Data Access

CATO is currently available in two different versions, including and excluding the assimilation of SBUV Version 8 vertical profiles in the uppermost layers. Please refer to the above mentioned publications for a closer description of these two versions.
The version of CATO excluding assimilation of SBUV profiles should only be used for altitudes below about 30 km because the reconstruction approach fails when ozone lifetime becomes short relative to the timescales of planetary wave motions.
The version with SBUV profile assimilation can be considered as a hybrid data set. SBUV profiles only affect the levels above 820 K potential temperature. The ozone profiles calculated with the CATO method are relaxed towards the SBUV profiles at these levels, the relaxation becoming more and more strong with altitude. At the highest levels CATO is therefore basically identical to zonal means of the SBUV Version 8 data set.
You can download monthly mean data (ASCII) format of CATO on either potential temperature levels (original vertical grid) or on pressure levels (linearly interpolated from potential temperature levels using the monthly mean pressure on the theta levels). You can also access CATO at full temporal resolution in netCDF format.
Please remember that CATO is represented on an equivalent latitude and not a geographical latitude grid.

Monthly mean data in ASCII format

• 
  Zonal mean values of total ozone columns in equivalent latitudes
  Each line contains the month YYYYMM followed by 30 values for the total ozone columns (including tropospheric columns added as zonal means in geographical coordinates) as a function of equivalent latitude. These values are centered at equivalent latitudes ELAT = -87, -81, -75, .., 75, 81, 87. They represent mean values in the latitude range [ELAT- 3,ELAT+3].
• 
  Vertical profiles of ozone subcolumn (DU) in potential temperature coordinates
  Values represent subcolumns (in Dobson Units, DU) in 15 potential temperature layers as a function of equivalent latitude (same 30 latitudes as above). The potential temperature layers are centered at 326, 340, 365, 400, 445, 500, 565, 640, 725, 820, 925, 1040, 1165, 1300 and 1445 K. The lowest layer ranges from 320 K to the mid-level between 326 and 340 K (i.e. to (326+340)/2), the second layer from (340+365)/2 to (365+400)/2, etc. Finally, the top layer ranges from (1300+1445)/2 to the top of the atmosphere.
  The file is organized as follows: the first line contains the values at the 30 different equivalent latitudes on the lowest layer for the first month (Jan 1979), the second line the 30 values on the second lowest layer, etc.. The values for the second month (Feb 1979) thus start on line 16, the values for March 1979 on line 32, etc.
• 
  Vertical profiles of ozone VMR (ppb) in potential temperature coordinates
  Values represent layer mean volume mixing ratios for same 15 potential temperature layers and 30 equivalent latitudes as previous data set.
  The file is organized in the same way as the previous data set.
• 
  Vertical profiles of ozone VMR (ppb) in pressure coordinates
  Values represent volume mixing ratios interpolated from the native potential temperature layers (previous data set) onto the following 14 pressure levels (from bottom to top level):
  190, 120, 90, 60, 40, 30, 20, 15, 10, 7, 5, 3.5, 2.5, 1.5 hPa.
  The file is organized as follows: the first line contains the values at the 30 different equivalent latitudes on the lowest pressure level for the first month (Jan 1979), the second line the 30 values on the second lowest layer, etc.. The values for the second month (Feb 1979) thus start on line 15, the values for March 1979 on line 29, etc.

Daily (6-hourly) data in netCDF format

Note: The CATO data set was reconstructed from total ozone data using a Kalman filter approach as described in Brunner et al. (JGR 2006). The state vector consists of a 2D equivalent latitude vs. potential temperature field in the stratosphere (O3_STRAT) and a 2D longitude vs. latitude field in the troposphere (O3_TROP) here defined as the atmosphere below the 320 K isentrope. Equivalent latitudes were calculated at 15 different potential temperature levels at the positions of total ozone observations using potential vorticity fields derived from ECMWF ERA-40 reanalysis data.

• Direct download of the 6-hourly netCDF files
  excluding SBUV
  or including SBUV
• Access through a DODS/Opendap Server to the data
  excluding SBUV or
  including SBUV

The file content is as follows:

• eqlat: The equivalent latitudes eqlats (degN):
  -87, -81, ... , 81, 87
• thlay: Potential temperature layer centers (K),
  thlay = 326, 340, 365, 400, 445, 500, 565, 640, 725, 820, 925, 1040, 1165, 1300, 1445
• thev: Potential temperature layer interfaces (bottom and top of each layer)
  thlev = 320, 333, 352.5, 382.5, 422.5, 472.5, 532.5, 602.5, 682.5, 772.5, 872.5, 982.5, 1102.5, 1232.5, 1372.5, infinity
  Note that the lowest layer ranges from thlev = 320 K to thlev = 333 K and is centered at thlay = 326 K.
• lon: The longitude centers (degE) of the tropospheric grid,
  lon = -175, -165, ... , 165, 175.
• lat: The latitude centers (degN) of the tropospheric grid,
  lat = -87, -81, ... , 81, 87
• lev2: Index of the bottom (lev2 = 0) and top (lev2 = 1) of the troposphere
• lpv: The discrete Lait PV values for which equivalent latitudes were calculated on each potential temperature layer center.
  Lait_PV = PV*(Theta/320K)**-4.5,
  lpv = -20.0, -19.8, -19.6, ... 19.6, 19.8, 20.0
• time: Central time of 6hr interval in units of days since the 1st January 00:00:00 UTC of the given year.
• O3_STRAT: Stratospheric ozone VMR (ppb, offset by -10000 ppb). The values represent mean values for the 6deg wide equivalent latitude band centered at "eqlat" and for the given potential temperature layer centered at "thlay".
• SDEV_O3_STRAT: Standard error of O3_STRAT (ppb, offset by -10000 ppb) given by the diagonal elements of the analysis error covariance matrix A (see CATO JGR paper).
• O3_TROP: The tropospheric residual ozone VMR (ppb, offset by -10000) centered on the "lon" x "lat" grid. As for O3_STRAT the values represent mean values for a given grid cell. The vertical limits of the tropospheric residuals are given by "P_TROP" (see below).
• SDEV_O3_TROP: Standard error of O3_TROP (ppb, offset by -10000)
• LOGP_STRAT: natural logarithm of equivalent zonal mean pressure (hPa) of potential temperature layer interfaces "thlev". For offset and scaling factors check variable attributes. This variable can be used to convert the layer mean VMR given by O3_STRAT into layer subcolumns in Dobson Units.
• P_TROP: Pressure at earth surface and at 320K level (hPa). For offset and scaling factor check variable attributes. This variable can be used to convert the VMR given by the variable O3_TROP into tropospheric residual columns in Dobson Units.
• equilat: equivalent latitudes asa function of (lpv,thlay). This variable can be used to reconstruct the full 3D ozone if the 3D PV-distribution for the given time is known. For offset and scaling factor check variable attributes.
• nobs: number of total ozone observations analyzed in this 6hr interval
• instrid: The instrument ID (Nimbus 7, EP Toms, etc.) of the satellite used as data source for the given 6hr time interval. Unfortunately, this is only available for some runs. Please contact me directly if needed.
• eqxing: The satellite equator crossing time (hh:mm). This information was used to split a given daily TOMS field into individual 6hourly subsets.

Author: Dominik Brunner
Institute for Atmospheric and Climate Science (IAC)
ETH Zurich, Switzerland