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The TM1 tracer model
Simulations were performed using the TM1 tracer model version 7.1 which was described in detail by Heimann and Keeling (1989). TM1 has a horizontal resolution of 7.9 degrees (180./23.) latitude by 10 degrees longitude, 9 sigma layers in the vertical, and a numerical time step of 4 hours. Wind fields are updated every 12 hours, sources every 24 hours.
The wind fields are based on meteorological observations on a 1.825 x 1.825 degree grid processed by the four-dimensional data assimilation system of the European Center for Medium-Range Weather Forecasts (ECMWF) for the Global Weather Experiment (GWE) from December 1978 through November 1979.
Vertical convection is described by a set of monthly transition matrices retained from a previous version of the tracer model, which used wind fields generated from a three-dimensional general circulation model (GCM) of the atmosphere developed for climate studies by Hansen et al. (1983). Following Heimann and Keeling (1989), I have reduced the convective matrices globally to 0.50 of their original values. There is no explicit boundary layer in the model.
The model variant used here included explicit horizontal diffusion coupled to vertical convection in the same way as described by Prather et al. (1987). This variant was used in Keeling et al. (1989) (e.g., labelled 'standard scenario' in figures 65 and 66, p. 349, and referred to in Table 7, p. 338 as 'with horizontal diffusion') and in i Iacobellis et al., 1994 (JGR). This produced an interhemispheric exchange time for fossil fuel of about 1.1 years (without explicit diffusion, the interhemispheric exchange time was about 1.4 years).
Each source was run for 4 years with initial concentration set to 0. The fields supplied to Transcom are for the fourth year; results are expressed in ppm. Surface fields were taken from the lowest model sigma level, typically extending between 1000 and 950 hPa. The fields at 200 and 500 hPa were linearly interpolated from the model sigma levels using a mean annual surface pressure field.
Fossil source
The global annual total was 5.276 GtC/year (for earth radius of 6375 km) The README file for the original Giss source indicate that the source is about 5.5 gtc/year; I assume that they used a different value for the earth radius than I did.
ff_surff.XX surface
ff_500mb.XX 500 hPa
ff_200mb.XX 200 hPa
where XX = 01 to 12 for Jan to Dec, and 13 for annual average
Seasonal biospheric source
The original monthly Giss values were taken as mid-month values. Since my runs are for 1979 with 365 days, I have assigned the Jan to Dec mid-months to days 16.,35.5,75.,105.5,136.,166.5,196.,228.,258.5,289.,319.5, 350., respectively. I wrapped the data by assigning the Dec value to day -15. and the value for Jan to day 381 and then linearly interpolated daily values between the mid-months to give 365 daily values. The annual total of the source was adjusted to zero in each model box.
biosurff.XX
bio500mb.XX
bio200mb.XX
where XX = 01 to 12 for Jan to Dec, and 13 for annual average
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