The ozone volume mixing ratios are vertically interpolated to the pressures of TM model levels from the pressure levels of the climatology (0.3, 0.5, 1, 2, 3, 5, 7, 10, 20, 30, 50, 70, 100, 150, 200, 300, 500, 700, and 1000 hPa) using Hermite interpolation (subroutine muherm). To calculate the pressures of the model levels a mean surface pressure of 1013 hPa is assumed. Perhaps it would be better to use about 985 hPa.
For the interpolation in latitude from the 10 degree grid of the climatology to the TM grid also Hermite interpolation is used.
The overhead ozone columns are calculated by multiplying by fac (where tst = 273.15 K = standard temperature, pst = 1.01325e5 Pa = standard pressure, gst = 9.80665 ms-2 = acceleration of gravity, rg = 287.3 = gas constant), and integrating over the pressure (dp) from the bottom of the layer to the top of the atmosphere. For TM3 the overhead ozone column is calculated at 5 model levels, at about 10,30,50,70, and 100 hPa. In a future version this will be done at all the TM model levels. Below the 100 hPa overhead column is used for the moment. Finally, the partial ozone columns and volume mizing ratios are scaled with the TOMS zonal mean monthly mean total ozone value.