We are now entering the upper atmosphere. This allows large electric currents to flow and also means that shortwave radio signals can 'bounce off' the atmosphere and return to Earth. The bottom of the green auroral light comes from near this height. The temperature has started to increase rapidly but as the atmosphere is so thin the amount of heat energy involved is very small. At polar latitudes there are very large electric currents flowing near this height which are associated with the aurora.
Sunlight splits atoms into ions and electrons.
At night the ions and electrons here recombine, so that there are about 100 times less free electrons and ions at night than by day. This is roughly the height of the top of the green aurora. The green glow comes from oxygen atoms, much like how orange light comes from sodium street lamps. All four Australian Antarctic stations have auroral video cameras to monitor the aurora in green light every clear night. 190 km We are entering the region known as the magnetosphere, where the Earth's magnetic field plays an important part in many of the processes which occur here.