Australian Weather Calendar: January 2020

January Photograph by Aaron Stanley, APS Photography

A bright light during dark days

It's not just the weather extremes that make Antarctica one of the harshest places to live in the world—the continent is subject to periods of complete darkness during winter, and 24 hours of daylight for a time over summer. Aaron Stanley experienced all the high and lows of life on the icy continent while working for the Bureau of Meteorology as a Technical Officer/Engineer at Davis Research Station in 2016. His account from the time paints a vivid picture of the conditions he braved to capture the aurora australis: 'The sun set for the final time here at Davis station on 2 June at 1:58 pm, just 24 minutes after sunrise. We will see the sun again in 38 days, but only for 45 minutes. To help illuminate the night sky, the aurora has been putting on a spectacular display that lasted three days! At 2 am on Monday morning I rang the aurora hotline, waking up my fellow aurora-hunting expeditioners to be greeted with a very fast-moving aurora overhead. Then again at 1 am on Tuesday morning there was a large, fast-moving band overhead. It was not for the faint-hearted, as the temperatures outside were between −27 and −30 °C. I would describe it as a pianist playing fast-tempo music of light with no sound, the beams moving rapidly and swirling. Not much sleep was acquired during this time.'

The science

The swathe of green light shown here is a space weather phenomenon called 'aurora australis' or the southern lights—a common sight in Antarctica but sometimes also visible from southern Australia. Auroras are the result of events that begin on the Sun. The Sun is so hot that high-energy plasma (a gas of electrically charged particles) can escape from its gravitational field—known as solar wind. As these charged particles approach Earth, they're directed by the planet's magnetic field towards the north or south poles. Upon entering the atmosphere, they collide with atoms and trigger light emissions. The patterns and shapes of the aurora are determined by the changing flow of charged particles and the varying magnetic fields. The colour emitted depends on how energetic the collisions are, where they occur in the atmosphere and which atoms and molecules are involved. Oxygen releases greenish-yellow or red light, while nitrogen releases dark red or blue light.