The relative impact of clear and cloudy sky infrared brightness temperatures within an ensemble data assimilation system

A regional-scale Observation System Simulation Experiment was used to examine the relative impact of simulated clear and cloudy-sky infrared brightness temperatures from the Advanced Baseline Imager (ABI) on cloud and thermodynamic analysis accuracy when using an ensemble Kalman filter (EnKF) data assimilation system. The case study tracked the evolution of several mid-latitude systems and their associated cloud features that occurred across the continental U.S. during 07 January 2008. A high-resolution “truth” simulation containing realistic cloud and thermodynamic properties was performed using the Weather Research and Forecasting (WRF) model. Data from the truth simulation was used to generate simulated ABI 8.5 μm brightness temperatures and conventional radiosonde, surface, and aircraft pilot observations containing realistic errors and the correct spatial distribution. Four assimilation experiments employing different combinations of conventional and brightness temperature observations were conducted with observations assimilated once per hour during a 24-hr period.

Overall, the assimilation results showed that the infrared brightness temperatures had a large positive impact on the simulated cloud field with a slightly positive to slightly negative impact on the thermodynamic fields. The best results were achieved when both clear and cloudy sky observations were assimilated. Comparison of various cloud and thermodynamic fields will be shown for each assimilation case.