The analysis is performed with the Ensemble Filter as described in Compo et al. (2010) based on the method of Whitaker and Hamill (2002). Observations of surface pressure and sea level pressure from the International Surface Pressure Databank station component version 2 (Yin et al. 2008), ICOADS (Woodruff et al. 2009), and the International Best Track Archive for Climatic Stewardship (IBTrACS, Kruk et al. 2010) were assimilated every six hours. The surface pressure observations have been made available through international cooperation facilitated by the Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative and working groups of the Global Climate Observing System and World Climate Research Programme. The short-term forecast ensemble is generated in parallel from 56 9-hour integrations of a state-of-the-art atmospheric general circulation model, a 2008 updated experimental version of the atmospheric component of NCEP's operational Climate Forecast System model (Saha et al. 2006). Briefly, the model has a spatial resolution of nearly 200-km on an irregular Gaussian grid in the horizontal (corresponding to a spherical harmonic representation of model fields truncated at total wavenumber 62, T62). In the vertical, we use finite differencing of 28 levels. The model has a complete suite of physical parameterizations as described in Kanamitsu et al. (1991) with recent updates detailed in Moorthi et al. (2001). Additional updates to these parameterizations are described in Saha et al. and include revised solar radiation transfer, boundary layer vertical diffusion, cumulus convection, and gravity wave drag parameterizations. In addition, the cloud liquid water is a prognostic quantity with a simple cloud microphysics parameterization. The radiation interacts with a fractional cloud cover that is diagnostically determined by the predicted cloud liquid water. The 2008 experimental version of the model used for the 20th Century Reanalysis also includes the radiativeeffects of historical time-varying CO2 concentrations, volcanic aerosol and solar variations using the longwave radiation model of Mlawer et al. (1997) and shortwave radiation model of Hou et al. (2002). The specified boundary conditions needed to run the model in atmosphere-only mode are taken from the time-evolving sea surface temperature and sea ice concentration fields of the HadISST1.1 dataset obtained courtesy of the United Kingdom Met Office Hadley Centre (Rayner et al. 2003).
Data variable and Path:
· Monthly and Long-Term