Climate Four Dimensional Data Assimilation (CFDDA) System
CFDDA is a dynamical downscaling system developed by NCAR to generate high-resolution climatographic analyses for any part of the world. At the heart of CFDDA is NCAR's Real Time Four Dimensional Data Assimilation system (RTFDDA; Liu et al. 2008), a mesoscale-model-based assimilation and forecasting system with versions based upon both the MM5 and its sequel, the Weather Research and Forecasting model (WRF; Skamarock et al. 2005). For the application described herein, we are using the WRF-based version of CFDDA (WRF Version 3.2.1) to create hourly regional analyses on a ~1-km horizontal grid, with 57 vertical levels. NASA MERRA analyses are used for initial and lateral boundary conditions, and serve as a starting point for the dynamical downscaling.
Throughout the integrations, CFDDA continuously assimilates standard surface and upper-air observations using the Newtonian relaxation technique. Observation data are obtained from the Advanced Data Processing datasets, available from the NCAR Research Data Archive. The global dataset contains both hourly and 6-hourly data reports collected by NCEP. The surface dataset includes mostly land reports, but a few ship observations also exist. The upper-air data are primarily standard rawinsonde measurements. The CFDDA solution is also nudged toward the driving NASA Modern Era Retrospective Reanalysis (MERRA) at the upper levels to preserve the large-scale state in CFDDA, and to ensure mass conservation. A time-invariant vertical grid nudging zone is used, from the model top down to about 3.0 km AGL (above the average height of the PBL). The underlying principle is for the CFDDA large-scale solution to closely follow that of the MERRA, while not impeding the ability of the assimilated observations and CFDDA to produce small-scale features, especially within the PBL.
WRF Model
The WRF Model is a next-generation mesocale numerical weather prediction system designed to serve both operational forecasting and atmospheric research needs. It features multiple dynamical cores, a 3-dimensional variational (3DVAR) data assimilation system, and a software architecture allowing for computational parallelism and system extensibility. WRF is suitable for a broad spectrum of spatial scales ranging from meters to thousands of kilometers.
The WRF Model has been developed through a collaboration between the National Center for Atmospheric Research (NCAR), the National Oceanic and Atmospheric Administration (the National Centers for Environmental Prediction (NCEP) and the Earth System Research Laboratory (ESRL) Global Systems Division (GSD), the U.S. Air Force Weather Agency (AFWA), the Naval Research Laboratory, Oklahoma University, and the Federal Aviation Administration (FAA).
