Experimental Real-Time GPCP Pentad (5-Day) Precipitation Analysis 1. Overview A real-time analysis of global pentad (5-day) precipitation has been constructed for the Global Precipitation Climatology Project (GPCP). Called Real-Time GPCP pentad analysis, it is defined by adjusting the real-time pentad CMAP analysis against the provisional data set of the GPCP version 2 monthly analysis. The real-time GPCP pentad analysis is created on a 2.5 deg lat/lon grid over the globe and is availabe the second day after the ending of the target pentad period. 2. Methodology The algorithms used to define the real-time GPCP pentad analysis is similar to those for the regular GPCP pentad analysis. A detailed description of the algorithms may be found in Xie et al. (2003). First, a real-time analysis of pentad CMAP is constructed by merging gauge observations and satellite estimates derived from GPI, OPI and SSM/I. The real-time analysis of pentad CMAP is then adjusted against the provisional data set of the GPCP Version 2 monthly analyses so that the accumulation of the real-time GPCP pentad analyses matches that of the monthly analysis. Since the provisional data set of monthly GPCP analysis is not available for most recent pentads, adjustment factors for the period are assumed to be the same as those for the last 3 months for which the monthly GPCP analyses are available. 3. Products Two sets of the outputs are produced: the binary data files and the graphic files in GIF format. i 3.1 Binary data files Stored in sub-directory 'data', the binary data file for each pentad is named as: gpcp_pen_rt.lnx.yyyypp where yyyy and pp stand for year and pentad numbers, respectively. In each pentad file, there are two global fields of 144x72 floating numbers in little endian byte order. The fisrt field is total precipitation (mm/day) and ther other monthly anomaly (mm/day). In each global field, the array of 144x72 starts from (1.25E,88.75S) goes west to east and then south to north. A sample fortran program to read the file is followed: ******************************************************************* dimension rain (144,72), anom (144,72) c open (unit=10, # file='gpcp_pen_rt.lnx.200351', # access='direct',recl=144*72*4) c read (10,rec=1) rain read (10,rec=2) anom c stop end ******************************************************************** 3.2 Graphic files Stored in sub-directory 'gif', there are 4 sets of graphic files for the real-time pentad GPCP analysis: a) gpcp_pen_rt_totl.yyyypp.gif a GIF file of total precipitation over the globe b) gpcp_pen_rt_totl_movie_yyyypp.gif a GIF movie of total precipitation for the most recent 18 pentads c) gpcp_pen_rt_anom.yyyypp.gif a GIF file of precipitation anomaly over the globe d) gpcp_pen_rt_anom_movie_yyyypp.gif a GIF movie of precipitation anomaly for the most recent 18 pentads 4) Cautions: Overall, the quality of this real-time GPCP pentad analysis is not as good as that for the regular analysis. We recommend that users use this real-time analysis for monitoring purpose and replace it with our regular analysis, when it becomes available, for quantitative applications. 5) References: Xie, P., et al., 2003: GPCP pentad precipitation analyses: An experimental dataset based on gauge observations and satellite estimates. J. Climate, 16, 2197 - 2214. 6) Contacts: Dr. Pingping Xie Climate Prediction Center 5200 Auth Road, #605 Camp Springs, MD 20746 Tel. (301)763-8000, Ext.7572 E-Mail: Pingping.Xie@noaa.gov