Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-1134
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
16 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
First Look at the Occurrence of Horizontally Oriented Ice Crystals over Summit, Greenland
Sebastian Cole1, Ryan R. Neely III.1,2, and Robert A. Stillwell3 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
2National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK
3Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, 80309, USA
Abstract. The microphysical properties of clouds play a significant role in determining their radiative effect; one of these properties is the orientation of ice crystals. A source of error in current microphysical retrievals and model simulations is the assumption that clouds are composed of only randomly oriented ice crystals (ROIC). This assumption is frequently not true, as evidenced by optical phenomena such as parhelia (commonly referred to as sundogs). Here, observations from the Cloud, Aerosol and Polarization Backscatter Lidar (CAPABL) at Summit, Greenland are utilized along with instruments that are part of the Integrated Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS) project in order to determine when, where and under what conditions horizontally oriented ice crystals (HOIC) occur at Summit, Greenland. Between July 2015 and May 2016, HOIC are observed on 86 days of the 335-day study. HOIC occurred within stratiform clouds on 48 days, in precipitation on 32 days and in cirrus clouds on 14 days. Analysis of all of the cases found that, on average, in comparison to ROIC, HOIC occur at higher temperatures, higher wind speeds and lower heights above ground level. Differences were also present in the relative humidities (RHs) at which HOIC and ROIC occurred in stratiform clouds and precipitation but not in cirrus clouds. Analysis over the whole study period revealed monthly variations in the abundance of HOIC with the number of detections peaking in April and October. Monthly changes were also present in the number of days containing HOIC. The results presented here aim to be the first step towards a comprehensive climatology and understanding of the microphysical processes that lead to the formation of HOIC at Summit, Greenland.

Citation: Cole, S., Neely III., R. R., and Stillwell, R. A.: First Look at the Occurrence of Horizontally Oriented Ice Crystals over Summit, Greenland, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1134, in review, 2017.
Sebastian Cole et al.
Sebastian Cole et al.
Sebastian Cole et al.

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