
outlines of a large cumulus could be seen through thin low scud. This
was not in the center but as much as forty miles away where the stuff
should have been most solid and where the sea was near its roughest. I
have seen the 'Eye' of a hurricane on land as a weather forecaster. At
that time we noticed a real breakup with stars and moonlight visible.
The wind and noise stopped for a while and we could see an occasional
bulging cumulus through the night. Whether this phenomenon is due
merely to less energy available over land than over water, I wouldn't
even guess. In any event we noticed no such complete break in the eye
at sea. In the center, so-called calm, though for my money it was
mighty rough, about all that we noticed was that the pounding rain
stopped for a minute or so. The clouds did not break clear through.
There was a slight breakup to perhaps five thousand feet. There were
bases of cumulus and several indefinite layers below this overcast
though. The terrific bouncing around also stopped. We were out of the
place in just a minute or two, so the eye couldn't have been much more
than five miles in diameter. Some of the other ships circled in the
center, saw a flock of birds milling around there, and noted violent
up and down drafts near its edge. We were in and out of the thing so
fast that, frankly, we hardly had time to notice anything. I think we
could have fallen the seven hundred feet to the water without my
knowing it, we were so busy with the camera, papers, and instruments.
"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.
Much of this fascinating work is done by the Air Weather Service of the
Air Force on routine daily flights, whether or not there is a tropical
storm to be studied. As an example, they have made daily flights from
Alaska to the North Pole and back, to keep tabs on the strange weather
up there. In this way, there--and in other parts of the world--they get
weather daily from places on land and sea where there are no weather
stations, no merchant ships to report, and no people to act as weather
observers. These flights are named after some bird common to the region.
The North Pole flight is called "Ptarmigan"; others are called
"Vulture," "Gull," etc. Special flights into tropical storms in the
Atlantic and Caribbean are called "Duck" missions.