There’s an interesting atmospheric phenomenon called Fata Morgana that will make an appearance along the horizon over the Ross Sea and Ice Shelf every now and then, and it is quite an awesome sight when you can see it right from McMurdo Station! The first time I saw it I didn’t know what was going on, so I took the opportunity to educate myself about it, and I would like to share that with all of you in this post, along with some pictures, of course!
fa·ta mor·ga·na (fä’tә môr-gä’nә): n. (Physics/General Physics) a mirage, attributed to the sorcery of Morgan le Fay [Italian, mirage, Morgan le Fay (from the belief that the mirage was caused by her witchcraft): fata, fairy (from Vulgar Latin fāta, goddess of fate) + Morgana, Morgan (probably from Old Irish Morrigain).]
A Fata Morgana is a type of complex mirage in which objects that are far away (particularly along the horizon in your field of view) are either distorted, inverted, or stretched in the vertical direction (or sometimes all of the above at the same time) so as to appear larger than they actually are. This type of mirage is commonly seen in the Polar Regions on cold days, as well as out in the open sea. Here’s a mild example of it:
If you’re as curious as I am, at this point you’re probably asking yourself how this happens. I’ll do my best to simplify the explanation (it took me quite some time and a lot of reading the same thing over and over again before I got a good grasp on it).
First off, there are a couple atmospheric conditions that are needed before you can see a Fata Morgana. One of those is that, of course, it has to be a cold day. This is important for another one of the required conditions: the presence of a “thermal inversion.” The way our atmosphere works is that as you go higher and higher the air gets colder and thinner (it expands and loses energy). A thermal inversion simply means that this pattern is reversed (or inverted): you get hot air sitting on top of cold air. On a really cold day, you can get a layer of hot air that flows over a layer of cold air, and the hot air can stay on top because it is less dense than cold air. If the temperature gradient is sharp enough (it goes from cold air below to hot air above over a relatively short distance) it will create something called an “atmospheric duct,” or a horizontal layer, in the lower atmosphere that can guide (or “duct”) light rays when they pass through it, following the curvature of the Earth. Another way of thinking about it is that, because the optical density and therefore the optical properties of hot air is also lower than those of cold air, you essentially end up with an optical lens (much like a camera lens) that can bend and re-direct the light as it goes through it. The presence of this atmospheric duct is very important because this is what creates the Fata Morgana: light is bent in the duct and arrives at your eye from a different direction than that from which it originated, making it seem like there is an object there. Here are a couple of illustrations that might help you understand that:
These figures basically depict a single point of the mirage (only one reflection, in a perfect situation), but if you can imagine that if you look in-between the mirage and the actual object you will see many other mirages of the same object, then you’re essentially imagining what happens during the Fata Morgana: you end up with a lot of mirages stacked on top of each other filling up that space, stretched from the actual object upwards into the atmosphere (the larger the atmospheric duct, the larger the effect will be) and with alternating inverted and right-side-up images, giving you the final view of a Fata Morgana.
Below are some pictures of the Fata Morgana that we have seen across the McMurdo Sound. Pretty amazing!
I have been keeping an eye out across the McMurdo Sound, trying to capture other cool Fata Morgana, but it’s been quite warm these past few weeks that we haven’t really seen much of it. As we head into the end of summer we will start getting more cold days and hopefully we’ll see more Fata Morgana. I will do my best to add some more pictures to this post through the rest of our time here!
In the meantime, enjoy these other beautiful examples of Fata Morgana from around the world (click on images for source link):
And lastly, because I’m a scientist… SOURCES:
– National Snow & Ice Data Center
– Leifi Physik
– Atmospheric Optics
– Smithsonian Magazine (Actually… awesome article about the Titanic – read it!)
– NASA Atmospheric Picture of the Day