Kouichi Shiraishi

On the lidar‐observed sandwich structure of polar stratospheric clouds (PSCs): 1. Implications for the mixing state of the PSC particles

A vertical sandwich structure of (type I) polar stratospheric clouds (PSCs), in which layers of relative depolarization are above and below a scattering layer has frequently been observed by lidar at Ny-Alesund, Svalbard, when the stratospheric temperature decreases to near the frost point of ice. Using lidar observations and backward trajectory analysis, we studied the time evolution of this structure and its temperature history. The main difference between the temperature history of PSCs in the scattering layer and those in the depolarization layer was the temperature at which the structure is observed. The small increase in the scattering ratio over time at the altitude of the depolarization maximum implies a slow nucleation of solid particles. These lidar observations including temperature histories suggest that the sandwich structure arises from the external mixing of two different types of particles. A large fraction of liquid particles, grown at low temperature, constitutes the scattering layer, while at higher temperatures, a very small fraction of solid particles is responsible for the depolarization layer.

Polar stratospheric clouds observed above Ny-Aalesund, Norway, and Dome Station, Antarctic

Lidar observations of stratospheric aerosols have been performed at Ny-Aalesund (79 degrees N, 12 degrees East), Svalbard every winter since January 1994. We detected many PSC events in the stratosphere under low temperature condition, especially in 1994/95, 1995/96, 1996/97 winter campaigns. Meanwhile in the Antarctic, lidar observations were made from April, 1997 to January, 1998 at Dome Fuji (78 degrees South, 40 degrees East), and many PSCs were detected almost every day from the end of May to mid October. In the Arctic, PSC layers at the initial stage of appearance were composed mainly of solid particles in each winter season and the layers at sufficiently low temperatures were composed of spherical particles. In the Antarctic, PSCs similar to those over Ny- Aalesund were also detected frequently while the polar vortex was developing or the vortex was unstable. But after a remarkable decrease in the temperature by the invasion of blocking high into the polar vortex, PSCs detected were mainly composed of solid particles.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Lidar-observed arctic PSCS over Svalbard

A lidar system was installed at Ny-Alesund, Svalbard in January 1994 to observe polar stratospheric clouds (PSCs). Observation campaigns were performed in the following seven winter seasons. The backscattering at 1064 and 532 nm, and the depolarization at 532 nm were observed by the lidar system. The results of observations in each winter season are summarized. A vertical sandwich structure of type I PSCs, in which layers of depolarization are above and below a scattering layer, has frequently been observed when the stratospheric temperature decreases to near the frost point of ice. An enhancement in scattering was observed at the altitude of the liquid PSC layer, but not at the altitudes of the solid layers. There tended to be a negative correlation between scattering ratio and depolarization ratio. The small increase in the scattering ratio over time at the altitude of the depolarization maximum implies a slow nucleation of solid particles. The lidar observations including temperature histories suggest that the sandwich structure arises from the external mixing of two different types of particles.