Large nitric acid trihydrate particles and denitrification caused by mountain waves in the Arctic stratosphere

[ 1] The contribution of stratospheric mountain waves to the formation of large nitric acid trihydrate (NAT) particles and subsequent denitrification of the Arctic polar vortex is calculated for the 1999/2000 winter using a three-dimensional (3-D) model. The model production mechanism involves the formation of NAT clouds with high particle number concentrations downwind of mountain wave ice clouds, as has been previously observed. These wave-induced NAT clouds then serve as ``mother clouds'' for the release of low concentrations of sedimenting NAT particles, following the mechanism of Fueglistaler et al. (2002a). Our calculations show that wave-induced NAT mother clouds can occupy up to 5 - 10% of the volume of air below the NAT temperature. NAT particles that have sedimented from the mother cloud bases can occupy in excess of 60% of the NAT supersaturated region. Integrated over the entire vortex at the end of the 1999/2000 simulation, it is estimated that denitrification due to this mechanism could potentially be responsible for as much as 80% of that observed. These results show that mountain waves may contribute to the occurrence of solid polar stratospheric clouds more than was previously thought and that they may play a significant role in denitrification.