Microphysical investigation of the seeder and feeder region of an Alpine mixed-phase cloud

Ramelli, Fabiola and Henneberger, Jan and David, Robert O. and Bühl, Johannes and Radenz, Martin and Seifert, Patric and Wieder, Jörg and Lauber, Annika and Pasquier, Julie T. and Engelmann, Ronny and Mignani, Claudia and Hervo, Maxime and Lohmann, Ulrike. (2021) Microphysical investigation of the seeder and feeder region of an Alpine mixed-phase cloud. Atmospheric Chemistry and Physics, 21 (9). pp. 6681-6706.

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Official URL: https://edoc.unibas.ch/83021/

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The seeder-feeder mechanism has been observed to enhance orographic precipitation in previous studies. However, the microphysical processes active in the seeder and feeder region are still being understood. In this paper, we investigate the seeder and feeder region of a mixed-phase cloud passing over the Swiss Alps, focusing on (1) fallstreaks of enhanced radar reflectivity originating from cloud top generating cells (seeder region) and (2) a persistent low-level feeder cloud produced by the boundary layer circulation (feeder region). Observations were obtained from a multi-dimensional set of instruments including ground-based remote sensing instrumentation (Ka-band polarimetric cloud radar, microwave radiometer, wind profiler), in situ instrumentation on a tethered balloon system, and ground-based aerosol and precipitation measurements. The cloud radar observations suggest that ice formation and growth were enhanced within cloud top generating cells, which is consistent with previous observational studies. However, uncertainties exist regarding the dominant ice formation mechanism within these cells. Here we propose different mechanisms that potentially enhance ice nucleation and growth in cloud top generating cells (convective overshooting, radiative cooling, droplet shattering) and attempt to estimate their potential contribution from an ice nucleating particle perspective. Once ice formation and growth within the seeder region exceeded a threshold value, the mixed-phase cloud became fully glaciated. Local flow effects on the lee side of the mountain barrier induced the formation of a persistent low-level feeder cloud over a small-scale topographic feature in the inner-Alpine valley. In situ measurements within the low-level feeder cloud observed the production of secondary ice particles likely due to the Hallett-Mossop process and ice particle fragmentation upon ice-ice collisions. Therefore, secondary ice production may have been partly responsible for the elevated ice crystal number concentrations that have been previously observed in feeder clouds at mountaintop observatories. Secondary ice production in feeder clouds can potentially enhance orographic precipitation.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Geowissenschaften > Umweltgeowissenschaften (Alewell)
UniBasel Contributors:Mignani, Claudia
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:European Geosciences Union
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:06 Sep 2021 15:27
Deposited On:06 Sep 2021 15:27

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