During this past summer season at McMurdo we experienced numerous occasions of heavy fog. The fog would form over the ocean/sea ice and would creep up the slopes into town and even up to the laboratory. This type of fog was particularly frustrating for running our lidar systems since it was so hard to predict. Even if the predictions were correct on whether or not the fog would form, it was impossible to know if it would make it up into the hills and over the Arrival Heights laboratory where the lidar systems are located. If it made it over the laboratory, it was difficult to know whether the fog would burn off quickly or remain stable over the lab. Since the lidar systems can take 1-2 hours to turn on and up to an hour to shut down, the consistent fog over the summer was troublesome.
Where did this fog come from? There are several possible formation mechanisms, but what we observed likely resulted from interactions between relatively moist air over the ocean or melting sea ice and much colder air over the ice shelf and continent. These types of fog are known as steam fog, advection fog, or upslope fog (depending on how the moist air and cold air come into contact).
If cold continental air moved out over the relatively warmer open water, it could produce steam fog, where rapid evaporation into the cold air leads to immediate condensation. If moist air from the ocean moved over the colder snow-covered surface, it would cool from below and form advection fog. Finally, if moist air was forced up the local terrain—such as into the hills or up the slopes around Ross Island—it would cool as it rose and form upslope fog.
These three different fog formation mechanisms were likely all a part of the fog that continued to bother us over the summer, which is a part of why it was so difficult to predict. All three types of fog can be seen in the photos below.
Above: This is likely steam fog, since it rests directly over the ocean and doesn’t expand over the land. It may be hard to see the ocean beneath the fog, but I can confirm that the fog rests over the ocean and stops at the shore, at the edge of town. The location points to the fog formation being caused by evaporation from the open water immediately condensing in the cold air.
Above: This is likely advection fog. Since the fog has formed only over the snow, it is most likely that moist air from the ocean blew over the snow and condensed into fog when it hit the relatively cooler temperatures. It may be difficult to tell due to the fog, but there is an expanse of ice and snow beneath the fog and the fog seems to barely come past the boundaries of the snow. On a clear day, it’s likely that the sun warms the volcanic dirt but not the snow, creating a temperature imbalance with cold air over the snow and warmer air over the soil, which results in advection fog over the snow that doesn’t expand far past the borders.
Above: This is an example of upslope fog. As the moist air is forced up the slope of the hill (likely by wind), it cools and forms upslope fog. In this image there is a combination of multiple different types of fog, including steam fog over the open ocean, and upslope fog in the places where it is forced up hills.
