Abstract
Ice fog, diamond dust, and light snow usually form over extremely cold weather conditions, and they affect both visibility and Earth’s radiative energy budget. Prediction of these hydrometeors using models is difficult because of limited knowledge of the microphysical properties at the small size ranges due to measurement issues. These phenomena need to be better represented in forecast and climate models; therefore, in addition to remote sensing accurate measurements using ground-based instrumentation are required. An imaging instrument, aimed at measuring ice fog and light snow particles, has been built and is presented here. The ice crystal imaging (ICI) probe samples ice particles into a vertical, tapered inlet with an inlet flow rate of 11 L min−1. A laser beam across the vertical air flow containing the ice crystals allows for their detection by a photodetector collecting the scattered light. Detected particles are then imaged with high optical resolution. An illuminating LED flash and image capturing are triggered by the photodetector. In this work, ICI measurements collected during the fog remote sensing and modeling (FRAM) project, which took place during Winter of 2010–2011 in Yellowknife, NWT, Canada, are summarized and challenges related to measuring small ice particles are described. The majority of ice particles during the 2-month-long campaign had sizes between 300 and 800 μm. During ice fog events the size distribution measured had a lower mode diameter of 300 μm compared to the overall campaign average with mode at 500 μm.
Highlights
Ice fog and light snow usually form at cold temperatures below -10 °C when ice nuclei exist in a supersaturated environment with respect to ice
The ice crystal imaging (ICI) has been operated at its first campaign, fog remote sensing and modeling (FRAM)-IF, over almost 60 days between 30 November 2010 and 30 January 2011
Its observations were performed during the fog remote sensing and modeling-ice fog (FRAM-IF) project, which took place in Yellowknife, NWT, Canada, during winter of 2010–2011
Summary
Ice fog and light snow usually form at cold temperatures below -10 °C when ice nuclei exist in a supersaturated environment with respect to ice. Ice fog and light snow are important weather phenomena as they affect aviation and transportation through visibility reduction (Gultepe et al 2015b) Forecasting of these weather phenomena, is difficult (Gultepe et al 2009, 2015b), but better knowledge of the microphysical properties of atmospheric ice particles is essential to the development of the meteorological forecast models. In addition to their role in aviation and transportation safety, these ice particles influence the radiative transfer in the atmosphere; they affect the Earth’s climate significantly (Gultepe et al 2015a, 2016). Climate modelling studies suggested that ice fog can significantly affect the radiative budget in the Arctic (Girard and Blanchet 2001) Both ice fog and light snow are dominated by smaller ice particles or crystals with sizes below 1 mm. Measurements of ice crystal shape and size, and their distribution are valuable for assessing climate change issues and for aviation applications
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