Studying Clouds in the Antarctic with Micro Pulse LiDAR

Researchers in the Australian Antarctic Science project collected aerosol data above the Southern Ocean to improve their understanding of the connection between clouds and climate change.

Evaporation and condensation are the basic concepts leading to cloud formation; however, many factors impact the end results. In general, as water vapor molecules rise from the surface of the Earth, they interact with aerosols (such as dust, gas, sea salt and pollen) and clump together around each particle. With only a few large aerosols present, large water droplets form and fall back to Earth as rain, snow, hail, etc. If there are many tiny particles in the atmosphere, only a small amount of moisture attaches to each one, which can lead to suppressed rain, drought or violent weather events. Air temperature, air pressure and the light-absorbing properties of different types of aerosol also play a role and add to the complexity. Studying the characteristics of the cloud-formation process provides more accurate input to climate models.

The Southern Ocean around Antarctica is a remote environment, far from most human sources of pollution. Although little data have been collected in the past, it is an attractive area for researchers to study due to the ocean’s impact on the Australian climate. The Australian Antarctic Science campaign, led by Dr. Robyn Schofield from the University of Melbourne, set out to answer questions about the aerosols in the atmosphere above the Southern Ocean to help fine-tune climate forecasts.

A mobile air chemistry lab named AIRBOX (Atmospheric Integrated Research facility for Boundaries and Oxidative Experiments) was used to collect the necessary data. Some of the meteorological instruments are housed in a customized shipping container, while the Mini Micro Pulse LiDAR (MiniMPL), which performs continuous aerosol and cloud profiling, is a stand-alone unit. The MiniMPL’s dual-polarization capability creates a vertical profile up to 15 km from the surface by discriminating between sea salt and other aerosol layers. This also provides the most accurate information about the local Planetary Boundary Layer (PBL) height, the layer of the atmosphere that interacts strongly with the surface and influences climate, weather and air quality.

In addition to the MiniMPL system, AIRBOX instruments include an ozone monitor; a trace gas analyser to measure greenhouse gases; a spectrometer to measure ultraviolet and visible light and chemicals; and a photometer to measure the in-situ aerosol optical absorption properties of PM2.5 and PM10 particles. There are nine sensors in total with extra room for “guest” instruments. With most of the sensors co-located in or around one container, the laboratory is easy to move to any desired location.

AIRBOX was installed on the icebreaker ship Aurora Australis from October 2018 to March 2019 to collect data during resupply trips serving permanent research stations located at Davis, Casey, and Mawson on the Antarctic continent and Macquarie Island in the Southern Ocean. This area offers a unique atmosphere with sea salt accounting for up to 70% of the aerosol content and lower clouds tend to form with very large water droplets and super-saturated droplets where water and ice co-exist. Although the connection between clouds, aerosols in the clouds, and climate change has been scientifically established, climate models could be improved by more in-depth research.

Researchers seek to validate theories about the connection between clouds and climate by determining where the aerosols that form clouds are coming from and what chemical processes are contributing to their formation, as well as assessing the light-absorbing properties of different types of aerosols and the unique characteristics of each particle.

For more information about AIRBOX research go to http://www.antarctica.gov.au/news/2018/seeding-southern-clouds or follow Dr. Schofield’s work at https://airbox.earthsci.unimelb.edu.au/.