Dr Simon Alexander: 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 difficulty 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

Australian Antarctic Science projects:

  • #4292: Antarctic Clouds and Radiation Experiment, Chief investigator
  • #4387: Precipitation over Land and the Southern Oceans (PLATO), Chief investigator
  • #4582: The Role of Shallow Convection, Mixed-phase Clouds, and Aerosols over the Southern Ocean
  • #4431: CAMMPCAN – Chemical and Mesoscale Mechanisms of Polar Cell Aerosol Nucleation
  • #4445: High-latitude gravity wave processes and their parameterization in climate models
  • #4469: Monitoring of the Atmosphere over the Australian and Antarctic regions using GNSS radio occultation

International Projects:

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”

Co-author of WMO Scientific Assessment of Ozone Depletion: 2022, Chapter 4 “Polar Ozone”

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).

McFarquhar, G. M., Bretherton, C., Marchand, R., Protat, A., DeMott, P. J., Alexander, S. P., Roberts, G. C., Twohy, C. H., Toohey, D., Siems, S., Huang, Y., Wood, R., Rauber, R. M., Lasher-Trapp, S., Jensen, J., Stith, J., Mace, G. G., Um, J., Jarvinen, E., Schnaiter, M., Gettelman, A., Sanchez, K. J., McCluskey, C. S., Russell, L. M., McCoy, I. L., Atlas, R., Bardeen, C. G., Moore, K. A., Hill, T. C. J., Humphries, R. S., Keywood, M. D., Ristovski, Z., Cravigan, L., Schofield, R., Fairall, C., Mallet, M. D., Kreidenweis, S.M., Rainwater, B., D’Alessandro, J., Wang, Y., Wu, W., Saliba, G., Levin, E. J. T., Ding, S., Lang, F., Truong, S. C. H., Wolff, C., Haggerty, J., Harvey, M. J., Klekociuk, A. R., McDonald, A. J. (2021), ‘Observations of clouds, aerosols, precipitation and surface radiation over the Southern Ocean: An overview of CAPRICORN, MARCUS, MICRE and SOCRATES’, Bulletin of the American Meteorological Society, 102, E894 – E928, doi:10.1175/ BAMS-D-20-0132.1

Tritscher, I., Pitts, M. C., Poole, L. R., Alexander, S. P., Cairo, F., Chipperfield, M. P., Grooß, J-. U., Höpfner, M., Lambert, A., Luo, B. P., Molleker, S., Orr, A., Salawitch, R., Snels, M., Spang, R., Woiwode, W., Peter, T. (2021), ‘Polar Stratospheric Clouds: Satellite observations, processes, and role in ozone depletion’, Reviews of Geophysics, 59, e2020RG000702, doi:10.1029/2020RG000702

Gehring, J., Vignon, É., Billaut-Roux, A.-C., Ferrone, A., Protat, A., Alexander, S. P., Berne, A., (2022), ‘The influence of orographic gravity waves on precipitation during an atmospheric river event at Davis, Antarctica’, Journal of Geophysical Research, 127, e2021JD035210, doi:10.1029/2021JD035210

Vignon, É., Alexander, S. P., DeMott, P. J., Sotiropoulou, G., Gerber, F., Hill, T. C. J., Marchand, R., Nenes, A., Berne, A. (2021), ‘Challenging and improving the simulation of mid-level mixed-phase clouds over the high-latitude Southern Ocean’, Journal of Geophysical Research, 126, e2020JD033490, doi:10.1029/2020JD033490

Alexander, S. P., McFarquhar, G. M., Marchand, R., Protat, A., Vignon, É., Mace, G. G. , Klekociuk, A. R. (2021), ‘Mixed-phase clouds and precipitation in Southern Ocean cyclones and cloud systems observed poleward of 64°S by ship-based cloud radar and lidar’, Journal of Geophysical Research, 126, e2020JD033626, doi:10.1029/2020JD033626

Kuma, P., McDonald, A. J., Morgenstern, O., Alexander, S. P., Cassano, J. J., Garrett, S., Halla, J., Hartery, S., Harvey, M. J., Parsons, S., Plank, G., Varma, V. and Williams, J. (2020), ‘Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations’, Atmospheric Chemistry and Physics, 20, 6607-6630, doi:10.5194/acp-20-6607-2020

See more of Dr Alexander's publications on ORCID.

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