Radar data from tiny meteors burning in the upper atmosphere are providing scientists at the Norwegian University of Science and Technology (NTNU) with unique insights into fluctuations in the wind and temperature 90 kilometres above the Earth.
The information can lead to better weather forecasts.
“Some 30–100 tonnes of ‘space dust’ slam into our planet daily, but it burns up in the atmosphere. When it vaporises it leaves a track that can be detected by radar,” explains Rosmarie de Wit, a PhD candidate in NTNU's Department of Physics.
The weather high in the atmosphere can reveal a great deal about weather developments down at ground level.
Meteorologists are keen to get information from the outer reaches of our atmosphere. The problem is that weather balloons don’t float high enough and satellites don’t orbit low enough to gather data from the edge of space.
One solution is to study the trails of ionized gas left from dust-sized meteors as they vaporise in our atmosphere.
Researchers with NTNU’s atmospheric team use an instrument called SKiYMET Meteor Radar to detect radio echoes from 15,000 invisible “shooting stars” daily as they flare above Trondheim and Mid-Norway.
The time elapsing before the trail from the grain of dust disintegrates reveals information about the temperature at this altitude. As with the contrail from a jet airliner, the way the meteor trail moves indicates the strength and direction of the wind.
Cosmonauts and astronauts returning to Earth were the first to find out - from first-hand experience - that turbulent weather is found high in the atmosphere.
When the wind blows over a mountain peak or a weather front is on its way, waves of air generated at the Earth’s surface reverberate up into the atmosphere.
“This is what causes the turbulence you can experience in a plane when it meets the peaks and troughs of wind waves − like a boat on choppy seas,” says Professor Patrick Espy of NTNU’s Department of Physics.
As the air gets thinner high in the atmosphere, the energy in waves moves the increasingly thinner air further and further.
“At an elevation of 85 kilometres you can have waves with eight-kilometre-high peaks coming at you with speeds of 20 metres a second,” which is about 70 km per hour, says Espy.
“If the waves get high enough, they eventually crest like breakers hitting a beach. These waves stir up the upper atmosphere much like ocean waves churn the sand on the beach and change the coastline,” explains Espy.
Solar heat is what normally controls which way the prevailing winds blow. The equator gets much more heat than the darker region toward a pole. So the wind blows toward the east in the winter and toward the west in the summer.
“These waves are abundant. They are so powerful when they crest 90 kilometres over the ground that they can actually overpower the influence of the Sun and turn the winds around in the opposite direction,” says Espy.
The NTNU researchers hope that a better understanding of what is happening nearly 100 kilometres above our heads will help meteorologists give us more accurate long-term weather forecasts.