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.

Abstract. Space borne infrared limb emission measurements by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) reveal the formation of a belt of polar stratospheric clouds (PSCs) of nitric acid trihydrate (NAT) particles over Antarctica in mid-June 2003. By mesoscale microphysical simulations we show that this sudden onset of NAT PSCs was caused by heterogeneous nucleation on ice in the cooling phases of large-amplitude stratospheric mountain waves over the Antarctic Peninsula and the Ellsworth Mountains. MIPAS observations of PSCs before this event show no indication for the presence of NAT clouds with volume densities larger than about 0.3 µm3/cm3 and radii smaller than 3 µm, but are consistent with supercooled droplets of ternary H2SO4/HNO3/H2O solution (STS). Simulations indicate that homogeneous surface nucleation rates have to be reduced by three orders of magnitude to comply with the observations.

Abstract. A new and improved setup of the SF6 retrieval together with a newly calibrated version of MIPAS-ENVISAT level 1b spectra (version 5, ESA data version 5.02/5.06) was used to obtain a new global SF6-data set, covering the total observational period of MIPAS from July 2002 to April 2012 for the first time. Monthly and zonally averaged SF6-profiles were converted into mean age of air using a tropospheric SF6-reference curve. The obtained data set of age of air was compared to airborne and balloon-borne age of air measurements. The temporal evolution of mean age of air was then investigated in 10° latitude and 1–2 km altitude bins. A regression model consisting of a constant and a linear trend term, 2 proxies for the quasi-biennial oscillation variation, sinusoidal terms for the seasonal and semi-annual variation and overtones was fitted to the age of air time series. The annual cycle for particular regions in the stratosphere was investigated and compared to other studies. The age of air trend over the total MIPAS-period consisting of the linear term was assessed and compared to previous findings of Stiller et al. (2012). While the linear increase of mean age is confirmed to be positive for the Northern mid-latitudes and Southern polar middle stratosphere, differences are found in the Northern polar upper stratosphere, where the mean age is now found to increase as well. The magnitude of trends in the Northern mid-latitude middle stratosphere is slightly lower compared to the previous version and the trends fit remarkably well to the trend derived by Engel et al. (2009). Negative age of air trends found by Stiller et al. (2012) are confirmed for the lowermost tropical stratosphere and lowermost Southern mid-latitudinal stratosphere. Differences to the previous data versions occur in the middle tropical stratosphere around 25 km, where the trends are now negative. Overall, the new latitude–altitude distribution of trends appears to be less patchy and more coherent than the previous one. The new data provide evidence of an accelerating shallow branch of the Brewer–Dobson circulation, at least in the Southern Hemisphere. Finally the age of air decadal trends are compared to trends calculated with simulated SF6 values by the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and good agreement is found. The hemispheric asymmetry in the trends found in the MIPAS data are also indicated in the trends calculated with simulated SF6 values by the KASIMA model.

putation of the photolysis rates, a scheme was adopted that accurately describes photolysis at large solar zenith angles

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