The Antarctic sky was filled with nocturnal clouds …

The Antarctic was populated by bright night clouds. the noctilucent clouds, which glow at night, are a typical phenomenon of polar summers. The AIM (Aeronomy of Ice in the Mesosphere of NASA) mission detected the first clouds on December 8 and the following days they filled the Antarctic sky.

Usually, rotating nocturnal clouds cover the pole. This season they have had a slow start and are rarer usual. Too appeared lateScientists generally expect them to appear in mid-November and last until mid-February.

How and why do nocturnal clouds form

The bright blue and white clouds travel about 75 kilometers high in a layer of the atmosphere called mesosphere. During the summer, this region has the three ingredients that darken they must form: extremely cold temperatures, water vapor and meteorite dust.

In summer, the mesosphere is more humid, because the relatively humid air circulating from the lower atmosphere brings more water vapor. Meteor dust comes from meteors, which turn to dust when they fall and burn in the atmosphere. Noctilucent clouds form when water molecules coalesce around this fine dust and freeze.

Also known as polar mesospheric clouds because they tend to cluster around the north and south poles, clouds help scientists better understand the mesosphere. The mesosphere is where the neutral atmosphere begins to pass into the electrically charged gases of space. From the mesosphere upwards, the atmosphere is constantly in motion, shaped by solar activity and near-Earth space above and the lower atmosphere below.

“Every year we look at things that might predict the start of the season, and then we research and try to assess where our understanding is at,” said James Russell, AIM principal investigator at Hampton University in Virginie, in a press release. Some factors that scientists consider are seasonal temperatures, the size of the ozone hole, air currents, and westerly winds.

he unusual weather conditions in Antarctica led scientists to expect late noctilucent clouds. The size of the ozone hole is at an all time high for this time of year. The westerly winds are blowing with unusual force. The polar vortex, which traps the icy air above the poles, is also very important. This all equates to a long winter, late spring, and a slow start to the nightly cloudy season.

Flying clouds also help scientists study gravity waves, which are powerful air waves that form when winds brush past disturbances on the Earth’s surface, such as mountain peaks, or churn rate. in weather systems. severe like thunderstorms. Gravity waves rise in the sky, connecting the lower and upper atmosphere. Observing the impact of nocturnal clouds is one way of studying how gravity waves affect the mesosphere in general. NASA’s AWE mission, due to launch in 2022, will also contribute to gravity wave research and complement AIM observations.

It is easy to think that gravity waves are waving upwards. But a study carried out earlier this year found that the most influential gravity waves for clouds – that is, the upper atmosphere – could be those that rise like an escalator – up and down. ‘before at the same time. Gravity waves that travel in this way tend to form during tropical monsoons, then rise up from the tropics and through latitudes. The study analyzed the value of eight nocturnal cloud seasons and combined observations from the AIM and NASA TIMED mission.

When AIM was launched in 2007, scientists believed they understood the relationship between noctilucent clouds and the solar cycle, the Sun’s natural cycle of activity over 11 years. But the connection appears to have disappeared by early 2005. Noctilucent clouds are sensitive to both water vapor and temperature in the upper atmosphere, and the solar cycle affects both at its altitude. However, even as the Sun progressed through its regular highs and lows, the clouds shone with more or less the same intensity. There seems to be a delicate balance that scientists do not yet fully understand.

“Nighttime clouds are affected by influences from above, like the Sun, but also from below, like gravity waves,” said Scott Bailey, AIM deputy senior researcher at Virginia Tech. “At this point, it seems the forces below are in control,” he added.

he The start of the 2020 Antarctic nighttime cloud season marks about one year in the current solar cycle, which debuted in December 2019. As AIM continues to imagine clouds, scientists hope the long-term growing record will give clues to these puzzles.

“Since the launch of AIM, we have found that the processes that control clouds are very complex,” said Russell. “We need as much data as possible.”