Model guided Lagrangian observation and simulation of mountain polar stratospheric clouds

Abstract

Gravity-wave-induced polar stratospheric clouds (PSCs) were observed over the Scandinavian mountains by airborne lidar on January 9, 1997. Guided by the forecasts of a mesoscale dynamical model, a flight path was chosen to lead through the coldest predicted region parallel to the wind at the expected PSC level (23–26 km). Because of the nearly stationary nature of the wave-induced PSC the individual filaments visible in the backscatter data of the clouds can be interpreted as air parcel trajectories. Assuming dry adiabatic behavior and fixing the absolute temperature to the ice frost point in the ice part of the cloud enables detailed microphysical simulations of the whole life cycle of the cloud particles. Optical calculations are used to adjust open parameters in the microphysical model by optimizing the agreement with the multichannel lidar data. This case is compared with former work from the Arctic winter 1994/1995. The influence of the stratospheric H₂SO₄ content and the cooling rate on the type of cloud particles (liquid ternary solution droplets or solid nitric acid hydrates) released from the ice part of the cloud is evaluated.