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TRMM/3A25/

3A25 Monthly Mean Product

SDTF Team*

（Satellite Data To Freshman）

Source:

http://www.satdatafresh.com/precipitation_TRMM.html

Last Revised March, 2020

*Correspond to Juliet at [email protected]

http://www.satdatafresh.com/precipitation_TRMM.html

mailto:[email protected]

TRMM_3A25 Monthly Mean Product User’s Guide

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Table of Contents

1 About the original data version .................................... 3

1.1 TRMM Introduction ....................................................... 3

1.2 Origin Data Source ......................................................... 3

2 Data Analysis Considerations ...................................... 4

2.1 Data Processing ............................................................ 4

2.3 Data saving ....................................................................... 4

3Files Product Format and Content…………………….6

3.1 rainMean1 ......................................................................... 7

3.2 surfRainMean1 ................................................................. 8

4 Plots Product List ......................................................... 8

4.1 rainmean1 ......................................................................... 8

4.2 surfRainMean1 ............................................................... 10

5 References ................................................................. 10

Appendices ................................................................... 11

A. Missing Origin Files Record ........................................... 11

How to site: Zhu, L., (2020, April 6), TRMM_3A25 Monthly Mean Product, Satellite Data To

Freshman, retrieved from http://www.satdatafresh.com.

Or in the text: Data retrieved from Satellite Data To Freshman (http://www.satdatafresh.com,last

access: YYYY, MM DD).


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1 About the original data version

1.1 TRMM Introduction

“TRMM *was a research satellite designed to improve our understanding of the

distribution and variability of precipitation within the tropics as part of the water cycle

in the current climate system. By covering the tropical and sub-tropical regions of the

Earth, TRMM provided much needed information on rainfall and its associated heat

release that helps to power the global atmospheric circulation that shapes both weather

and climate.

Since its launch in 1997, The Precipitation Radar* (PR) looked through the

precipitation column, and provided new insights into tropical storm structure and

intensification and the TRMM Microwave Imager (TMI) measured microwave energy

emitted by the Earth and its atmosphere to quantify the water vapor, the cloud water,

and the rainfall intensity in the atmosphere.

On April 15, 2015, TRMM officially ended, after the spacecraft depleted its fuel

reserves.” -from Introduction of TRMM. [1]

1.2 Origin Data Source

The data we use to produce TRMM_3A25 monthly product is from the dataset

TRMM_3A25: TRMM Radar Rainfall Statistics L3 1 month (5×5) and (0.5×0.5) degree

V7 (3A25: Spaceborne Radar Rainfall),which is available on the website

（https://disc.gsfc.nasa.gov/datasets/TRMM_3A25_7/summary?keywords=TRMM_3A25）.

As a near equatorial non solar synchronous orbit satellite (with inclination of 35 degrees

from the equator), the detection range covers as much of the tropics as possible, and the

spatial scope of the data is from 50°S to 50°N.

https://pmm.nasa.gov/TRMM/PR

https://pmm.nasa.gov/TRMM/TMI

https://disc.gsfc.nasa.gov/datasets/TRMM_3A25_7/summary?keywords=TRMM_3A25


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And the temporal coverage is from December,1997 to March, 2015.

As for the data source, “The primary objective of algorithm 3A25 is to compute various

rainfall statistics over a month from the level 2 PR products.”-from TRMM.V7.3A25

User’s Guide.[2] “The level2 PR products” refers to the dataset 2A25: Precipitation

Radar Rainfall Rate and Profile, which “produces an estimate of vertical rainfall rate

profile for each radar beam”, and “the rainfall rate estimate is given at each resolution

cell of the PR radar”. -from TRMM.V7.2A25 User’s Guide.[3]

The 3A25 data contains precipitation rate at several levels and two spatial resolutions.

“The statistics are derived at two spatial resolutions: (1) a standard space scale of 5

degrees by 5 degrees (latitude × longitude) cells and (2) a high resolution subset of 0.5

degree × 0.5 degree cells.“-from TRMM.V7.3A25 User’s Guide.[2]

But the version of resolution: 0.5 degree × 0.5 degree cells is still not available. We

only choose the precipitation product with resolution 5 degrees × 5 degrees.

_____________________________________________________________________

*For more details of TRMM, please view https://pmm.nasa.gov/TRMM/mission-overview.

*For more details of Precipitation Radar, please view https://pmm.nasa.gov/TRMM/PR.

*For more details of TRMM Microwave Imager, please view https://pmm.nasa.gov/TRMM/tmi.

2 Data Analysis

2.1 Data Processing

We didn’t do any data processing to the origin data but convert the file format from

HDF4 to Formatted binary, as it is already monthly mean level 3 data.

2.3 Data saving

Generally, for a matrix of dimension [M’, N’], the first index runs along the vertical,

the second index runs along the horizontal. The pixel centers are at integer positions

ranging from 0 to N = N’ - 1 horizontally and from 0 to M = M’ - 1 vertically. Matrix

https://pmm.nasa.gov/TRMM/mission-overview



https://pmm.nasa.gov/TRMM/TMI

https://pmm.nasa.gov/TRMM/tmi


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Placing figure below shows how the data is filled in the bounding box. In this example,

[0, M] determines the min latitude and the max longitude of grids, while [0, N]

determines the min longitude and the max latitude of grids.

The explanation of the 2D-matrix placement

In the csv* files, the coordinates (longitude, latitude) of each grid cell is determined

by the center point. The first row and first column record the corresponding

coordinates.

However, in txt files, the coordinates are not included.

An example of the data saving in csv


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When plotting data, the projection direction can be seen in the picture below.

An example of Data plane projection

*About the file format, please turn to chapter3.

3 Files Product Format and Content

The data products are available in format of csv and txt.

There would be a zip file named 3A25.yyyymm.7.zip (“yyyy”: year, “mm” :month).


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3.1 rainMean1

Field Name Definition Dimension Units Format Data

type

coverage

rainMean1.path

average

Rain Rate

Mean 1 gives

means of

non-zero

rain rates

over 5o × 5o

boxes for

one month.

The

rain rates

are

determined

in 2A-25 and

evaluated

for the path-

average and

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

rainMean1.At 2

km

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

rainMean1.At 4

km

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

rainMean1.At 6

km

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

rainMean1.At

10 km

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:


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at the fixed

heights of 2,

4, 6, 10 and

15 km. It

ranges from

0.0 to 5000.0

mm/month.

[2]

40°S-40°N

rainMean1.At

15 km

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

3.2 surfRainMean1

Field Name Definition Dimension Units Format Data

type

coverage

surfRainMean1 Mean of non-

zero near-

surface rain

rate at a

horizontal

resolution of

5o × 5o. It

ranges from

0.0 to 3000.0

mm/month.

[2]

Latitude,

Longitude

mm/hr “.csv”,

“.txt”

Float Spatial:

40°S-40°N

4 Plots Product List

4.1 rainmean1

For each level, the precipitation rate is plotted into a picture in “png” format.


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File name (yyyy: year ;mm: month) Spatial

resolution

Field name format

3A25.yyyymm.rainMean1.At2km.png 5°×5° rainMean1.At 2 km png





3A25.yyyymm.rainMean1.path_average

.png

5°×5° rainMean1.path

average

png


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Two examples of 3A25 rainMean1 plots

4.2 surfRainMean1

File name Field name format

TRMM_2B31_surfaceprecipitationrate_lps1.yyyy-

mm.png

The surface

rainfall rate

(liquid plus

solid)

png

An example of 3A25 surfrainMean1 plots

5 References

[1] Introduction of TRMM, data retrieved from https://pmm.nasa.gov/TRMM.

[2] File Specification 3A25(Version7),

https://storm-pps.gsfc.nasa.gov/storm/data/docs/filespec.TRMM.V7.3A25.pdf

[3] File Specification 2A25(Version7),

https://storm-pps.gsfc.nasa.gov/storm/data/docs/filespec.TRMM.V7.2A25.pdf

___________________________________________________________________

†If you have some suggestions or questions, please contact Zheng Minglin at

[email protected] or Ding Qirong at [email protected].

https://pmm.nasa.gov/TRMM


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Appendices

A. Missing Origin Files Record

Because of some special reasons, such as satellite anomalies, clouds covering, there

are some days/months of which data is missing. Here are the records.

Year Month

2014 2014-11 2014-12

2015 2015-01

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