Measuring up virtual clouds: an instrument simulator approach to cloud model evaluation

The ability of a high-resolution three-dimensional cloud model to reproduce correctly the observed cloud structure is tested in a case study of low-level clouds occurred over north central Oklahoma on March 3, 2000. The case study is based on continuous ground-based observations from the Atmospheric Radiation Measurement Program, in-cloud aircraft observations, as well as imagery from the Terra platform and NASA high-flying ER-2 aircraft. Instead of limiting the model-to-observation comparison to a few highly integrated cloud characteristics, such as a cloud fraction or averaged liquid water profile, we employ a concept of an instrument simulator. In the approach, applied here to in-situ, ground-based, satellite, and suborbital measurements, we simulate how a specific sensor would see the synthetic cloud fields, focusing not only on a faithful representation of measured parameters but also on mimicking sensor?s sampling methods. For example, aircraft observations are compared with analogous samples of model fields taken along the simulated flight paths and simulated top of the atmosphere radiances, obtained using a 3D radiative transfer model, are sampled using specific instrument pixel size for a more direct comparison with observations. Benefits and limitations of the approach will be discussed and statistical significance of the comparisons will be assessed.