Spectroscopic evidence for NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds

Abstract

Abstract.We have analyzed mid-infrared limb-emission measurements of polar stratospheric clouds (PSCs) by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) during the Antarctic winter 2003 with respect to PSC composition. Coincident Lidar observations from McMurdo were used for comparison with PSC types 1a, 1b and 2. Application of new refractive index data of β-NAT have allowed to accurately simulate the prominent spectral band at 820 cm −1 observed by MIPAS at the location where the Lidar instrument observed type 1a PSCs. Broadband spectral fits covering the range from 780 to 960 cm −1 and from 1220 to 1490 cm −1 showed best agreement with the MIPAS measurements when spectroscopic data of NAT were used to simulate the MIPAS spectra. MIPAS measurements collocated with Lidar observations of Type 1b and Type 2 PSCs could only be reproduced by assuming a composition of supercooled ternary H 2 SO 4 /HNO 3 /H 2 O solution (STS) and of ice, respectively. Particle radius and number density profiles derived from MIPAS were generally consistent with the Lidar observations. Only in the case of ice clouds, PSC volumes are partly underestimated by MIPAS due to large cloud optical thickness in the limb-direction. A comparison of MIPAS cloud composition and Lidar PSC-type determination based on all available MIPAS-Lidar coincident measurements revealed good agreement between PSC-types 1a, 1b and 2, and NAT, STS and ice, respectively. We could not find spectroscopic evidence for the presence of nitric acid dihydrate (NAD) from MIPAS observations of PSCs over Antarctica in 2003.

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…The ice PSCs are formed at synoptic-scale temperatures of up to 4-10 K above T ice . NAT particles are observed further downstream of the Antarctic Peninsula, which is consistent with the ice particles serving as condensation nuclei for NAT formation (Carslaw et al, 1998a;Höpfner et al, 2006b;Eckermann et al, 2009). Although mountain wave activity is most frequent at the Antarctic Peninsula (Hoffmann et al, 2016a), other orographic features in Antarctica can also play a role in PSC formation.…”

“…Case studies of mountain waves induced by the Scandinavian Mountains showed that the waves can cause localized cooling of up to 10-15 K (Carslaw et al, 1998b;Dörnbrack et al, 1999Dörnbrack et al, , 2002. The Antarctic Peninsula is another well-known hot spot for the formation of PSCs from mountain waves in the Southern Hemisphere (Wu and Jiang, 2002;Shibata et al, 2003;Höpfner et al, 2006b;Baumgaertner and McDonald, 2007;Eckermann et al, 2009;Orr et al, 2015). In the Antarctic polar stratosphere, waveinduced PSC formation is particularly important in fall or spring, whereas synoptic-scale temperatures in winter are usually well below the PSC formation threshold (Campbell and Sassen, 2008;McDonald et al, 2009;Noel and Pitts, 2012).…”

A multi-wavelength classification method for polar stratospheric cloud types using infrared limb spectra

“…The resulting resolution is usually sufficient to highlight differences in the continuum-like emission of the different PSC types. Aerosol and cloud particles rarely produce narrow spectral features, and the strong spectral signature of NAT at 820 cm −1 is an exception Höpfner et al, 2006a).…”

“…A transmission limit of 0.9 was defined to select the wavelength regions. In addition, wavelength regions used in former studies (Spang et al, , 2004(Spang et al, , 2005aHöpfner et al, 2006a, b) were taken into account. The CSDB spectra were generated with the Karlsruhe Optimized and Precise Radiative transfer Algorithm (KOPRA) model (Stiller, 2000), which takes single scattering into account (Höpfner, 2004).…”

“…Table 1 presents a summary of the parameter space covered by the input parameters of the model runs, including the particle size distribution (PSD). Refractive indices for NAT by Biermann et al (2000) and Höpfner et al (2006a), for ice by Toon et al (1994), and for STS by Biermann et al (2000) were applied for the computation of the single scattering properties of spherical particles.…”