TDLAS trace gas measurements within mountain waves over northern Scandinavia during the POLSTAR campaign in early 1997

Trace gas measurements of CO and N2O were performed over Northern Scandinav ia during a mountain wave event in the night 1./2. February 1997. The data were taken during the POLSTAR I campaign on board the DLR research aircraft Falcon by the newly developed tunable diode laser absorption spectrometer TRISTAR. Strong tropospheric winds almost perpendicular to the Scandinavian mountain ridge led to the formation of mountain waves. Due to the steep gr adient in the CO mixing ratio around the tropopause these mountain waves re sulted in extensive modulations in the CO signal. Peak-to-peak amplitudes o f up to 70 ppbv and horizontal wavelengths in the order of 10 to 20 km were recorded. Vertical fluxes of CO in the tropopause region are calculated us ing the CO data and the vertical wind data taken from the standard meteorol ogical equipment of the DLR aircraft. The vertical eddy exchange coefficien t shows values comparable to or even greater than those calculated for trop opause folds. We conclude that mountain wave events seem to play an importa nt role as a mechanism for troposphere/ stratosphere exchange of chemical c onstituents.