Assessing the cloud radiative bias at Macquarie Island in the ACCESS-AM2 model

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Pei, Zhangcheng, Fiddes, Sonya L., French, W. John R., Alexander, Simon P., Mallet, Marc D., Kuma, Peter, McDonald, Adrian
• Format: Text
• Language: English
• Published: 2023
• Subjects: Macquarie Island; Southern Ocean
• Online Access: https://doi.org/10.5194/acp-23-14691-2023; https://acp.copernicus.org/articles/23/14691/2023/

As a long-standing problem in climate models, large positive shortwave radiation biases exist at the surface over the Southern Ocean, impacting the accurate simulation of sea surface temperature, atmospheric circulation, and precipitation. Underestimations of low-level cloud fraction and liquid water content are suggested to predominantly contribute to these radiation biases. Most model evaluations for radiation focus on summer and rely on satellite products, which have their own limitations. In this work, we use surface-based observations at Macquarie Island to provide the first long-term, seasonal evaluation of both downwelling surface shortwave and longwave radiation in the Australian Community Climate and Earth System Simulator Atmosphere-only Model version 2 (ACCESS-AM2) over the Southern Ocean. The capacity of the Clouds and the Earth’s Radiant Energy System (CERES) product to simulate radiation is also investigated. We utilize the novel lidar simulator, the Automatic Lidar and Ceilometer Framework (ALCF), and all-sky cloud camera observations of cloud fraction to investigate how radiation biases are influenced by cloud properties. Overall, we find an overestimation of + 9.5 ± 33.5 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="0adb11167a4b4eb853fdfbc6c50f311f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-14691-2023-ie00001.svg" width="58pt" height="10pt" src="acp-23-14691-2023-ie00001.png"/> </svg:svg> W m −2 for downwelling surface shortwave radiation fluxes and an underestimation of - 2.3 ± 13.5 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c8eb1663afd2ed22a36e2c02777e79ec"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-14691-2023-ie00002.svg" width="58pt" height="10pt" src="acp-23-14691-2023-ie00002.png"/> </svg:svg> W m −2 for downwelling surface longwave radiation ...