README FILE Erythemal Exposure and Irradiance Data Products The erythemal noontime irradiance in a 1x1.25 degree grid in located in /pub/eptoms/data/erythemal and /pub/nimbus7/data/erythemal in units of milli-watts/m^2/nm The 305, 310, 324, 380, and erythemal noon irradiances on a 1x1 degree grid are located in /pub/eptoms/data/uv_ery_4_wavelengths and /pub/nimbus7/data/uv_ery_4_wavelengths NASA Goddard Space Flight Center Code 916 Greenbelt, MD 20770 Documentation for Noontime Irradiances and Daily Erythemal Exposure in the directory /pub/eptoms/data/uv_ery_4_wavelengths and /pub/nimbus7/data/uv_ery_4_wavelengths All of the data in this directory are on a 1x1 degree grid The units for the 305, 310, 324, 380, and erythemal_noon irradiances are milli-watts/m^2/nm The units for the erythemal exposure are joules/m^2 Each value code consists of three digits: a 1 digit exponent (E), and a 2 digit mantissa (M). A decimal point is implied between the two digits of the mantissa. Together, E and M encode a value of M*10^E . For example, the value code "342" represents the value 4.2*10^3 . Note that a value code of "999" is a fill-value, used where TOMS data were unavailable. Contacts Dr. Jay. R. Herman Code 916.0 NASA Goddard Space Flight Center Greenbelt, MD 20770 herman@tparty.gsfc.nasa.gov David Larko Code 916.0 NASA Goddard Space Flight Center Greenbelt, MD 20770 larko@carioca.gsfc.nasa.gov ================================================================================ OLD Documentation Files This file is the general README file for the Erythemal Exposure data product developed at NASA Goddard Space Flight Center (GSFC). More complete documentation for this data product is available in Adobe PostScript form (file erynotes.ps) and in Adobe Portable Document Format (PDF) form (file erynotes.pdf). The PostScript file may be printed directly on a PostScript printer. The PDF file may be viewed and/or printed using the Adobe Acrobat Reader ("acroread"), available at no cost from Adobe's web site: http://www.adobe.com/prodindex/acrobat/readstep.html Data Product The Erythemal Exposure data product is an estimate of the daily integrated ultraviolet irradiance, calculated using a model for the susceptibility of caucasian skin to sunburn (erythema). This can be interpreted as an index of the potential for biological damage due to solar irradiation, given the column ozone amount and cloud conditions, as determined from measurements made with the Total Ozone Mapping Spectrometer (TOMS), on each day. The biological action spectrum used is that due to McKinlay and Diffey, which has been adopted as a standard by the Commission Internationale de l'Eclairage (CIE). The solar irradiances used in the calculation have units of nW m^{-2} nm^{-1} (nanowatts per square meter per nanometer; the "square meter" refers to the area on a horizontal surface, the "nanometer" refers to the wavelength of the light). Thus, after integrating over wavelength and time, one is left with units of J m^{-2} (Joules per square meter). Please see the section in the complete documentation (erynotes.ps or erynotes.pdf) titled "A note on the units of the exposure" for a discussion. Format of the Data Files Each file consists of 3 header records, followed by 2160 data records. The data records are organized in 180 groups of 12 records. The first 11 records in each group contain 25 three-digit value codes; the 12th record contains 13 value codes, followed by the numerical value of the center latitude of the band. Each group corresponds to a single 1 degree wide latitude band, and each value code corresponds to a cell of dimensions 1 degree latitude by 1.25 degrees longitude. Each value code consists of three digits: a 1 digit exponent (E), and a 2 digit mantissa (M). A decimal point is implied between the two digits of the mantissa. Together, E and M encode a value of M*10^E . For example, the value code "342" represents the value 4.2*10^3 . Note that a value code of "999" is a fill-value, used where TOMS data were unavailable. The following format specifications are recommended for reading the data records (all at once) from an Erythemal Exposure data file. The value codes may be read as integers into a single integer array of dimensions (288,180) (using the FORTRAN or IDL subscripting convention). They must then be decoded into the values they represent. The recommended format specification for reading the data is (179(11(1X,25I3,/),1X,13I3,/),11(1X,25I3,/),1X,13I3) Alternatively, the values may be read into an integer array of dimensions (2,288,180), where the element (1,ilon,ilat) (FORTRAN) or (0,ilon,ilat) (IDL) is the exponent E for the value at the grid cell (ilon,ilat), and the element (2,ilon,ilat) (FORTRAN) or (1,ilon,ilat) (IDL) is the mantissa M . The recommended format specification in this case is (179(11(1X,25(I1,I2),/),1X,13(I1,I2),/),11(1X,25(I1,I2),/),1X,13(I1,I2)) Code Samples Code samples are included in the following files: codestubs read_ery.fc read_ery.fp read_ery.c test_re.f See the complete documentation for a description of the contents of these files. References Please see the complete documentation for a list of literature references relevant to this data product. Contacts Dr. Jay. R. Herman Code 916.0 NASA Goddard Space Flight Center Greenbelt, MD 20770 herman@tparty.gsfc.nasa.gov Dr. Edward A. Celarier Software Corporation of America Beltsville, MD 20705 celarier@jwocky.gsfc.nasa.gov