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TRMM Composite Climatology


The TRMM Composite Climatology (TCC) is a climatology (or map of mean values) of surface precipitation based on 13 years of data from the Tropical Rainfall Measuring Mission (TRMM). The TCC takes advantage of the information from multiple estimates of precipitation from TRMM to construct mean value maps over the tropics (36°N - 36°S) for each month of the year at 0.5° latitude-longitude resolution. The first-time use of both active and passive microwave instruments on board TRMM has made it the foremost satellite for the study of precipitation in the tropics and has led to a better understanding of the underlying physics and distribution of precipitation in this region. The TCC utilizes the TRMM multiple estimates to provide an answer to the overarching goal of TRMM: How much rain is falling in the Tropics? The TCC also includes estimates of the error for the mean values, constructed from a calculation of the variation among the input estimates. It is hoped that this new climatology will be useful to the user community as a ready comparison with other non-TRMM analyses and for comparison with numerical models, including those used for retrospective “re-analysis” and for climate simulations. It should also be useful as an educational reference for understanding tropical rainfall.

One of the main goals of the Tropical Rainfall Measuring Mission (TRMM) has been to accurately define the climatological surface rainfall in the tropics. This TRMM Composite Climatology (TCC) consists of a merger of selected TRMM rainfall products over both land and ocean to give a "TRMM-best” climatological estimate. Inputs to the composite were selected based on knowledge of the performance of the retrievals, limitations of the algorithms, and the presence of artifacts. Over ocean the rainfall estimates used for the TCC are from TMI (2A12), PR (2A25,near surface) and combined TMI-PR (2B31). Over land the rainfall estimates from the TRMM Multi-satellite Precipitation Analysis (TMPA, 3B43) are used to replace those from the TMI, because the land estimates from 2A12 (Version 6) are known to overestimate surface rainfall during the warm season. Other adjustments or quality control steps are taken, including adjusting the post-boost PR data to match the pre-boost (more sensitive) PR retrievals and eliminating small artifacts related to coastlines and islands. Maps of month-of-the-year climatologies of all four products (including adjustments and quality control steps) are then calculated at 0.5° latitude-longitude resolution from 36°N to 36°S, using twelve years (1998-2009) of TRMM V6 data. A simple mean of the three products (a different set of three over land and ocean) produces the final TCC estimate. In addition to the mean precipitation estimates, the TCC includes the variation among the three estimates (in terms of the standard deviation,σ) at each point to give an estimate of the error in the estimated mean value, at least in a relative sense.

Further information can be obtained from the following publication:

Adler, R. F., J.-J. Wang, G. Gu, and George J. Huffman, 2009: A ten-year tropical rainfall climatology based on a composite of TRMM products. J. Meteorol. Soc. Japan, 87A, 281-293. [Abstract] [PDF]


An beta application was developed to provide the user community with a user friendly interface to efficiently generate visualization of the data. Please see the TRMM Composite Climatolgy Visualization Tool.


Data Access

The data can be obtained through the following means:


Direct FTP:

The file name means:
<type>.<month>.<TRMM version>.bin
Each file contains gridded data with a resolution of 0.5 degree. The data are from west to east starting from 0.25E (720 grids), and north to south starting from 35.75N (144 grids). The unit of TCC rainfall is mm/day.

Reading the Data

 The following is the Fortran program to read the data: 
	real rain(720,144) 
	open(unit=22,file=file_name,access='direct', &recl=103680,form='unformatted') 
	rain close(22)



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Last updated: Apr 24, 2012 04:19 PM ET