A-train CALIOP and MLS observations of early winter Antarctic polar stratospheric clouds and nitric acid in 2008

Abstract

Abstract. A-train Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Microwave Limb Sounder (MLS)observations are used to investigate the development of polar stratospheric clouds (PSCs) and the gas-phase nitric acid distribution in the early 2008 Antarctic winter. Observational evidence of gravity-wave activity is provided by Atmospheric Infrared Sounder (AIRS) radiances and infrared spectroscopic detection of nitric acid trihydrate (NAT) in PSCs is obtained from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Goddard Earth Observing System Data Assimilation System (GEOS-5 DAS) analyses are used to derive Lagrangian trajectories and to determine temperature-time histories of air parcels. We use CALIOP backscatter and depolarization measurements to classify PSCs and the MLS measurements to determine the corresponding gas-phase HNO 3 as a function of temperature. For liquid PSCs the uptake of HNO 3 follows the theoretical equilibrium curve for supercooled ternary solutions (STS), but at temperatures about 1 K lower as determined from GEOS-5. In the presence of solid phase PSCs, above the ice frost-point, the HNO 3 depletion occurs over a wider range of temperatures (+2 to −7 K) distributed about the NAT equilibrium curve. Rapid gas-phase HNO 3 depletion is first seen by MLS from from 23-25 May 2008, consisting of a decrease in the volume mixing ratio from 14 ppbv (parts per billion by volume) to 7 ppbv on the 46-32 hPa (hectopascal) pressure levels and accompanied by a 2-3 ppbv increase by renitrification at the 68 hPa pressure level. The observed region of depleted HNO 3 is substantially smaller than the region bounded by the NAT existence temperature threshold. Temperature-time histories of air parcels demonstrate that the depletion is more clearly correlated with prior exposure to temperatures a few kelvin above the frost-point. From the combined data we infer the presence of large-size NAT particles with effective radii >5-7 µm and low NAT number densities <1 × 10 −3 cm −3 . This denitrification event is observed close to the pole in the Antarctic vortex before synoptic temperatures first fall below the ice frost point and before the widespread occurrence of large-scale NAT PSCs. An episode of mountain wave activity detected by AIRS on 28 May 2008 led to wave-ice formation in the rapid cooling phases over the Antarctic Peninsula and Ellsworth Mountains, seeding an outbreak of NAT PSCs that were detected by CALIOP and MIPAS. The NAT clouds formed at altitudes of 18-26 km in a polar freezing belt and appear to be composed of relatively small particles with estimated effective radii of around 1 µm and high NAT number densities >0.2 cm −3 . This NAT outbreak is similar to an event previously reported from MIPAS observations in mid-June 2003.

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

“…These contours roughly represent the streamlines of the geostrophic wind and the NAT clouds are along contours crossing the AP region. These observations are in line with the mountain wave seeding hypothesis for PSCs as described and proofed with AIRS and MIPAS data by Eckermann et al (2010) or to the MIPAS NAT-belt events in mid-June 2003 and 2008 previously reported by Höpfner et al (2006b) and Lambert et al (2012), respectively. Preliminary analyses of all MIPAS and AIRS SH observations suggest that generally, the early winter conditions in mid-June facilitate meteorological conditions to form a mountain-wave-induced NAT belt (8 out of 10 winter).…”

“…Spang et al, , 2005Höpfner et al, 2006bHöpfner et al, , 2009Eckermann et al, 2009;Lambert et al, 2012;Arnone et al, 2012). Its main strength is the classification of clouds where the radiances are dominated by NAT particles with radii smaller than 3 µm (Höpfner et al, 2006a).…”

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

“…The use of Atmospheric Infrared Sounder (AIRS) observations for that purpose was first explored by Eckermann et al (2009) and Lambert et al (2012). In this paper, we present a new AIRS data set on gravity wave activity in the polar lower stratosphere that can be used to study the impact of gravity-waveinduced temperature fluctuations on PSC formation in more detail.…”

Polar stratospheric cloud climatology based on CALIPSO spaceborne lidar measurements from 2006–2017

“…Similar to the approach used by Lambert et al (2012), P13, and Lambert and Santee (2017) transformed to T-T eq space, where T eq is defined as T NAT , T STS , or T ice , depending on the CALIOP composition classification, and is calculated using the Hanson and Mauersberger (1988) (T NAT ), Carslaw et al (1995) (T STS ), and Murphy and Koop (2005) (T ice ) relationships with the coincident MLS HNO 3 and H 2 O abundances. T eq for ice PSCs remains the same as in Figures 11(a) and 11(c) and the ice PSC distributions are identical to those in Figures 11(a) and 11(c).…”

“…prior to 2008 (see Lambert et al, 2012). The Aura MLS detects thermal microwave emission from the Earth's limb along the 5 line-of-sight in the forward direction of the Aura spacecraft flight track (Waters et al, 2006).…”