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Beautiful sub-auroral arcs across the sky: what we know so far about the phenomenon

October 14, 2017

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The first noctilucent clouds of the season are here!

May 26, 2017

We have been waiting a long time for their return. As planet Earth's mesosphere gets colder, the nucleation of ice particles and the right conditions are giving birth to NLC clouds, and it's happened last night for the first time!

 

 

On the night of May 25th-26th, a noctilucent cloud (NLC) display was visible from Ordrup strand, Odsherred in Denmark. Mainly type I and II were visible, and they started rising from the northern horizon at about 12.50 pm UTC as a type I front, developing into type II till about 2 in the morning UTC. 

 


This phenomenon, also known as noctilucent (from Latin, 'night shining') clouds, is usually observed at mid to high latitudes, between 50 and 65 degrees North and South from the equator. Nonetheless they can be seen at lower latitudes low on the horizon, but it is usually too dark. At higher latitudes, the summer sun never sets, making it impossible to see them.
 

 
In the summer the Earth is at its farthest away position from the sun on its orbit ellipse, causing the upper layer of the atmosphere, called the mesosphere, to cool down significantly. This layer is virtually dry but very little moisture can be brought from different origins (some speculate from meteorites or shooting stars, rockets...). This moisture gets instantly frozen into super tiny ice crystals that dance and form patterns in the mesosphere currents. These particles are usually not visible to us because the sun's rays pass in front of them. But let's say some lower clouds (tropospheric clouds) were to block these rays in front leaving some back rays to illuminate the night sky? If all these conditions are present, a great spectacle of noctilucent clouds is possible for you to observe!

 

 

Last night was a weak display but not unusual for the season, as the clouds are just starting to develop (See on the panorama above).

 

 

I was really excited about the real first NLC display this season that I erased some real-time footage, and also made some rookie shooting mistake, resulting in an annoying flicker, so please excuse me about that. However, you can taste the atmosphere of the whole night, plunged into the deep twilight: what a mesmerizing moment.

It is very promising, and I have a hunch we are going to witness some great shows this season! Keep in tune for more exciting NLC videos!
 

 

 

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