Direct comparisons of ice cloud macro- and microphysical properties simulated by the Community Atmosphere Model version 5 with HIPPO aircraft observations

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 (N-i) and ice water content (IWC) for ice crystals larger than 75 mu m in diameter.

Modeled IWC and N i are more sensitive to the threshold diameter for autoconversion of cloud ice to snow (D-cs) while simulated ice crystal mean size is more sensitive to ice nucleation parameterizations than to D-cs. Our results highlight the need for further improvements to the sub-grid RH variability and ice nucleation and growth in the model.