Microphysics of clouds in the Southern Ocean: Comparisons between airborne in situ microphysical measurements with simulations from the Community Earth System Model (CESM)

Southern clouds are a critical part of the earth's energy budget, and significant biases in the climatology of these clouds exist in models used to predict climate change. To address these issues, we compare in situ measurements of cloud microphysical properties (concentrations and amounts of ice and liquid) taken during the HIAPER (the NSF/NCAR G-V aircraft ) Pole-to-Pole Observations (HIPPO) multi-year field campaign with simulations from the Community Earth System Model (CESM). Due to the large differences in the time and distance scales between the simulations and the in situ sampling, an oversampling technique involving a model grid box containing the location of the aircraft and adjacent grid boxes is used to construct a model analog to the in situ time series of data. When the simulations are compared in this manner with the measurements, the global climate model captures several features found in the in situ data, such as the general locations of cloud encounters and the approximate locations of supercooled liquid water. Cloud microphysical properties show large scatter, but are comparable between the model and observations. Sensitivity tests are conducted to show how altering the model parameterizations changes the ability to reproduce observations, as well as overall global climate statistics. These results are intended to show how we can connect large scale simulations with field observations to better understand the performance of the models in simulating the major microphysical features of Southern Ocean clouds.