An intercomparison of results from three trajectory models

Three three-dimensional trajectory models(LAGRANTO, TRAJKS and FLEXTRA), all driven with analysis wind fields from the European Centre for Medium-Range Weather Forecasts, are intercompared. The comparison has three parts: first, a case study of strong ascent in a warm conveyor belt is performed; second, a large set of back trajectories from the tropopause region over Europe and the mid-latitude Atlantic Ocean is investigated; third, a set of low-level trajectories is compared. It is found that the degree of model accordance depends on the interpolation methods used. If all models use linear spatial interpolation, their respective trajectories closely agree with each other (deviations of 2% or less for the average distance between the starting and ending points after 48 h). Compared to other sources of errors, such as inaccuracies in the wind fields or insufficient temporal and spatial resolution of the data set, these differences are of minor importance. The intercomparison also shows that all three models have been implemented correctly. Non-linear spatial interpolation leads to a stronger vertical motion than linear interpolation and, in the case study, enhanced the quality of the results.