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TCC Analysis Tool FAQ

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Information about the TCC analysis tool

1) What is TCC?

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.
2) What are the procedures to construct TCC?
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 thirteen years (1998-2010) 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. 
 3) Why do we care about the standard deviation of TCC components?
In addition to the mean precipitation estimates, the TCC includes the variation among the three estimates (in terms of the standard deviation) at each point. Standard deviation of TCC inputs is a measure of dispersion and an estimate of bias error. This error estimate is correlated with actual bias error (as determined by gauge validation data). The error estimates can be used to provide bias error information for individual locations, zonal means and the tropics as whole. These error estimates should be valuable in comparison with other estimates or in comparison with model calculations.
4) What are TCM and TCA?
TCM and TCA are new TRMM composite products at the individual monthly scale. First, composites of three TRMM products are produced for 3-month running means at 2.5° latitude-longitude to obtain sufficient sampling and avoid aliasing. Second, the results are then disaggregated in time (down to a month) and space (0.5°) using 0.5° TMPA (3B43) to produce the TRMM Composite Monthly (TCM) of surface rainfall. Finally, the difference between the TCM and TCC becomes the TRMM Composite Anomaly (TCA) of the month. These products are useful in examining ENSO and other inter-annual phenomena with estimates based on the composite approach and are complementary to the climatology (TCC).
5) What is the future plan?
TCC will be updated with TRMM Version 7 after careful examination/validation of product results. The new TCC will hopefully use 2A12 over land. 
Reference: 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.
6) How to use this tool?
a) Select a base dataset and an overlay dataset
b) Select a plot type (i.e., Overlay of Lat-Lon Maps)
c) Select an area of interest using a computer mouse or type in latitudes and longitudes
d) Select a time period
e) Select or provide information for the color bar (for lat-lon map only)
f) Click on the “Generate Plot” button and the plot will be available in a new window
7) Can I get the data of a plot?
No, currently this capability is not available, but we have plans to add the capability in the future. To download the data:
8) What are the functions?
Overlay of Lat-Lon Maps (to be added)
Difference of Lat-Lon Maps
Normalized Difference of Lat-Lon Maps
Overlay of Time Series, Area-averaged
Difference of Time Series, Area-averaged
Normalized Difference of Time Series, Area-averaged
Scatter Plot
Scatter Plot, Time-averaged
Scatter Plot, Area-averaged
9) What is the best way to use the color bar?
We recommend using the default (dynamic) for the first plot. After that, you could fine tune the color bar using the customized option.
10) How to plot a single dataset?
Select the same dataset in both base dataset and overlay dataset.
11) What are the data resolutions?
0.5 deg. X 0.5 deg. latitude-longitude resolution from 36°N to 36°S
12) How can I download and save a plot in my computer?
Right click (e.g., in Firefox) on the plot, select "Save Image As". In the "Save Image" window, fill in "your_filename.gif" in "File name:". Click on "Save"
13) How can I add the plot in MS PowerPoint?
1) Right click (e.g., in Firefox) on the plot, select "Copy Image". In MS PowerPoint, right click a slide and choose “Paste”.
Or, 2) Save the plot. In MS PowerPoint, click on "Insert" and choose "From File" from "Picture". Select the saved image file.


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Last updated: Feb 17, 2012 02:19 PM ET