|Coverage||Global tropics (40N-40S, 0-360E)|
|Time Period||December 1997 - Present|
|Resolution||5 x 5 and 0.5 x 0.5 degree, monthly|
A number of climate rainfall products are produced from the passive microwave (TMI) and precipitation radar (PR) sensors on board the Tropical Rainfall Measuring Mission (TRMM) satellite, which was launched in November of 1997. The TRMM monthly or climate rainfall products, referred to as the level 3 products, are derived primarily from accumulations of the TRMM level 2 products, or instantaneous rainfall estimates corresponding to the original satellite snapshot views. The availability of multiple rainfall products from the various TRMM rainfall sensors is due to the fact that each one has various strengths and weaknesses. As a result, the "best" rainfall estimate is application dependent. The TRMM PR provides the highest spatial resolution (~4 km), most information content, the best vertical resolution (80 levels), and the most directly measured surface rainfall estimates for many application. The swath width of the PR, however, is around 1/3 of the TMI swath width resulting is significantly poorer sampling for many climate applications.
The current version is version 6
The 3A25 dataset is an accumulation of the TRMM 2A25 PR retrieval algorithm. This dataset contains monthly mean values of the surface rainfall rate, vertical rain profile, stratiform/convective fraction, and numerous other related parameters. Gridded monthly averages are provided at both 5 x 5 degree and 0.5 x 0.5 degree resolutions. The 2A25 retrieval algorithm used for this product is based on the technique by [Iguchi et al., 2000].
In an attempt to explain discrepancies in interannual variability of tropical mean rainfall between PR (2A25) and TMI (2A12) estimates, Robertson et al.  compared monthly mean values of the PR path integrated attenuation (PIA) with surface rain rates. They found that the variability in PIA closely matched variability in the TMI rain estimates, suggesting that uncertainties in the assumed drop size distribution and the associated attenuation/reflectivity/rainfall relationships inherent in single-frequency radar methods is a serious issue for climate studies.