Abstract
Abstract. Ambient concentrations of ice-forming particles measured during ship expeditions are collected and summarised with the aim of determining the spatial distribution and variability in ice nuclei in oceanic regions. The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient ice nuclei show 1 to 2 orders of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential ice nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into tropical, temperate and polar climate zones. We find that concentrations of ice nuclei in these meridional zones follow temperature spectra with similar slopes but vary in absolute concentration. Typically, the frequency with which specific concentrations of ice nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured ice nuclei concentration on board research vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately −36 ∘C but none at warmer temperatures that could bias ship-based measurements.
Highlights
A small fraction of atmospheric aerosol particles possesses properties that induce the nucleation of ice
We present a summary of ship-based measurements from the literature and extend this data set with unpublished data dating back as far as 1996 and measurements from several recent ship expeditions
The smaller the sample volume, the higher the limit of detection and vice versa, i.e. larger sample air volumes allow the detection of low concentrations, while smaller sample volumes are more suitable for accessing high concentrations
Summary
A small fraction of atmospheric aerosol particles possesses properties that induce the nucleation of ice. A. Welti et al.: Ship-based measurements of IN concentration ice nucleating particles (Vali et al, 2015). The concentration of IN active at a certain temperature affects the extent of ice crystal formation in clouds. DeMott et al, 2010) and ship-based observations in the Southern Ocean between Australia and Antarctica (Bigg, 1973). We present a summary of ship-based measurements from the literature and extend this data set with unpublished data dating back as far as 1996 and measurements from several recent ship expeditions. Unpublished −15 ◦C data include observations from the Pacific Ocean (SHIpborne Pole to Pole Observations – SHIPPO; U.S Department of Energy’s Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment – ACAPEX), Southern Ocean (TAN1502) and central Arctic Ocean (Arctic Ocean Expedition – AOE-96 and AOE-2001)
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