Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations

Beck, Alexander; Henneberger, Jan; Fugal, Jacob P.; David, Robert O.; Lacher, Larissa; Lohmann, Ulrike

doi:10.5194/acp-18-8909-2018

Cited by 31 publications

(40 citation statements)

References 45 publications

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“…The particles they found were clay and related minerals and were assumed to have initiated the formation of the crystals. Bigg (1996) suggested repeating the experiments by Kumai and Francis (1962) and looking at the ice nucleation properties of these particles. One reason it can be misleading to equate ice residuals with INPs is that MPCgenerated ice crystals can contain cloud condensation nuclei (CCN) which have been collected upon riming but have not acted as INPs.…”

Section: Introductionmentioning

confidence: 99%

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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Ice crystal numbers can exceed the numbers of icenucleating particles (INPs) observed in mixed-phase clouds (MPCs) by several orders of magnitude, also at temperatures that are colder than − 8 • C. This disparity provides circumstantial evidence of secondary ice formation, also other than via the Hallett-Mossop process. In a new approach, we made use of the fact that planar, branched ice crystals (e.g. dendrites) grow within a relatively narrow temperature range (i.e. −12 to −17 • C) and can be analysed individually for INPs using a field-deployable drop-freezing assay. The novelty of our approach lies in comparing the growth temperature encoded in the habit of an individual crystal with the activation temperature of the most efficient INP contained within the same crystal to tell whether it may be the result of primary ice formation. In February and March 2018, we analysed a total of 190 dendritic crystals (∼ 3 mm median size) deposited within MPCs at the high-altitude research station Jungfraujoch (3580 m a.s.l.). Overall, one in eight of the analysed crystals contained an INP active at −17 • C or warmer, while the remaining seven most likely resulted from secondary ice formation within the clouds. The ice multiplication factor we observed was small (8), but relatively stable throughout the course of documentation. These measurements show that secondary ice can be observed at temperatures around −15 • C and thus advance our understanding of the extent of secondary ice formation in MPCs, even where the multiplication factor is smaller than 10.

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Section: Introductionmentioning

confidence: 99%

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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“…Due to the fact that INP occurrence in the measured snow samples have been determined as non-site specific, the studies conducted at Jungfraujoch, measuring the free troposphere are representative for INP assessments across the Swiss Alps. 15 several orders of magnitude higher than INP concentrations (Wex et al, 2010), secondary ice processes can play an important in the evolution of supercooled clouds (Beck et al, 2018;Hallett and Mossop, 1974;Lauber et al, 2018;Mignani et al, 2019;Petters and Wright, 2015). Yet the process of ice multiplication is not fully understood, with multiplication factors ranging from one to multiple orders of magnitude (Mignani et al, 2019;Wang, 2013).…”

Section: Inp Concentration Parameterizationmentioning

confidence: 99%

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Brennan

David

Borduas-Dedekind

2019

Preprint

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Ice nucleating particles (INPs) produce ice from supercooled water droplets through heterogeneous 10 freezing in the atmosphere. Since the concentration of ice crystals affects the radiative properties of clouds as well as precipitation, constraining the liquid water to ice ratio could help reduce aerosol-cloud interaction uncertainties. INPs have been collected at the Jungfraujoch research station (at 3500 m a.s.l.) in central Switzerland; yet spatially diverse data on INP occurrence in the Swiss Alps are scarce and remain uncharacterized. We address this scarcity through our Swiss Alpine snow sample study which 15 took place during the winter of 2018. We collected a total of 88 fallen snow samples across the Alps at different locations, altitudes, terrains, times since last snowfall and depths. The INP concentrations were measured using the homebuilt DRoplet Ice Nuclei Counter Zurich (DRINCZ) and were then compared to spatial, meteorological and physiochemical parameters. We also extend an alternative way of displaying frozen fraction (FF) versus temperature data through visualizing freezing temperatures as a 20boxplot to field collected samples. This plotting method displays the freezing temperature in one dimension, instead of the former two dimensions of FF vs temperature, allowing a condensed display of freezing temperature measurements. In the collected snow samples, large variability in INP occurrence was found, even for samples collected 10 m apart on a plain and 1 m apart in depth. Furthermore, undiluted samples had INP concentrations ranging between 1 and 100 INP ml -1 of snow water over a 25 temperature range of −5 to −19 C. From this field-collected data set, we parameterize the INP concentrations per milliliter of meltwater as a function of temperature with the following equation * ( ) = − . − . , comparing well with previously reported precipitation data presented in Petters and Wright, 2015. 30 When assuming a cloud water content of 0.4 g m -3 and a critical INP concentration for glaciation of 10 m -3 , the majority of the snow precipitated from clouds with glaciation temperatures between −5 and −20 °C. Based on the observed variability in INP concentrations, we conclude that studies conducted at the high-altitude research station Jungfraujoch are representative for INP measurements in the Swiss Alps. Furthermore, the INP concentration precipitation estimates allow us to extrapolate the 35 concentrations to a cloud frozen fraction. Indeed, this approach for estimating the liquid water to ice ratio in mixed phase clouds compares well with aircraft measurements, ground-based lidar and satellite retrievals of cloud frozen fractions. In all, the generated parameterization for INP concentrations in meltwater could help estimate cloud glaciation temperatures.

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“…The winch has a line speed of 1 m s −1 forward and reverse, which allows a vertical profile of 500 m in 8 minutes. 15 The instrument package is installed at the kiel of the HoloBalloon platform. The key component is the HOLographic Imager for Microscopic Objects (HOLIMO 3B) (see Sect.…”

Section: Description Of the Holoballoon Measurement Platformmentioning

confidence: 99%

“…Commonly, microphysical in situ measurements within the PBL are performed using a variety of measurement platforms, such 15 as research aircraft (e.g. Sassen et al 1999, Verlinde et al 2007), helicopters (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

Ramelli¹,

Beck²,

Henneberger³

et al. 2019

Preprint

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Conventional techniques to measure boundary layer clouds such as research aircrafts are unable to sample in orographic or densely-populated areas. In this paper, we present a newly developed measurement platform on a tethered balloon system (HoloBalloon) to measure in situ vertical profiles of microphysical and meteorological cloud properties up to 1 kilometer above ground. The main component of the HoloBalloon platform is a holographic imager, which uses digital in-line holography to image cloud particles in a velocity independent sample volume, making it particularly well suited for measure-5 ments on a balloon. The unique combination of holography and balloon-borne measurements allows observations with high spatial resolution, covering cloud structures from the kilometer down to the millimeter scale.We present observations of a supercooled low stratus cloud (high fog event) during a Bise situation over the Swiss Plateau in February 2018. In situ microphysical profiles up to 700 m altitude above the ground and at temperatures down to -8°C and wind speeds up to 15 m s −1 were performed. We were able to capture unique microphysical features from the kilometer down to the 10 meter scale. For example, we observed cloud regions with decreased cloud droplet number concentration (<0.5 CDN C) and cloud droplet size at scales of 30-50 meters. These cloud inhomogeneities could arise from adiabatic compression and heating and subsequent droplet evaporation in descending air parcels. Moreover, we observed conditions favorable for the formation of boundary layer waves and Kelvin-Helmholtz instability at the cloud top. This potentially influenced the cloud structure on a scale of 10-30 kilometers, which is reflected in the variability of the CDNC. 15

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Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations

Cited by 31 publications

References 45 publications

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

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