P56 Impact of land model assimilation and calibration on coupled land-atmosphere prediction

Santanello, Joseph A., National Aeronautics and Space Administration (NASA), Sujay Kumar, Science Applications International Corporation and NASA, Christa Peters-Lidard, and Ken Harrison, NASA

Land-atmosphere (L-A) interactions play a critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface heat and moisture budgets, as well as controlling feedbacks with clouds and precipitation that lead to the persistence of dry and wet regimes. Recent efforts to quantify the strength of L-A coupling in prediction models have produced diagnostics that integrate across both the land and PBL components of the system. In this study, we examine the impact of improved specification of land surface states, anomalies, and fluxes on coupled WRF forecasts during the summers of extreme dry (2006) and wet (2007) land surface conditions in the U.S. Southern Great Plains. The improved land initialization and surface flux parameterizations are obtained through land data assimilation and calibration approaches in the Noah land surface model using the new optimization/uncertainty estimation and data assimilation subsystems in NASA's Land Information System (LIS-OPT/UE and LIS-DA). The impact of the assimilation vs. calibration on the a) spinup of the land surface used as initial conditions, and b) the simulated heat and moisture states and fluxes of the coupled WRF simulations is then assessed. Results indicate that the offline calibration leads to systematic improvements in land-PBL fluxes and near-surface temperature and humidity, and in the process provide guidance on the questions of what, how, and when to calibrate land surface models for coupled model prediction. Data assimilation results are preliminary, but suggest that improvements to the initial soil moisture states of WRF simulations are possible using current satellite remote sensing, and it highly dependent on the period of interest and scaling approaches used.