Analysis of polar stratospheric clouds using temperature and aerosols measured by the Alomar R/M/R lidar

Abstract

In this work we analyze and interpret stratospheric temperature and polar stratospheric cloud measurements made with the ALOMAR Rayleigh Mie Raman (R/M/R) lidar located at Andøya (69°N, 16°E) in northern Norway. The ALOMAR R/M/R lidar is in operation since July 1994. Vertical profiles of polar stratospheric clouds (PSCs) are measured at three different wavelengths and used to classify PSC types. Vertical temperature profiles of the stratosphere are also obtained with the lidar by using the rotational Raman technique. The backscatter ratios at three different wavelengths and the Angstrom coefficients derived from backscatter ratio are used to study the dependence of the PSC aerosol properties on the measured air temperature. We observed PSCs during the cold winters 1994/1995, 1995/1996, and 1996/1997. The clouds are classified in three types, Ia, Ib, and II. The temperature at which type Ib PSCs appear fits well with Supercooled Ternary Solution (STS) theory, while the type Ia PSCs are often measured at temperatures above TNAT. Trajectory analysis indicates that the type Ia and type Ib PSCs are characterized by different thermal histories. The last part of the paper is devoted to the interpretation of the results that are not in full agreement with the current theories of the formation of PSCs. In fact, it is found that a subtype of PSC, characterized by different values of optical parameters is measured inside clouds composite of different PSCs types. Moreover, it is observed that for a large fraction of the type Ia PSC observations the prevailing air temperature is above the thermodynamic equilibrium temperature for NAT PSCs