Radiative Effects of Secondary Ice Enhancement in Coastal Antarctic Clouds.

Autor: Young, G., Lachlan‐Cope, T., O'Shea, S. J., Bower, K. N., Choularton, T. W., Gallagher, M. W., Dearden, C., Listowski, C.
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Zdroj: Geophysical Research Letters; 2/28/2019, Vol. 46 Issue 4, p2312-2321, 10p
Abstrakt: Secondary ice production (SIP) commonly occurs in coastal Antarctic stratocumulus, affecting their ice number concentrations (Nice) and radiative properties. However, SIP is poorly understood and crudely parametrized in models. By evaluating how well SIP is captured in a cloud‐resolving model, with a high‐resolution nest within a parent domain, we test how an improved comparison with aircraft observations affects the modeled cloud radiative properties. Under the assumption that primary ice is suitably represented by the model, we must enhance SIP by up to an order of magnitude to simulate observed Nice. Over the nest, a surface warming trend accompanied the SIP increase; however, this trend was not captured by the parent domain over the same region. Our results suggest that the radiative properties of microphysical features resolved in high‐resolution nested domains may not be captured by coarser domains, with implications for large‐scale radiative balance studies over the Antarctic continent. Plain Language Summary: Climate models do not always represent clouds well—particularly in Antarctica—because we do not fully understand them on a small scale. Clouds can affect the temperature of the surface by reflecting energy from the Sun or trapping in heat from below; therefore, they play a crucial role in Antarctica, where warming surfaces are affecting how the ice shelves are melting. We need a variety of measurements of Antarctic clouds to understand them, including how many droplets or ice crystals they contain. Using measurements from the "Microphysics of Antarctic Clouds" project, we found evidence that, at certain temperatures, significantly more ice particles can be rapidly produced when fragile ice crystals or freezing droplets break up. We use these measurements to improve how cloud ice crystals are simulated in a weather model and consider implications for the frozen surface as a result of these changes. We found better agreement with our measurements by making the ice crystals multiply more efficiently in the model. As a result, less cloud cover was simulated and more energy from the Sun reached the surface, suggesting that the Antarctic surface may be subject to more warming than we originally thought. Key Points: Increasing modeled secondary ice production (SIP) by 10 times improves agreement with ice number concentration observations in AntarcticaEnhanced SIP reduces cloud fraction and increases amount of shortwave radiation reaching the surface over a high‐resolution nested domainSIP‐induced changes in cloud radiative forcing over the high‐resolution nest are not captured by the coarse parent domain [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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