Widespread solid particle formation by mountain waves in the Arctic stratosphere

Observations of polar stratospheric clouds (PSCs) by lidar show that the clouds often contain solid particles, which are most likely composed of nitric acid hydrates. However, laboratory experiments indicate that such hydrate particles are not easily formed under Arctic synoptic scale conditions, suggesting that solid PSC particles should be rather rare. Here we show results from a model study indicating that mountain-induced mesoscale temperature perturbations may be an important source of nitric acid hydrate particles in the Arctic. Multiple Arctic vortex trajectories were combined with a global mountain wave forecast model to calculate the potential for solid particle formation during December and January 1994/1995. The mountain wave model was used to calculate adiabatic cooling over several thousand ridge elements. Nitric acid hydrate particles were assumed to form in the mountain waves according to several microphysical mechanisms, and were then advected using polar vortex-filling synoptic trajectories to generate maps of solid particle occurrence. The calculations show that mountain waves may be a significant source of PSCs containing solid particles that are observed on the synoptic scale. In particular, the east coast of Greenland, the Norwegian mountains, and the Urals are found to be solid particle sources, with the PSCs often predicted to survive several thousand kilometers downstream.