CTM model evaluation strategy

1. General concept

Model simulated tracer fields can be compared one-by-one with observed data included in the ETHmeg database. For each month between Jan 1995 and Dec 1998 a table can be obtained containing the times and positions of all observations availabe during that month. This information can then be used during a model run to interpolate at each model time step the simulated tracer fields to all measurement points available for that time. Thus for each observation point a corresponding set of interpolated model values is generated. The time and position table contains an additional column called ID which allows linking each observation point to the corresponding campaign and flight, and thus to the corresponding tracer measurements. For each campaign(and measurement platform) a specific range of ID numbersis reserved. IDs are numbered sequentially according to the flight number.

2. Step-by-step instructions

• Download the time and position tables (e.g. 199501_all.txt) by anonymous ftp from our server bach.ethz.ch, directory pub_read/dominik/TRADEOFF_INPUT for those months for which you would like to perform a model run. Or use your browser on this link. Please make sure enough observation data (for the tracers of interest) is available forthis time period.
• Download the Fortran90 example code obs_pos_interpol.f90 which allows reading in the TIMEPOS information into your model and to perform simple linear interpolation of your tracer fields to the corresponding observation points. This routine should be called at the end of each model time step. The code example of course needs some adaption for your model (change of variable names etc.).
• Run your model over the selected time period, now including calls to obs_pos_interpol at the end of each model time step and thus producing the one-by-one model output to be compared to the corresponding observations.
• Login to the TRADEOFF observation database as public user and obtain the tracer data from the campaigns of interest. Your model output is now unambiguously related to these observation data through the date/time and ID fields.

Note: the ETHmeg database focuses on the following tracers: O₃, CO, OH, HO₂, H₂O₂, H₂O, NO, NO₂, HNO₃, and PAN. Partly other tracers were included as well.