MESOSCALE INFLUENCE ON LONG-RANGE TRANSPORT - EVIDENCE FROM ETEX MODELING AND OBSERVATIONS

During the first European Tracer Experiment (ETEX) tracer gas was rele ased from a site in Brittany, France, and subsequently observed over a range of 2000 km. Hourly measurements were taken at the National Envi ronmental Research Institute (NERI) located at Riso, Denmark, using tw o measurement techniques. At this location, the observed concentration time series shows a double-peak structure occurring between two and t hree days after the release. By using the Danish Emergency Response Mo del of the Atmosphere (DERMA), which is developed at the Danish Meteor ological Institute (DMI), simulations of the dispersion of the tracer gas have been performed. Using numerical weather-prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF) by DERMA , the arrival time of the tracer is quite well predicted, so also is t he duration of the passage of the plume, but the double-peak structure is not reproduced. However, using higher-resolution data from the DMI version of the HIgh Resolution Limited Area Model (DMI-HIRLAM), DERMA reproduces the observed structure very well. The double-peak structur e is caused by the influence of a mesoscale anti-cyclonic eddy on the tracer gas plume about one day earlier. (C) 1998 Elsevier Science Ltd. All rights reserved.