NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite has captured five complete polar seasons of noctilucent (NLC) or “night-shining” clouds with an unprecedented horizontal resolution of 3 miles by 3 miles. Results show that the cloud season turns on and off like a “geophysical light bulb” and they reveal evidence that high altitude mesospheric “weather” may follow similar patterns as our ever-changing weather near the Earth’s surface…
These bright “night-shining” clouds, which form 50 miles above Earth’s surface, are seen by the spacecraft’s instruments, starting in late May and lasting until late August in the north and from late November to late February in the south. The AIM satellite reports daily observations of the clouds at all longitudes and over a broad latitude range extending from 60 to 85 degrees in both hemispheres.
The clouds usually form at high latitudes during the summer of each hemisphere. They are made of ice crystals formed when water vapor condenses onto dust particles in the brutal cold of this region, at temperatures around minus 210 to minus 235 degrees Fahrenheit. They are called “night shining” clouds by observers on the ground because their high altitude allows them to continue reflecting sunlight after the sun has set below the horizon. They form a spectacular silvery blue display visible well into the night time.
Sophisticated multidimensional models have also advanced significantly in the last few years and together with AIM and other space and ground-based data have led to important advances in understanding these unusual and provocative clouds…
1. Temperature appears to control season onset, variability during the season, and season end. Water vapor is surely important but the role it plays in NLC variability is only now becoming more understood,
2. Large scale planetary waves in the Earth’s upper atmosphere cause NLCs to vary globally, while shorter scale gravity waves cause the clouds to disappear regionally;
3. There is coupling between the summer and winter hemispheres: when temperature changes in the winter hemisphere, NLCs change correspondingly in the opposite hemisphere.
You don’t have to be a meteorologist to be interested in the weather. Even when it’s happening dozens of kilometers up in the atmosphere.