GES DISC DAAC Data Guide:
Legates Surface and Ship Observation of Precipitation

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Summary:

The Legates Surface and Ship Observation of Precipitation Data Set was produced by Dr. David Legates, University of Oklahoma, and Dr. Cort Willmott, University of Delaware. The data set represents a global climatology of mean monthly precipitation based upon traditional land-based rain gauge measurements and shipboard measurements. The rain gauge measurements were collected from existing sources, coding errors were corrected and redundant station information removed. The result of these steps provided a data base of 24,635 spatially independent terrestrial station records and 2223 oceanic grid records. A procedure for correcting the gauge-induced biases was implemented to remove the systematic errors associated with traditional rain gauge collection methods. The corrected monthly precipitation measurements were then interpolated to a 0.5 degree latitude by 0.5 degree longitude grid using a spherically based interpolation procedure. This climatology is largely representative of the 60-year period from 1920 to 1980; with greater weight given to the more recent (data-rich) years.

Table of Contents:

• 1 Data Set Overview
• 2 Investigator(s)
• 3 Theory of Measurements
• 4 Equipment
• 5 Data Acquisition Methods
• 6 Observations
• 7 Data Description
• 8 Data Organization
• 9 Data Manipulations
• 10 Errors
• 11 Notes
• 12 Application of the Data Set
• 13 Future Modifications and Plans
• 14 Software
• 15 Data Access
• 16 Output Products and Availability
• 17 References
• 18 Glossary of Terms
• 19 List of Acronyms
• 20 Document Information

1. Data Set Overview:

Data Set Identification:

Legates Surface and Ship Observation of Precipitation

Data Set Introduction:

The Legates surface and ship observation of precipitation data set consists of a global climatology of monthly mean precipitation values, using traditional land-based gauge measurements and shipboard estimates.

Objective/Purpose:

The objective of this data set is to provide an improved climatology data set that is based upon a spatially dense network of terrestrial rain gauge station measurements and accurate estimates of oceanic precipitation that have been corrected for major biases inherent in gauge collection procedures.

Summary of Parameters:

This global data set contains monthly mean precipitation.

Discussion:

This information is not available at this time.

Related Data Sets:

Jaeger Monthly Mean Global Precipitation

2. Investigator(s):

Investigator(s) Name and Title:

Dr. David R. Legates

Department of Geography

College of Geosciences

University of Oklahoma

Norman, OK 73019

and

Dr. Cort J. Wilmont

Department of Geography

Center for Climatic Research

University of Delaware

Newark, DE 19176

Title of Investigation:

Mean Seasonal and Spatial Variability in Gauge Corrected, Global Precipitation

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:

Data are compiled from terrestrial precipitation gauge measurements in their traditional setting (elevated above the ground and possibly with a gauge shield) and the indirect oceanic precipitation estimation technique of Dorman and Bourke. This procedure estimates precipitation using a statistically-derived relationship between gauge catch and the current weather code of the surface synoptic record taken on board ships (see references). Long-term monthly mean values were compiled from these measurements and estimates. Biases (underestimates) resulting from the effect of the precipitation gauge were subsequently estimated and removed from these monthly mean precipitation data by taking into account local variations in gauge type, height of the gauge above the ground, air temperature, wind speed, and general regional sheltering.

4. Equipment:

Sensor/Instrument Description:

Collection Environment:

Ground and aboard ships.

Source/Platform:

Meteorological Stations and Ships.

Source/Platform Mission Objectives:

This information is not available at this time.

Key Variables:

Precipitation, predominantly rain and snow.

Principles of Operation:

Rain gauges data collection methods vary. The collection of precipitation measurements occurs on a periodic basis.

Sensor/Instrument Measurement Geometry:

The rain gauges used for the terrestrial gauge measurements were used in their traditional setting (elevated above the ground and possibly with a gauge shield). The data is based upon 24,635 independent stations which provided a dense network in the industrialized countries of North America, Europe, and East Asia. Station distribution in the arid, mountainous, and polar regions, however, are less dense.

Manufacturer of Sensor/Instrument:

The manufacturer of the rain gauges varies.

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:

Global archives of monthly precipitation compiled by Wernstedt (1972), Willmott, et al. (1981) and the National Center for Atmospheric Research (Spangler and Jenne, 1984) provided most of the terrestrial data for this climatology data set. To improve the spatial resolution in the above mentioned regions, monthly averages were obtained from an additional 208 stations in Australia, New Guinea, and Indonesia, 584 stations in China and the Far East, and ten stations in Antarctica. Five stations in the Sahara also provided monthly precipitation averages.

6. Observations:

Data Notes:

There are no data notes for this data set.

Field Notes:

There are no field notes for this data set.

7. Data Description:

Spatial Characteristics:

Spatial Coverage:

The data set is global in coverage. The data is based upon 24,635 independent stations which provided a dense network in the industrialized countries of North America, Europe, and East Asia. Station distribution in the arid, mountainous, and polar regions, however, are less dense.

Spatial Coverage Map:

Spatial Resolution:

The spatial resolution of the data is 0.5 degree latitude by 0.5 degree longitude grids.

Projection:

No projection was used to process the data since the data are directly related to geographic areas.

Grid Description:

The data are on a 0.5 x 0.5 degree grid for the area from 90N to 90S and 180W to 180E.

Temporal Characteristics:

Temporal Coverage:

In order to achieve a dense spatial resolution, virtually all station records from the existing sources were used even though they were based upon differing time periods. Most of the data was observed between 1920 and 1980, therefore, this climatology is largely representative of that 60 year period. The data file spans the period from 1920 to 1980.

Temporal Coverage Map:

This climatology contains monthly mean precipitation for each month of the 60 year period.

Temporal Resolution:

The temporal resolution is monthly.

Data Characteristics:

Parameter/Variable:

The key parameter is precipitation.

Variable Description/Definition:

Precipitation - Any or all forms of liquid or solid water particles that fall from the atmosphere and reach the surface of the Earth. It includes drizzle, rain, snow, snow pellets, snow grains, ice crystals, ice pellets, and hail. Precipitation is also defined as a measurement of the quantity, expressed in centimeters or milliliters of liquid water depth, of the water substance that has fallen at a given location in a specified amount of time.

Unit of Measurement:

The monthly mean precipitation data are in millimeters.

Data Source:

Rain gauges.

Data Range:

The range of the data is from 0 to approximately 5500 mm.

Sample Data Record:

90.0 -180.0   15   11   18   14   11   11   27   30   43   23   21   17   241   
89.5 -180.0   15   10   18   13   11   11   27   30   42   22   19   16   234   
89.0 -180.0   12    5   16   10   10    8   27   28   38   18   13   11   196   
88.5 -180.0    9    2   15    8    8    5   26   25   35   14    7    7   161   
88.0 -180.0    7    2   15    8    7    4   26   25   35   14    5    6   154   
87.5 -180.0    6    2   15    8    6    4   25   24   35   14    4    6   149
    

8. Data Organization:

Data Granularity:

A general description of data granularity as it applies to the IMS appears in the EOSDIS Glossary.

The data for the entire period of record is contained in a single file. This file is in UNIX compress format of the size 5.4 Megabyte (uncompressed size is approximately 21 Megabyte

Data Format:

The monthly mean precipitation total is stored in a 361 by 721 element array. The data is in ASCII format. The name of the file is: legates.cor.Z

9. Data Manipulations:

Formulae:

Derivation Techniques and Algorithms:

The rain gauge measurements were collected from existing sources, coding errors were corrected and redundant station information removed. The result of these steps provided a data base of 24,635 spatially independent terrestrial station records and 2223 oceanic grid records. A procedure for correcting the gauge-induced basis was implemented to remove the systematic errors associated with traditional rain gauge collection methods.

For this data set, the oceanic precipitation is estimated using the method of Dorman and Bourke (1979). Their method was derived from a technique proposed by J. S. Sawyer and later refined by Tucker (1961).

The method of Tucker has been determined to be suitable for estimating oceanic preipitation only in the mid-latitudes. In the tropics, the increased rainfall intensity reduced the effectiveness of Tucker's method. Dorman and Bourke (1978) also observed that the error was systematic and highly correlated to air temperature. They developed a set of regression equations, one for each month, to remove the error from Tucker's estimates. Dorman and Bourke used shipboard observations from 1950 to 1972 to estimate average monthly precipitation for the Pacific and Atlantic Oceans north of 30 degrees South at the vertices of a 2 degree latitude by 5 degree longitude lattice. These estimates were used in the development of this data set.

Dorman and Bourke could not obtain reliable estimates for the Indian and Southern Ocean south of 30 degrees South. For these regions, this data set used the estimates of Jaeger's (1983) global precipitation climatology. Jeager used a variation of the typical precipitation frequency approach to generate his estimates.

The estimates of Jaeger and those of Dorman and Bourke are not commensurate. Systematic differences between the two approaches had to be resolved before the estimates could be used for this data set. Jaeger's estimates were converted into values compariable with Dorman and Bourke by applying multiple linear regression to data from the Atlantic and Pacific Oceans north of 30 degrees South.

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:

This information is not available at this time.

Calculated Variables:

Terrestrial and oceanic precipitation.

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:

This information is not available at this time.

Data Verification by Data Center:

This information is not available at this time.

11. Notes:

Limitations of the Data:

This information is not available at this time.

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:

This data set can be used to verify general circulation model (GCM) prognostications of the seasonal precipitation cycle and GCM dynamics, as ground truth for evaluating and calibrating precipitation estimates obtained from radars and satellites, and as a basis for evaluating climate change.

13. Future Modifications and Plans:

The processing of this data set is complete.

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 format is included in the documentation distributed with the data set.

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:

These datasets are available from the Goddard DAAC.

ANONYMOUS FTP:

The legates precipitation data set resides on DAAC anonymous FTP. The data files may be accessed from this document,
Legates Surface and Ship Observation of Precipitation

or directly via FTP:

ftp disc1.gsfc.nasa.gov

login: anonymous

password: < your email address >

cd data/hydrology/precip/legates

Data Center Status/Plans:

The GSFC DAAC will continue to archive and distribute updates received from the data producer. The Goddard DAAC plans to periodically check with the data producer regarding the data set revisions.

16. Output Products and Availability:

Data sets are available on anonymous ftp.

17. References:

Dorman, C. E. and Bourke, R. H., 1979: Precipitation over the Pacific Ocean, 30S to 60N. Monthly Weather Review, Vol 107, 896-910.

Dorman, C. E. and Bourke, R. H., 1981: Precipitation over the Atlantic Ocean, 30S to 70N. Monthly Weather Review, Vol 109, 554-563.

Jaeger, L., 1983: Monthly and Areal Patterns of Mean Global Precipitation. in Street-Perrott, A. et al. (eds) Variations in the Global Water Budget, D. Reidel, Dordrecht, p. 129.

Legates, D.R., 1987: A Climatology of Global Precipitation. Publications in Climatology, Vol. 40(1), 84 pp.

Legates, D.R. and C.J. Wilmott, 1990: Mean Seasonal and Spatial Variability in Gauge-Corrected, Global Precipitation. International Journal of Climatology, Vol. 10, 111-127.

Spangler, W. M. L and Jenne, R. L., 1984: World Monthly Surface Station Climatology. National Center for Atmospheric Research. 14 pp.

Wernstedt, F. L., 1972: World Climatic Data. Climatic Data Press.

Willmott, C. J., Mather, J. R., and Rowe, C. M., 1981: Average Monthly and Annual Surface Air Temperature and Precipitation Data for the World. Part 1: The Eastern Hemisphere. Part 2: The Western Hemisphere. Publications in Climatology, Vol 34, 395 pp and 378 pp.

18. Glossary of Terms:

See the EOSDIS Glossary for a more general listing of terms related to the Earth Observing System project.

19. List of Acronyms:

See the EOSDIS Acronyms for a more general listing of terms related to the Earth Observing System project.

URL

Uniform Resource Locator

20. Document Information:

Document Revision Date:

August 1, 1996

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/legates_rain_gauge_dataset.html