Level3 - Selected Monthly Rainfall Data Set

TRMM Level 3: Selected Monthly Rainfall Data Set

January, 2000
July, 2004
October, 2005
May, 2006

1. Description

This document describes the data set for the monthly surface rainfall. The data set was selected from the Tropical Rainfall Measuring Mission (TRMM) Level 3 standard products (monthly and latitude-longitude grid), the Precipitation Radar (PR), the TRMM Microwave Imager (TMI), the PR and TMI combined algorithm (COMB) and "TRMM and Others Combined" algorithm (TRMM, geosynchronous IR and rain gauges) for the user's convenience.

This data set was compiled and supplied by the Earth Observation Research Center, Japan Aerospace Exploration Agency (JAXA EORC).

The browse images and data show the global monthly accumulated rainfall [mm/month]. However, the standard products of PR and "TRMM and Others Combined" only include the monthly mean rain rate [mm/hour]. Therefore, we also calculate and include the monthly accumulated rainfall of those products in the data set for intercomparison of those rainfall products. In addition, the monthly mean of "TRMM and Others Combined" were derived from all pixels regardless of rainfall existence. On the other hand, pixels in which rainfall exists were used for calculation of the PR monthly mean value.

The data set is written in 4-byte real binary (big endian) format and can be accessed easily. Also, you can easily draw the images using GrADS software. Details of the GrADS software and samples of the GrADS description file are presented at the end of this document.

The monthly accumulated rainfall is estimated as rainfall at the surface except for PR. The PR algorithm uses the Near-Surface Rain Rate in Level 2 (2A25) products. It is the rain intensity at the nearest bin from the surface, which is not influenced by ground clutter in each angle bin. The height is about 500 m from the surface at nadir, and 2000m at the edge of the observation swath.

The original TRMM Level 3 standard products, PR Level 3 (3A25), TMI Level 3 (3A11) and COMB Level 3 (3B31), "TRMM and Others Combined" Level 3 (3B43) are processed and supplied by the NASA Goddard Space Flight Center (GSFC) and the JAXA Earth Observation Center (EOC).

Detailed documentation for standard products can be found at TRMM Web Site :

http://www.eorc.jaxa.jp/TRMM/document/text2/trmm_handbook_j.pdf (11.2MB)

and the NASA GSFC TSDIS ftp sever :

http://pps.gsfc.nasa.gov/tsdis_redesign/SelectedDocs.html

2. Parameters

There are five rainfall parameters produced by different algorithms.

1) 3A11
Monthly accumulated surface rainfall [mm/month] produced by the TMI 3A11 algorithm.

2) 3A25G1

Monthly mean rain rate [mm/hour] of Grid 1 (low resolution) at near surface produced by the PR 3A25 algorithm.
"mean" is EXCLUDING "no rain" pixels.
Number of rain pixels in Grid 1 at near surface.
Total number of pixels in Grid 1.
Monthly accumulated rainfall [mm/month] of Grid 1 at near surface.

NOTE: Monthly accumulated rainfall is calculated by using the monthly mean rain rate, number of rain pixels and total number of pixels in 3A25. The calculation method is:

accumulated rainfall = mean rain rate x (rain pixel/total pixel)
x 24 x days in each month

3) 3A25G2

Monthly mean rain rate [mm/hour] of Grid 2 (high resolution) at near surface produced by the PR 3A25 algorithm.
"mean" is EXCLUDING "no rain" pixels.
Number of rain pixel in Grid 2 at near surface.
Total number of pixels in Grid 2.
Monthly accumulated rainfall [mm/month] of Grid 2 at near surface.

NOTE: Monthly accumulated rainfall of 3A25G2 is calculated by using the same method as for 3A25G1.

4) 3B31_COMB
Monthly accumulated surface rainfall [mm/month] produced by the COMB 3B31 algorithm.

NOTE: The standard products of 3B31 for product version 4 were missing from Dec. 1997 to Jan. 1998.

5) 3B31_TMI
Monthly accumulated surface rainfall [mm/month] produced by using the TMI 2A12 standard products.

NOTE: This parameter is included in the standard product of COMB 3B31.

NOTE: The level 3 algorithm for TMI (3A11) differs from the level 2 algorithm for TMI (2A12). Therefore, monthly accumulated rainfall of 3A11 also differs from that of 2A12.

6) 3B43

Monthly mean hourly rainfall [mm/hour] produced by using TRMM, geosynchronous IR and rain gauges.
"mean" is INCLUDING "no rain" pixels.
Monthly accumulated rainfall [mm/month].

NOTE: Monthly accumulated rainfall was calculated as follows. accumulated rainfall = hourly rainfall x 24 x days in each month.

NOTE: This data set doesn't include 3B43 products of product version 4.

3. Data (binary) Download

You can get binary data from the following anonymous FTP site.Directories of data files are separated by product version.

ftp://ftp.eorc.jaxa.jp/pub/TRMM/L3_data/

4. Format of the data set

1) Data format

Data type

single precision real (4 bytes)
big endian

Matrix size

   a. 3A11, 3A25G1, 3B31_COMB and 3B31_TMI : 72 (LON) x 16 (LAT)
   b. 3A25G2 : 720 (LON) x 148 (LAT)
   c. 3B43 Ver.5 : 360 (LON) x 80 (LAT)
   d. 3B43 Ver.6 : 1440 (LON) x 400 (LAT)

2) Coverage

a) 3A11, 3A25G1, 3B31_COMB and 3B31_TMI
180W --> Eastward --> 180E
40S --> Northward --> 40N

Item (1,1) stores the value centered at 177.5W and 37.5S.
Item (72,16) stores the value centered at 177.5E and 37.5N.

b) 3A25G2
180W --> Eastward --> 180E
37S --> Northward --> 37N

Item (1,1) stores the value centered at 179.75W and 36.75S.
Item (720,148) stores the value centered at 179.75E and 36.75N.

c) 3B43 Ver.5
180W --> Eastward --> 180E
37S --> Northward --> 37N

Item (1,1) stores the value centered at 179.5W and 39.5S.
Item (360,80) stores the value centered at 179.5E and 39.5N.

d) 3B43 Ver.6
180W --> Eastward --> 180E
50S --> Northward --> 50N

Item (1,1) stores the value centered at 179.875W and 49.875S.
Item (1440,400) stores the value centered at 179.875E and 49.875N.

3) Resolution

Temporal: Monthly

Horizontal:

a) 3A11, 3A25G1, 3B31_COMB and 3B31_TMI
5.0 degree (LON) x 5.0 degree (LAT)

b) 3A25G2
0.5 degree (LON) x 0.5 degree (LAT)

c) 3B43 Ver.5
1.0 degree (LON) x 1.0 degree (LAT)

d) 3B43 Ver.6
0.25 degree (LON) x 0.25 degree (LAT)

4) Missing

Missing value: -9999.9

5. Example program for F77

1) For 3A11, 3B31_COMB and 3B31_TMI


C

C  TO READ (3A11, 3B31_COMB, 3B31_TMI) RAINFALL  

C 

	parameter (idim = 72, jdim = 16) 

	parameter (rmiss = -9999.9) 

      real*4 rain(idim,jdim)

C  OPEN DATA FILE 

	open(10,file='3A11.rain.199801.5.grd', access='direct', 

     $  form='unformatted', status='old', recl=4*idim*jdim, err=99)  

C  READ DATA

	read(10,rec=1) rain

C  CLOSE 

    99 close(10) 

C  STOP 

	stop 

	end

2) For 3A25G1


C

C  TO READ (3A25G1) RAINFALL  

C 

	parameter (idim = 72, jdim = 16) 

	parameter (rmiss = -9999.9) 

      real*4 rr(idim,jdim), pix(idim,jdim),

　　 $  ttl(idim,jdim), rain(idim,jdim)

C  OPEN DATA FILE 

	open(10,file='3A25G1.rain.199801.5.grd', access='direct', 

     $  form='unformatted', status='old', recl=4*idim*jdim, err=99) 

C  READ RAIN RATE (mm/hour)

	read(10,rec=1) rr

C  READ RAIN PIXEL NUMBER

	read(10,rec=2) pix

C  READ TOTAL PIXEL NUMBER

	read(10,rec=3) ttl

C  READ ACCUMULATED RAINFALL (mm/month) 

	read(10,rec=4) rain

C  CLOSE 

　　99 close(10) 

C  STOP 

	stop 

	end

3) For 3A25G2


C

C  TO READ (3A25G2) RAINFALL  

C

	parameter (idim = 720, jdim = 148) 

 	parameter (rmiss = -9999.9) 

	real*4 rr(idim,jdim), pix(idim,jdim),

     $  ttl(idim,jdim), rain(idim,jdim)

C  OPEN DATA FILE 

	open(10,file='3A25G2.rain.199801.5.grd', access='direct', 

     $  form='unformatted', status='old', recl=4*idim*jdim, err=99) 

C  READ RAIN RATE (mm/hour)

	read(10,rec=1) rr

C  READ RAIN PIXEL NUMBER

	read(10,rec=2) pix

C  READ TOTAL PIXEL NUMBER

	read(10,rec=3) ttl

C  READ ACCUMULATED RAINFALL (mm/month) 

	read(10,rec=4) rain

C  CLOSE 

    99 close(10) 

C  STOP 

	stop 

	end

4) 3B43 Ver.5


C  

C   TO READ (3B43 Ver.5) RAINFALL  

C   

	parameter (idim = 360, jdim = 80) 

	parameter (rmiss = -9999.9) 

	real*4 rr(idim,jdim), rain(idim,jdim)

C   OPEN DATA FILE 

	open(10,file='3B43.rain.199801.5.grd', access='direct', 

       2  form='unformatted', status='old', recl=4*idim*jdim, err=99) 

C   READ HOURLY RAINFALL (mm/hour)

	read(10,rec=1) rr

C   READ ACCUMULATED RAINFALL (mm/month) 

	read(10,rec=2) rain

C   CLOSE 

     99 close(10) 

C   STOP 

	stop 

	end

5) 3B43 Ver.6


C  

C   TO READ (3B43 Ver.6) RAINFALL  

C   

	parameter (idim = 1440, jdim = 400) 

	parameter (rmiss = -9999.9) 

	real*4 rr(idim,jdim), rain(idim,jdim)

C   OPEN DATA FILE 

	open(10,file='3B43.rain.200401.6.grd', access='direct', 

       2  form='unformatted', status='old', recl=4*idim*jdim, err=99) 

C   READ HOURLY RAINFALL (mm/hour)

	read(10,rec=1) rr

C   READ ACCUMULATED RAINFALL (mm/month) 

	read(10,rec=2) rain

C   CLOSE 

     99 close(10) 

C   STOP 

	stop 

	end

6. Notice

1) If you want to use the browse images of this data set in publications, please contact the EORC TRMM Office ( ).

2) If you use this data set in publications, please include the following credits:

"We used the parameter subsetting of TRMM Level 3 standard products that were processed and provided by the National Aeronautics and Space Administration and the Japan Aerospace Exploration Agency for analysis."

3) Also, we would appreciate receiving a preprint and/or reprint of those publications utilizing the data set for inclusion in the TRMM bibliography. These publications should be sent to:

The EORC TRMM Office
Earth Observation Research Center
22nd Floor Office Tower X, Harumi Triton Square,
1-8-10, Harumi, Chuo-ku, Tokyo 104-6023, JAPAN
FAX: +81-3-6221-9017

4) Please contact us for any comments, problems or questions at e-mail address :

7. Display using GrADS

The Data is written in GrADS "float data" format.

The Grid Analysis and Display System (GrADS) is an interactive desktop tool, which is available on almost UNIX workstations, Apple Macintosh, and DOS or Linux based PCs. You can get free GrADS software via anonymous ftp.

The URL of the GrADS Home Page is:

http://grads.iges.org/grads/head.html

For more information about GrADS, please read the GrADS documentation located on the GrADS Home Page.

Here, you can easily display the data using the following GrADS descriptor files.

1) Example for 3A11


DSET  3A11.rain.9901.5.grd

TITLE 3A11 monthly surface rainfall [Ver.5]

UNDEF -9999.9

XDEF  72 LINEAR -177.5 5.0

YDEF  16 LINEAR  -37.5 5.0

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  1

tmi  0  0   3A11 monthly rainfall [mm/month]

ENDVARS

2) Example for 3A25G1


DSET  3A25G1.rain.9901.5.grd

TITLE 3A25 Grid 1 near surface rainfall [Ver.5]

UNDEF -9999.9

XDEF  72 LINEAR -177.5 5.0

YDEF  16 LINEAR  -37.5 5.0

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  1

prh1  0  0  3A25 hourly rain rate at near surface [mm/hour]

pix1  0  0  rain pixel number at near surface

tl1  0  0  total pixel number at near surface

prm1  0  0  accumulated monthly rainfall [mm/month]

** calculated by prh1*(pix1/ttl1)*24*HoursInEachMonth 

ENDVARS

3) Example for 3A25G2


DSET  3A25G2.rain.9901.5.grd

TITLE 3A25 Grid 2 near surface rainfall [Ver.5]

UNDEF -9999.9

XDEF 720 LINEAR -179.75 0.5

YDEF 148 LINEAR  -36.75 0.5

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  1

prh2  0  0  3A25 hourly rain rate at near surface [mm/hour]

pix2  0  0  rain pixel number at near surface

ttl2  0  0  total pixel number at near surface

prm2  0  0  accumukated monthly rainfall [mm/month]

** calculated by prh2*(pix2/ttl2)*24*HoursInEachMonth 

ENDVARS

4) Example for 3B31_COMB


DSET  3B31_COMB.rain.9901.5.grd

TITLE 3B31_COMB monthly surface rainfall [Ver.5]

UNDEF -9999.9

XDEF  72 LINEAR -177.5 5.0

YDEF  16 LINEAR  -37.5 5.0

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  1

comb   0  0   3B31_COMB monthly rainfall [mm/month]

ENDVARS

5) Example for 3B31_TMI


DSET  3B31_TMI.rain.9901.5.grd

TITLE 3B31_TMI monthly surface rainfall [Ver.5]

UNDEF -9999.9

XDEF  72 LINEAR -177.5 5.0

YDEF  16 LINEAR  -37.5 5.0

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  1

tmi12  0  0   3B31_TMI monthly rainfall [mm/month]

ENDVARS

6) Example for 3B43 Ver.5


DSET  3B43.rain.199901.5.grd

TITLE 3B43 monthly surface rainfall [Ver.5]

UNDEF -9999.9

XDEF 360 LINEAR -179.5 1.0

YDEF  80 LINEAR  -39.5 1.0

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR jan1999 1mo

VARS  2

prh3  0  0   3B43 hourly rainfall [mm/hour]

prm3  0  0   3B43 monthly rainfall [mm/month]

ENDVARS

7) Example for 3B43 Ver.6


DSET  3B43.rain.200404.6.grd

TITLE 3B43 monthly surface rainfall [Ver.6]

UNDEF -9999.9

XDEF 1440 LINEAR -179.875 0.25

YDEF  400 LINEAR  -49.875 0.25

ZDEF  1 LEVELS 1.0

TDEF  1 LINEAR apr2004 1mo

VARS  2

prh3  0  0   3B43 hourly rainfall [mm/hour]

prm3  0  0   3B43 monthly rainfall [mm/month]

ENDVARS

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