Interannual variations of early winter Antarctic polar stratospheric cloud formation and nitric acid observed by CALIOP and MLS

Abstract

Abstract. We use satellite-borne measurements collected over the last decade (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) from the Aura Microwave Limb Sounder (MLS) and the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) to investigate the nitric acid distribution and the properties of polar stratospheric clouds (PSCs) in the early winter Antarctic vortex. Frequently, at the very start of the winter, we find that synoptic-scale depletion of HNO 3 can be detected in the inner vortex before the first lidar detection of geophysically associated PSCs. The generation of "sub-visible" PSCs can be explained as arising from the development of a solid particle population with low number densities and large particle sizes. Assumed to be composed of nitric acid trihydrate (NAT), the sub-visible PSCs form at ambient temperatures well above the ice frost point, but also above the temperature at which supercooled ternary solution (STS) grows out of the background supercooled binary solution (SBS) distribution. The temperature regime of their formation, inferred from the simultaneous uptake of ambient HNO 3 into NAT and their Lagrangian temperature histories, is at a depression of a few kelvin with respect to the NAT existence threshold, T NAT . Therefore, their nucleation requires a considerable supersaturation of HNO 3 over NAT, and is consistent with a recently described heterogeneous nucleation process on solid foreign nuclei immersed in liquid aerosol. We make a detailed investigation of the comparative limits of detection of PSCs and the resulting sequestration of HNO 3 imposed by lidar, mid-infrared, and microwave techniques. We find that the temperature history of air parcels, in addition to the local ambient temperature, is an important factor in the relative frequency of formation of liquid/solid PSCs. We conclude that the initiation of NAT nucleation and the subsequent development of large NAT particles capable of sedimentation and denitrification in the early winter do not emanate from an ice-seeding process. Finally, we investigate the patterns of interannual variability and compare the relative formation frequency of liquid and solid PSCs in the Antarctic lower polar stratosphere using the results of a cluster analysis to synthesize the combined CALIOP and MLS measurements into a relatively small number of interrelated categories.

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

“…This is consistent with the findings of Lambert et al (2016) that in a number of years there were signatures of uptake of gas-phase HNO 3 by PSC particles up to a week before PSCs were first detected by CALIOP. 20…”

“…It should be noted that all measured and derived quantities for non-features are also retained in the v2 data product. A comprehensive discussion of so-called "sub-visible" PSCs can be found in the paper by Lambert et al (2016), who show that they often can be detected through gas-phase uptake of HNO 3 as observed by MLS even though they are not detectable as PSCs by CALIOP. daily basis as a function of altitude and DMP equivalent latitude based on nearly coincident "cloud-free" Aura MLS data, where the CALIOP PSC data themselves are used to filter out MLS data affected by uptake in the cloud particles.…”

“…We will refer to these papers herein as P07, P09, P11, and P13, respectively, and refer to the P07/P09/P11/P13 algorithm sequence as Version 1.0 (v1). Data products from v1 have compared favorably with PSC observations from MIPAS (Höpfner et al, 2009), groundbased lidar (Achtert and Tesche, 2012), and Aura MLS (P13; Lambert et al, 2016). However, several known deficiencies in the v1 algorithm were highlighted in P13, one being that the effects of measurement noise on the inferred PSC composition 10…”

Comparison of ECHAM5/MESSy Atmospheric Chemistry (EMAC) simulations of the Arctic winter 2009/2010 and 2010/2011 with Envisat/MIPAS and Aura/MLS observations

“…NAT formation in EMAC is already initiated at T NAT -3 K, which is a rather high threshold temperature for NAT formation. This is usually the temperature at which STS formation is initiated since for the formation of NAT particles usually temperatures lower than T NAT -3 K are required (Peter and Grooß, 2012;Lambert et al, 2016). However, this approach is commonly applied for simulating PSCs in atmospheric models (e.g.…”

The MIPAS/Envisat climatology (2002–2012) of polar stratospheric cloud volume density profiles

“…(1) the optical constants themselves are not perfect (Ortega et al, 2006;Iannarelli and Rossi, 2015); (2) particles may be present with different phases and composition (e.g., α-NAT, α-NAD, β-NAD) as laboratory studies indicate their possible existence under polar stratospheric conditions (Grothe et al, 2008;Stetzer et al, 2006;Möhler et al, 2006); and (3) PSC particle shapes different from spherical ones, as seen in the laboratory (Grothe et al, 2006), can have an effect even at wavelengths in the thermal infrared (Wagner et al, 2005;Woiwode et al, 2016). We have implicitly accounted for those errors by the large variability of optical constants of β-NAT, STS, and ice during the optimization of the retrieval baseline configuration.…”