Ice formation in remote regions: From nucleation to multiplication: Insights from combining in situ measurements with remote sensing observations

• Main Author: Wieder, Jörg
• Other Authors: Lohmann, Ulrike, Henneberger, Jan, Kanji, Zamin A, Duplissy, Jonathan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ETH Zurich 2022
• Subjects: CLOUDS (METEOROLOGY); Aerosols and Clouds; Aerosols; Ice Nucleation; Ice Nucleating Particles; Ice nuclei; PRECIPITATION/INFLUENCE OF TOPOGRAPHY (METEOROLOGY); Orographic clouds; Orographic precipitation; METEOROLOGY; Arctic; Arctic clouds; ALPS (EUROPEAN MOUNTAINS); Field measurements; Climate; info:eu-repo/classification/ddc/550; Earth sciences; Rime
• Online Access: https://hdl.handle.net/20.500.11850/565134; https://doi.org/10.3929/ethz-b-000565134

Clouds, with their global average spatial coverage of nearly 70%, are an important constituent in Earth’s atmosphere. Clouds redistribute fresh water and alter Earth’s radiative balance, thus, impacting the climate. Both precipitation formation and the radiative response of clouds are strongly related to the fraction of ice in them. The varying abundance of aerosol particles needed for cloud formation and the complex interplay between cloud particles during cloud evolution complicate an accurate representation of clouds in weather and climate models. This is especially critical in orographic regions, which frequently trigger precipitation, and in highly climate sensitive regions like the Arctic, which currently experiences warming at an unprecedented rate. In these regions, mixed-phase clouds (MPCs) consisting of ice crystals and supercooled cloud droplets are frequently ob- served and persistently prevail. In an MPC, ice nucleating particles (INPs), a subclass of atmospheric aerosol particles, are needed for the formation of primary ice crystals. Quantifying the abundance of INPs is challenging given their sparse atmospheric concentration. Compared to the global average, atmospheric INP concentrations are even lower in remote regions such as the Alps or the Arctic, additionally contributing to uncertainties in model simulations. In addition, the amount of ice crystals can be increased by different processes (e. g., rime splintering, or fragmentation during ice-ice or drop-ice collisions) – commonly referred to as secondary ice production. While different processes leading to secondary ice production have been identified, the occurrence and magnitude of ice enhancement in the atmosphere remain uncertain. This thesis aims to constrain the abundance and variability of atmospheric INPs in remote regions, thereby improving the predictability needed for the representation of MPCs in numerical models, and to assess the prevalence of secondary ice formation occurring in MPCs. During three field campaigns, each lasting ...