## Advanced / Satellite / FTP NASA TOMS

The FTP menu gets TOMS (Total Ozone Mapping Spectrometer) data from the following site and directories:

ftp://jwocky.gsfc.nasa.gov/pub/{eptoms|nimbus7}/data/aerosol/{year}/
file = L3_aersl_{ept|n7t}_{year}{month}{day}.txt

More current information is available from the README files on the NASA server.

TOMS Earthprobe datasets are located in the following directory paths:

data/ozYYYY/gaYYMMDD.ept (YYYY=1996 >>) (EarthProbe still reporting data)
  Daily gridded (g), ASCII (a) files from year YY, month MM and day DD. The data in these ASCII files are in the format used for the Nimbus-7 and Meteor-3 CD-ROM. Details of this format are explained in the EarthProbe Data Products User's Guide, EARTHPROBE_USERGUIDE.PDF, available in the parent directory. A stub program, RDGRID.FOR may be used to read these datasets.

The values are in 3 digit groups 111222333444555
Sample ozone value: 234 = 234 du 0 = fill value

data/reflYYYY/gaYYMMDD.epr
  Daily reflectivity data. Format similar to that of ozone data.
  The vales are in 3 digit groups 111222333444555
  Sample reflectivity value: _83 = 83% 999=fill value

data/a1YYYY/gaYYMMDD.epa
  Daily aerosol data. Format similar to that of ozone data.

  The data are an aerosol index formed directly from the measured radiances in two TOMS channels. Positive values generally represent absorbing aerosols (dust and smoke) while negative values represent nonabsorbing aerosols. The identification is not perfect because of geophysical reasons (e.g., aerosol too low to the ground). There will soon be a corresponding data set of optical depths and single scattering albedos.

  The values are in 3 digit groups 111222333444555
  The numbers have been multiplied by 10
  --1=0.1 -11=1.1 111=11.1
  999 = missing or bad data
  -- stands for blanks

References:

- Herman, J.R., P.K. Bhartia, O.Torres, C. Hsu, C. Seftor, E. Celarier, Global Distribution of UV-Absorbing Aerosols From Nimbus-7/TOMS Data, J.Geophys. Res., 102, 16,911-16,922, 1997.
- Torres, O., P.K. Bhartia, J.R. Herman, Z. Ahmad, and J. Gleason, Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation: Theoretical basis, J. Geophys. Res. 103, 17099-17110, 1998.

UV Erythemal Irradiance

data/uvYYYY/gaYYMMDD.epe
  Daily uv data. RDGRID.FOR may be used to read these data but see 1README.UV and erynotes.pdf for information about interpreting/decoding the uv data file format.

The values are in 3 digit groups 111222333444555
123 = 2.3x10^1 J/m2 -23 = 2.3 --3 = 0.3 999 = missing or bad data

data/monthly_averages/gmYYMM.ept .
  This directory contains gridded monthly (gm) averages of ozone data from year YY and month MM. At least 20 days of data must be available for monthly averages to be considered valid.
  Monthly averages of aerosol, UV and reflectivity are also provided in directories located in a path structure similar to that for ozone averages.

The Fortran statements that wrote the data records of these monthly files are:

               DO 570 IL=1,180
               DO 560 jj=1,288
          560  OZONE(JJ)=ozav(JJ,IL)
               write(21,'(1X,25I3)') (OZONE(jj),jj=1,275)
               write(21,'(1X,13I3,1A17)') (OZONE(jj),jj=276,288), latlab(IL)
          570  CONTINUE

data/overpass/OVPxxx.ept
  A subset (seconds UT, latitude, longitude, total ozone, surface reflectivity, solar zenith angle,aerosol index, SOI index, etc) of EarthProbe data specific to a particular latitude-longitude location. xxx designates a numerical site location as listed in file "1Sitelist" in this directory.

Fortran statements that can be used to read the 1st header record and the data records in the OVPxxx files are the following:
For the header record:

               CHARACTER*28 site_name
               INTEGER*4    site_id, site_alt
               REAL*4       site_lat, site_lon
               Read(lun,2) site_name, site_id, site_lat,site_lon, site_alt
             2 Format(A30,4X,I3,7X,F7.2,7X,F7.2,7X,I4)

and for the data records:

    Format(F7.1,1X,I4,1X,I3,1X,I5,2X,I2,1X,F6.2,1X,F7.2,1X,
    I3,1X,I3,1X,F5.2,1X,F5.1,1X,F5.1,1X,F6.2,1X,I4)

1README, in this directory, provides more information about the OVPxxx files.

data/zonal_means/zm_month.ept and zmday_ YY.ept
  Zonal means files. File "zm_month.ept" contains monthly averages of zonal mean column ozone over each 5 degrees of latitude for each year of EarthProbe operation to date. Additional files, named "zmday_YY.ept" (YY=96, 97...) provide zonal means on a daily basis. At least 2/3 of possible data must be present for a zonal mean to be considered valid.

The Fortran statements that wrote the header and data records of file zm_month are the following:

              CHARACTER*69 MONLAB
              Data MONLAB/'Jan   Feb   Mar   Apr   May   Jun   Jul   Aug   Sep
             & Oct   Nov   Dec'/
              do 20 j=1,37
              lat(j)=-95 + 5*j
           20 continue
              write(22,'(8x,A69)') MONLAB
              DO 300 IZ=1,36
              write(22,'(I3,I4,12f6.1)') lat(IZ),lat(IZ+1),(ozm(IM,IZ),IM=1,12)
         300  CONTINUE
              write(22,'(I3,I4,12f6.1)') -65,0,(ozm(IM,37),IM=1,12)
              write(22,'(I3,I4,12f6.1)') 0,65,(ozm(IM,38),IM=1,12)
              write(22,'(I3,I4,12f6.1)') -65,65,(ozm(IM,39),IM=1,12)

The Fortran statement that wrote the data records of the zmday_YY files is:

               write(21,'(A12,F9.3,1X,36F6.1,3X,3F6.1)') date,yd,zmd

If these EarthProbe/TOMS data are downloaded and used in publication, please give proper credit to the NASA/GSFC TOMS Ozone Processing Team (OPT).

For more information on the EarthProbe/TOMS data set, contact

  Dr. Richard D. McPeters
  Code 916
  NASA Goddard Space Flight Center
  Greenbelt, MD 20771
  mcpeters@wrabbit.gsfc.nasa.gov

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