scholarly journals Small ice particles at slightly supercooled temperatures in tropical maritime convection

2020 ◽  
Vol 20 (6) ◽  
pp. 3895-3904
Author(s):  
Gary Lloyd ◽  
Thomas Choularton ◽  
Keith Bower ◽  
Jonathan Crosier ◽  
Martin Gallagher ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Dust Particles ◽  
Cumulus Clouds ◽  
Desert Dust ◽  
Ice Nuclei ◽  
Production Processes ◽  
Ice Particles ◽  
Small Crystals ◽  
Vapour Diffusion ◽  
Very High

Abstract. In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and −5 ∘C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µm). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about −10 ∘C, the zone in which the first ice was observed in these clouds. The small ice particles were observed to grow rapidly by vapour diffusion, riming, and possibly through collisions with supercooled raindrops, causing these to freeze and potentially shatter. This in turn leads to the further production of secondary ice in these clouds. Hence, although the numbers of primary ice particles are small, they are very effective in initiating the rapid glaciation of the cloud, altering the dynamics and precipitation production processes.

scholarly journals Small Ice Particles at Slightly Supercooled Temperatures in Tropical Maritime Convection

2019 ◽  
Author(s):  
Gary Lloyd ◽  
Thomas Choularton ◽  
Keith Bower ◽  
Jonathan Crosier ◽  
Martin Gallagher ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Dust Particles ◽  
Cumulus Clouds ◽  
Desert Dust ◽  
Ice Nuclei ◽  
Production Processes ◽  
Ice Particles ◽  
Small Crystals ◽  
Vapour Diffusion ◽  
Very High

Abstract. In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and −5 °C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µm). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about −10 °C, the zone in which the first ice was observed in these clouds. The small ice particles were observed to grow rapidly by vapour diffusion, riming, and possibly through collisions with supercooled raindrops, causing these to freeze and potentially shatter. This in turn leads to the further production of secondary ice in these clouds. Hence, although the numbers of primary ice particles are small, they are very effective in initiating the rapid glaciation of the cloud, altering the dynamics and precipitation production processes.

scholarly journals Investigating the role of dust in ice nucleation within clouds and further effects on regional weather system over East Asia – Part I: model development and validation

2017 ◽  
Author(s):  
Lin Su ◽  
Jimmy C.H. Fung
Keyword(s):  
East Asia ◽  
Source Region ◽  
Model Development ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Weather System ◽  
Microphysics Scheme ◽  
Ice Nuclei ◽  
Cloud Ice ◽  
Ice Water

Abstract. The GOCART–Thompson microphysics scheme, which couples the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and aerosol-aware Thompson microphysics scheme, has been implemented in the Weather Research and Forecast model coupled with Chemistry (WRF-Chem), to quantify and evaluate the effect of dust on the ice nucleation process in the atmosphere by serving as ice nuclei. The performance of the GOCART-Thompson microphysics scheme in simulating the effect of dust in atmospheric ice nucleation is then evaluated over East Asia during spring in 2012, a typical dust-intensive season. Based upon the dust emission reasonably reproduced by WRF-Chem, the effect of dust on atmospheric cloud ice water content is well reproduced. With abundant dust particles serving as ice nuclei, the simulated ice water mixing ratio and ice crystal number concentration increases by one order of magnitude over the dust source region and downwind areas during the investigated period. The comparison with ice water path from satellite observations demonstrated that the simulation of cloud ice profile is substantially improved by applying the GOCART–Thompson microphysics scheme in the simulations. Additional sensitivity experiments are carried out to optimize the parameters in the ice nucleation parameterization in the GOCART–Thompson microphysics scheme, and the results suggest that the calibration factor in the ice nucleation scheme should be set to 3 or 4. Lowering the threshold relative humidity with respect to ice to 100 % for the ice nucleation parameterization leads to further improvement in cloud ice simulation.

scholarly journals Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide – Part 2: Deposition nucleation and condensation freezing

2019 ◽  
Vol 19 (2) ◽  
pp. 1059-1076 ◽  
Author(s):  
Yvonne Boose ◽  
Philipp Baloh ◽  
Michael Plötze ◽  
Johannes Ofner ◽  
Hinrich Grothe ◽  
...  
Keyword(s):  
Active Sites ◽  
Mineral Dust ◽  
Atmospheric Transport ◽  
Chemical Imaging ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Full Potential ◽  
Nucleation Behavior ◽  
Crystal Water ◽  
Desert Dust

Abstract. Mineral dust particles from deserts are amongst the most common ice nucleating particles in the atmosphere. The mineralogy of desert dust differs depending on the source region and can further fractionate during the dust emission processes. Mineralogy to a large extent explains the ice nucleation behavior of desert aerosol, but not entirely. Apart from pure mineral dust, desert aerosol particles often exhibit a coating or are mixed with small amounts of biological material. Aging on the ground or during atmospheric transport can deactivate nucleation sites, thus strong ice nucleating minerals may not exhibit their full potential. In the partner paper of this work, it was shown that mineralogy determines most but not all of the ice nucleation behavior in the immersion mode found for desert dust. In this study, the influence of semi-volatile organic compounds and the presence of crystal water on the ice nucleation behavior of desert aerosol is investigated. This work focuses on the deposition and condensation ice nucleation modes at temperatures between 238 and 242 K of 18 dust samples sourced from nine deserts worldwide. Chemical imaging of the particles' surface is used to determine the cause of the observed differences in ice nucleation. It is found that, while the ice nucleation ability of the majority of the dust samples is dominated by their quartz and feldspar content, in one carbonaceous sample it is mostly caused by organic matter, potentially cellulose and/or proteins. In contrast, the ice nucleation ability of an airborne Saharan sample is found to be diminished, likely by semi-volatile species covering ice nucleation active sites of the minerals. This study shows that in addition to mineralogy, other factors such as organics and crystal water content can alter the ice nucleation behavior of desert aerosol during atmospheric transport in various ways.

scholarly journals Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components

2014 ◽  
Vol 14 (4) ◽  
pp. 1853-1867 ◽  
Author(s):  
D. O'Sullivan ◽  
B. J. Murray ◽  
T. L. Malkin ◽  
T. F. Whale ◽  
N. S. Umo ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Experimental Methodology ◽  
Dust Particles ◽  
Soil Dust ◽  
Source Regions ◽  
Ice Nuclei ◽  
Wide Range ◽  
Mineral Components ◽  
Droplet Sizes ◽  
Biogenic Components

Abstract. Agricultural dust emissions have been estimated to contribute around 20% to the global dust burden. In contrast to dusts from arid source regions, the ice-nucleating abilities of which have been relatively well studied, soil dusts from fertile sources often contain a substantial fraction of organic matter. Using an experimental methodology which is sensitive to a wide range of ice nucleation efficiencies, we have characterised the immersion mode ice-nucleating activities of dusts (d < 11 μm) extracted from fertile soils collected at four locations around England. By controlling droplet sizes, which ranged in volume from 10−12 to 10−6 L (concentration = 0.02 to 0.1 wt% dust), we have been able to determine the ice nucleation behaviour of soil dust particles at temperatures ranging from 267 K (−6 °C) down to the homogeneous limit of freezing at about 237 K (−36 °C). At temperatures above 258 K (−15 °C) we find that the ice-nucleating activity of soil dusts is diminished by heat treatment or digestion with hydrogen peroxide, suggesting that a major fraction of the ice nuclei stems from biogenic components in the soil. However, below 258 K, we find that the ice active site densities tend towards those expected from the mineral components in the soils, suggesting that the inorganic fraction of soil dusts, in particular the K-feldspar fraction, becomes increasingly important in the initiation of the ice phase at lower temperatures. We conclude that dusts from agricultural activities could contribute significantly to atmospheric IN concentrations, if such dusts exhibit similar activities to those observed in the current laboratory study.

scholarly journals Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide – Part 1: Immersion freezing

2016 ◽  
Vol 16 (23) ◽  
pp. 15075-15095 ◽  
Author(s):  
Yvonne Boose ◽  
André Welti ◽  
James Atkinson ◽  
Fabiola Ramelli ◽  
Anja Danielczok ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Minor Importance ◽  
Data Set ◽  
Nucleation Behavior ◽  
Desert Dust ◽  
Mineral Phases ◽  
Nucleation Activity ◽  
Ice Nucleation Activity

Abstract. Desert dust is one of the most abundant ice nucleating particle types in the atmosphere. Traditionally, clay minerals were assumed to determine the ice nucleation ability of desert dust and constituted the focus of ice nucleation studies over several decades. Recently some feldspar species were identified to be ice active at much higher temperatures than clay minerals, redirecting studies to investigate the contribution of feldspar to ice nucleation on desert dust. However, so far no study has shown the atmospheric relevance of this mineral phase.For this study four dust samples were collected after airborne transport in the troposphere from the Sahara to different locations (Crete, the Peloponnese, Canary Islands, and the Sinai Peninsula). Additionally, 11 dust samples were collected from the surface from nine of the biggest deserts worldwide. The samples were used to study the ice nucleation behavior specific to different desert dusts. Furthermore, we investigated how representative surface-collected dust is for the atmosphere by comparing to the ice nucleation activity of the airborne samples. We used the IMCA-ZINC setup to form droplets on single aerosol particles which were subsequently exposed to temperatures between 233 and 250 K. Dust particles were collected in parallel on filters for offline cold-stage ice nucleation experiments at 253–263 K. To help the interpretation of the ice nucleation experiments the mineralogical composition of the dusts was investigated. We find that a higher ice nucleation activity in a given sample at 253 K can be attributed to the K-feldspar content present in this sample, whereas at temperatures between 238 and 245 K it is attributed to the sum of feldspar and quartz content present. A high clay content, in contrast, is associated with lower ice nucleation activity. This confirms the importance of feldspar above 250 K and the role of quartz and feldspars determining the ice nucleation activities at lower temperatures as found by earlier studies for monomineral dusts. The airborne samples show on average a lower ice nucleation activity than the surface-collected ones. Furthermore, we find that under certain conditions milling can lead to a decrease in the ice nucleation ability of polymineral samples due to the different hardness and cleavage of individual mineral phases causing an increase of minerals with low ice nucleation ability in the atmospherically relevant size fraction. Comparison of our data set to an existing desert dust parameterization confirms its applicability for climate models. Our results suggest that for an improved prediction of the ice nucleation ability of desert dust in the atmosphere, the modeling of emission and atmospheric transport of the feldspar and quartz mineral phases would be key, while other minerals are only of minor importance.

scholarly journals Influence of particle size on the ice nucleating ability of mineral dusts

2009 ◽  
Vol 9 (18) ◽  
pp. 6705-6715 ◽  
Author(s):  
A. Welti ◽  
F. Lüönd ◽  
O. Stetzer ◽  
U. Lohmann
Keyword(s):  
Particle Size ◽  
Size Dependence ◽  
Water Saturation ◽  
Mineral Dust ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Ice Nuclei ◽  
Mineral Dusts ◽  
Measured Activation ◽  
Formation Efficiency

Abstract. The recently developed Zurich Ice Nucleation Chamber (ZINC) was used to explore ice nucleation of size-selected mineral dust particles at temperatures between −20°C and −55°C. Four different mineral dust species have been tested: montmorillonite, kaolinite, illite and Arizona test dust (ATD). The selected particle diameters are 100 nm, 200 nm, 400 nm and 800 nm. Relative humidities with respect to ice (RHi) required to activate 1% of the dust particles as ice nuclei (IN) are reported as a function of temperature. An explicit size dependence of the ice formation efficiency has been observed for all dust types. 800 nm particles required the lowest RHi to activate. Deposition nucleation below water saturation was found only below −30°C or −35°C dependent on particle size. Minimum RHi for 1% activation were 105% for illite, kaolinite and montmorillonite at −40°C, respectively 110% for ATD at −45°C. In addition, a possible parameterisation for the measured activation spectra is proposed, which could be used in modeling studies.

scholarly journals Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

2005 ◽  
Vol 5 (3) ◽  
pp. 3391-3436 ◽  
Author(s):  
C. M. Archuleta ◽  
P. J. DeMott ◽  
S. M. Kreidenweis
Keyword(s):  
Sulfuric Acid ◽  
Relative Humidity ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Nucleation Behavior ◽  
Ice Nuclei ◽  
Homogeneous Freezing

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between −45 and −60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

scholarly journals The ice-nucleating ability of quartz immersed in water and its atmospheric importance compared to K-feldspar

2019 ◽  
Author(s):  
Alexander D. Harrison ◽  
Katherine Lever ◽  
Alberto Sanchez-Marroquin ◽  
Mark A. Holden ◽  
Thomas F. Whale ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Mineral Dust ◽  
Aqueous Suspension ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Plagioclase Feldspar ◽  
Desert Dust ◽  
Site Density ◽  
Cloud Regime

Abstract. Mineral dust particles are thought to be an important type of ice-nucleating particle (INP) in the mixed-phase cloud regime around the globe. While K-feldspar has been identified as being a particularly important component of mineral dust for ice nucleation, it has been shown that quartz is also relatively ice nucleation active. Given quartz typically makes up a substantial proportion of atmospheric desert dust it could potentially be important for cloud glaciation. Here, we survey the ice-nucleating ability of 10 α-quartz samples (the most common quartz polymorph) when immersed in microlitre supercooled water droplets. Despite all samples being α-quartz, the temperature at which they induce freezing varies by around 12 °C for a constant active site density. We find that some quartz samples are very sensitive to ageing in both aqueous suspension and air, resulting in a loss of ice-nucleating activity, while other samples are insensitive to exposure to air and water over many months. The sensitivity to water and air is perhaps surprising as quartz is thought of as a chemically resistant material, but this observation suggests that the active sites responsible for nucleation are less stable than the bulk of the material. We find that the quartz group of minerals are generally less active than K-feldspars, although the most active quartz samples are of a similar activity to some K-feldspars. We also find that the quartz samples are generally more active than the plagioclase feldspar group of minerals and the albite end-member has an intermediate activity. Using both the new and literature data, active site density parameterisations have been proposed for quartz, K-feldspar, plagioclase and albite. Combining these parameterisations with the typical atmospheric abundance of each mineral and comparing the results with atmospheric ice-nucleating particle concentrations, supports previous work that suggests that K-feldspar dominates, rather than quartz (or other minerals), the ice nucleation particle population in desert dust aerosol.

scholarly journals Ice formation and development in aged, wintertime cumulus over the UK: observations and modelling

2012 ◽  
Vol 12 (11) ◽  
pp. 4963-4985 ◽  
Author(s):  
I. Crawford ◽  
K. N. Bower ◽  
T. W. Choularton ◽  
C. Dearden ◽  
J. Crosier ◽  
...  
Keyword(s):  
Particle Production ◽  
Ice Crystals ◽  
Dust Particles ◽  
Ice Formation ◽  
Crystal Formation ◽  
Surface Acting ◽  
Model Simulations ◽  
Ice Nuclei ◽  
Ice Particles ◽  
High Concentrations

Abstract. In situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of a line of small cumulus clouds, using Radar and Lidar, as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than −8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed, near cloud top, temperatures (−7.5 °C). The role of mineral dust particles, consistent with concentrations observed near the surface, acting as high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L−1) could be produced by secondary ice particle production providing the observed small amount of primary ice (about 0.01 L−1) was present to initiate it. This emphasises the need to understand primary ice formation in slightly supercooled clouds. It is shown using simple calculations that the Hallett-Mossop process (HM) is the likely source of the secondary ice. Model simulations of the case study were performed with the Aerosol Cloud and Precipitation Interactions Model (ACPIM). These parcel model investigations confirmed the HM process to be a very important mechanism for producing the observed high ice concentrations. A key step in generating the high concentrations was the process of collision and coalescence of rain drops, which once formed fell rapidly through the cloud, collecting ice particles which caused them to freeze and form instant large riming particles. The broadening of the droplet size-distribution by collision-coalescence was, therefore, a vital step in this process as this was required to generate the large number of ice crystals observed in the time available. Simulations were also performed with the WRF (Weather, Research and Forecasting) model. The results showed that while HM does act to increase the mass and number concentration of ice particles in these model simulations it was not found to be critical for the formation of precipitation. However, the WRF simulations produced a cloud top that was too cold and this, combined with the assumption of continual replenishing of ice nuclei removed by ice crystal formation, resulted in too many ice crystals forming by primary nucleation compared to the observations and parcel modelling.

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