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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Nov 2018

Research article | 12 Nov 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Using spectra characteristics to identify ice nucleating particle populations during winter storms in the Alps

Jessie M. Creamean1,2,a, Claudia Mignani3, Nicolas Bukowiecki4, and Franz Conen3 Jessie M. Creamean et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 2Physical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 3Department of Environmental Sciences, University of Basel, Switzerland
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland
  • anow at: Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

Abstract. One of the least understood cloud processes is modulation of their microphysics by aerosols, specifically of cloud ice by ice nucleating particles (INPs). To investigate INP impacts on cloud ice and subsequent precipitation formation, measurements in cloud environments are necessary but difficult given the logistical challenges associated with airborne measurements and separating interstitial aerosol from cloud residues. Additionally, determining the sources of INPs is important given the dependency of glaciation temperatures on the mineral or biological components and diversity of such INP populations. Here, we present results from a comparison of INP spectral characteristics in air, cloud rime, and fresh fallen snow for storm days at the High-Altitude Research Station, Jungfraujoch. The goal of the study was two-fold: (1) to assess variability in wintertime INP populations found in-cloud based on air mass direction during snowfall and (2) to evaluate INPs between different sample types using normalized differential INP spectra. INP freezing temperatures and concentrations were consistently higher on average from the southeast as compared to the northwest for rime, snow and especially aerosol samples which is likely a result of air mass influence from boundary layer terrestrial and marine sources in Southern Europe, the Mediterranean, and North Africa. For all three sample types combined, average onset freezing temperatures were −7.7 and −12 °C for southeasterly and northwesterly days, respectively, while INP concentrations were 3 to 20 times higher when winds arrived from the southeast. Southeasterly aerosol samples typically had bimodal freezing spectra – indicating a putative influence from biological sources – while bimodality of the rime and snow varied depending on meteorological context. Evaluating normalized differential INP spectra exhibited variable modality and shape – depending on the types of INPs present – and may serve as a viable method for comparing different sampling substances and assessing the possible mixed mineral and biological versus only biological contributions to INP sample populations.

Jessie M. Creamean et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
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Jessie M. Creamean et al.
Jessie M. Creamean et al.
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Short summary
Aerosols that serve as seeds for cloud ice formation are important to study because they impact cloud radiative properties, lifetime, and precipitation formation. We present an investigation of ice nucleating particles (INPs) from aerosol, rime, and snow samples collected in clear and cloudy conditions during winter storms in the Swiss Alsp. INPs were more abundant and effective when storms originated from the south. We use spectral characteristics to investigate warm versus cold mode INPs.
Aerosols that serve as seeds for cloud ice formation are important to study because they impact...