23 Sep 2022
23 Sep 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Occurrence of Polar Stratospheric Clouds as derived from Ground-based Zenith DOAS Observations using the Colour Index

Bianca Lauster1,2, Steffen Dörner1, Carl-Fredrik Enell3, Udo Frieß2, Myojeong Gu1, Janis Pukīte1, Uwe Raffalski4, and Thomas Wagner1 Bianca Lauster et al.
  • 1Max Planck Institute for Chemistry, Mainz, Germany
  • 2University of Heidelberg, Heidelberg, Germany
  • 3EISCAT Scientific Association, Kiruna, Sweden
  • 4Swedish Institute of Space Physics, Kiruna, Sweden

Abstract. Polar stratospheric clouds (PSCs) are an important component of ozone chemistry in polar regions. Studying the ozone-depleting processes requires a precise description of PSCs on a long-term basis. Although satellite observations already yield high spatial coverage, continuous ground-based measurements covering long time periods can be a valuable complement. In this study, differential optical absorption spectroscopy (DOAS) instruments are used to investigate the occurrence of PSCs based on the so-called colour index (CI), i.e. the colour of the zenith sky. Defined as the ratio between the observed intensities of scattered sunlight at two wavelengths, it provides a method to detect PSCs during twilight even in the presence of tropospheric clouds. We present data from instruments at the German research station Neumayer, Antarctica (71 °S, 8 °W) as well as Kiruna, Sweden (68 °N, 20 °E), which are in operation for more than 20 years. For a comprehensive interpretation of the measurement data, the well-established radiative transfer model McArtim is used and radiances of scattered sunlight are simulated at several wavelengths for different solar zenith angles and various atmospheric conditions. The aim is to improve and evaluate the potential of this method. It is then used to infer the seasonal cycle and the variability of PSC occurrence throughout the time series measured in both hemispheres. A good agreement is found to satellite retrievals with deviations particularly in spring. The unexpectedly high signal observed in the DOAS data during spring time suggests the influence of volcanic aerosol. This is also indicated by enhanced aerosol extinction as seen from OMPS data but is not captured by other PSC climatologies. The presented approach allows the detection of PSCs for various atmospheric conditions not only for individual case studies but over entire time series, which is a decisive advance compared to previous work on the PSC detection from ground-based instruments. Apart from the interannual variability, no significant trend is detected for either measurement station. The averaged PSC relative frequency amounts to about 37 % above the Neumayer station and about 18 % above Kiruna.

Bianca Lauster et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-647', Alain Sarkissian, 11 Oct 2022
  • RC2: 'Comment on acp-2022-647', Anonymous Referee #2, 03 Nov 2022

Bianca Lauster et al.

Bianca Lauster et al.


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Short summary
Polar stratospheric clouds (PSCs) are an important component in ozone chemistry. Here, we use two differential optical absorption spectroscopy (DOAS) instruments in the Antarctic and Arctic to investigate the occurrence of PSCs based on the colour index, i.e. the colour of the zenith sky. Additionally using radiative transfer simulations, the variability and the seasonal cycle of PSC occurrence are analysed and an unexpectedly high signal during spring suggests the influence of volcanic aerosol.