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Sunday, June 12, 2011

Aurora Australis

We are only a few days away from the winter solstice (that will occur on June 21 here in the Southern hemisphere).  This is also the darkest of the polar night, yet the sky is all but dark.  We have been blessed this year with spectacular auroras.  Some are brighter, some more colorful, and some have more structure than others, but a day does not go by without auroras showing off in our sky.  I spend an average of 3 hours outside every day, and I would be hard pressed to remember a day when I did not see auroras.  Auroras are produced by charged particles (electrons and protons) emitted by the sun.  When these particles approach our planet, they follow the field lines of our magnetic field, and therefore move towards the polar regions, where the magnetic field lines concentrate.  Before they can reach the magnetic poles, though, at a height of about 300 km from the surface of the earth, they excite oxygen molecules, which then glow just like a fluorescent light does.  Because the particles coming from the sun move at supersonic speed, so do the auroras.  They seem to constantly dance in the sky, 300 km above us.  Some of them last 10 or 15 minutes; others last as long as one hour.  This has been a very good year for observing auroras, as the sun is approaching a maximum in its emission of particles: a maximum that occurs with a periodicity of 11 years.  The South Pole, located approximately 1,000 km away from one of the two magnetic poles of the earth, is one of the best locations on the planet to observe auroras, and that is why a lot of the scientific research that we do here has to do with observing auroras and correlating the observations with other celestial phenomena.
It takes good photographic equipment, a tripod, a lot of patience, and tolerance to the cold to take good pictures of auroras.  Lacking a good camera and patience, I thank Christy and Jens for letting me use some of their photos in this blog.  All the photos shown here are raw images.  Typical exposure times are about 10 seconds.

This is what most auroras look like here at the Pole: spanning a large portion of the sky, glowing green.  Notice the stars in the sky and the Atmospheric Research Observatory at the bottom of the frame.  This aurora happened on June 6.  Photo by Christy.

This aurora, on May 25, shows some interesting structure, twisting away at the far right, and with a hint of red color.  In the foreground are the pole marker on the right and the sign commemorating the arrival of Amundsen and Scott 99 years ago.  Photo by Christy.

I call this a lenticular aurora, covering a large portion of the sky in a round shape.  This aurora occurred only a few days ago, on June 9, and was part of a series of auroras that came on display almost continuously for a period of 12 hours following a massive ejection of particles from the sun called a coronal mass ejection (CME).  We were alerted to this event from observations of the sun made by NASA.  Typically, it takes two days for the particles emitted in a CME to reach the earth and manifest themselves as auroras, so we had time to get ready.  Photo by Christy.

This is a beautiful, bright, and colorful aurora that occurred on May 3.  On the left is the Amundsen-Scott South Pole Station.  Photo by Jens.

I was skiing to the Ice Cube Laboratory under a nice aurora, on May 2, when I met Jens, who was walking to the same building, but had stopped to take a photo of the aurora.  I like his photo because it gives a realistic representation of how a typical aurora brightens the surroundings.  In the background are, from left to right, the 10-meter South Pole Telescope, and MAPO, a building that houses two additional microwave telescopes.

Auroras happen all the time, in the summer and in the winter.  It is just that during the summer we cannot see them because the light from the sun overwhelms them.  A full moon, though, is not sufficient to blind some of the brightest auroras, as shown here on May 19.  Photo by Christy.

As I said, auroras move very rapidly.  In this sequence taken by Christy an Aurora is seen starting at the horizon, then move overhead.  All the photos are taken under the same exposure settings.  The time stamp below each photo gives an idea of the speed at which the aurora is moving.  Also notice how much brighter it gets as the aurora moves overhead.  The building on the right is NOAA's Atmospheric Research Observatory.

This is what an aurora looks like to the eyes of a research camera.  It happens to be one of the experiments that I am responsible for.  This image is taken by a high resolution, black and white, all-sky camera, that takes 180 degrees images of the sky through several color filters tuned to the particular frequencies of the light emitted by the auroras.  Because of the filters, this camera is mostly insensitive to other lights, such as the light from the moon, which appears as a yellow spot on top of the image.  In reality the moon is much much brighter than the aurora, but the trick with the filters allows the aurora to be clearly visible.  These images are publicly available on the website where you can see the evolution of auroras at the South Pole hour by hour.  Another interesting website is where, in the austral winter, you can see time lapse images of auroras shown as movies.  Those photos were taken a few years ago by Robert Schwartz, who is wintering here with us again this year.

Finally, a quick note on the weather.  Despite global warming, we had the coldest May on record here at the South Pole, with an average temperature of -62.6 C (-80.7 F).  Luckily it was not a windy month, so my outdoor activities were not impacted.  On May 27 the thermometer dipped for the first time below the -100 F limit, reaching a minimum of -103.4 F (-75.2 C), as seen in this screenshot from the weather page of our intranet.  The photos on our weather page changes every 15 seconds and serve us a reminder of the world that awaits us back when our time here at the Pole will come to an end only five months from now.

1 comment:

  1. Marco,
    Thanks for the photos and the explanation. I had no idea how quickly the auroras move across the sky. You mention that your are still skiing in the dark and cold. If you have time and energy to answer questions, what do you wear that is different from your summer togs and how do the skis glide at 60-80 below? Thanks.