Microphysical properties of wave polar stratospheric clouds retrieved from lidar measurements during SOLVE/THESEO 2000

Abstract

Mountain wave induced ice clouds in the stratosphere are known to cause the formation of nitric acid hydrate particles downwind. Understanding the microphysical properties of these solid particles is important because they may contribute to a general background of solid polar stratospheric clouds (PSCs) that is observed but whose origin is not understood. Based on the limited set of observations of PSCs directly attributable to mountain waves, it has not been possible to determine their general microphysical properties. Here we analyze lidar observations from the SOLVE/THESEO 2000 campaign. Between December 1999 and March 2000, seven of the twelve flights of the DC‐8 aircraft showed clear signs of mountain wave induced clouds, with nitric acid hydrate clouds often extending many hundreds of kilometers downwind of mountains. On the basis of T‐matrix calculations, we have developed a technique to estimate the microphysical properties of spherical and nonspherical particles from multiwavelength backscatter and depolarization data from the Goddard Space Flight Center/Langley Research Center (GSFC/LaRC) aerosol lidar. The technique allows particle radius, condensed mass, and number densities of ice, nitric acid trihydrate, and liquid PSCs to be estimated. Ice clouds were found to contain approximately 1–3 ppmv of condensed water with a number density from 1 to 10 cm −3 and a narrow size distribution width with mode radii from 1 to 1.5 μm. Nitric acid hydrate particles downwind of the ice clouds were consistent with 1–5 ppbv condensed HNO 3 , a number density from 0.5 to 2 cm −3 , and mode radius around 0.5 μm. These hydrate clouds are characterized by high aerosol backscatter and depolarization and are distinct from type 1a clouds that are observed away from mountains, which have low aerosol backscatter.