Why is the upper atmosphere relevant for life on earth?

Air pressure in the  upper mesosphere lower thermosphere region (70-120km) is so low that you cannot breathe, and your blood would boil unless your body was protected by a space suit. So, why should we care? Astronauts are also part of "life on earth", and therefore their opinion also counts: When they approach earth from space, their space ship suffers an atmospheric breaking effect already as high as 120 km (this is what NASA calls "re-entry interface").

And for people on the ground? See below, "mesopause change".

The mesosphere is coupled with the ionosphere above and the stratosphere below. This means that the global circulation of the atmosphere cannot be understood by studying only the troposphere and stratosphere. The global circulation is influenced by waves that can break in the upper atmosphere. Those waves are produced in the lower atmosphere, but their upward propagation is favored or inhibited by wind systems at intermediate levels (e.g. stratospheric jets). The old idea that the "stratification" of the stratosphere means that interactions between atmospheric layers are impossible, and meteorology therefore has to deal only with the lower atmosphere, the "troposphere", is a thing of the past. The atmosphere can only be successfully described and understood as a whole. The upper limit of this "whole" is continually shifted upwards by the need to include more and more of the upper atmospheric layers in order to model the atmosphere reliably.


What is airglow?

Airglow is part of the reason why the night sky appears brighter than from starlight alone (at places far from contamination by artificial illumination). It is light emitted in the middle and upper atmosphere due to exothermic chemical reactions. Especially in the mesopause region (at altitudes of 80 to 100 km), the main source of airglow are hydroxyl molecules (OH), from a narrow layer at 86 km with a thickness of less than ten kilometers. It has a strong emission in the near infrared range. There are also emissions from oxygen atoms (a green spectral line), from sodium atoms (a pair of yellow lines), and oxygen atoms (near infrared range).

The molecular emissions can be used to determine temperature at the respective emission heights. Doing so with the atomic lines requires very high spectral resolution, but it can also be done.

See also the definition used by the American Meteorological Society.


What is a "network"?

Like an "old boy network", it´s a social system where people with similar background help each other.

But also, nowadays it´s a way of using hi tech communications to bring people from different parts of the world together to make them work more efficiently.

In NDMC, neither are we all "old", nor are we all "boys"; that´s why the second interpretation applies.


What is "mesopause change"?

While "global change" means increasing temperatures in the lower atmosphere due to increased shielding of outgoing infrared radiation by higher concentration of greenhouse gases, above heights where greenhouse gases are effective, temperatures must go down. This cooling effect is expected to be much stronger than the heating at ground level, because of the smaller heat capacity of the rarified air, so that long-term trends should be easier to detect in the mesosphere/mesopause region.