Land Data Assimilation Systems (LDAS) of the National Centers for Environmental Modeling Prediction (NCEP): Current Status and Future Plan

The Land Data Assimilation Systems (LDAS) of the National Centers for Environmental Modeling Prediction (NCEP) have become an important part of the NCEP operational product suite. Two examples are the NCEP operational North American Land Data Assimilation System Version 2 (NLDAS-2) and the NCEP operational Climate Forecast System Reanalysis's Global Land Data Assimilation System (CFSR/GLDAS). The NLDAS-2 is a standalone uncoupled LDAS system which runs four widely applied land surface models using observed/reanalysis surface meteorological forcing to produce surface energy fluxes (e.g. sensible and latent heat), water fluxes (e.g., evapotranspiration and total runoff/streamflow), and various state variables (snow water equivalent, soil moisture, soil temperature, land surface skin temperature). Its purpose is to support the National Integrated Drought Information System (NIDIS) and operational drought monitoring and prediction activities. The CFSR/GLDAS is a semi-coupled system which runs the Noah land surface model using gauge- and satellite-based observed precipitation and Climate Forecast System Reanalysis (CFSR) surface meteorological forcing to produce land state variables to feedback into CFS Version 2. Its purpose is to provide the optimal initial conditions to improve climate forecast skill (e.g. 1-12 months). These operational systems provide us good experiences and frameworks for future developments and upgrades.

Based on above the frameworks, the future NCEP Global Forecast System (GFS/GLDAS, as with CFSR/GLDAS, but with focus on medium-range weather prediction) is being developed to support the upgraded GFS by providing more reasonable land-state initial conditions to the GFS. Its purpose is to improve short-to-mid-term weather forecast skill. For the NCEP regional weather prediction system, e.g., North American Modeling System (NAM), a standalone NAM-LDAS system is being developed to improve short-term regional weather forecast skill by providing the optimal initial conditions to the NAM (The current operational NLDAS-2 domain does not span the larger NAM domain). The tests and analyses about these developments are underway.

Besides the development of the new LDAS systems cited above, the currently operational NLDAS-2 and CFSR/GLDAS will be upgraded to next versions through (1) using improved surface forcing data, (2) fixing existing problems cited by the user community, (3) extending spatial coverage and increasing resolutions from coarse to finer scales, (4) upgraded land-surface model versions, (5) adding actual data assimilation algorithms, and (6) usingtransitioning to the NASA's Land Information System (LIS)-based framework. Based on these concepts, the operational NLDAS-2 is being updated by (a) closing a 3.5-day time lag to achieve truly real-time status, (b) fixing US-Canada and US-Mexico border discontinuity features (e.g precipitation forcing), and (c) using surface meteorological forcing data from a newly completed rerun of NCEP's N. American Regional Reanalysis (NARR). Planned longer-term future upgrades include adopting finer resolution (0.03125 degrees), LIS-NLDAS, and a “unified” NLDAS (e.g., combination of NLDAS-2 and NAM/LDAS). To overcome the discontinuity issue arising from the application of six multi-year streams in CFSR, a continuous one-stream standalone CFSR/GLDAS is being developeding by using the newly released CPC 0.25 degree global daily gauge precipitation product to support the next version of both the CFS and WCRP's Global Integrated Drought Information System (GIDIS). These upgraded systems are being tested in preparation for future operational implementation.