13. DESCRIPTIVE FILE ON THE MAGNETIC MEDIA The following is a listing of the first file provided on the magnetic media distributed by CDIAC. The file provides variable descriptions, formats, units, and other pertinent information about each file associated with this database. TITLE OF THE DATABASE Rattlesnake Mountain Observatory (46.4 degrees N, 119.6 degrees W) Multispectral Optical Depth Measurements: 1979-1994 CONTRIBUTORS Nels R. Larson Pacific Northwest Laboratory P.O. Box 999 Richland, Washington 99352-0999 U.S.A. Joseph J. Michalsky Atmospheric Sciences Research Center 100 Fuller Road Albany, New York 12205 U.S.A. Brock A. LeBaron Utah Bureau of Air Quality P.O. Box 16690 Salt Lake City, Utah 84116-0690 U.S.A. SCOPE OF THE DATA The numeric data package (NDP) contains measurements of total optical depths for the 428 nm, 486 nm, 535 nm, 785 nm, and 1010 nm wavelength bands; derived total column aerosol optical depths for each band; and smoothed background tropospheric aerosol optical depths. The total optical depth measurements were obtained by a multipurpose photometer installed at the Rattlesnake Mountain Observatory (46.4 degrees N, 119.6 degrees W at an elevation of 1088 m above mean sea) and operated by Pacific Northwest Laboratory (PNL), Richland, Washington. The mobile automatic scanning photometer (MASP) began operation in March 1979 and has provided continous data since August, 5, 1979. This database contains information from August 5, 1979, to September 2, 1994. Measurements of the attenuation of direct solar radiation are taken by the photometer for different wavelengths using 12 filters. Five of these filters (i.e., those for 428 nm, 486 nm, 535 nm, 785 nm, and 1010 nm wavelengths, with respective half-power widths of 2, 2, 3, 18, and 28 nm) are suitable for monitoring variations in the total optical depth of the atmosphere. The measurement routine used to obtain the direct-sun, daytime data samples begins at sunrise and is repeated every 5 minutes until sunset. In each 5 minute sampling period all 12 filters are scanned. This scanning process takes 2-minutes per sampling interval. During the direct Sun measurements the Sun's position is recalculated once per minute to an accuracy of 0.5 degrees. With the positional accuracy of the instrument of 0.3 degrees the maximum possible error in pointing the instrument at the Sun is < 1 degree. To make the direct measurement a sun-centered raster scan is made. Each scan has dimensions of 5.0 degrees in azimuth by 3.0 degrees elevation and generates 110 samples. The largest raster value is then saved. This sampling process results in the collection of 12 samples per hour for each filter. To determine the total optical depth for each wavelength, the samples taken between air-mass numbers 2 to 6 during cloud free periods in the morning and afternoon are grouped into morning and afternoon observation sets. Thus, the number of sets may vary from 0 to 2 per day, with the number of sample points in each set varying based on the daily change in the Sun's zenith elevation and the presence or absence of clouds. The data that the researchers used to infer the total atmospheric optical depth for each wavelength are time stamped based on the midpoint of the sampling periods used in each observation set. Because some samples may have been deleted from each 2-to-6 air-mass interval due to clouds, the time stamp associated with each observation set does not simply define the midpoint for the 2 to 6 air-mass interval, but the midtime between the first point and the last point used in calculating the optical depth. The radiation measurements obtained for each observation set are converted to total optical depths based on the following equation: T = ln(I0y) - ln(Iy) , ----------------- m where Iy is the spectral irradiance measured at the surface for wavelength y, I0y is the spectral irradiance for y at the top of the atmosphere, m is the equivalent air-mass in the direction of the Sun normalized to the mass of air in the zenith direction (i.e., relative atmospheric path length), and T is the total optical depth at y in the zenith direction. The spectral irradiance at the surface is directly measured by the MASP, irradiance at the top of the atmosphere is derived based on Langley regression, and m is the relative path length (air-mass number) of the samples used in the observational set and is derived from Rozenberg's formula relating solar zenith angle to air-mass. This equation provides a more accurate air-mass value than the simple geometrical relation where air-mass is the secant of the zenith angle. In this database, only samples taken between air-mass numbers 2 and 6 have been used; this converts to time periods when the Sun is ~30 to 9.3 degrees above the horizon. To determine the value of ln(I0y) and T for each wavelength, a plot of ln(Iy) vs m was made from the data samples in each observation set, and a Langley regression performed. The intercept and slope of the regression line are ln(I0y) and T, respectively. The value of T at y comprises four components and may be written as: ç T = çTa + To + Tm + Tr , where the subscripts denote aerosol, ozone, molecular, and Rayleigh optical depths. Values for To, Tm, and Tr are known and can be subtracted from T, leaving us with the total column aerosol optical depth for each wavelength. Values for To and Tr were calculated based on the work of Van Heuklon, and Hansen and Travis, respectively, and the contribution of Tm was assumed to be zero since the five filters were selected to avoid virtually all forms of molecular absorption with the exception of aerosols. The calculated Rayleigh optical depths are 0.007311, 0.020183, 0.095607, 0.141625, and 0.238906 for the 1010 nm, 785 nm, 535 nm, 486 nm, and 428 nm filters, respectively. After the total column aerosol optical depth was determined for each band, it was partitioned into tropospheric and stratospheric components. The procedure for separating the total aerosol optical depth into its components is based on the assumption that the aerosol optical depth of the troposphere, though highly variable, has a predictable underlying seasonal behavior. The background aerosol data were derived from measurements taken during periods of low stratospheric loading from June 15, 1987, to June 15, 1991, inclusive, folded into a single year. The "year" was then smoothed using a locally weighted regression method. By removing this seasonal behavior from Ta, a residual aerosol optical depth was derived that was assumed to be the contribution from the stratosphere. Thus, the equations described above were used to convert solar irradiance measurements taken at the surface to total optical depths for each wavelength. These total optical depths were then corrected for ozone and Rayleigh scattering and total column aerosol optical depths obtained. The estimated background aerosol optical depths were then subtracted from çTa to obtain the residual (estimated stratospheric) aerosol optical depth for each wavelength. FILE DESCRIPTIONS The data were initially received in flat ASCII files and required minimal reformatting. This NDP consists of 1 flat ASCII documentation file, 1 SAS program, 1 FORTRAN program, and 8 ASCII data files, for a total of 11 digital files. The flat ASCII documentation file (NDP053.TXT) contains most of the information contained in Part 2 of this document, with postscript graphics and special control characters and graphic symbols removed. The SAS and FORTRAN files (ALL.SAS and ALL.FOR) are in ASCII formats and contain programs to read and print the flat ASCII data files. The eight ASCII data files contain, for five wavelengths, total optical depths (ALLT2.ASC), the standard error of the Langley determination of the total optical depths (ALLT2ERR.ASC), smoothed total optical depths (ALLT2S.ASC), total aerosol optical depths (ALLA2.ASC), smoothed aerosol optical depths (ALLA2S.ASC), estimated background aerosol optical depths (BACKGRD.ASC), residual aerosol optical depths (ALLA2R.ASC), and smoothed residual aerosol optical depths (ALLA2RS.ASC). FILE FORMATS The data in the data files were derived directly from the total optical depths calculated from the MASP measurement and were derived in the following order: ALLT2.ASC, ALLT2ERR.ASC, and ALLT2S.ASC. The aerosol optical depth files were derived from ALLT2.ASC as follows: ALLA2.ASC and ALLA2S.ASC. File BACKGRD.ASC was then subtracted from ALLA2.ASC to obtain ALLA2R.ASC and ALLA2RS.ASC (these files are estimates of the stratospheric aerosol optical depth). All eight data files are formatted in the same manner. The FORTRAN and SAS programs (ALL.FOR and ALL.SAS) provided with this NDP allow the user to read and print, with minimal modification, the contents of each data file. A summary of the FORTRAN statements used to read the data follows: REAL YEAR, NM1010, NM785, NM535, NM486, NM428 10 READ (5,100,END=999) YEAR, NM1010, NM785, NM535, 1 NM486, NM428 GOTO 10 C 100 FORMAT(F10.5,5F8.4) Table 4 provides a listing of the variables contained in each data file. The variable formats are identical for all eight ASCII data files. Table 4. Variable formats for the eight flat ASCII data files. ------------------------------------------------------------- Variable Variable Variable Column Variable name type width Start End description ------------------------------------------------------------- YEAR Real 10 1 10 Time stamp for each observational set. Values are in year.fraction format. Values accurate to 1 minute. NM1010 Real 8 11 18 Data for the 1010-nm wavelength filter. NM785 Real 8 19 26 Data for the 785-nm wavelength filter. NM535 Real 8 27 34 Data for the 535-nm wavelength filter. NM486 Real 8 35 42 Data for the 486-nm wavelength filter. NM428 Real 8 43 50 Data for the 428-nm wavelength filter. --------------------------------------------------------------- 14. LISTING OF THE FORTRAN AND SASTM DATA RETRIEVAL PROGRAMS This section lists the FORTRAN and SAS programs provided by CDIAC to read and print the contents of the ASCII data files. The two programs shown below (ALL.FOR and ALL.SAS) have been designed to be used with all eight ASCII data files with minimal modification (i.e., changing the name of the input file). ALL.FOR C********************************************************* C* FORTRAN PROGRAM TO READ AND PRINT FILES ALLT2.ASC, * C* ALLT2ERR.ASC, ALLT2S.ASC, ALLA2.ASC, ALLA2S.ASC, * C* ALLA2R.ASC, ALLA2RS.ASC, AND BACKGRD.ASC. * C********************************************************* REAL YEAR, NM1010, NM785, NM535, NM486, NM428 C********************************************************* C* OPEN FILES FOR INPUT/OUTPUT * C********************************************************* OPEN(UNIT=5,FILE='allt2.asc') OPEN(UNIT=6,FORM='PRINT') C********************************************************* C* READ AND PRINT YEAR.FRACTION AND TOTAL OPTICAL OR * C* AEROSOL DEPTHS FOR 5 WAVELENGTHS. * C********************************************************* 10 READ (5,100,END=999) YEAR, NM1010, NM785, NM535, 1 NM486, NM428 WRITE(6,110) YEAR, NM1010, NM785, NM535, 1 NM486, NM428 GOTO 10 C 100 FORMAT(F10.5,5F8.4) 110 FORMAT(1X,F10.5,5F8.4) C********************************************************* C*CLOSE FILES AND EXIT GRACEFULLY * C********************************************************* 999 CLOSE(UNIT=5) CLOSE(UNIT=6) STOP END ALL.SAS /* THIS PROGRAM READS AND PRINTS THE CONTENTS OF FILE ALLT2.ASC. CHANGE INFILE NAME TO PRINT FILES ALLT2ERR.ASC, ALLT2S.ASC, ALLA2.ASC, ALLA2S.ASC, ALLA2R.ASC, ALLA2RS.ASC, AND BACKGRD.ASC */ OPTIONS LS=75 PS=65; DATA DEPTH; INFILE './allt2.asc'; INPUT YEAR 10.5 NM1010 NM785 NM535 NM486 NM428; PROC PRINT NOOBS; FORMAT YEAR 10.5; RUN; 15. VERIFICATION OF DATA TRANSPORT After the data files provided with this NDP are loaded onto a system, or downloaded from CDIAC's anonymous FTP area, the user should check to verify that the files have not been corrupted in transport. This may be done by generating some or all of the statistics presented in Table 5. These statistics are included as a tool to ensure proper reading of the eight ASCII data files and should not be construed as either a summary or an indicator of trends in the data. These statistics were obtained using the SAS software package with the PROC MEANS procedure. These statistics may be duplicated using other statistical packages or computer languages. Table 5. Statistical characteristics of the numeric variables in the eight ASCII data files. --------------------------------------------------------------- File name Variable N Mean Std. Dev. Minimum Maximum --------------------------------------------------------------- ALLT2.ASC YEAR 2169 1987.35 4.1857731 1979.59 1994.67 NM1010 2169 0.0521685 0.0339624 0.0030000 0.2395000 NM785 2169 0.0793119 0.0406188 0.0180000 0.2735000 NM535 2169 0.1941314 0.0487121 0.1129000 0.5257000 NM486 2169 0.2299527 0.0525812 0.1351000 0.6386000 NM428 2169 0.3402344 0.0607183 0.2359000 0.8001000 ALLT2ERR.ASC YEAR 2169 1987.35 4.1857731 1979.59 1994.67 NM1010 2169 0.0031233 0.0016285 0.0006000 0.0158000 NM785 2169 0.0031494 0.0016306 0.0008000 0.0148000 NM535 2169 0.0035638 0.0022722 0.0009000 0.0250000 NM486 2169 0.0042135 0.0025279 0.0013000 0.0235000 NM428 2169 0.0071237 0.0037278 0.0018000 0.0282000 ALLT2S.ASC YEAR 2169 1987.35 4.1857738 1979.59 1994.67 NM1010 2169 0.0497653 0.0288188 0.0144000 0.1746000 NM785 2169 0.0767928 0.0349821 0.0333000 0.2336000 NM535 2169 0.1895863 0.0354300 0.1303000 0.3359000 NM486 2169 0.2242478 0.0359460 0.1594000 0.3724000 NM428 2169 0.3330098 0.0385482 0.2558000 0.4898000 ALLA2.ASC YEAR 2169 1987.35 4.1857731 1979.59 1994.67 NM1010 2169 0.0448626 0.0339549 0 0.2321000 NM785 2169 0.0566324 0.0405648 0 0.2506000 NM535 2169 0.0727139 0.0482412 0 0.4056000 NM486 2169 0.0806623 0.0524418 0 0.4897000 NM428 2169 0.1012282 0.0607150 0 0.5611000 ALLA2S.ASC YEAR 2169 1987.35 4.1857738 1979.59 1994.67 NM1010 2169 0.0424707 0.0288216 0.0072000 0.1700000 NM785 2169 0.0541236 0.0349194 0.0107000 0.2086000 NM535 2169 0.0681527 0.0348450 0.0100000 0.2098000 NM486 2169 0.0749053 0.0357201 0.0109000 0.2163000 NM428 2169 0.0939047 0.0384982 0.0185000 0.2492000 ALLA2R.ASC YEAR 2169 1987.35 4.1857731 1979.59 1994.67 NM1010 2169 0.0191247 0.0325577 -0.0278000 0.2020000 NM785 2169 0.0240145 0.0388352 -0.0324000 0.2150000 NM535 2169 0.0291336 0.0457584 -0.0472000 0.3644000 NM486 2169 0.0317047 0.0498039 -0.0652000 0.4421000 NM428 2169 0.0352311 0.0577417 -0.0693000 0.4967000 ALLA2RS.ASC YEAR 2169 1987.35 4.1857738 1979.59 1994.67 NM1010 2169 0.0167009 0.0275359 -0.0111000 0.1360000 NM785 2169 0.0214135 0.0333040 -0.0092000 0.1674000 NM535 2169 0.0244740 0.0322253 -0.0142000 0.1537000 NM486 2169 0.0259101 0.0328810 -0.0168000 0.1498000 NM428 2169 0.0278258 0.0352972 -0.0275000 0.1628000 BACKGRD.ASC YEAR 669 0.5282713 0.2324004 -0.0030100 1.0047300 NM1010 669 0.0248658 0.0069869 0.0091000 0.0374000 NM785 669 0.0315368 0.0086413 0.0129000 0.0485000 NM535 669 0.0420392 0.0117443 0.0168000 0.0652000 NM486 669 0.0471555 0.0134666 0.0167000 0.0707000 NM428 669 0.0640024 0.0150460 0.0276000 0.0867000 --------------------------------------------------------------- The following listings contain the first five and last five lines in each of the eight ASCII data files. Sample listing from ALLT2.ASC 1979.59347 0.0226 0.0424 0.1520 0.1799 0.2858 1979.59470 0.0337 0.0648 0.1897 0.2343 0.3473 1979.59741 0.0351 0.0532 0.1560 0.1962 0.2850 1979.60018 0.0407 0.0574 0.1514 0.1798 0.2800 1979.60169 0.0286 0.0550 0.1735 0.2130 0.3121 ... 1994.63026 0.0434 0.0652 0.1772 0.2132 0.3303 1994.63185 0.0951 0.1306 0.2854 0.3342 0.4708 1994.63301 0.0267 0.0551 0.1660 0.2039 0.3024 1994.66583 0.0756 0.1166 0.2703 0.3211 0.4475 1994.66749 0.0683 0.1007 0.2352 0.2841 0.4043 Sample listing from ALLT2ERR.ASC 1979.59347 0.0025 0.0025 0.0071 0.0067 0.0069 1979.59470 0.0033 0.0027 0.0061 0.0129 0.0057 1979.59741 0.0033 0.0025 0.0074 0.0109 0.0095 1979.60018 0.0042 0.0038 0.0049 0.0056 0.0040 1979.60169 0.0029 0.0031 0.0095 0.0100 0.0132 ... 1994.63026 0.0023 0.0035 0.0027 0.0040 0.0087 1994.63185 0.0027 0.0025 0.0025 0.0040 0.0127 1994.63301 0.0028 0.0044 0.0037 0.0045 0.0128 1994.66583 0.0052 0.0061 0.0023 0.0061 0.0111 1994.66749 0.0020 0.0025 0.0031 0.0033 0.0113 Sample listing from ALLT2S.ASC 1979.59351 0.0336 0.0576 0.1656 0.2031 0.3074 1979.59473 0.0335 0.0578 0.1680 0.2020 0.3059 1979.59741 0.0336 0.0573 0.1666 0.2023 0.3053 1979.60022 0.0334 0.0582 0.1687 0.2017 0.3073 1979.60168 0.0334 0.0575 0.1686 0.2029 0.3027 ... 1994.63025 0.0557 0.0890 0.2220 0.2657 0.3807 1994.63184 0.0558 0.0895 0.2235 0.2656 0.3848 1994.63306 0.0560 0.0897 0.2237 0.2673 0.3835 1994.66577 0.0607 0.0965 0.2369 0.2846 0.4006 1994.66748 0.0616 0.0975 0.2385 0.2836 0.4015 Sample listing from ALLA2.ASC 1979.59347 0.0153 0.0197 0.0308 0.0307 0.0468 1979.59470 0.0264 0.0421 0.0686 0.0851 0.1083 1979.59741 0.0278 0.0306 0.0349 0.0470 0.0460 1979.60018 0.0334 0.0348 0.0303 0.0306 0.0410 1979.60169 0.0213 0.0324 0.0525 0.0638 0.0731 ... 1994.63026 0.0361 0.0426 0.0565 0.0641 0.0913 1994.63185 0.0878 0.1080 0.1647 0.1851 0.2318 1994.63301 0.0193 0.0324 0.0454 0.0548 0.0633 1994.66583 0.0683 0.0941 0.1501 0.1721 0.2085 1994.66749 0.0610 0.0781 0.1150 0.1352 0.1653 Sample listing from ALLA2S.ASC 1979.59351 0.0265 0.0355 0.0461 0.0541 0.0664 1979.59473 0.0262 0.0351 0.0460 0.0545 0.0655 1979.59741 0.0264 0.0350 0.0458 0.0541 0.0656 1979.60022 0.0263 0.0348 0.0461 0.0536 0.0663 1979.60168 0.0263 0.0349 0.0458 0.0539 0.0669 ... 1994.63025 0.0483 0.0663 0.1011 0.1160 0.1434 1994.63184 0.0488 0.0667 0.1017 0.1166 0.1443 1994.63306 0.0490 0.0668 0.1025 0.1180 0.1448 1994.66577 0.0538 0.0740 0.1155 0.1351 0.1634 1994.66748 0.0541 0.0743 0.1159 0.1356 0.1666 Sample listing from ALLA2R.ASC 1979.59347 -0.0126 -0.0152 -0.0188 -0.0265 -0.0280 1979.59470 -0.0015 0.0072 0.0189 0.0280 0.0337 1979.59741 0.0000 -0.0045 -0.0148 -0.0100 -0.0286 1979.60018 0.0057 -0.0004 -0.0195 -0.0263 -0.0337 1979.60169 -0.0063 -0.0028 0.0026 0.0069 -0.0017 ... 1994.63026 0.0112 0.0104 0.0104 0.0118 0.0198 1994.63185 0.0629 0.0759 0.1187 0.1328 0.1602 1994.63301 -0.0055 0.0004 -0.0006 0.0026 -0.0083 1994.66583 0.0432 0.0628 0.1067 0.1221 0.1396 1994.66749 0.0359 0.0470 0.0719 0.0856 0.0972 Sample listing from ALLA2RS.ASC 1979.59351 -0.0020 -0.0005 -0.0040 -0.0036 -0.0089 1979.59473 -0.0019 -0.0004 -0.0039 -0.0035 -0.0087 1979.59741 -0.0019 -0.0003 -0.0037 -0.0033 -0.0085 1979.60022 -0.0018 -0.0003 -0.0034 -0.0031 -0.0082 1979.60168 -0.0017 -0.0002 -0.0033 -0.0030 -0.0081 ... 1994.63025 0.0223 0.0331 0.0547 0.0634 0.0714 1994.63184 0.0227 0.0334 0.0555 0.0639 0.0728 1994.63306 0.0227 0.0336 0.0561 0.0644 0.0727 1994.66577 0.0276 0.0416 0.0691 0.0815 0.0924 1994.66748 0.0284 0.0420 0.0705 0.0821 0.0931 Sample listing from BACKGRD.ASC -0.00301 0.0094 0.0131 0.0177 0.0175 0.0285 0.00473 0.0095 0.0132 0.0180 0.0178 0.0288 0.03267 0.0103 0.0140 0.0197 0.0191 0.0308 0.04024 0.0104 0.0141 0.0202 0.0194 0.0312 0.04087 0.0104 0.0141 0.0202 0.0195 0.0313 ... 0.97744 0.0091 0.0129 0.0170 0.0169 0.0278 0.98564 0.0092 0.0130 0.0173 0.0172 0.0281 0.98608 0.0092 0.0130 0.0173 0.0172 0.0281 0.99699 0.0094 0.0131 0.0177 0.0175 0.0285 1.00473 0.0095 0.0132 0.0180 0.0178 0.0288 OTHER SUGGESTED READING: An assessment of the impact of volcanic eruptions on the Northern Hemisphere's aerosol burden during the last decade. By J. J. Michalsky, E. W. Pearson, and B. A. LeBaron. 1990. Journal of Geophysical Research 95(D):5677-5688. Radiometric characterization of Mount Pinatubo's stratospheric aerosols over northern mid-latitudes. By N. R. Larson and J. J. Michalsky. Submitted to the Journal of Geophysical Research for publication in 1996.