scholarly journals Direct evidence for secondary ice formation at around −15 °C in mixed-phase clouds

2018 ◽  
Author(s):  
Claudia Mignani ◽  
Jessie M. Creamean ◽  
Lukas Zimmermann ◽  
Christine Alewell ◽  
Franz Conen
Keyword(s):  
Direct Evidence ◽  
Mixed Phase ◽  
Ice Formation ◽  
Research Station ◽  
Multiplication Factor ◽  
Ice Crystal ◽  
Narrow Temperature Range ◽  
Snow Crystals ◽  
Ice Multiplication ◽  
Mixed Phase Clouds

Abstract. Ice crystal numbers can exceed the numbers of ice-nucleating particles (INP) observed in mixed-phase clouds by several orders of magnitude also at temperatures that are colder than required for the Hallett-Mossop process (−3 °C to −8 °C). These observations provide circumstantial evidence of secondary ice formation. Attempting a more direct observational approach we made use of the fact that planar, branched snow crystals (e.g. dendrites) grow within a relatively narrow temperature range (about −12 °C to −17 °C) and can be analysed individually for INP using a field-suitable drop freezing assay technique. During February and March 2018, we analysed 190 dendritic crystals (an average of ∼3 mm in size and between 1.3 to 7.6 mm) deposited within mixed-phase clouds at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.), Switzerland. Overall, one in eight of these crystals contained an INP active at −17 °C or warmer, while the remaining seven of eight 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 the experiment. These measurements show that secondary ice can be observed at temperatures around −15 °C in the atmosphere and thus advance our understanding of the extent of secondary ice formation in mixed-phase clouds, even where the multiplication factor is smaller than 10.

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

2019 ◽  
Vol 19 (2) ◽  
pp. 877-886 ◽  
Author(s):  
Claudia Mignani ◽  
Jessie M. Creamean ◽  
Lukas Zimmermann ◽  
Christine Alewell ◽  
Franz Conen
Keyword(s):  
Mixed Phase ◽  
Ice Formation ◽  
Research Station ◽  
Multiplication Factor ◽  
Ice Crystal ◽  
Activation Temperature ◽  
Individual Crystal ◽  
New Type ◽  
Ice Multiplication ◽  
Mixed Phase Clouds

Abstract. Ice crystal numbers can exceed the numbers of ice-nucleating 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.

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

2016 ◽  
Vol 16 (8) ◽  
pp. 4945-4966 ◽  
Author(s):  
Robert J. Farrington ◽  
Paul J. Connolly ◽  
Gary Lloyd ◽  
Keith N. Bower ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
Wrf Model ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystal ◽  
Field Campaign ◽  
Orographic Clouds ◽  
Ice Multiplication ◽  
Ice Production ◽  
Surface Ice ◽  
Mixed Phase Clouds

Abstract. 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 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 nucleating particle (INP) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing INP 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 flux of surface 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.

scholarly journals Supplementary material to "Direct evidence for secondary ice formation at around −15 °C in mixed-phase clouds"

2018 ◽  
Author(s):  
Claudia Mignani ◽  
Jessie M. Creamean ◽  
Lukas Zimmermann ◽  
Christine Alewell ◽  
Franz Conen
Keyword(s):  
Direct Evidence ◽  
Mixed Phase ◽  
Ice Formation ◽  
Supplementary Material ◽  
Mixed Phase Clouds

Importance of Secondary Ice Production to Ice Formation and Phase of High-Latitude Mixed-Phase Clouds during SOCRATES and MARCUS

2021 ◽  
Author(s):  
Xi Zhao ◽  
Xiaohong Liu ◽  
Vaughan Phillips ◽  
Sachin Patade ◽  
Minghui Diao ◽  
...  
Keyword(s):  
High Latitude ◽  
Mixed Phase ◽  
Ice Formation ◽  
Ice Production ◽  
Mixed Phase Clouds

scholarly journals Chemical composition and mixing-state of ice residuals sampled within mixed phase clouds

2011 ◽  
Vol 11 (6) ◽  
pp. 2805-2816 ◽  
Author(s):  
M. Ebert ◽  
A. Worringen ◽  
N. Benker ◽  
S. Mertes ◽  
E. Weingartner ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Carbonaceous Material ◽  
Mixed Phase ◽  
Research Station ◽  
Mixing State ◽  
Anthropogenic Component ◽  
Significant Enrichment ◽  
Alpine Research ◽  
Main Component ◽  
Mixed Phase Clouds

Abstract. During an intensive campaign at the high alpine research station Jungfraujoch, Switzerland, in February/March 2006 ice particle residuals within mixed-phase clouds were sampled using the Ice-counterflow virtual impactor (Ice-CVI). Size, morphology, chemical composition, mineralogy and mixing state of the ice residual and the interstitial (i.e., non-activated) aerosol particles were analyzed by scanning and transmission electron microscopy. Ice nuclei (IN) were identified from the significant enrichment of particle groups in the ice residual (IR) samples relative to the interstitial aerosol. In terms of number lead-bearing particles are enriched by a factor of approximately 25, complex internal mixtures with silicates or metal oxides as major components by a factor of 11, and mixtures of secondary aerosol and carbonaceous material (C-O-S particles) by a factor of 2. Other particle groups (sulfates, sea salt, Ca-rich particles, external silicates) observed in the ice-residual samples cannot be assigned unambiguously as IN. Between 9 and 24% of all IR are Pb-bearing particles. Pb was found as major component in around 10% of these particles (PbO, PbCl2). In the other particles, Pb was found as some 100 nm sized agglomerates consisting of 3–8 nm sized primary particles (PbS, elemental Pb). C-O-S particles are present in the IR at an abundance of 17–27%. The soot component within these particles is strongly aged. Complex internal mixtures occur in the IR at an abundance of 9–15%. Most IN identified at the Jungfraujoch station are internal mixtures containing anthropogenic components (either as main or minor constituent), and it is concluded that admixture of the anthropogenic component is responsible for the increased IN efficiency within mixed phase clouds. The mixing state appears to be a key parameter for the ice nucleation behaviour that cannot be predicted from the sole knowledge of the main component of an individual particle.

scholarly journals The Horizontal Ice Nucleation Chamber (HINC): INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch

2017 ◽  
Vol 17 (24) ◽  
pp. 15199-15224 ◽  
Author(s):  
Larissa Lacher ◽  
Ulrike Lohmann ◽  
Yvonne Boose ◽  
Assaf Zipori ◽  
Erik Herrmann ◽  
...  
Keyword(s):  
High Altitude ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Saharan Dust ◽  
Research Station ◽  
Minimum Detectable Concentration ◽  
The North ◽  
New Instrument ◽  
Marine Air ◽  
Mixed Phase Clouds

Abstract. In this work we describe the Horizontal Ice Nucleation Chamber (HINC) as a new instrument to measure ambient ice-nucleating particle (INP) concentrations for conditions relevant to mixed-phase clouds. Laboratory verification and validation experiments confirm the accuracy of the thermodynamic conditions of temperature (T) and relative humidity (RH) in HINC with uncertainties in T of ±0.4 K and in RH with respect to water (RHw) of ±1.5 %, which translates into an uncertainty in RH with respect to ice (RHi) of ±3.0 % at T > 235 K. For further validation of HINC as a field instrument, two measurement campaigns were conducted in winters 2015 and 2016 at the High Altitude Research Station Jungfraujoch (JFJ; Switzerland, 3580 m a. s. l. ) to sample ambient INPs. During winters 2015 and 2016 the site encountered free-tropospheric conditions 92 and 79 % of the time, respectively. We measured INP concentrations at 242 K at water-subsaturated conditions (RHw = 94 %), relevant for the formation of ice clouds, and in the water-supersaturated regime (RHw = 104 %) to represent ice formation occurring under mixed-phase cloud conditions. In winters 2015 and 2016 the median INP concentrations at RHw = 94 % was below the minimum detectable concentration. At RHw = 104 %, INP concentrations were an order of magnitude higher, with median concentrations in winter 2015 of 2.8 per standard liter (std L−1; normalized to standard T of 273 K and pressure, p, of 1013 hPa) and 4.7 std L−1 in winter 2016. The measurements are in agreement with previous winter measurements obtained with the Portable Ice Nucleation Chamber (PINC) of 2.2 std L−1 at the same location. During winter 2015, two events caused the INP concentrations at RHw = 104 % to significantly increase above the campaign average. First, an increase to 72.1 std L−1 was measured during an event influenced by marine air, arriving at the JFJ from the North Sea and the Norwegian Sea. The contribution from anthropogenic or other sources can thereby not be ruled out. Second, INP concentrations up to 146.2 std L−1 were observed during a Saharan dust event. To our knowledge this is the first time that a clear enrichment in ambient INP concentration in remote regions of the atmosphere is observed during a time of marine air mass influence, suggesting the importance of marine particles on ice nucleation in the free troposphere.

scholarly journals Effects of Entrainment and Mixing on the Wegener–Bergeron–Findeisen Process

2020 ◽  
Vol 77 (6) ◽  
pp. 2279-2296
Author(s):  
Fabian Hoffmann
Keyword(s):  
Molecular Diffusion ◽  
Scale Effects ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Small Scale ◽  
Liquid Droplets ◽  
Ice Crystal ◽  
Slowing Down ◽  
Linear Eddy Model ◽  
Mixed Phase Clouds

Abstract The growth of ice crystals at the expense of water droplets, the Wegener–Bergeron–Findeisen (WBF) process, is of major importance for the production of precipitation in mixed-phase clouds. The effects of entrainment and mixing on WBF, however, are not well understood, and small-scale inhomogeneities in the thermodynamic and hydrometeor fields are typically neglected in current models. By applying the linear eddy model, a millimeter-resolution representation of turbulent deformation and molecular diffusion, we investigate these small-scale effects on WBF. While we show that entrainment is accelerating WBF by contributing to the evaporation of liquid droplets, entrainment may also cause aforementioned inhomogeneities, particularly regions filled with exclusively ice or liquid hydrometeors, which tend to decelerate WBF if the ice crystal concentration exceeds 100 L−1. At lower ice crystal concentrations, even weak turbulence can homogenize hydrometeor and thermodynamic fields sufficiently fast so as to not affect WBF. Independent of the ice crystal concentration, it is shown that a fully resolved entrainment and mixing process may delay the nucleation of entrained aerosols to ice crystals, thereby delaying the uptake of water vapor by the ice phase, further slowing down WBF. All in all, this study indicates that, under specific conditions, small-scale inhomogeneities associated with entrainment and mixing counteract the accelerated WBF in entraining clouds. However, further research is required to assess the importance of the newly discovered processes more broadly in fully coupled, evolving mixed-phase cloud systems.

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

2015 ◽  
Vol 15 (18) ◽  
pp. 25647-25694 ◽  
Author(s):  
R. J. Farrington ◽  
P. J. Connolly ◽  
G. Lloyd ◽  
K. N. Bower ◽  
M. J. Flynn ◽  
...  
Keyword(s):  
Wrf Model ◽  
Surface Flux ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Field Campaign ◽  
Orographic Clouds ◽  
Ice Multiplication ◽  
Ice Production ◽  
Surface Ice ◽  
Mixed Phase Clouds

Abstract. 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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