On the cusp of our atmosphere live a thin group of seasonal electric-blue clouds. Forming 50 miles (80 km) above the poles in summer, these clouds are known as noctilucent clouds or polar mesospheric clouds (PMCs). This summer, a NASA balloon mission observed these clouds over the course of five days at their home high in Earth’s atmosphere. The resulting photos, which scientists have just begun to analyze, will help to better understand turbulence in the atmosphere, as well as in oceans and lakes and the atmospheres of other planets, and may even improve weather forecasting.
Atmospheric turbulence – small-scale, irregular air motions characterized by winds that vary in speed and direction – is important because it mixes and churns the atmosphere and causes water vapor, smoke, and other substances, as well as energy, to become distributed both vertically and horizontally.
On July 8, 2018, NASA’s PMC Turbo mission launched a giant balloon to study noctilucent clouds 50 miles (80 km) 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, cameras aboard the balloon captured 6 million high-resolution images filling up 120 terabytes of data storage. The images include a variety of noctilucent cloud displays, revealing the processes leading to turbulence. Scientists are now beginning to go through the images and the first look has been promising.
Noctilucent (also called night-shining) clouds coalesce as ice crystals on tiny meteor remnants in the upper atmosphere. The results make brilliant blue rippling clouds that are visible just after the sun sets in polar regions during the summer. These clouds are affected by what’s known as atmospheric gravity waves — caused by the convecting and uplifting of air masses, such as when air is pushed up by mountain ranges. The waves play major roles in transferring energy from the lower atmosphere to the mesosphere.
Dave Fritts is principal investigator of the PMC Turbo mission at Global Atmospheric Technologies and Sciences in Boulder, Colorado. He said in a statement:
This is the first time we’ve been able to visualize the flow of energy from larger gravity waves to smaller flow instabilities and turbulence in the upper atmosphere. At these altitudes you can literally see the gravity waves breaking – like ocean waves on the beach – and cascading to turbulence.
The balloons were equipped with seven specially-designed imaging systems to observe the clouds. Each included a high-resolution camera, a computer control and communications system, and 32 terabytes of data storage. The seven imaging systems were arranged to create a mosaic of wide views extending 100 miles (160 km) across, with each narrow view able to image turbulence features as small as 20 yards (918 meters) wide. A lidar — or laser radar — measured the precise altitudes of the clouds as well as the temperature fluctuations of the gravity waves above and below the clouds.
Learning about the causes and effects of turbulence will help scientists understand not only the structure and variability of the upper atmosphere, but other areas as well. Turbulence happens in fluids across the universe and the results will help scientists better model it in all systems. Ultimately, the results will even help improve weather forecast models.
Bottom line: In July 2018, a NASA balloon mission floated over the Arctic to study noctilucent clouds 50 miles (80 km) above the surface.