Aerosol-related effects on the occurrence of heterogeneous ice formation over Lauder, New Zealand/Aotearoa

• Main Authors: Hofer, Julian, Seifert, Patric, Liley, J. Ben, Radenz, Martin, Uchino, Osamu, Morino, Isamu, Sakai, Tetsu, Nagai, Tomohiro, Ansmann, Albert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; New Zealand; Southern Ocean; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/egusphere-2023-2173; https://noa.gwlb.de/receive/cop_mods_00069357; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00067744/egusphere-2023-2173.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2173/egusphere-2023-2173.pdf

The presented study investigates the efficiency of heterogeneous ice formation in natural clouds over Lauder, New Zealand/Aotearoa. Aerosol conditions in the middle troposphere above Lauder are subject to huge contrasts. Clean, pristine airmasses from Antarctica and the Southern Ocean arrive under southerly flow conditions while high aerosol loads can occur when air masses are advected from nearby Australia. This study assesses how these contrasts in aerosol load affect the ice formation efficiency in stratiform midlevel clouds in the heterogeneous freezing range (−40 °C to 0 °C). For this purpose, an 11-year dataset was analyzed from a dual-wavelength polarization lidar system operated by National Institute of Water & Atmospheric Research (NIWA) at Lauder in collaboration with the National Institute for Environmental Studies in Japan and the Meteorological Research Institute of the Japan Meteorological Agency. These data were used to investigate the efficiency of heterogeneous ice formation in clouds over the site as a function of cloud-top temperature as in previous studies at other locations. The Lauder cloud dataset was put into context with lidar studies from contrasting regions such as Germany and southern Chile. The ice formation efficiency found at Lauder is lower than in polluted mid-latitudes (i.e., Germany) but higher than for example in southern Chile. Both, Lauder and southern Chile are subject to generally low free-tropospheric aerosol loads, which suggests that the low ice formation efficiency at these two sites is related to low ice-nucleating particle (INP) concentrations. However, Lauder sees episodes of continental aerosol, more than does southern Chile, which seems to lead to the moderately increased ice formation efficiency. Trajectory-based tools and aerosol model re-analyses are used to relate this cloud dataset to the aerosol load and the air mass sources. Both analyses point clearly to higher ice formation efficiency for clouds which are more strongly influenced by continental ...