Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Fore...

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Bibliographic Details
Published in:Atmospheric Chemistry and Physics
Main Authors: Farrington, Robert, Connolly, Paul, Lloyd, G., Bower, Keith, Flynn, M. J., Gallagher, Martin, Field, P. R., Dearden, Christopher, Choularton, Thomas
Format: Article in Journal/Newspaper
Language:English
Published: 2016
Subjects:
Inupiaq
Online Access:https://research.manchester.ac.uk/en/publications/6ffa8e97-4483-43b0-8d9d-6df381f9dc0a
https://doi.org/10.5194/acp-16-4945-2016
Description
Summary:This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between the 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nuclei (IN) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing IN concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A surface flux of hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

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