There are two merged precipitation data sets:
1) Rain gauge, OPI, MSU, GPI, 2 SSM/I products, and model output;
2) Rain gauge, OPI, MSU, GPI, and 2 SSM/I products.
where OPI stands for OLR-based precipitation index (reference given below).

Pingping provided the following remarks on this data set:
1) The pentad CMAP is created using basically the same algorithm and input data sources as we used for the monthly CMAP (see Xie and Arkin,1997 for details), a paper describing the pentad data set is under draft.

2) Major differences between the pentad and monthly CMAP have been found over South and North American Continents where the pentad data present smaller precipitation due to under reports in gauge observations.

3) Overall, the monthly data set has better quality than the pentad data set and we suggest that our users use this pentad data set as a supplement for situations when the monthly CMAP is not sufficient for their purposes.

4) The current version of the pentad is experimental in nature and contains some flaws that we may or may not know.

5) In this data set, we divide every year into 73 pentads even when there are 366 days. The pentad 12 contains an additional day to include Feb 29 in that case.

A comparison of the CMAP and Global Precipitation Climatology Project (GPCP) merged precipitation datasets is given by:
Yin, X., A. Gruber, and P. Arkinc, 2004: Comparison of the GPCP and CMAP Merged Gauge-Satellite Monthly Precipitation Products for the Period 1979-2001. J. Hydromet., 5, 1207-1222.

Big GIF | GIF | JPG | PDF | PostScript
The plotting routine is very simple --- there are no negative precipitation amounts. Blue for zero.