For the first time this Antarctic winter, but a little later than usual, polar stratospheric clouds have been detected up to 25 kilometres above Davis research station.
The research is part of a long-term monitoring program to see how atmospheric changes from global warming at the surface may affect the Antarctic ozone hole.
The thin high altitude cloud layers are being investigated by the Australian Antarctic Division’s recently-commissioned POLAR (polarisation light detection and ranging) instrument, which sends pulses of green laser light through the atmosphere.
Polar stratospheric clouds play an important role in the formation of the annual Antarctic ozone hole by enhancing the potency of human-produced ozone destroying chemicals.
The clouds consist of tiny droplets of watery nitric and sulphuric acid mixed with ice crystals, and form in the very low temperatures of an Antarctic winter.
AAD atmospheric physicist Dr Andrew Klekociuk said his team first detected the clouds between altitudes of 16 and 25 km on 13 June.
“This is about two weeks later than our detections in earlier years”, Dr Klekociuk said.
“The upper levels of the atmosphere at the edge of Antarctica were a few degrees warmer than the long-term average in early June, and this delayed the appearance of the clouds until temperatures above Davis fell below their formation threshold of about -80°C.”
The above-average temperatures were likely caused by disturbances to the Antarctic stratosphere, which is the atmospheric region above 12 km altitude.
Such disturbances are a usual feature of the Antarctic winter, due to the influence of strong weather systems moving over the Southern Ocean.
Dr Klekociuk said that weather balloon measurements show temperatures in the stratospheric cloud layers were between -88 and -94°C.
“We expect to detect further layers of polar stratospheric clouds over the coming weeks as the Antarctic atmosphere continues to cool in the winter darkness”, he said.
The POLAR instrument is central to the Antarctic Cloud and Radiation Experiment (ACRE) research project led by Dr Simon Alexander, an atmospheric scientist at the AAD.
ACRE is assessing the properties of clouds over coastal Antarctica and the Southern Ocean to improve the accuracy of Australian weather forecasting and climate modelling.
“Our POLAR instrument automatically measures the location and properties of clouds and small particles in the atmosphere using pulses of green laser light”, Dr Alexander said.
“Together with other measurements from Davis research station and over the Southern Ocean, we are gathering important new details on the structure of Antarctic clouds and how they interact with the flow of energy in the atmosphere.”
POLAR began measurements at Davis in November 2018, after spending two years at Macquarie Island, and will run until the end of this year.
