PNNL

Abstract

High-latitudinal clouds have significant influences on the Earth’s radiative balance. We examined observations of cloud and radiative properties from two field campaigns in the Southern Ocean and Antarctica and compared them with two global climate model simulations. A cyclone compositing method is used to define four quadrants relative to the extratropical cyclone centers and quantify “dynamics-cloud-radiation” relationships. Observations show larger asymmetry in cloud and radiative properties between western and eastern sectors at McMurdo compared with Macquarie Island. Most observed quantities at McMurdo are higher in the western (i.e., post-frontal) than the eastern (frontal) sector, including cloud fraction, LWP, net surface shortwave and longwave radiation (SW and LW), except for IWP being higher in the eastern sector. The two models were found to overestimate (underestimate) cloud fraction and liquid water path (LWP) at Macquarie Island (McMurdo Station), and consistently underestimate ice water path (IWP) at both locations. Biases of cloud fraction, LWP, and IWP are positively (negatively) correlated with biases of SW (LW). The fact that both models show consistent positive SW biases in both sectors at both locations regardless of the changing signs of LWP or cloud fraction biases suggests that the persistent negative IWP biases may have become one of the leading causes of radiative biases over the high southern latitudes, after correcting the underestimation of supercooled liquid water in the older model versions. By examining multi-scale factors from cloud microphysics to synoptic dynamics, this work will help increase the fidelity of climate simulations in this remote region.