Evaluation of trajectories calculated from ecmwf data against constant volume balloon flights during etex

Abstract This paper validates trajectories calculated from ECMWF analyses against the tracks of constant volume balloons (CVBs) released during the European tracer experiment (ETEX). The altitudes of the calculated trajectories were adjusted to the altitudes of the respective balloons in short intervals to allow direct comparisons. The agreement between the calculated trajectories and the balloon tracks was very good for the first experiment (individual errors from 1 to 26%, average 15%), and excellent (errors from 2 to 11%, average 6%) for the second one. The agreement for the second experiment was probably partly better because the CVBs travelled above the planetary boundary layer, but the small errors also indicate that the ECMWF fields of the horizontal wind were of exceptionally good quality in the second experiment. This is in sharp contrast to the results of the dispersion models which all failed in the prediction of the perfluorocarbon tracer dispersion for the second experiment. A likely explanation for this is that vertical motions, possibly on small scales, were not correctly captured by the ECMWF analyses, but it is not possible to clarify this with the CVB data.

[1]  S. F. Mueller,et al.  Comparisons of Tetroon and Computed Trajectories , 1983 .

[2]  A. Stohl.  Computation, accuracy and applications of trajectories—A review and bibliography , 1998 .

[3]  A. Stohl,et al.  Validation of a Long-Range Trajectory Model Using Gas Balloon Tracks from the Gordon Bennett Cup 95 , 1997 .

[4]  S. Petterssen.  Weather Analysis And Forecasting. 1st Ed. , 1940 .

[5]  J. F. Clarke,et al.  Assessment of model simulation of long-distance transport , 1983 .

[6]  Sverre Petterssen,et al.  Weather analysis and forecasting , 1940 .

[7]  A. Stohl,et al.  Interpolation Errors in Wind Fields as a Function of Spatial and Temporal Resolution and Their Impact on Different Types of Kinematic Trajectories , 1995 .

[8]  Calculation of the relative influence of cloud layers on received ultraviolet and integrated solar radiation , 1978 .

[9]  F. Girardi,et al.  The field campaigns of the European Tracer Experiment (ETEX): overview and results , 1998 .

[10]  R. Draxler.  Trajectory optimization for balloon flight planning , 1996 .

[11]  A. Stohl,et al.  Accuracy of trajectories as determined from the conservation of meteorological tracers , 1998 .

[12]  A. Stohl,et al.  Validation of the lagrangian particle dispersion model FLEXPART against large-scale tracer experiment data , 1998 .

[13]  B. Bénech,et al.  Comparison of constant volume balloons, model trajectories and tracer transport during ETEX , 1998 .

[14]  D. H. Pack,et al.  METEOROLOGY OF LONG-RANGE TRANSPORT , 1978 .

[15]  R. Draxler,et al.  Sensitivity of three-dimensional trajectories to the spatial and temporal densities of the wind field , 1990 .

[16]  H. Formayer,et al.  Diagnostic Downscaling of Large-Scale Wind Fields to Compute Local-Scale Trajectories , 1997 .