There are more silvery clouds due to human activity

Shining clouds at night can be a diagnostic tool that allows you to better understand how human activity is changing the meteorology of the mesosphere.

When the sky is dark and the Sun is just below the horizon, silvery clouds seem like ghosts in the sky. These twinkling lights, which for a long time were located only in the coldest corners of the Earth's atmosphere — at the poles, steadily crept to lower latitudes, feeding on fresh ice crystals.

How and why are these "ghosts" formed and what can they teach us?

The Earth's mesosphere, an atmospheric layer at an altitude of 50-80 kilometers, is home to polar mesospheric clouds, also known as silvery clouds. They can usually be seen in the sky of the Arctic and Antarctic in the summer months, when the humidity in the upper atmosphere is high. These clouds are formed from water ice crystals at the edge of space, where the mesosphere is the coldest.

However, over the past few decades, people have introduced a large amount of water vapor into the atmosphere as a result of industrial and agricultural activities, leading these ghostly clouds away from the poles.

Moreover, human-induced climate change is steadily cooling the mesosphere and thermosphere, making conditions more favorable for silvery clouds. Scientists want to better understand how these changes in the upper atmosphere will affect the appearance of silvery clouds, as well as how these clouds can be used as diagnostic tools to understand the meteorology of this often invisible part of the Earth's atmosphere.

A group of researchers launched a mission called Super Soaker, which in January 2018 sent three sounding rockets into the mesosphere from a facility in Fairbanks. One of the rockets carried a canister with 220 kilograms of clean water. This canister was blown up at an altitude of 85 kilometers. Two other rockets, as well as a ground-based lidar system, monitored meteorological conditions before, during and after the explosion.

The researchers found that a small silvery cloud formed just 18 seconds after the water was released, and lasted for several minutes. The explosive release of water created ice filaments of a meter in size, which quickly cooled the air by 25 °C and played a crucial role in the formation of the cloud.

"For the first time, it has been experimentally demonstrated that the formation of polar mesospheric clouds is directly related to water vapor cooling," said Irfan Azim, chief scientist at Astra in Louisville, Colorado, and principal investigator of Super Soaker.