If you are in the right place at the right time, and turn your eyes to the sky, you may see something more beautiful: Wisps of cloud, high in the sky, shining gently though the sun has already slipped under the horizon.
These are nocturnal clouds, or shining at night, appearing at dusk in summer, at high levels (but never seen from within the pole circle). They consist of accumulations of ice crystals high in the atmosphere, at mesospheric heights between 76 and 85 kilometers (47 to 53 miles) above the Earth’s surface.
These tips are too obvious to see during the day, but after the sun sets under the horizon, the final rays reach high into the atmosphere, even if the star itself is not visible from the planet’s surface. There, these rays light up the clouds, causing them to shine against the dark skies. For this reason, these glorious clouds are also known as mesospheric polar clouds.
They’re incredibly beautiful – and could be scientifically useful.
“What has sparked a lot of interest in these clouds is their fragility – they occur just on the edge of high-capacity working conditions, where it is extremely dry and very cold,” he said. Richard Collins space physics from the University of Alaska, Fairbanks.
“They are a very sensitive signal of changes in the high atmosphere – changes in temperature and / or changes in water mist.”
Collins and his team thought that these clouds may have had something to do with the presence of a water valve in the upper atmosphere. So they did the same sensible thing: They loaded a suborbital rocket with water and fired it into the sky over Alaska to see if they could carry out noctilucent cloud.
To ensure that they did not mix their artificial clouds with those that were occurring naturally, they chose to launch the rocket into the pre-colored winter sky, when conditions do not appear to be so long. more suited to the formation of natural clouds than they are in summer.
On January 26, 2018, the Super Soaker rocket mission launched, with one sound rocket carrying 220-kilograms (485-pounds) of water in two canisters. Two other sound rockets went together, carrying trimethyl aluminum (TMA) detectors to monitor wind movement.
Ground test of water distribution. (NASA Wallops Flight Facility)
At an altitude of 85 kilometers, the water was released in extreme heat. Just 18 seconds later, a laser beam from Rayleigh LIDAR detected a ground-based noctilucent cloud. Over three minutes, the cloud appeared to have descended from a maximum altitude of 92 kilometers (57 miles) down to 78 kilometers (48 miles).
To find out what happened and why the cloud was shaping, the team had to be creative. Although they had an air temperature measurement, they did not have a direct measurement of the cloud temperature, so they ran simulations of night cloud formation. The symbolic conditions under which the cloud was created allowed the team to detect the temperature change that should have occurred in the experiment.
(NASA Wallops Flight Facility / Flat Poker Search Field / Zayn Roohi)
Above: Super Soaker Timelapse Launched. The green laser beam seen at the top left is the LIDAR conduit used to measure the artificial cloud.
The only way the cloud was formed was by a drop in temperature around 25 degrees Celsius (45 degrees Fahrenheit). This suggested that the presence of the water valve itself, which was released from the canisters, was to blame for this temperature drop. The increase in humidity increased the temperature of the freezing point, when the water vapor condenses on ice crystals.
The combination in the falling temperature and the increase in freezing allows the two temperatures to exceed it, which in turn causes the water mist to freeze in ice crystals.
“This is the first time a person has experimentally proven that the formation of mesospheric polar clouds in the mesosphere is directly related to cooling by a water valve itself,” said space physicist Irfan Azeem of aerospace company Astra, LLC.
This could explain, the researchers said, why night clouds appear to follow space launches. Water valves are very common in spaceflight, and scientists have seen the link many times in the Arctic summer.
In the polar mesosphere, in summer, the researchers say there is a “continuous and dynamic” rise, which tends to carry a water valve from lower altitudes and create the same effect that was observed. the team in their Super Soaker test.
“Perhaps this explains why the formation of mesospheric clouds with space traffic is seen more easily in summer than in winter,” they wrote in their paper.
“Nevertheless, while space traffic water extraction serves as a reservoir for mesospheric cloud production, this study suggests that the saw can actively cool the mesosphere and promotes the formation of mesospheric clouds, even in pole winter. “
So cloud-viewers could have a new way of predicting when they are going to happen: by following a place’s launch charts carefully.
The team ‘s research was published in the Journal of Geophysical Research: Space Physics.