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Researchers are hoping for bad weather – so they can fly straight into the storm

A large-scale flight campaign on both sides of the Atlantic Ocean aims to uncover why some cyclones develop into storms, while others fizzle out.

In the coming weeks, low pressure systems approaching Europe from the Atlantic Ocean will be met by three research aircrafts.
Ellen Viste
Ellen Viste Communications ADVISER
Presented by: Presented by: Presented by: University of Bergen
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Instruments on the ground show what happens when weather strikes, and satellites see the clouds from above. 

But if you want to know what goes on inside a developing cyclone, you have to enter the storm. 

Over the next few weeks, researchers from ten countries gather at an Irish airport to fly in bad weather.

Research aircraft will head straight into low-pressure centres

Low-pressure centres form above the Atlantic Ocean and blow eastward towards Europe. 

The journey, which spans several thousand kilometres, can take several days – long enough for some of them to develop into powerful storms.

During the measurement campaign, an American research plane will head for the clouds on the western side of the ocean, where these cyclones form. 

When the same lows approach land on the eastern side, they will be met by three planes from the base in Ireland. All the aircrafts are loaded with instruments measuring the air and clouds outside. 

Setting the stage for the next storm

Rising air is the cause of the clouds and rain associated with weather systems. As air ascends, it cools, and water vapor in the air turns into ice crystals or water droplets. 

But this time, rising air is not the researchers' main interest.

“The aim is to understand how air sinks before rising in a storm,” says Harald Sodemann.

Harald Sodemann has participated in many measurement campaigns using aircrafts to study weather.

He is a professor of meteorology at the University of Bergen's Bjerknes Centre and the Geophysical Institute.

“This sinking air sets the stage for new cyclones following the first. Also, some of the strongest gusts are caused by sinking,” he says.

Flying at all levels

Sodemann leads the Norwegian contribution to the operation, which has been under preparation for a decade. While it goes on, around a hundred people – pilots, mechanics, and meteorologists – will be gathered at Shannon International Airport near Limerick.

Three airplanes are ready to take off when cyclones approach over the Atlantic Ocean.

A German airplane will circle above the lows, at an altitude of 10,000 metres, which is common for commercial flights. Instruments directed downwards will provide a bird's eye view of the weather. 

A smaller German plane will fly low and see the storms from below.

Having collaborated with French researchers for many years, Harald Sodemann has had the opportunity to install one of his instruments in the French aircraft. In total, 48 institutions in 10 countries are involved.

Between the two, a French airplane will steer into and out of the clouds, with instruments directed both upwards and downwards. 

Together, the three planes will register what goes on in all parts of the cyclone.

Sinking air picks up speed from altitudes of several thousand metres

Extratropical cyclones are followed by warm fronts and cold fronts, which are boundaries between warm and cold air. 

On weather charts, fronts are shown as red and blue curves, but in reality they are boundary surfaces that rise up into the atmosphere. 

Along these fronts, warm and moist air slides up over colder air, which leads to clouds and rain.

Rising air is an important characteristic of low pressure systems and fronts. But behind the cold front, dry air sinks. When the sinking air reaches the surface of the ocean, it takes up large amounts of water vapor and becomes extremely unstable. Together with strong winds, this contributes to rough weather there and then, as well as in new weather systems that come after the original cyclone.

Ahead of a cold front, mild and moist air is driven northwards. Behind the front, air sinks from altitudes of 5,000 to 6,000 metres. 

Because this air is dry and maintains a high speed, strong evaporation occurs when it reaches the surface of the sea.

Water vapor from the ocean makes the air moist, warm, and light – almost explosively unstable. The air rises quickly in convective clouds, and this disturbance high in the atmosphere helps form new storms.

Several thousand metres above the ground, wind speeds are high, and the sinking air maintains some of its momentum. Together with other factors, this can create a sting jet, which produces stronger wind gusts than any other phenomenon in our part of the world.

All instruments are attached to sturdy racks inside the aircrafts. The researchers can follow the measurements on a screen. Harald Sodemann and Sophie Bounissou are ready to go.

Water vapor makes the air traceable

“This is the first time the interaction between rising and sinking air is studied in such an aircraft campaign,” says Harald Sodemann.

Norway does not have its own atmospheric research aircraft, but one of Sodemann's instruments has been installed in the French plane, operated by the French national meteorological institute (Météo-France), the French national centre for scientific research (CNRS), and the French national space agency.

While the airplane flies into and out of the clouds, air is sucked from outside the fuselage into Sodemann's instrument. Inside the instrument, an infrared laser records water isotopes, which are different variants of water molecules in the air.

Some water isotopes are heavy, while others are lighter. The distribution between heavy and light isotopes can reveal how the air has absorbed moisture from the ocean and subsequently released it as clouds and rain. 

These isotopes also allow researchers to trace where the air has been earlier and which regions it passed through.

This instrument registers water isotopes in air drawn from outside the hull through the black hose. The image shows the set-up before other instruments were added to the rack.

The researchers need of bad weather

Personnel have been at the airport in Ireland since the end of January, preparing planes and instruments for takeoff. Sodemann admits he is becoming nervous.

“A million things can go wrong. We prepare for a thousand alternatives, and the problem will be number one thousand and one,” he says.

His main concern is the weather. 

To find out how rough weather works, they need low pressure systems, preferably long chains of cyclones. 

“A large, blocking high over Ireland would be disastrous,” he says.

But long-range forecasts look promising. The high pressure regions seem to stay put over the Norwegian Sea and Scandinavia, while lows steer towards the British Isles and Central Europe. 

This winter's weather pattern, which has been bad for the ski season in Western Norway, is good for those who wish to fly into storms over the Atlantic Ocean.

“The mood is good in Ireland now,” says Sodemann.

Before leaving Bergen Harald Sodemann was excited to see how European weather would develop in February and March.

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