An amazing video: a recent NASA long-duration balloon mission observed a thin group of seasonal electric blue clouds which are known as noctilucent clouds or polar mesospheric clouds (PMCs). Forming 50 miles (80 km) above polar regions in summer they are Earth’s uppermost clouds and only visible around twilight. PMCs are composed of ice crystals that glow bright blue or white when reflecting sunlight.

A recent NASA long-duration balloon mission observed noctilucent clouds or polar mesospheric clouds (PMCs) over the course of five days at their home in the mesosphere (see Notes 1). The resulting video is amazing.

Noctilucent Clouds

Also known as Polar mesospheric clouds (PMCs) or night-shining clouds, Noctilucent clouds are tenuous cloud-like phenomena in the upper atmosphere of Earth. They consist of ice crystals and are only visible during astronomical twilight. Noctilucent roughly means “night-shining” in Latin.

They are most often observed during the summer months from latitudes between 50° and 70° north and south of the Equator. They are visible only during local summer months and when the Sun is below the observer’s horizon, but while the clouds are still in sunlight.

Noctilucent clouds
Forming 50 miles (80 km) above polar regions in summer they are Earth’s uppermost clouds and only visible around twilight. Image: Kevin Cho

Atmospheric motions like airflow over mountains or thunderstorms can disturb the atmosphere and cause waves that can propagate to very high altitudes. These waves are known as gravity waves. Although they are invisible, they can be seen as they move through Noctilucent clouds.

Gravity waves lead to turbulence: chaotic movement in the atmosphere that can influence weather and climate and their predictions. But, the exact causes and effects of turbulence are not well understood.

To better understand this complex process, on July 8, 2018, NASA’s PMC Turbo mission launched a giant balloon to study PMCs at a height of 50 miles above the surface. For five days, the balloon floated through the stratosphere from its launch at Esrange, Sweden, across the Arctic to Western Nunavut, Canada.

During its flight, a laser radar on the balloon measured the altitudes of Noctilucent clouds and the atmospheric temperatures that affect their formation and brightness. Also, cameras aboard the balloon captured 6 million high-resolution images filling up 120 terabytes of data storage – most of which included a variety of PMC displays, revealing the processes leading to turbulence. Scientists are now beginning to go through the images and the first look has been promising.

A better understanding of turbulence can help to improve weather forecast models and our understanding of processes around Earth which affect our satellites and assets in the orbit.


  1. The mesosphere (from Greek mesos “middle” and sphaira “sphere”) is the layer of the Earth’s atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define its limits: it begins at the top of the stratosphere (sometimes called the stratopause) and ends at the mesopause, which is the coldest part of Earth’s atmosphere with temperatures below -143 °C (-225 °F; 130 K). The exact upper and lower boundaries of the mesosphere vary with latitude and with the season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at heights from 50 to 65 km (164,000 to 213,000 ft; 31 to 40 mi) above the Earth’s surface and the upper boundary (mesopause) is usually around 85 to 100 km (53 to 62 mi).


M. Özgür Nevres

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