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GES DISC DAAC Data Guide: Arkin and Janowiak GPI: IR-Based Monthly Rainfall for the GPCP

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Summary:

The Arkin and Janowiak global monthly mean rainfall data derived from infrared satellite observations, and known as "GOES Precipitation Index (GPI)", was generated under theGlobal Precipitation Climatology Project (GPCP) which is a World Meteorological Organization/World Climate Research Program (WMO/WCRP) effort. The data are based upon satellite derived (infrared) monthly rainfall estimates data from GMS, GOES and Meteosat sources. The data are monthly estimates for the period from January, 1986 to December, 1995. The extent of the data ranges from latitudes of 40 degrees South to 40 degrees North and longitudes of 180 degrees East to 180 degrees West.

Table of Contents:

1. Data Set Overview:

Data Set Identification:

Arkin and Janowiak GPI: IR-Based Monthly Rainfall for the GPCP

Data Set Introduction:

The monthly rainfall estimates are based upon infrared radiometer measurements which are an intermediate product of the WMO/WCRP effort. Each rainfall data file consists of 2.5 degree by 2.5 degree gridded monthly accumulations of estimated rainfall. The primary source of information over the tropical oceans is infrared (IR) data from polar-orbiting and geostationary satellites. The estimates are generated using a simple cloud-top temperature-thresholding algorithm. This method of using cloud-top brightness temperatures, observed by satellites, can be used to infer areas of deep convention. Since most rainfall in the tropical regions is associated with convection, this method is useful of estimation of rainfall in those areas.

Objective/Purpose:

This data set was generated for the GPCP which is reponsible for producing global analyses of large-scale monthly rainfall climatology data using satellite and conventional data.

Summary of Parameters:

The parameter for this data set is monthly average rainfall.

Discussion:

For a discussion, please refer to Janowiak and Arkin (1991).

Related Data Sets:

The following related data sets are available from the Goddard Space Flight Center (GSFC)) Distributed Active Archive Center (DAAC):

Chang SSM/I Derived Monthly Rain Indices
GPCP v1a Combined Precipitation
SSM/I Pathfinder Precipitation Daily Product
SSM/I Pathfinder Precipitation Pentad Product
SSM/I Pathfinder Precipitation Monthly Product.

2. Investigator(s):

Investigator(s) Name and Title:

Phillip Arkin
Office of Global Programs
Oceanic and Atmospheric Research
NOAA
Washington, D.C.

and

John E. Janowiak
Climate Analysis Center
National Meteorological Center
National Weather Service
NOAA
Washington, D.C.

Title of Investigation:

GPI: IR-Based Monthly Rainfall for the GPCP

Contact Information:

Please direct all queries to Goddard Space Flight Center (GSFC) DAAC Help Desk.
DAAC Help Desk:
The DAAC help desk also provides additional information on the Goddard DAAC system capabilities, and other supported datasets. The Help Desk can be reached at:
EOS Distributed Active Archive Center (DAAC)
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet:daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
3. Theory of Measurements:
This information is not available at this time.
4. Equipment:

Sensor/Instrument Description:

Collection Environment:

Satellite.

Source/Platform:

The platforms for this data set are GMS, GOES, Meteosat satellites.

Source/Platform Mission Objectives:

This information is not available at this time.

Key Variables:

The primary variable measured by these instruments is brightness temperature.

Principles of Operation:

This information is not available at this time.

Sensor/Instrument Measurement Geometry:

This information is not available at this time.

Manufacturer of Sensor/Instrument:

This information is not available at this time.

Calibration:

Specifications:

This information is not available at this time.

Tolerance:

This information is not available at this time.

Frequency of Calibration:

This information is not available at this time.

Other Calibration Information:

This information is not available at this time.
5. Data Acquisition Methods:
The Goddard DAAC obtains the monthly rainfall data set via an ftp transfer from the data producer's ftp site.
6. Observations:

Data Notes:

No data notes are available at this time.

Field Notes:

No field notes are available at this time.
7. Data Description:

Spatial Characteristics:

Spatial Coverage:

The data set contains monthly globally merged rainfall grid estimates extending from latitudes of 40 degrees North to 40 degrees South and longitudes of 180 degrees West to 180 degrees East. The data progresses in order from North to South, and West to East.The first grid element correspond to values centered at 88.75 degrees North, 178.75 degrees West.

Spatial Coverage Map:

The rainfall estimates cover the region from latitudes of 40 degrees North to 40 degrees South and longitudes of 180 degrees West to 180 degrees East as shown below.
spatial coverage

Spatial Resolution:

The spatial resolution of the data is 2.5 degree latitude by 2.5 degree longitude grids.

Projection:

Cylindrical Equidistant.

Grid Description:

The Arkin and Janowiak GPCP monthly rainfall data are mapped to a 2.5 degree equal area grid over the region from 40 degrees South to 40 degrees North and 180 degrees East to 180 degrees West.

Temporal Characteristics:

Temporal Coverage:

The data are monthly estimates for the period from January, 1986 to December, 1995.

Temporal Coverage Map:

The map that provides the temporal distribution of the monthly rainfall estimates is presently unavailable.

Temporal Resolution:

The data set consists of monthly rainfall estimates in the units of mm/day.

Data Characteristics:

ParameterAverage Monthly Rainfall DefinitionMonthly average of rainfall as estimated by satellite measurements Units of Measurementmm/day Data Range 0-35 mm

Sample Data Record:

The following is a sample of a partial month of the monthly rainfall data set.
9406 0.53 0.69 0.65 0.47 0.25 0.26 0.29 0.19 0.06 0.08 0.07 0.06 0.09 0.14 0.15 0.19 0.29 0.35 0.32 0.36 0.64 0.67 0.68 0.43 0.13 0.05 0.21 0.76 1.33 1.95 2.30 2.09 1.86 1.73 1.73 1.91 1.73 2.42 4.15 5.37 4.88 3.43 3.36 4.17 4.96 5.06 3.57 3.10 3.15 2.93 3.62 4.56 4.06 3.48 3.10 3.03 3.04 2.92 3.32 5.03 6.21 6.98 6.96 7.60 6.27 6.38 5.95 5.18 5.38 5.21 5.17 5.01 5.44 8.29 8.77 7.22 6.68 5.32 3.26 2.36 2.02 1.93 1.83 1.49 1.21 1.08 0.87 0.62 0.50 0.64 0.57 0.34 0.26 0.22 0.22 0.76 1.51 1.33 1.87 1.75 1.35 2.37 3.81 5.83 6.03 5.27 5.28 5.20 3.69 3.34 2.81 3.17 2.51 1.73 1.23 2.00 2.72 3.10 2.98 2.77 2.26 1.56 1.84 1.84 1.96 1.93 2.16 2.65 3.53 1.36 0.93 0.62 0.60 0.77 0.54 0.18 0.03 0.04 0.08 0.14 0.25 0.48 0.74
   
8. Data Organization:

Data Granularity:

A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary.
The complete data set covering the period from January, 1986 to December 31, 1995 is contained in one file and has a file size of approximately 4.4 Mb.

Data Format:

The data set is in ASCII format and the file name is:
gpi_mth_sat-merged_mmday_asc_0186-1295
9. Data Manipulations:

Formulae:

Derivation Techniques and Algorithms:

The monthly rainfall estimates were generated using geostationary satellite data. Arkin (1979) investigated the relationship between cloud-top brightness temperatures and observed rainfall using data from GATE (Hudlow and Patterson, 1979). This work indicated a high correlation between the fractional coverage of "cold" clouds and observed rainfall. The work of Richards and Arkin (1981) determined that the highest correlation between the parameters was produced using a 2.5 degree latitude/longitude spatial scale. An estimation method using linear regression was developed. The regression procedure yielded the simple estimation equation:
R = [3 mm h-1] X [frac] X [hours]
where R is the rainfall estimate in millimeters; frac is the fractional coverage of cloud-top temperature < 235K for the desired 2.5 degree latitude/longitude region; and hours indicate the number of hours in the observation period.
The estimation technique was applied to the cloud-top brightness temperatures for GMS, GOES, and Meteosat geostationary satellite data in order to estimate the monthly accumulated rainfall in the global tropics.

Data Processing Sequence:

Processing Steps:

This information is not available at this time.

Processing Changes:

This information is not available at this time.

Calculations:

Special Corrections/Adjustments:

A reduction correction has been applied to GPI estimates produced from Geostationary IR coverage at large zenith angles (i.e. > 33 deg). A systematic bias was found by comparisons of GPI estimates computed separately from each Geostionary Satellite's IR data in overlap regions. The satellite with the larger zenith angle yielded a larger amount of cloud colder than GPI's temperature threshold of 235 K relative to other satellite. This correction removes (partially at least) this bias.

Calculated Variables:

This information is not available at this time.

Graphs and Plots:

This information is not available at this time.
10. Errors:

Sources of Error:

This information is not available at this time.

Quality Assessment:

Data Validation by Source:

This information is not available at this time.

Confidence Level/Accuracy Judgement:

This information is not available at this time.

Measurement Error for Parameters:

This information is not available at this time.

Additional Quality Assessments:

The missing values are identified as -9999.

Data Verification by Data Center:

The Goddard DAAC completes visual inspection of the data files that comprise the data set to ensure that the data set is complete and that the files were not corrupted during the file transfer from the data producer.
11. Notes:

Limitations of the Data:

The rainfall estimates are valid for the tropics and warm season extratropics, and will indicate rainfall in regions of persistant thick cirrus. The estimates are only valid in these regions because temperature is the only parameter used in the estimation scheme.

Known Problems with the Data:

This information is not available at this time.

Usage Guidance:

This information is not available at this time.

Any Other Relevant Information about the Study:

This information is not available at this time.
12. Application of the Data Set:
Applications of this data set include the exploration of the rainfall variations in the tropics over a long time period (1986 to 1995), the relationship between the rainfall variations and the El Nino Southern Oscillation (ENSO) conditions that occur in the Pacific during that time period, and as supplemental information to conventional rainfall data which are often scarce in the tropics.
13. Future Modifications and Plans:
The data producer provides periodic updates to the data set with increased temporal coverage. The Goddard DAAC will work with the data producer to include the additional data in the archive.
14. Software:

Software Description:

No software is provided with this data set. However, a brief sample Fortran code that provides information on how to read the data set is as follows:
                Real Precip(144,32)
                     Open(unit=20,acess='direct',file=input file,
                    .      status='readonly',form=''unformated',recl=4608)
                     Do 200 irec=1,108 200 read(20,rec=irec) precip       

Software Access:

This information is not applicable for this data set.
15. Data Access:

Contact Information:

Goddard Space Flight Center DAAC User Services.

Data Center Identification:

GSFC Distributed Active Archive Center

Procedures for Obtaining Data:

This data set is available via several ways: by contacting the GSFC DAAC User Services, by accessing the DAAC/EOSDIS Archive Search and Order Utilities, the WWW interface, or Anonymous FTP.
GSFC DAAC User Services:
The DAAC User Services or Help Desk also provides additional information on the Goddard DAAC system capabilities, and other supported datasets. The Help Desk can be reached at:
     EOS Distributed Active Archive Center (DAAC)
     Code 610.2 NASA Goddard Space Flight Center Greenbelt, Maryland 20771 Internet:daacuso@daac.gsfc.nasa.gov
     301-614-5224 (voice)
     301-614-5268 (fax)
DAAC SEARCH AND ORDER SERVICES:
ANONYMOUS FTP:
The GPCP-GPI precipitation global data set resides on DAAC anonymous FTP. The data files may be accessed from this document,
ftp gifArkin and Janowiak GPCP-GPI Data
or directly via FTP at
ftp disc1.gsfc.nasa.gov
login: anonymous
password: < your internet address >
cd data/hydrology/precip/arkin/gpcp_gpi
mget *

Data Center Status/Plans:

The Goddard DAAC plans to periodically check with the data producer regarding updates to the data set.
16. Output Products and Availability:
Data sets are provided on ftp .
17. References:
Arkin, P.A., 1979: The Relationship Between the Fractional Coverage of High Cloud and Rainfall Accumulations during GATE over the B-array, Mon. Wea. Rev.,, 107, 1382-1387.
Hudlow, M.D., and V. Patterson, 1979: GATE Radar Rainfall Atlas, NOAA Spec. Rep., 155 pp., Cent. for Environ. Assessment Serv., NOAA.
Janowiak, J.E. and P.A. Arkin, 1991: Rainfall Variations in the Tropics During 1986-1989, as Estimated From Observations of Cloud-Top Temperatures, J. Geophys. Res., 96, Supplement, 3359-3373.
Richards, F., and P.A. Arkin, 1981: On the Relationship Between Satellite-Observed Cloud Cover and Precipitation, Mon. Wea. Rev., 5, 1081-1093.

Brightness Temperature

Effective temperature of a blackbody radiating the same amount of energy per unit area at the same wavelength as the observed body. Also called effective temperature.

DAAC

Distributed Active Archive Center

GMS

Geostationary Meteorological Satellite

GOES

Geostationary Operational Environmental Satellites

IR

Infrared

GSFC

Goddard Space Flight Center

Meteosat

Meteorological Satellite

URL

Uniform Resource Locator
20. Document Information:

Document Revision Date:

Fri May 10 11:51:13 EDT 2002

Document Review Date:

August 1, 1996

Document ID:

Not available at this time.

Citation:

Not available at this time.

Document Curator:

Suraiya Ahmad (ahmad@daac.gsfc.nasa.gov)

Document URL:

http://disc.sci.gsfc.nasa.gov/DATASET_DOCS/arkin_gpcp_gpi_dataset.html
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