The dynamics of the atmosphere

30 April 2024

Since 1982, a long-term research study from the University of Canterbury has been examining the dynamics in the atmosphere above Antarctica, producing one of the longest records for Antarctica's atmospheric winds and wind speed. The dynamics studied vary from the wind speed created by atmospheric tides to the types of clouds, and snowfall.

One of the instruments that has the capability of measuring the winds and tides in the middle atmosphere, – about 100km altitude, is the medium-frequency (MF) radar system. The MF radar is a transmitter located at Scott Base that fires pulses of radio waves into the atmosphere via a single antenna. The radio waves hit electrons in the middle atmosphere. Some of this energy is then radiated back down towards the Earth’s surface, where it is picked up by three sets of receiving antennas at Arrival Heights (an area on Ross Island that is dedicated to long-term science in Antarctica). The analysis of the travel time of the radio waves provides information on the altitude of the scattering layers and wind motion in the middle atmosphere.

Like the tides we know in the ocean, the ones in the atmosphere move around, controlling and influencing many processes that affect our climate today. Atmospheric and oceanic tides share many of the same features, but two attributes truly distinguish the two. As many will know, oceanic tides are motivated by the moon's gravitational pull, whereas atmospheric tides are excited by the sun's heating of the atmosphere.

The team completing maintenance on research equipment. Photo: Graeme Plank

Another feature that varies between the two types of tides is that atmospheric tides move through the air, where the thickness of the air changes with increased altitude. This means the tides get bigger as they move higher up because the air gets thinner. In contrast, in the oceans, the water doesn't change much in thickness as you go deeper, so the tides don't necessarily get bigger with depth.

The project also investigates clouds and snowfall with an instrument that shoots infrared light from a laser into the sky. The infrared light bounces off the clouds back to earth and tells us about the altitude, type, and position of the clouds. Researchers are measuring the snowfall in correspondence with the data gathered on the clouds. Looking at the statistics, they can determine things about the type of snow and the type of clouds that the snow falls from — to work out how efficient different clouds are for snowfall at the surface of Antarctica. It also helps to tell explain the weather systems that are happening at certain times and the processes involved. As climate models are poor at telling us about snowfall and clouds, this team is striving to potentially marry the two to understand precipitation and snowfall over Antarctica through their work with the Deep South National Challenge.

Why care about snow and clouds? It is apparent today that Antarctica's glaciers and sea ice are melting due to climate change. However, climate change is also making the air warmer, resulting in the clouds holding more precipitation (moisture), and the extra humidity means that there will be more snowfall over Antarctica. Increased temperatures therefore have the potential to melt the ice, but also to increase snowfall. Studies have shown that in Greenland, increased temperatures have caused glaciers to retreat further inland, but in turn, the increased precipitation has also intensified snowfall in the area, which has slowed warming in the short term.

As the world warms more, atmospheric rivers—which are defined as slender, extremely moist corridors that stretch from low to high latitudes—will likewise become more common. Because Antarctica is the world's largest desert, atmospheric rivers are relatively uncommon there; however, they are not unheard of.

According to Professor Adrian McDonald of the University of Canterbury, who has worked on the project for 21 years, "one atmospheric river that reached Antarctica in about 2016 created one big snowfall event that basically offset all melting in Antarctica for a year, which was equivalent to 1 ml of sea level rise." This is why it is so important to collect and comprehend this data.

In response to being questioned about this research, Adrian responded, "Long-term records have surprised us before; for example, the ozone hole was discovered by an instrument that was from the 1920s rather than the modern satellites that were put up there specifically to find it. These long-term records are really important for discovering change that is over the planet."

Overall, the information helps Adrian and his team understand how variations in the middle atmosphere are linked to changes in the Earth’s surface climate and monitor the impact of human-induced change on the Antarctic atmosphere. Data are also used to improve global climate models.

K055 photo 1 – The team completing maintenance on research equipment. Photo: Graeme Plank

Top photo: A 360 view of the team completing maintenance on the wind mast that helps provide data for the overall research project.