26 Jan 2022
26 Jan 2022
Status: this preprint is currently under review for the journal ACP.

Retrieving ice nucleating particle concentration and ice multiplication factors using active remote sensing validated by in situ observations

Jörg Wieder1, Nikola Ihn1, Claudia Mignani2, Moritz Haarig3, Johannes Bühl3, Patric Seifert3, Ronny Engelmann3, Fabiola Ramelli1, Zamin A. Kanji1, Ulrike Lohmann1, and Jan Henneberger1 Jörg Wieder et al.
  • 1ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
  • 2Department of Environmental Sciences, University of Basel, Basel, Switzerland
  • 3Leibniz Institute for Tropospheric Research, Leipzig, Germany

Abstract. Understanding the evolution of the ice phase within mixed-phase clouds (MPCs) is necessary to reduce uncertainties related to the cloud radiative feedback in climate projections and precipitation initiation. Both primary ice formation via ice nucleating particles (INPs) and secondary ice production (SIP) within MPCs are unconstrained, not least because of the lack of atmospheric observations. In the past decades, advanced remote sensing methods have emerged which provide high resolution data of aerosol and cloud properties and could be key in understanding microphysical processes on a global scale. In this study, we retrieved INP concentrations, and ice multiplication factors (IMFs) in wintertime orographic clouds using active remote sensing and in situ observations obtained during the RACLETS campaign in the Swiss Alps. INP concentrations in air masses dominated by Saharan dust and continental aerosol were retrieved from a polarization Raman lidar and validated with aerosol and INP in situ observations on a mountaintop. A calibration factor of 0.0204 for the global INP parameterization by DeMott et al. (2010) is derived by comparing in situ aerosol and INP measurements improving the INP concentration retrieval for continental aerosols. Based on combined lidar and radar measurements, the ice crystal number concentration and ice water content were retrieved and validated with balloon-borne in situ observations, which agreed with the balloon-borne in situ observations within an order of magnitude. For seven cloud cases the ice multiplication factors (IMFs), defined as the quotient of the ice crystal number concentration to the INP concentration, were calculated. The median IMF was around 80 and SIP was active (defined as IMFs > 1) nearly 85 % of the time. SIP was found to be active at all observed temperatures (−30 °C to −5 °C) with highest IMFs between −20 °C and −5 °C. The introduced methodology could be extended to larger datasets to better understand the impact of SIP not only over the Alps but also at other locations and for other cloud types.

Jörg Wieder 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-2022-67', Anonymous Referee #1, 21 Feb 2022
  • RC2: 'Comment on acp-2022-67', Anonymous Referee #2, 30 Apr 2022

Jörg Wieder et al.

Jörg Wieder et al.


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Short summary
Ice formation and its evolution in mixed-phase clouds are still uncertain. We evaluate the lidar retrieval of ice nucleating particle concentration in dust-dominated and continental air masses over the Swiss Alps with in situ observations. A calibration factor to improve the retrieval from continental air masses is proposed. Ice multiplication factors are obtained with a new method utilizing remote sensing. Our results indicate that secondary ice production occurs at temperatures down to −30 °C.