Cecile Hannay

Cecile Hannay has concentrated on short-range forecasts with global climate models. The forecasts are initialized from atmospheric analyses and compared to observations and analyses to examine process errors associated with the model formulation. This approach provides an excellent method of examining parameterizations as it allows direct comparison of the parameterized variables (e.g. clouds) with observations from field campaigns.

Cecile used the forecast framework for an atmospheric model intercomparison of Southeast Pacific stratocumulus with the ECWMF, NCAR and GFDL models. She showed that a key problem common to the models is that the planetary boundary layer (PBL) is too shallow compared to observations. However, as the complexity of the PBL scheme increases, the models produce deeper PBL. All the models capture a strong diurnal cycle in the liquid water path but there are large differences in the amplitude and the phase compared to observations. This, in turn, affects the radiative fluxes at the surface and the surface energy budget. This is particularly relevant for coupled simulations as this can lead to large SSTs bias. Cecile recently submitted a paper documenting this intercomparison.

Cecile is involved in the ongoing international GCSS Pacific Cross-section Intercomparison (GPCI). The GPCI compares both forecast and climate model simulations along a vertical cross-section extending from the California coast to the central Pacific ITCZ. The main goal of this intercomparison is to evaluate and improve the representation of tropical and subtropical cloud and precipitation processes in weather and climate prediction models. Cecile contributed to climate and forecasts simulations for the formal intercomparison. She also analyzed forecasts along the cross-section to assess candidate parameterizations for the next generation model, CAM4.

Cecile is also deeply involved in the CAM development. In particular, she contributed to the evaluation of new parameterizations and help to understand their interactions with the rest of the model. She has assisted various efforts for CAM 4 development and has helped scientists from the AMP and visitors.