University of Washington TRMM Data Set

V07 (2A25-based) Regions (Old version numbering system)		v07 (GPM-based) Regions (Most recent algorithms used)

NOTE: Between March and July of 2020, we added masks for the extreme events (BSR, DCC, DWC, WCC) to the interpolated data files. Since there can be multiple of each type of extreme event associated with a single interpolated file, each event has a unique number associated with it (e.g. all the dcc_mask pixels belonging to the first DCC in a file are assigned values of '1', all the dcc_mask pixels belonging to the second DCC in a file are assigned values of '2', etc). That same number is included in the event statistics in the tabular files, so the user knows exactly which mask belongs with each event.

NOTE: (Oct 19, 2022) I have begun to process the latest version of the TRMM products (v07). Since the same algorithms are now being run on TRMM PR and GPM 2Ku data, we can confidently compare the output data from the two satellites. In order to facilitate this, I have changed the v07 TRMM regions so that they match the GPM v07 regions (with the exception that they terminate at +/- 40 instead of +/-67 latitudes). I will start with NAM and SAM and will continue from there.

BATCH DOWNLOADING: You can use wget to download data quickly. For example if you want to download all the interpolated files from South America for August of 2005, you could use one of the following commands. Don't forget the slash (/) at the end of the URL. And do not use brackets around your username and password.

OLD DATA SET: wget --debug --tries=10 --http-user=[login] --http-password=[password] --no-host-directories -r --cut-dirs=1 -A nc4 http://trmm.atmos.washington.edu/uw2/AFC/interp_data/2005/08/
NEW DATA SET: wget --debug --tries=10 --http-user=[login] --http-password=[password] --no-host-directories -r --cut-dirs=1 -A nc4 https://trmm.atmos.washington.edu/v07/AFC/interp_data/2005/08/

1. General Information

This website provides access to the database of the sixteen year University of Washington study of the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) datasets. The data, methods and analysis are described in the review paper by Houze, Rasmussen, Zuluaga, and Brodzik (2015). The months of the database upon which the paper is based (December/January/February and June/July/August) are currently available. The remaining months will be gradually filled in.

The products in this data base are derived from 2A23, 2A25 and 2H25 TRMM-PR version 7 orbital data products (v07-2014) and from the 2APR version 7A orbital data products (v07). The newest version is accessible via the NASA STORM database.

2. Regions

The data are stored by regions of the globe, represented by the boxes in the maps above. By clicking inside a box on a map, the user will go to the page containing the analysis products for that selected region. One can accomplish the same thing by going here for v07 (old) or v07 (new) data and clicking on the region of interest.

3. Overview

The NASA PR products 2A25/2APR and 2H25 are provided in bins along the slant range of the antenna beam. In the University of Washington database, these data in radar coordinates are geolocated and interpolated into a three-dimensional Cartesian grid and stored for analysis. From this dataset it is possible to identify structures of reflectivity echoes that satisfy certain criteria. Six types of echo objects are identified: detectable rain areas (DRA), isolated shallow echoes (ISE), deep convective cores (DCC), wide convective cores (WCC), deep-wide convective cores (DWC), and broad stratiform rain areas (BSR). Specific, defining characteristics of each of the objects are defined in section 5, below.

For all the classifications except DRA, the calculations are based on two different sets of thresholds - strong (str) and moderate (mod). Each object identified by these criteria is provided in netcdf format in both gridded (dimensioned by latitude and longitude) and tabular (dimensioned by instance or case) form. These gridded and tablular netcdf files contain information of the monthly climatology and individual properties of the identified echo objects. So, for example, the broad stratiform data from January of 2000 is contained in 4 files - strong thresholds and gridded, strong thresholds and tabular, moderate thresholds and gridded, and moderate thresholds and tabular.

4. Interpolated Data

Our echo feature products (DRA, SHI, DCC, WCC, DWC and BSR) and our corrected reflectivity and latent heating (only for the old v07) fields are based on an interpolated dataset that we produce from the TRMM archived data identified as 2A25/2APR (specifially, the sub-product, attenuation corrected reflectivity) and 2H25 (latent heating). The TRMM archive provides these data in range bins along the slant range of the radar beam, i.e. in "radar coordinates." For each of the above-described regions, the 2A25/2APR and 2H25 data in each range bin are first geolocated and then interpolated into a regular three-dimensional Cartesian grid. The interpolated grid size is 0.05° (approximately 5 km) in the horizontal at 80/176 vertical levels (separated by 0.25 km) for the 2A25/2APR reflectivity factor, and 19 levels (separated by 0.5 km for the first three levels and 1 km thereafter) for 2H25 latent heating. We remapped all data from 1998 to 2013 with the same horizontal resolution despite the change in orbital altitude of the TRMM satellite from 350 to 402 km in 2001, which changed the PR pixel size from 4.3 to about 5 km. Details of the methods applied for correcting the geolocation and the interpolation of the datasets can be found in Houze et al. (2007)

Additionally, nearest neighbor interpolation is used to re-grid the 2A25/2APR Near Surface Rain and Rain Type products corresponding to the selected areas into a two-dimensional 0.05° grid. The interpolated netcdf files contain all of this information with appropriate meta-data containing accurate descriptions of the stored variables. Note that the files contain two versions of the interpolated Rain Type variable. One contains the original 2A25/2APR values (ranging from 100 to 313 and including values of -88 for no rain and -999 for missing data). The other has a simplified version of the categories assigning values of (1) for stratiform, (2) for convective, and (3) for other.

5. Identification of Echo Objects

The UW database contains information on six types of radar echo objects derived from the interpolated Cartesian data described above.

• Detectable Rain Area (DRA) An area in the interpolated data consisting of two or more contiguous reflectivity pixels containing detectable radar echoes. (Only available for older, 2A25-based data.)
• Isolated Shallow Echo (ISE) This feature is an area of contiguous pixels containing detectable reflectivity and identified in the 2A25/2APR Rain Type product as the Shallow Isolated type of echo. It consists of echoes whose tops are at least 1 km below the 0°C level and may be thought of as regions governed primarily by warm rain processes.
• Deep Convective Core (DCC) This feature is a three-dimensional echo object that is convective (as designated by the TRMM 2A25/2APR product) and exceeds both an intensity threshold and a height threshold. Moderate (strong) DCCs are those that exceed a threshold intensity of 30 (40) dBZ and an echo-top height threshold of 8 (10) km. This category, whether defined by the moderate or strong threshold, is associated with young, vigorous convection.
• Wide Convective Core (WCC) This feature is a three-dimensional echo object that is convective (as designated by the TRMM 2A25/2APR product) and exceeds both an intensity threshold and a horizontal area threshold. Moderate (strong) WCCs are those that at some altitude exceed a threshold intensity of 30 (40) dBZ and a horizontal echo-area threshold of 800 km² (1,000 km²). These echo volumes represent extremely intense convection that has organized upscale into mesoscale areas of active, widespread convection.
• Deep-Wide Convective Core (DWC) This feature is a three-dimensional convective echo object that satisfies both the DCC and WCC criteria for either moderate or strong thresholds.
• Broad Stratiform Region (BSR) This feature is a contiguous region of stratiform echo (as designated by the TRMM 2A25/2APR product) and exceeds a horizontal area threshold. Moderate (strong) BSRs are those that exceed a horizontal echo-area threshold of 40,000 km² (50,000 km²). These echoes represent parts of mature and very well-developed mesoscale convective systems.

6. Echo Objects Masks

Mask fields have been added to the interpolated data files for each echo object and threshold. Each one is assigned a unique identifier (1, 2, 3, etc) that corresponds to the 'core_id' field in the tabular data files.

7. File Naming Convention

The file naming convention is consistent throughout the website. The files are stored in directories first by region and then by data type.

For the interpolated data, the convention is: [version]_[orbit].[yyyymmdd].[hhmmss]_[region].nc where

• [version]
  • 'TPR7_uw2' is based on TRMM-PR version 7 (2A25 algorithm-based) data and the UW's version 2 products
  • 'TRMM2APR7_uw4' is based on TRMM-PR version 7 (GPM algorithm-based) and the UW's version 4 products
• [orbit] = five-digit orbit number
• [yyyymmdd] = year, month and day
• [hhmmss] = hour, minute and second
• [region] = three letter abbreviation for the region of interest

For the classified radar echo objects, the convention is: [version]_[classification]_[threshold]_[type]_[yyyymm]_[region].nc. where

• [version]
  • 'TPR7_uw2' is based on TRMM-PR version 7 (2A25 algorithm-based) data and the UW's version 2 products
  • 'TRMM2APR7_uw4' is based on TRMM-PR version 7 (GPM algorithm-based) and the UW's version 4 products
• [classification] = one of 'BSR', 'DCC', 'DRA', 'DWC', 'SHI' or 'WCC'
• [threshold] = one of 'str', 'mod' or 'xxx'
• [type] = one of 'tab' or 'grd'
• [yyyymm] = year and month
• [region] = three letter abbreviation for the region of interest

So a typical filename might look like this - 'TPR7_uw2_BSR_str_tab_200012_SAM.nc'. This file would contain broad stratiform (BSR) data based on strong (str) thresholds in 'tabular' format (tab) for December of 2000 for the South America (SAM) region.

DRA is a special case since we do not use different thresholds. In that instance, threshold is set to 'xxx'.

Overlapping

Since our analyses started as a series of regional studies which eventually spanned most of the globe, the data is meant to overlap at the edges of all the global regions. It is suggested that if a user needs to combine information from two or more regions for a singular analysis, a careful 'stitching' of the data must be accomplished to avoid identifying overlapped echo elements multiple times.

8. References

Houze, R. A., Jr., D. C. Wilton, and B. F. Smull, 2007: Monsoon convection in the Himalayan region as seen by the TRMM Precipitation Radar. Quart. J. Roy. Meteor. Soc., 133, 1389-1411.

Houze, R. A., Jr., K. L. Rasmussen, M. D. Zuluaga, and S. R. Brodzik, 2015: The variable nature of convection in the tropics and subtropics: A legacy of 16 years of the Tropical Rainfall Measuring Mission (TRMM) satellite. Rev. Geophys., in revision.

9. Note of Appreciation

Erich Stocker of NASA/Goddard Spaceflight Center provided invaluable help with the processing of the data and products provided via this website.

10. Citation to be used for data and products obtained from this site

In all publications and presentations based on the information provided via this website, please acknowledge the University of Washington with a statement like this: "Data for this study comes from the University of Washington TRMM Data Set located at http:// trmm.atmos.washington.edu and supported by the NASA Earth Sciences PMM Program".

For questions, contact us here.