A low-ozone episode during the European heatwave of August 2003

An intense low-ozone episode (LOE) was observed over Scandinavia and the North Sea in the middle of August 2003. The LOE occurred under exceptional meteorological conditions. associated with a severe heatwave over Europe. The column ozone minimum for summer (June, July and August) 2003 was reached during the event. Using meteorological analyses, satellite ozone observations from the Total Ozone Mapping Spectrometer and the Michelson Interferometer for Passive Atmospheric Sounding aboard the Environment Satellite, we demonstrate that the LOE results from the conjunction of a deep tropospheric blocking over Europe, and a displaced Arctic pool of low-ozone air in the stratosphere, above the anticyclone. The anticyclonic anomaly is part of a Rossby wave train that is apparent throughout the troposphere, and Whose influence is felt Lip to 50 hPa. In the mid-stratosphere (e.g. 30 hPa) long-period westward propagating planetary waves dominate, with a ridge extending over northern Europe in mid-August. We band-pass filtered the geopotential field to isolate sub-monthly fluctuations, and calculated three-dimensional wave activity fluxes for quasi-stationary, quasi-geostrophic disturbances embedded in a zonally asymmetric basic state. Results clearly indicate that upward wave fluxes in the lower stratosphere originate from the Atlantic sector. upstream of the maturing blocking.