Direct comparisons of ice cloud macro- and microphysical properties simulated by the Community Atmosphere Model version 5 with HIPPO aircraft observations
Chenglai Wu1,2, Xiaohong Liu1, Minghui Diao3, Kai Zhang4, Andrew Gettelman5, Zheng Lu1, Joyce E. Penner6, and Zhaohui Lin21Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USA 2International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 3Department of Meteorology and Climate Science, San Jose State University, San Jose, California, USA 4Pacifit Northwest National Laboratory, Richland, Washington, USA 5National Center for Atmospheric Research, Boulder, Colorado, USA 6Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Michigan, USA
Received: 09 Dec 2016 – Accepted for review: 12 Jan 2017 – Discussion started: 16 Jan 2017
Abstract. In this study we evaluate cloud properties simulated by the Community Atmosphere Model Version 5 (CAM5) using in-situ measurements from the HIAPER Pole-to-Pole Observations (HIPPO) for the period of 2009 to 2011. The modeled wind and temperature are nudged towards reanalysis. Model results collocated with HIPPO flight tracks are directly compared with the observations, and model sensitivities to the representations of ice nucleation and growth are also examined. Generally, CAM5 is able to capture specific cloud systems in terms of vertical configuration and horizontal extension. In total, the model reproduces 79.8 % of observed cloud occurrences inside model grid boxes, and even higher (94.3 %) for ice clouds (T ≤ −40 °C). The missing cloud occurrences in the model are primarily ascribed to the fact that the model cannot account for the high spatial variability of observed relative humidity (RH). Furthermore, model RH biases are mostly attributed to the discrepancies in water vapor, rather than temperature. At the micro-scale of ice clouds, the model captures the observed increase of ice crystal mean sizes with temperature, albeit with smaller sizes than the observations. The model underestimates the observed ice number concentration (Ni) and ice water content (IWC) for ice crystals larger than 75 μm in diameter. Modeled IWC and Ni are more sensitive to the threshold diameter for autoconversion of cloud ice to snow (Dcs), while simulated ice crystal mean size is more sensitive to ice nucleation parameterizations than to Dcs. Our results highlight the need for further improvements to the sub-grid RH variability and ice nucleation and growth in the model.
Wu, C., Liu, X., Diao, M., Zhang, K., Gettelman, A., Lu, Z., Penner, J. E., and Lin, Z.: Direct comparisons of ice cloud macro- and microphysical properties simulated by the Community Atmosphere Model version 5 with HIPPO aircraft observations, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1106, in review, 2017.