What effects do auroras have on the Earth?

Very minor. Like the proverbial 'miner's canary' they are just passive indicators that something is not well with the Earth's magnetic field and space environment. Directly below an auroral display, the magnetic field of the Earth is modified slightly because of the particle 'electric' currents generated by the incoming particles that, incidently, produce the aurora. When aurora are prevalent, the magnetic field of the Earth and the ionosphere are rapidly changing and this can effect surface communication which uses the ionosphere as a reflector to bounce the signals. Aurora just tell you something is going on, but they are not the causes of the activity....just the shadows on the wall!

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY Education and Public Outreach program.