Characteristics of Arctic polar stratospheric clouds in the winter of 1996/1997 inferred from ILAS measurements

Abstract

[1] The Improved Limb Atmospheric Spectrometer (ILAS) captured many polar stratospheric cloud (PSC) events in the Northern Hemisphere during the winter and early spring of 1997. Simultaneous measurements of nitric acid and aerosols by ILAS made it possible to infer PSC composition. The aerosol extinction coefficient and nitric acid data were compared with the theoretically predicted values for supercooled ternary solution (STS), nitric acid dihydrate (NAD), and nitric acid trihydrate (NAT) at thermodynamic equilibrium to classify PSC types. The observations showed that in 1997, both nitric-acid-containing solid and liquid PSCs formed over the Arctic during winter and early spring, until mid-March. The STS PSCs were observed early in the PSC season, in mid-January. Most of the PSCs observed late in the PSC season had features of nitric-acid-containing hydrates. An intensive analysis of the temperature histories suggested that most of the STS events observed in January had experienced the thermal conditions necessary for the formation of liquid PSCs. The nitric-acidcontaining hydrates observed in March seemed not to have been influenced by any mountain-induced lee waves. The process of nitric-acid-containing hydrate formation based on synoptic scale temperature change is discussed.

Stratospheric ozone loss in the 1996/1997 Arctic winter: Evaluation based on multiple trajectory analysis for double‐sounded air parcels by ILAS

“…Thus, care should be taken especially when ILAS observed ice PSCs. In this study we eliminated all the ozone data that may have been affected by PSCs occurrence, according to the information on PSCs detection provided by Saitoh et al [2002].…”

High Resolution Dynamics Limb Sounder observations of polar stratospheric clouds and subvisible cirrus

“…As temperatures decrease below 195 K, NAT particles and ternary solution droplets [Tabazadeh et al, 1994;Carslaw et al, 1995] form, particle size, area and volume densities, and PSC extinctions increase. Examples of observations of increases in extinction as temperatures decrease are illustrated in CLAES extinction [Massie et al, 1994], Improved Limb Atmospheric Spectrometer (ILAS) [Saitoh et al, 2002], and POAM III [Benson et al, 2006] data. Figures 7a -7d display significant increases in extinction below 195 K. All of the data points correspond to HIRDLS cloud extinction precisions better than 50%.…”

3-D microphysical model studies of Arctic denitrification: comparison with observations

“…However, methods of including such processes in largescale models have not yet been developed. However, several other studies have concluded that a significant proportion of observed PSCs cannot be explained by mesoscale ice-formation but by synoptic scale temperature changes (Spang et al, 2001;Saitoh et al, 2002;Fromm et al, 2003;Pagan et al, 2004).…”

“…Tabazadeh et al (2001) have suggested that homogeneous nucleation of NAT may occur at a rate sufficient to denitrify the Arctic stratosphere based on extrapolation of laboratory data by Salcedo et al (2001). However, Knopf et al (2002) have performed new laboratory measurements which indicate that homogeneous nucleation of NAT is too slow to form NAT PSCs, even at temperatures several K below T NAT .…”