Peter Kuma

Science and Software

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

Zhangcheng Pei^{1, 2, 3}, Sonya L. Fiddes^{1, 2}, W. John R. French^{4, 1}, Simon P. Alexander^{4, 1}, Marc D. Mallet¹, Peter Kuma⁵, Adrian McDonald⁶

¹Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
²Australian Research Council Centre of Excellence for Climate Extremes, University of Tasmania, Hobart, Australia
³College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, China
⁴Australian Antarctic Division, Kingston TAS, Australia
⁵Department of Meteorology, Stockholm University, Stockholm, Sweden
⁶School of Physical and Chemical Sciences, University of Canterbury, Christchurch, Aotearoa/New Zealand

Abstract

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 W m^-2 for downwelling surface shortwave radiation fluxes and an underestimation of  W m^-2 for downwelling surface longwave radiation in ACCESS-AM2 in all-sky conditions, with more pronounced shortwave biases of W m^-2 occurring in summer. CERES presents an overestimation of W m^-2 for the shortwave and an underestimation of W m^-2 for the longwave in all-sky conditions. For the cloud radiative effect (CRE) biases, there is an overestimation of W m^-2 in ACCESS-AM2 and an underestimation of W m^-2 in CERES. An overestimation of downwelling surface shortwave radiation is associated with an underestimated cloud fraction and low-level cloud occurrence. We suggest that modeled cloud phase is also having an impact on the radiation biases. Our results show that the ACCESS-AM2 model and CERES product require further development to reduce these radiation biases not just in shortwave and in all-sky conditions, but also in longwave and in clear-sky conditions.

Journal:

Atmospheric Chemistry and Physics

Volume:

23

Number:

23

Pages:

14691–14714

DOI:

10.5194/acp-23-14691-2023

Submitted:

27 February 2023

Accepted:

28 September 2023

Published:

29 November 2023

License:

Open access / Creative Commons Attribution 4.0 International (CC BY 4.0)

Document