Dr Simon Alexander – Atmospheric physicist

Qualifications: BSc (Hons), PhD

Research interests

I am an atmospheric physicist and my current research focusses on understanding the unique nature of clouds, precipitation and aerosols over the Southern Ocean and the Antarctic.

Clouds remain one of the largest sources of uncertainty in estimating global climate sensitivity. Cloud and aerosols present over the Southern Ocean are different from those in other regions of the world, due to the pristine, clean air.

One aspect of my job is co-ordinating and participating in the field deployment of instruments to monitor clouds and precipitation, including deploying specialised lidars and radars. Recently, AAD was a key partner in several major international efforts to increase our understanding of cloud processes in the high southern latitudes. These included two ship-based campaigns (one aboard our icebreaker Aurora Australis) and a major aircraft-based sampling mission, along with deployments to Macquarie Island and Davis.

We are using these data for the following key purposes. Many climate and forecast models have difficulty simulating the correct sea surface temperatures over the Southern Ocean, which is likely due to the difficultly within models of establishing the correct cloud cover, phase (ice or liquid), thickness and cloud-aerosol interactions. The result of this is that models let too much sunlight reach the ocean’s surface, heating it up. Evaluating actual surface-based (and aircraft) cloud observations against models allows us to diagnose where and why models are failing to correctly simulate cloud properties. We are also working on the characterisation of supercooled (sub-zero) liquid water clouds and the conditions in which supercooled drizzle occurs over coastal Antarctica (crucial for example for aviation purposes); and are working on the evaluation of satellite cloud and rainfall products over the Southern Ocean.

Other research interests of mine in the past included the Antarctic ozone layer; stratospheric clouds, small-scale dynamics and their interactions in relation to ozone depletion; gravity wave sources in the Antarctic; and, prior to my employment at AAD, deep tropical convection.

Current projects

AAS Projects:

Chief investigator:

Antarctic Clouds and Radiation Experiment (#4292)

Precipitation over Land and the Southern Oceans (#4387)

Co-investigator:

The Role of Shallow Convection, Mixed-phase Clouds, and Aerosols over the Southern Ocean (#4582)

CAMMPCAN – Chemical and Mesoscale Mechanisms of Polar Cell Aerosol Nucleation (#4431)

High-latitude gravity wave processes and their parameterization in climate models (#4445)

Monitoring of the Atmosphere over the Australian and Antarctic regions using GNSS radio occultation (#4469)

International Projects:

US NSF/NCAR funded SOCRATES (Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study) aircraft campaign

US Department of Energy ARM Mobile Facility: MARCUS campaign

US Department of Energy ARM MICRE field deployment

International/national collaborations

Co-author of WMO Scientific Assessment of Ozone Depletion: 2014, Chapter 3 “Polar Ozone”

Contributing author to WMO Scientific Assessment of Ozone Depletion: 2018, Chapter 4 “Polar Stratospheric Ozone – Past, Present & Future”

Committee Member, International Commission on Polar Meteorology (2015 – present)

Member, SCAR Action Group on Antarctic Clouds and Aerosols (2019 – present)

Co-Project Leader (Atmosphere), Australian Antarctic Partnership Program (2019 – present)

My work depends upon collaborating closely with scientists from a range of research institutes and universities currently including: Bureau of Meteorology, CSIRO, University of Melbourne, Monash University, NASA, University of Oklahoma, University of Washington, Colorado State University, Kitami University, UK Met Office, University of Canterbury, École Polytechnique Fédérale de Lausanne (EPFL).

Related links

MARCUS Ship Campaign: https://www.arm.gov/research/campaigns/amf2017marcus

SOCRATES Aircraft Campaign: https://www.eol.ucar.edu/content/socrates-project-overview

Cool Cloud Study http://www.antarctica.gov.au/magazine/2016-2020/issue-33-december-2017/science/cool-cloud-study

Climate models to benefit from subantarctic cloud watch http://www.antarctica.gov.au/magazine/2016-2020/issue-30-june-2016/science/climate-models-to-benefit-from-subantarctic-cloud-watch

Aurora Australis clouds campaign (ABC) https://www.abc.net.au/news/2017-10-29/antarctic-research-aurora-australis/9097100

Macquarie Island clouds (ABC) https://www.abc.net.au/news/2016-03-25/antarctic-scientists-monitoring-clouds-to-understand-weather/7274250

Publications

Alexander, S. P. and Protat, A. (2019), ‘Vertical profiling of aerosols with a combined Raman-elastic backscatter lidar in the remote Southern Ocean marine boundary layer (43 – 66°S, 132 – 150°E)’, Journal of Geophysical Research, 124, doi:10.1029/2019JD030628

Protat, A., Klepp, C., Louf, V., Petersen, W. A., Alexander, S. P., Barros, A., Leinonen, J. and Mace, G. G., (2019), ‘The latitudinal variability of oceanic rainfall properties and its implication for satellite retrievals. Part 1: Drop Size Distribution Properties’, Journal of Geophysical Research, doi:10.1029/2019JD031010, in press

Vignon, É., Picard, G., Duràn-Alarcòn, C., Alexander, S. P., Gallée, H., Berne, A. (2020), ‘Gravity wave excitation during the coastal transition of an extreme katabatic flow in Antarctica’, Journal of the Atmospheric Sciences, 77, 1295 – 1312, doi:10.1175/JAS-D-19-0264

Sato, K., Inoue, J., Alexander, S. P., McFarquhar, G., Yamazaki, Y. (2018), ‘Improved reanalysis and prediction of atmospheric fields over the Southern Ocean using campaign-based radiosonde observations’, Geophysical Research Letters, 45, 11406 – 11413, doi:10.1029/2018GL079037

ORCID:

https://orcid.org/0000-0001-6823-8857

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