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IT IS sunrise in the Australian outback, and the lightening eastern sky
reveals a strange sight. A huge cylindrical cloud, several kilometres in
diameter, stretches across the horizon. As the Sun rises, the cloud moves
south-west, casting a dark shadow over the houses of Burketown.

The cloud is known as a Morning Glory because it moves into the area around
sunrise and evaporates in just a few hours. When they catch it in time, the
Morning Glory carries with it an airborne festival: hosts of glider pilots and
hang-gliders love to surf on its top edge. The rush of the ride and the beauty
of the phenomenon has made this small Queensland town on the Gulf of Carpentaria
a Mecca for gliding enthusiasts. “It’s the most amazing sight,” says pilot
Russell White. “I’ve seen vertical walls of cloud more than three kilometres
high, illuminated by the full Moon and burnished by the dawn rising behind.”

Observed from the ground, the massive cloud seems to move serenely across the
sky, its base just 100 metres above the rooftops. But the moist air trapped
within the cloud is far from calm. It is rolling and churning: hit the wave in
the wrong way and it could damage your plane or even hurl it straight to the
ground. And while the coastal weather conditions in Burketown create a clearly
visible cloud, elsewhere in the world these atmospheric waves form in dry air,
creating an invisible menace that can cripple aircraft in mid-air or suddenly
fling a plane off its runway approach. If your pilot can’t see the wave coming,
you could be in big trouble.

No one understands exactly how Morning Glories form, and even less is known
about predicting their arrival. But now a meteorologist based at the University
of Munich thinks he can see Morning Glories—even invisible
ones—coming. If he’s right, it’s good news for glider pilots, and even
better news for airline passengers.

Morning Glories are known to occur over land and sea in many parts of the
world, including other areas of Australia, Germany, Qatar and the English
Channel. In Oklahoma, an observation network for tornadoes often picks up the
signal of invisible Morning Glories passing by. But if you want to study them
with any hope of gleaning some understanding of their origin, Burketown is the
place to go.

Although they are still unpredictable in Burketown, it is the only place on
Earth that can boast a season of visible Morning Glories. They put in an
appearance often enough between August and October to attract both glider pilots
and those hoping to understand what makes the clouds form. In 1979, Smith, then
based at Monash University in Melbourne, flew on the first scientific flight
into a Morning Glory. It was an exciting experience, he says, especially when
the plane suddenly plunged earthwards on entering the cloud. “The instrument
needles went off the scale,” he recalls.

Since that first data-gathering flight, many more attempts have been made to
monitor and analyse Morning Glories. Most meteorologists now accept that they
form when two masses of air come together
(see Diagram). The particular
triangular shape of the Gulf Coast peninsula means there is often a westerly sea
breeze flowing towards an easterly one there. The breezes meet along what
meteorologists call a convergence line, and this line moves south-west as one
air mass ploughs into another. The head of the colder air is slowed and heated
by the warmer air. This sets up a convection current: the warmed air rises and
its place is taken by the cold air behind it.

But, as the ground cools through the night, a stable, cool layer of air
develops just above the Earth’s surface. This has two effects: it softens the
interface between the cold and the warm air, and it acts as a kind of lubricant,
allowing the colder air mass to move smoothly and quickly above the ground.
These changes are enough to produce a growing bump at the head of the cold air
mass. By early morning the bump is well established, pushing a wave of rising
air before its leading edge. If the air is moist, the water vapour condenses as
it rises—generating the spectacular rolling cloud.

Although the meteorologists are happy with this explanation of the mechanism,
Smith says it is hard to take measurements within a Morning Glory to confirm the
theory. “Much of what we know is based on results from laboratory measurements
and numerical modelling,” he says.

Smith has used water to recreate these solitary waves. He part-filled a long
tank with water, in which he dissolved a large amount of salt to simulate the
cool, moderately heavy air layer produced by the cooling ground, then carefully
poured a coloured layer of unsalted water on top. The coloured
water—analogous to the warm air mass—remained in a distinct layer
above the saltwater.

Smith then lifted a vertical partition at one end of the water channel to
release a body of more heavily salted water representing the cold air mass. When
it hit the freshwater layer, the heavily salted water formed circulating waves
that rolled along on top of the lower layer, exactly mimicking the action of a
Morning Glory.

Satisfied by this result, Smith began work on a computer simulation. Together
with Julie Noonan from Monash University, he created programs that could process
a set of given meteorological parameters—air masses, pressure fronts,
humidity, temperature, wind directions and so on—to give a simulation of
how the atmospheric conditions would subsequently evolve. The researchers were
able to set the average conditions for the area and then watch the fictional
weather develop.

The simulation showed a particular pattern of wind directions along the
convergence line. And when a solitary wave forms on this line, the wind pattern
is even more intricate. “Morning Glory waves are an embroidery on the
convergence line,” says Smith. The data from the simulation, combined with his
analysis of the perfect conditions to form the clouds, told Smith what should
appear on the weather maps.

He then took his model to Gordon Jackson at the office of Australia’s Bureau
of Meteorology in Darwin. Here they used the BoM’s computers to turn back the
clock and set the weather parameters to map three September days in 1996. On
both the second and third days a Morning Glory had cut across the dawn skies
over Burketown. They ran the BoM’s model forward to see if the model generated
the weather that actually happened. It did: on the first evening they saw the
wind pattern associated with a forming Morning Glory. On the evening of the
second day, the same pattern emerged. The convergence lines that the model
generated on the second and third mornings were even in the same position and
with the same orientation as the observations. “It predicted the convergence
lines beautifully on the two days where Morning Glories appeared,” says
Smith.

Smith and Jackson plan to submit their results for publication later this
year, but will first check to see if their prediction model works for other
occasions when Morning Glories appeared, as well as on days when they didn’t.
“We want to make sure it forecasts none when there are none,” Jackson says.

Michael Reeder, a meteorologist based at Monash University, is impressed. He
says this new insight into Morning Glory formation could easily be harnessed for
making predictions. “I think this kind of forecast is probably well within the
capacity of current numerical weather prediction models,” he says. Doug
Christie, an expert on Morning Glories who monitors atmospheric disturbances for
the United Nations, agrees. “We understand the mechanisms, and the computer
models now have the speed and resolution to predict these things,” he says.

He also thinks such work would help improve safety for aircraft. He has
analysed the weather conditions associated with a number of air disasters, and
combined it with physical evidence, such as flight recorder data, from the
crashes. His studies suggest that invisible Morning Glories may be responsible
for a third of the world’s weather-related aircraft crashes, mainly those put
down to the general diagnosis of “wind shear”. The Delta Airlines flight that
crashed at Dallas Fort Worth in August 1985, killing 137 people, was caused by
an invisible Morning Glory, he says. He cites a 1974 crash that killed 97 people
on the final approach to Pago Pago in American Samoa as a classic case. The
flight crew had reduced thrust when they encountered a headwind and updraught,
but when the updraught disappeared on the other side of the wave the aircraft
descended rapidly and crashed 1200 metres short of the runway. “This is
precisely the behaviour one would expect from a head-on encounter with a
solitary wave disturbance,” Christie says. “It would clearly be an important
contribution to air safety if air traffic controllers could predict and observe
the passage of these solitary wave disturbances.”

As well as general meteorological predictions for an area, Christie would
also like to see arrays of suitably located micro-pressure sensors near
airports. These, he says, would identify the characteristic air disturbances,
which maintain their shape and identity as they roll in over large distances.
Such an array would act as a fail-safe to warn pilots of a nearby solitary wave
undetected by meteorologists.

Smith and Jackson believe their insights into the formation of convergence
lines will also help monitor other weather patterns. They are beginning with
storm predictions: convergence lines are important mechanisms in the formation
of thunderstorms and squall lines. They hope to have prototype warning models
available for the Darwin office of the BoM within a year. “At the moment, we can
warn of a squall line six hours ahead. This method would increase the lead time
to 12 hours,” Jackson says. The research may also lead to an ability to
understand and forecast other violent winds, such as the Gulf of Papua’s Guba
and the Strait of Malacca’s Sumatra.

The meteorologists have yet to convince the glider pilots of their new
predictive techniques, however. Pilots like Rob Thompson have a lot of respect
for the progress meteorologists have made in understanding Morning Glories, and
agree that the meeting air masses are important. But he also feels there is more
to the phenomenon: experience gained in the air gives a useful perspective, he
says. “The meteorologists go to Burketown and look up. We’re looking down,
flying through all the layers of the atmosphere and know what’s happening.”

On the day before a Morning Glory appears Thompson has noticed markedly
different wind directions at different altitudes over the Gulf. He believes
these shifting winds produce “standing waves” in the atmosphere and cause long,
thin cigar-shaped clouds to appear at particular altitudes. “The relationship
between standing waves at altitude and Morning Glories the next day warrants a
great deal of investigation,” he says.

Smith believes the pilots’ observations should be taken seriously. “I doubt
that many meteorologists know much more about the phenomenon than the pilots,”
he says. However, he adds, there is not much dialogue between the
communities.

For their part, the pilots are willing to share their experience in the
pursuit of reliable Morning Glory predictions. Geoff Pratt, a pilot with an
impressive track record in finding Morning Glories—he caught ten clouds in
two weeks last season—says he would like to work with a meteorologist on
developing forecasts. “It would be valuable to get a pilot’s experience combined
with a meteorologist’s knowledge,” he says.

The weather bureau has no immediate plans to issue Morning Glory forecasts
for the glider pilots, but Smith believes that could happen if thrill-seeking
tourists start flocking to Burketown. Russell White would certainly welcome some
help: it could save him some hideously early mornings, he says. He occasionally
succeeds in forecasting the weather conducive to a good morning’s cloud surfing,
but usually he just gets up for a 4 am take-off anyway. Surfing the burnished
cloud of the Morning Glory—dangerous or not—has him hooked. “Even if
none of the signs are there, I prepare to launch anyway,” he says. “It’s
frustrating to miss one.”