Southern Ocean precipitation from the Macquarie Island Cloud and Radiation Experiment (MICRE)

Science

Understanding the nature of precipitation over the Southern Ocean (SO) is crucial to understanding cloud properties in this region. Climate models struggle to simulate SO clouds correctly, with significant impacts on global climate sensitivity (how much the Earth is likely to warm due to increases in greenhouse gases). Studies assessing the performance of climate simulations rely primarily on satellite measurements and reanalysis (weather prediction model assessment of the atmospheric state) to evaluate climate models in remote regions like the SO (due to the lack of available surface measurements). However, there is limited confidence in the satellite and reanalysis data for the SO. This study examines precipitation characteristics obtained from a recent field campaign located at Macquarie Island, in the middle of the SO, and uses these data to examine precipitation from (arguably) the best available satellite data set over the region, namely that from the NASA CloudSat radar.

Impact

The data and publication highlighted here document many physical characteristics of SO precipitation, which will be helpful in evaluating both models and satellite data sets. As regards the CloudSat radar precipitation retrievals, in particular, the study reveals some good and some poor aspects of these data, and importantly, suggests some pathways to improving the satellite data.

Summary

The wide-spread low-altitude clouds that dominate total cloud cover of the SO are frequently precipitating with liquid, frozen, and mixed-phase precipitation. The primary addition that MICRE measurements and the present analysis provide to previous data sets and studies comes from having a year of W-band radar, ceilometer, and disdrometer measurements that allow for a more detailed examination of seasonal, diurnal, and synoptic variations in surface precipitation type and particle size (in addition to accumulation) than has previously been possible. A few of the key results are summarized in the associated highlight slide with more to be found in the published article (Tansey et al. 2022). This is one of several papers documenting MICRE data sets. An earlier paper by Hinkelman and Marchand (2020) examined the diurnal cycle of surface radiative fluxes and showed that CERES satellite retrievals have a significant seasonally varying bias in the surface longwave fluxes. A third paper looking at low cloud properties and their dependence on environmental factors is coming.  MICRE was part of a coordinated set of SO experiments that took place between 2016 to 2018, an overview of which can be found in Mcfarquhar et al. (2020).

Hinkelman, LM, and R Marchand. 2020. "Evaluation of CERES and CloudSat surface radiative fluxes over Macquarie Island, the Southern Ocean." Earth and Space Science 7(9): e2020EA001224, https://doi.org/ 10.1029/2020EA001224

McFarquhar, GM, et al. 2020. "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(4): E894-E928, https://doi.org/10.1175/BAMS-D-20-0132.1

Tansey, E, R Marchand, A Protat, SP Alexander, and S Ding. 2022. "Southern Ocean precipitation characteristics observed from CloudSat and ground instrumentation during the Macquarie Island Cloud and Radiation Experiment (MICRE): April 2016 to March 2017." Journal of Geophysical Research: Atmospheres 127(5): e2021JD035370, https://doi. org/10.1029/2021JD035370