Noctilucent clouds (NLC's) are one of nature’s most fascinating and intriguing astronomical phenomena. They are very elusive and only form when the right conditions are met. They are made of tine ice crystals that strangely appear in the summer in the northern hemisphere, when the lower part of our atmosphere is at its warmest and the upper part at its coldest because of gas expanding upwards. Around the summer mesopause, if temperatures drop below minus 120 Celsius, the rare moisture present can aggregate onto dust particles and nucleate, forming the ice particles visible in noctilucent clouds. However NLC’s are visible only when the light hits these crystals with the right scattering geometry. That happens when the sun is between 6 and 18 degrees below the horizon, and mostly when NLC’s are in the shadow of lower tropospheric cloud blocking the excessive sunlight for the viewer to see. These conditions are met essentially around the poles (between 45 and 60° north), where mesospheric temperatures are cold enough and the sun lingers in the nautical twilight. Below 45°N mesospheric temperatures may be too high and above 60°N twilights may be too bright. As beautiful as these electric-silver-blue clouds can get, they are our only way into realistically viewing what forces are at play 83km above our heads, far from the reach of airplanes or satellites. They serve as a visual indicator of wind shears, gravity waves and other disturbances that would otherwise be invisible. However they remain very mysterious and much still needs to be learned from them. That is why conducting research is challenging but important, so that we may uncover the secrets of the Earth’s weather at the edge of space, and perhaps discover more about hypothetical connections with our changing global climate. That is why I have devoted some of my free time to studying and recording noctilucent clouds from Denmark, as a way of promoting citizen science. My goal was to capture these mind-boggling shining clouds up-close using commercial cameras and time-lapse to reveal their fine structures like never before. In late June 2017, a team of research astronauts called Project PoSSUM invited me to participate in the first ever airborne NLC research campaign in my capacity as astrophotographer and science communicator. We traveled to High Level in northern Alberta, Canada as part of an international citizen-science team to study NLC’s. We operated from High Level Airport from 24 June through 7 July. Our goal was to study the clouds that form at altitudes of 83 kilometers in the polar mesosphere from a Mooney M20K research aircraft that is specially equipped with scientific camera systems designed to image the clouds. By carefully coordinating the flights with two ground stations, the team hopes to build tomography or three-dimensional images of the fine internal structures of the clouds from which turbulence and instabilities in the upper atmosphere may be better understood.
The 2017 noctilucent cloud season was a really strange one. It started off strongly at an average date of May 26th, but shortly afterwards NLC’s simply vanished. Nothing to be seen in three weeks as mesospheric temperatures were said to be too high for the clouds to form. A mesospheric ‘heat wave’ from which they would have a hard time recovering. They eventually showed up again around the end of June with normal brightness, right at the peak of the season. As I was working with citizen-astronaut candidate and graduates in Alberta, we witnessed some gorgeous displays of overlapping NLC’s and auroras, NLC’s and thunderstorms, but the pinnacle of the season was surely on July 4th, where NLC's certainly threw us a fireworks party. In spite of previously announced concerning weather conditions, we cancelled our flight sortie, but as they popped out of the blue behind breaking rain clouds anyway, we set up our ground instrument to get valuable data. No one could believe what they were seeing: huge gravity waves, countless narrow billows and even jagged-edged lacunous troughs! The whole display was moving in sync resembling an actual ocean of ice in the night sky. This chronological short film narrates the challenges, surprises and experiences of the 2017 noctilucent cloud season. I put together the different time-lapse and real-time sequences I have been taking on my own and with project PoSSUM to show the hidden beauty of noctilucent clouds. My goal is to reach out and educate the general public about this mesmerizing phenomena that many amateurs can gaze at during the short summer nights. All you have to do is to remain curious and take some time to go out there and watch!
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