What causes red auroras?

Question

What causes red auroras?

Answer 1

"All-red auroras are seen near the beginnings of large magnetic storms, and only during some of these. At such times, large numbers of electrons originating on the sun stream into the high atmosphere. There they strike oxygen atoms resident at altitudes 200 to 500 km and cause them to emit quanta of pure red light. Normal green auroras and green auroras tinged with reddish lower borders occur at much lower altitude, typically near 100 km. The electrons that produce these auroras are more energetic than those creating blood-red auroras so they penetrate more deeply into the atmosphere. During their passage through the upper reaches, these electrons also cause red emissions from oxygen atoms but the red color usually is so much weaker than the green that it is detected only with special instruments." T. Neil Davis

Answer 2

Aurora is a diffuse of light appearing in the sky, particularly in the North and South Polar regions where it is known as the 'aurora borealis' and 'aurora australis' respectively. the lights assume a great variety of forms, and appear more frequently as arcs and 'curtains'. there is also a beautiful fan-like form known as the 'corona' or 'auroral crown'. the colour of light varies from white to red to blue and is occasionally green. it is unsteady and flickering , and sometimes sweeps swiftly across the sky in waves. some auroras can cover vast areas from horizon to horizon. displays can last a few hours or several days. it was discovered that a polar aurora occurs from 20 to 30 hours after the appearance of a 'flare' on the Sun's surface