What’s your favourite atmospheric layer?

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Scientists love to classify. While biologists get all excited about their felis silvestris catus and particle physicists can’t stop talking about that charmonium hybrid state, geophysicists quench their thirst for classification by slicing the atmosphere into layers.

What etymology tells you

The atmospheric layers are mostly defined by their physical properties and how they differ from their neighbours. Their names were chosen in an attempt to represent these characteristics. For example, troposphere – the lowest region, up to roughly 15 km in altitude, where weather happens – literally means “sphere of changes”, because turbulence plays an important role there. Next, we have the stratosphere and its stratified structure (roughly 15 to 50 km), the hot thermosphere (roughly 90 to 600 km) and the far-off exosphere (above 600 km) where the density is so low that molecules follow ballistic trajectories without colliding with each other.

Since “the more the merrier”, you can subdivide the main layers or define new layers which overlap. Cue the ionosphere in its ionized state, the D, E and F regions which absorb different radiation wavelengths, the homosphere, the heterosphere, the anacoustic zone… All named after their physical properties.

Mysterious mesosphere

The exception to the rule is the mesosphere, the layer of interest for the SCRAP experiment. Approximately located between 50 and 90 km in altitude, it is too high to be reached by aircrafts and too low for spacecrafts, meaning we have to rely on sounding rockets or indirect observations to learn about it. Because of that, the mesosphere is by far the most poorly understood layer of the atmosphere, to the point that its name basically means “that stuff in between” and that some have started dubbing it “the ignorosphere”.

Hopefully, the SCRAP experiment will contribute to unravel the mysteries of the mesosphere and to expose the expose the mechanisms behind polar mesospheric summer echoes.

A beautiful NASA photograph showing that the layers were not chosen randomly (the troposphere appears orange in the picture, the stratosphere is white and the mesosphere is the light-blue region).



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