Searching for the elusive Polar Front

July 4th, 2018

Previous research from the ACC group aboard the Aurora Australis during a marine science voyage, SIPEXII, found that the number of atmospheric aerosols measured as we crossed the Antarctic Polar Front were an order of magnitude higher than those further north in the Southern Ocean (see figure below). Together with extensive trajectory studies, this measurement gave a brief insight into the aerosol formation chemistry that exists in the Antarctic and Southern Ocean region – a pristine region critical for the global climate. In particular, it showed that the atmosphere south of the Polar Front was distinct from the Antarctic continent or the Southern Ocean itself.

Aerosol number concentrations measured during SIPEXII show an order of magnitude step change as we crossed the Polar Front. Wind roses, calculated using in-situ data from either side of the front are shown to confirm the expected easterly and westerly patterns of the Polar and Ferrel Cells respectively. Note than CN3, CN10 and CN3-10 refer to aerosol number concentrations >3 nm, > 10 nm, and 3-10 nm, respectively.

However, due to the limited instrumentation deployed on this previous voyage, we could only go so far to understanding this phenomenon. In order to better understand the chemistry and physics of this region, we recently deployed a comprehensive atmospheric suite aboard the Aurora Australis while it undertakes its resupply seasons in 2017/18 and 2018/19. This gives us the opportunity to cross the Polar Front multiple times, as the ship traverses from Hobart to Australia’s Antarctic bases, and spend valuable time within the sea-ice region, the atmosphere of which has only been measured a handful of times.

There is a lot of data to sort through, and we are working through it rapidly along with a national and international research team. We hope that by better understanding the chemistry of this region, and by increasing the number of observations, that the significant biases in earth system and climate models that exist in the region can be reduced.

One of the optical instruments, the MAX-DOAS collects scattered sunlight from the port-side of the ship. Photo: Maximilien Desservettaz