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- System Characteristics - MERRA Research Other Links |
Precipitation Variations:
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| The Global Precipitation Climatology Project (GPCP) is a data set produced by the international GEWEX program which contains monthly averaged precipitation rates (mm/day) for the time period Jan 1979 through the present. The GPCP data set combines satellite and gauge measurements of precipitation. The GPCP Version 2 documentation explains that the data are merged at the NASA GSFC Laboratory of Atmospheres and includes rain gauges, GPI, OPI, SSM/I scattering, SSM/I emission, and TOVS. |
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These images are time series of the monthly mean precipitation from 1979 to 2001. The top series covers the entire globe, whereas the second row compares means over land (left) versus ocean (right). The compared data sets are GEOS4-CERES (purple), NCEP-R2 (cyan), ERA-40 (green), JRA-25 (orange), and GPCP (blue). The time series also include a MEAN (magenta) of the four analysis systems. Click on any image to expand it in a separate window. Note that in 1987, at the same time as the introduction of SSM/I data, the GEOS4 reanalysis shifts away from following GPCP and becomes more like the other reanalyses 
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| The CPC Merged Analysis of Precipitation (CMAP) is a data set produced by NOAA which contains monthly averaged precipitation rates (mm/day) for the time period Jan 1979 to Aug 2005. The standard data set incorporates 5 satellite measurements of precipitation: GPI, OPI, SSM/I scattering, SSM/I emission, and MSU. Note that the primary differences between CMAP and GPCP are that GPCP includes rain gauge measurements and treats TOVS data differently. The enhanced CMAP data set also includes NCEP reanalysis data. |
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These images are time series of the correlation between monthly means of precipitation against CMAP from 1979 to 2001. The top series covers the entire globe, whereas the second row compares means over land (left) versus ocean (right). The compared data sets are GEOS4-CERES (magenta), NCEP-R2 (cyan), ERA-40 (green), and JRA-25 (orange). Also plotted is the correlation between GPCP (purple) and CMAP, which not surprisingly is very high. Click on any image to expand it in a separate window. Note that in 1987, at the same time as the introduction of SSM/I data, the JRA-25 reanalysis shifts to and maintains a closer correlation with CMAP. 
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GMAO Website Curator: James Gass |
