Throughout January 1989 polar stratospheric clouds were frequently observed over Ny-¿lesund/Svalbard by means of a lidar instrument. The aerosol layer was located between 17 and 24 km altitude and showed signs of a downward movement. The presence of PSC's suggests that the same chemical processes, that lead to the springtime ozone depletion in the southern hemisphere may go on during the Arctic polar night. ¿ American Geophysical Union 1990