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Preprints
https://doi.org/10.5194/acp-2019-1173
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1173
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Feb 2020

Submitted as: research article | 04 Feb 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Microphysics and dynamics of snowfall associated to a warm conveyor belt over Korea

Josué Gehring1, Annika Oertel2, Étienne Vignon1, Nicolas Jullien3, Nikola Besic4, and Alexis Berne1 Josué Gehring et al.
  • 1Environmental Remote Sensing Laboratory (LTE), EPFL, Lausanne, Switzerland
  • 2Institute for Atmospheric and Climate Science (IAC), ETH, Zurich, Switzerland
  • 3Department of Geosciences, University of Fribourg, Fribourg, Switzerland
  • 4Centre Météorologie Radar, Météo France, Toulouse, France

Abstract. On 28 February 2018, 57 mm of precipitation associated to a warm conveyor belt (WCB) fell within 21 h over South Korea. To investigate how the large-scale circulation influenced the microphysics of this intense precipitation event, we used radar measurements, snowflake photographs and radiosounding data from the International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic winter games. The WCB was identified with trajectories computed with analysis wind fields from the Integrated Forecast System global atmospheric model. The WCB was collocated with a zone of enhanced wind speed of up to 45 m s−1 at 6500 m a.s.l., as measured by a radiosonde and a Doppler radar. Supercooled liquid water (SLW) with concentrations exceeding 0.2 g kg−1 was produced during the rapid ascent within the WCB. Vertical profiles of polarimetric radar variables show during the most intense precipitation period a peak and subsequent decrease in differential reflectivity as aggregation starts. Below the peak in differential reflectivity, the specific differential phase shift continues to increase, indicating early riming of oblate crystals and secondary ice generation. We hypothesise that the SLW produced in the WCB led to intense riming. Moreover, embedded convection in the WCB and turbulence at its lower boundary enhanced aggregation by increasing the probability of collisions between particles. This suggests that both aggregation and riming occurred prominently in this WCB. This case study shows how the large-scale atmospheric flow of a WCB provides ideal conditions for rapid precipitation growth involving SLW production, riming and aggregation. Future microphysical studies should also investigate the synoptic conditions to understand how observed processes in clouds are related to the large-scale circulation.

Josué Gehring et al.

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Josué Gehring et al.

Josué Gehring et al.

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Latest update: 02 Jun 2020
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Short summary
In this study, we analyse how large-scale meteorological conditions influenced the local enhancement of snowfall during an intense precipitation event in Korea. We used atmospheric models, weather radars and snowflake images. We found out that a rising airstream in the warm sector of the low pressure system associated to this event influenced the evolution of snowfall. This study highlights the importance of interactions between large and local scales in this intense precipitation event.
In this study, we analyse how large-scale meteorological conditions influenced the local...
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