18th Conference on Hydrology


Validation of the North American Land Data Assimilation System (NLDAS) Using Data from Oklahoma Mesonet OASIS Sites

Kodi L. Nemunaitis, Oklahoma Climate Survey and University of Oklahoma, Norman, OK; and J. B. Basara, B. A. Cosgrove, D. Lohmann, K. E. Mitchell, and P. R. Houser

The Oklahoma Mesonet is an automated network of 115 remote, hydrometeorological stations across Oklahoma. Each station measures ten core parameters which include: air temperature and relative humidity at 1.5 m, wind speed and direction at 10 m, barometric pressure, rainfall, incoming solar radiation, bare and vegetated soil temperatures at 10 cm below ground level, and soil moisture at 5, 25, 60, and 75 cm.

In 1999, the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project upgraded 90 sites with a suite of instruments capable of measuring the surface energy balance. In addition, a subset of 10 OASIS sites, designated OASIS Super Sites, were instrumented to measure the components of the surface energy balance with enhanced accuracy.

A team of federal agencies and universities which includes the NCEP Environmental Modeling Center, NASA Goddard Space Flight Center, NWS/OHD, NESDIS/ORA, Princeton University, Rutgers University, the University of Washington, University of Maryland, and the University of Oklahoma is developing a Land Data Assimilation System (LDAS) for use at both North American (NLDAS) and global scales (GLDAS). The NLDAS infrastructure consists of uncoupled land surface models forced with precipitation observations, output from the Eta model based data assimilation system (EDAS), solar radiation from the GOES satellite, and radar precipitation estimates. It is being developed to initialize and improve the simulation of land surface states and energy fluxes in coupled and uncoupled land model components of numerical forecast models. The NLDAS system is expected to reduce forecast errors by providing better initial condition for the land surface component in NWP and climate models.

Retrospective simulation data sets, provided in collaboration with the NLDAS Group, simulate energy fluxes from the Mosaic and Noah land surface models for the summer 2000 period. The model-simulated energy fluxes are compared with the OASIS surface flux data sets. In terms of a regional approach, these preliminary results show that net radiation is captured very well by both models. Sensible heat flux is overestimated by the Noah model and underestimated by the Mosaic model. Latent heat flux is slightly underestimated by the Noah model and overestimated by the Mosaic model and the ground heat flux is slightly overestimated by the Noah model and highly overestimated by the Mosaic model. Further investigations of additional candidate days and closer inspection of individual sites allow for a more complete validation effort.

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Session 2, Modeling and Analysis of Large-Scale Hydrological Processes (Room 6E)
Tuesday, 13 January 2004, 1:30 PM-5:30 PM, Room 6E

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