The delay has caused to me think about my time in Antarctica and how much things have changed in the 5 weeks I’ve been here. The weather, which was brutally cold when we first arrived has moderated substantially. During the first couple of weeks of our time in Antarctica we needed to bundle up and cover all exposed bits of skin to face temperatures in the -40s F and wind chills as cold as -90 F.

Waiting on the sea ice to drive from McMurdo to Pegasus. This photo was taken on September 2nd when the temperature was near -30 F with strong winds creating bitter wind chill temperatures and blowing snow. On the next day the temperature dropped to -49 F, which set the all-time record low temperature for McMurdo in September.

Now our high temperatures are around 0 F and it is warm enough that for short walks around the base we can go outside in light fleece jackets without wearing a hat or gloves. It is amazing how quickly the human body adjusts to this harsh environment, since before we arrived in Antarctica I’m certain we all would have thought that a temperature near 0 F was bitterly cold and required bundling up in many layers of clothes.

When we arrived in late August the sun was up for just over 5 hours per day, and was barely peeking above the horizon, with pitch black nights. Today, the sun was up for nearly 15 hours, with the night sky not getting completely dark as the sun skims just below the southern horizon at midnight.

McMurdo at night.

One thing I had been hoping to see on this trip was the Southern Lights. On the night of our first successful Aerosonde flight to Terra Nova Bay I was fortunate enough to step out of the lab for a little while to get some fresh air and noticed the Southern Lights shimmering overhead.

Southern Lights over Black Island and Mt. Discovery. A faint glow from the sun is seen over the southern horizon in this picture taken near midnight.

On my previous trips to Antarctica I’ve never experienced sunrise or sunset, as it had been light 24 hours per day for months on end. I’ve enjoyed watching the sunrise and sunset every day while here for this WinFly trip.

Sunrise over Ross Island.

The cold Antarctic atmosphere is capable of creating some stunning, and sometimes disorienting, optical phenomena. One interesting optical effect we’ve seen quite a bit of is called a fata morgana. A fata morgana only occurs when there is a sharp increase in temperature with height through a thin layer of the atmosphere. When temperature increases with height in the atmosphere it is referred to as an inversion, since this is normally the opposite of what normally occurs in the lower part of the atmosphere. When a very strong inversion exists light reflected from objects on the horizon gets bent, causing objects near the ground to appear to be elevated. In the case of small rocks near the ground, these rocks appear to be large cliffs.

Fata morgana from Pegasus runway. In this photo you can notice distortion near the horizon, at the base of the mountains and also about halfway up the side of the mountains. These areas that appear to be cliffs are actually optical illusions called fata morgana.

The distortion of light as it passes through the atmosphere is not confined to just near the surface. One day while watching the moon pass behind Mt. Discovery I noticed that the moon was not circular in shape, but instead had an irregular outline. The wavy appearance of the moon’s outline was due to differential distortion of the light reflected from the moon as it passed through the atmosphere.

Moon over Mt. Discovery. Note the distortion in the circular shape of the moon. This is most evident on the top left side of the moon in this image.

An atmospheric phenomenon that is unique to the polar regions in winter is polar stratospheric clouds. Almost all clouds that we see in the atmosphere form in the lowest layer of the atmosphere, known as the troposphere, which extends to a height of about 6 miles in the Antarctic. Polar stratospheric clouds form at heights of 9 miles or more, in the layer of the atmosphere known as the stratosphere. Normally no clouds form in the stratosphere due to the dry conditions in this layer of the atmosphere, but at very cold temperatures, what little water does exist can condense to form clouds. Polar stratospheric clouds form at temperatures less than -78 C (-108 F) and are often made up of both frozen water and nitric acid. These clouds are more commonly referred to as nacreous clouds, with the root of the word nacre meaning mother of pearl. The name comes from the stunning mother of pearl coloration of these clouds.

Nacreous clouds from Pegasus ice runway.

Because these clouds are so high in the atmosphere they remain lit by the sun long after the surface and lower clouds have fallen into shadow as the sun sets. This is similar to how the top of a tall building remains lit by the setting sun after the base of the building has already passed into shadow.

Nacreous clouds over Hut Point and McMurdo Sound. The building visible on the horizon is the hut built for Robert Falcon Scott’s first Antarctic expedition at the start of the 20th century.

While I’ve enjoyed this trip to Antarctica more than any of my previous trips, and am very happy with the data we’ve collected I’m hoping that my next blog post will be from New Zealand or back home in Colorado.