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Free keywords:
low-level jet; ozone concentration; secondary ozone maximum;
turbulent transport; trace gas advection
Abstract:
During the field campaign performed within the SANA-project (readjustment of the atmosphere in the five new federal states of the Federal Republic of Germany) at a flat, rural site in eastern Germany, several cases of a jumplike increase of ozone at the surface under stable conditions during the nights have been observed. The concentration jumps of ozone are on the order of 1/2 to 2/3 of the days maximum and the level is significantly higher than under normal conditions with stable stratification. The cases are correlated with an increase in wind speed, wind shear and a downward flux of ozone. In the case selected here, the increase in turbulence is caused by the evolution of a low-level jet (LLJ) with the core just above the top of surface inversion. The analysis of wind profile measurements at the aerological stations in north-eastern Germany reveals a spatial extension of the low-level jet of up to 600 km in length and 200 km in width, Thus the significance of the LLJ on the transport capability of the atmosphere is twofold: due to the large spatial extent of the LLJ and the high wind speed at the jet core level air pollutants are transported overhundreds of kilometers during one night. Secondly, due to the strong wind shear between the jet core and the ground pollutants can be mixed to the ground far away from the release area. (C) 1997 Elsevier Science Ltd.
