Atmospheric Solar Transmission Index at Mauna Loa 1. TYPE OF DATA 1.1 Parameter/Measurement 1.2 Unit of Measurement 1.3 Data Source 1.4 Data Set Identification 2. SPATIAL CHARACTERISTICS 2.1 Spatial Coverage 2.2 Spatial Resolution 3. TEMPORAL CHARACTERISTICS 3.1 Temporal Coverage 3.2 Temporal Resolution 4. INSTRUMENT DESCRIPTION 4.1 Mission Objectives 4.2 Key Satellite Flight Parameters 4.3 Principles of Operation 4.4 Instrument Measurement Geometry 5. DATA PROCESSING SEQUENCE 5.1 Processing Steps and Data Sets 5.2 Derivation Techniques/Algorithms 5.3 Special Corrections/Adjustments 5.4 Processing Changes 6. QUALITY ASSESSMENT 6.1 Data Validation by Producer 6.2 Confidence Level/Accuracy Judgment 6.3 Usage Guidance 7. CONTACTS FOR DATA PRODUCTION INFORMATION 8. OUTPUT PRODUCTS AND AVAILABILITY 8.1 Tape Products 8.2 Film Products 8.3 Other Products 9. DATA ACCESS 9.1 Archive Identification 9.2 Procedures for Obtaining Data 9.3 NCDS Status/Plans 10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION 11. REFERENCES 11.1 Satellite/Instrument/Data Processing Documentation 11.2 Journal Articles and Study Reports 11.3 Archive/DBMS Usage Documentation 12. RELATED DATA SETS 13. SUMMARY/SAMPLE 14. NOTES ENDOFTOC 1. TYPE OF DATA 1.1 Parameter/Measurement. Relative transmission derived from consecutive direct solar irradiance measurements. 1.2 Unit of Measurement. Nondimensional. 1.3 Data Source. Ground-based tracking pyrheliometer 1.4 Data Set Identification. Data were acquired from a single fixed location at the NOAA Mauna Loa Observatory. The data provide information on the long-term relative transmission of direct sunlight through the cloud-free atmosphere above the site. Because the site is so remote and efforts are made to eliminate the influence of local contamination sources, the data can be considered representative of a larger region. 2. SPATIAL CHARACTERISTICS 2.1 Spatial Coverage. Mauna Loa, Hawaii: 19.533 deg N, 155.578 deg W. Station elevation at Mauna Loa, Hawaii is 3.4 km. 2.2 Spatial Resolution. Point data. 3. TEMPORAL CHARACTERISTICS 3.1 Temporal Coverage. The data set began in January of 1958 and extends to December, 1990. 3.2 Temporal Resolution. One value per day from early morning hours when the sun is unobscured by water clouds. Over 33 years, data have been obtained on 49% of the days each year on the average. 4. INSTRUMENT DESCRIPTION 4.1 Mission Objectives. The objective of this data set is to monitor long-term atmospheric solar transmission in support of climate studies and provide satellite ground truth data. 4.2 Key Satellite Flight Parameters. N/A 4.3 Principles of Operation. Radiant heating of blackened thermophile is measured relative to a cold junction with controlled exposure. 4.4 Instrument Measurement Geometry. The instrument is sun-tracking with a 5.8 deg field-of-view. The electromagnetic spectral band covered by the instrument is approximately 0.30 to 2.8 micrometers. 5. DATA PROCESSING SEQUENCE 5.1 Processing Steps and Data Sets. Instrument output, recorded as an analog voltage, is recorded on stripcharts only prior to 1976 and subsequently by digital computer since 1976. Continuous trace is manually examined for variability indicative of clouds during critical times of air masses 2 to 5 times each day. If the morning is determined to be cloud free, voltage values are extracted for specific times. Tentative calibration is applied and transmission index calculated from the formula in section 5.2 below. (note: Calibration is a linear multiplier of the voltage and cancels in the ratio). Tentative irradiance values and transmission index results are examined for reasonable and representative values. Data are then included in the long-term records. 5.2 Derivation Techniques/Algorithms. The derived transmission index is calculated from the following formula: 4 ATI= 1/3 I (sub i +1)/ I (sub i) i=2 where i = relative air mass (approximately 1/COSINE (solar zenith angle)) I = direct beam solar irradiance measured at the time corresponding to a solar position, i. Data are only obtained when the sun is unobstructed by any identifiable water or ice cloud. Also, the data are for only the morning hours because local air circulations potentially contaminate the site later each day. Variability in the index is caused primarily by total column aerosols, water vapor, and ozone. The major dips in the record lasting several years are due to volcanic aerosols in the stratosphere. Although the calculated transmission number is called an "index", the value does have an actual physical explanation, but one that is different from the usual rigorous application of the word "transmission". 5.3 Special Corrections/Adjustments. None. 5.4 Processing Changes. The data processing procedure switched to computer data acquisition in 1976 and computer-assisted data reduction in 1979. 6. QUALITY ASSESSMENT 6.1 Data Validation by Producer. No specific comparison available. An empirical Low Resolution Transmittance (LOWTRAN) method has been used to model the transmission index for certain conditions, and agreement to the third decimal place is typical. The LOWTRAN code is available from the National Climatic Data Center in Ashville, North Carolina. 6.2 Confidence Level/Accuracy Judgment. Daily values are potentially accurate (and precise) to 0.001 assuming that the atmosphere remained constant over the approximately 2 hours during which the data were obtained. 6.3 Usage Guidance. See assumption in section 6.2 above. Areal representativeness can not be substantiated but is often assumed to be zonally representative of background conditions. A physical understanding of the calculation of the index and its inherent stability is recommended. Most published analyses of the record use smoothed monthly averages. There is a decrease in the day to day variance following 1979 when computer aided processing began. 7. CONTACTS FOR DATA PRODUCTION INFORMATION Ellsworth G. Dutton NOAA/Climate Monitoring and Diagnostics Lab. Mail Code R/E/CG1 325 Broadway Boulder, CO 80303 303-497-6660 (voice) 303-497-6290 (Fax) 8. OUTPUT PRODUCTS AND AVAILABILITY 8.1 Tape Products. None. 8.2 Film Products. None. 8.3 Other products. 8.3.1 "Atmospheric Solar Transmission Index at Mauna Loa" on floppy disk. Medium/Specifications: IBM PC-compatible floppy disk in ASCII format. Format and Content: The data are stored as ASCII characters in one file for the entire time period. Year, month, day of month, and transmission index are recorded for each record. Data Quantity/Rate: 1 file, 100 kb Status: Available. Plans/Schedule: Measurements ongoing. Data updates yearly or on request. 8.3.2 "Atmospheric Solar Transmission at Mauna Loa", Hardcopy Listing Medium/Specifications: Data are available as a computer printout with one line containing year, month, day of month, and transmission index. Format and Content: ASCII listing. Data Quantity/Rate: One hardcopy listing, about 10 pages. Status: Available. Plans/Schedule: Measurements ongoing. Data updates yearly or on request. 8.3.3 "Atmospheric Solar Transmission at Mauna Loa" in Common Data Format. Medium/specifications: The data are stored online in a special data-set-independent format, designated the Common Data Format (CDF). This format is self-describing in that all information required to analyze these data are contained in the data file itself. The format is supported by the NASA Climate Data System (NCDS) for data retrieval and manipulation. Format and Content: Data are stored as a single binary data file in Common Data Format (CDF). Data Quantity/Rate: One binary file of approximately 101 kilobytes. Status: Available. Plans and Schedules: Data acquisition is ongoing. Data updates will be made as new data become available. 9. DATA ACCESS 9.1 Archive Identification. The data set is available to users of NASA's Climate Data System (NCDS) and is distributed on the Greenhouse Effect Detection Experiment (GEDEX) CD-ROM. The disk will utilize the ISO 9660 standard. For information on access to NCDS or this data set, contact: NCDS User Support Office NASA/Goddard Space Flight Center Code 934 Data Management System Facility Greenbelt, MD 20771 (301) 286-3209 FTS: 888-3209 TCP/IP: NCDSUSO@NSSDCB.GSFC.NASA.GOV NSI DECnet: NCF::NCDSUSO 9.2 Procedures for Obtaining Data. The data are obtained through online access via NCDS. Interested NASA-sponsored and university researchers should contact the NCDS User Support Office to obtain a computer account. 9.3 NCDS Status/Plans. NCDS will continue to support these data online. The data are stored in a special data-set-independent format, designated the Common Data Format (CDF) and are accessible through the NCDS data system. The data are referenced by the data set name CMDL-MLOA_SOLTRN-DAILY. 10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION Current investigator Ellsworth G. Dutton NOAA/Climate Monitoring and Diagnostics Lab. Mail Code R/E/CG1 325 Broadway Boulder, CO 80303 USA 303-497-6660 (voice) 303-497-6290 (Fax) 11. REFERENCES 11.1 Satellite/Instrument/Data Processing Documentation a. "Geophysical Monitoring for Climatic Change Annual Summary." Reports 1 through 18 (1973-1989), NOAA/ERL Boulder, CO 80303. 11.2 Journal Articles and Study Reports a. DeLuisi, J.J., E.G. Dutton, K. L. Coulson, T.E. DeFoor and B.G. Mendonca, 1983. "On Some Radiative Features of the El Chichon Volcanic Stratospheric Dust Cloud as Cloud of Unknown Origin Observed at Mauna Loa." J. Geophys Res., 88: 6769-6772. b. Dutton, E.G., and J.J. DeLuisi, 1983. "Spectral Extension of Direct Solar Radiation by the El Chichon Cloud During December," Geophys. Res. Lett., 10: 1013-1016. c. Dutton, E.G., DeLuisi, J.J. and Austring, A. P. 1985. "Interpretation of Mauna Loa Atmospheric Transmission Relative to Aerosols, Using Photometric Precipitable Water Amounts," J. Atmos. Chem., 3: 53-68. d. Dutton, E.G., 1989, Comments on "Major Volcanic Eruptions and Climate: A Critical Evaluation", Journal of Climate., 3: 587-588. e. Ellis, H.T. and Pueschel, R.F. 1971. "Solar Radiation: Absence of Air Pollution Trends at Mauna Loa," Science, 172: 845-846. f. Hoyt, D.V. 1979a. "Apparent Atmospheric Transmission Using the Pyrheliometric Ratioing Technique,' Appl. Opt., 18: 2530-2531. g. Mendonca, B.G., Hanson, K.J. and DeLuisi, J.J. 1978. "Volcanically Related Secular Trends in Atmospheric Transmission at Mauna Loa Observatory, Hawaii," Science, 202: 513-515. 11.3 Archive/DBMS Usage Documentation a. Olsen, L.M., Closs, J.W., Vanderpool, J.R. and Humberson, W., November 1991. "NASA's Climate Data System Primer: Version 4.0." National Space Science Data Center, NASA Goddard Space Flight Center, Greenbelt, Maryland. 12. RELATED DATA SETS 12.1 Hourly Surface Solar Irradiance at NOAA/CMDL Baseline Sites, including Mauna Loa, Barrow, Alaska, American Samoa, and the South Pole. This data set is available through NCDS or from NOAA/CMDL in Boulder, Colorado. 13. SUMMARY/SAMPLE The NCDS system provides a sample X-Y plot of solar transmission in the Data Applications subsystem. The name of the plot is CMDL-MLOA_SOLTRN-DAILY. 14. NOTES Mauna Loa Observatory is currently operated by NOAA/Climate Monitoring and Diagnostics Laboratory of Boulder, Colorado; Director, Eldon Ferguson. On site observatory staff of 8; Director, Russell Schnell. *92/03/02