Relationships between Immersion Freezing and Crystal Habit for Arctic Mixed-Phase Clouds—A Numerical Study

AbstractThe number concentration of ice particles in Arctic mixed-phase clouds is a major controlling factor of cloud lifetime. The relationships between ice nucleation mode and ice crystal habit development are not yet constrained by observations. This study uses a habit-predicting microphysical scheme within a 3D large-eddy simulation model to evaluate the relationship between immersion freezing and ice habit in a simulated Arctic mixed-phase cloud case. Three immersion freezing parameterizations are considered: a volume-dependent freezing scheme (VF), a parameterization limited to activated droplets (C-AC), and a parameterization limited to coarse aerosol particles (C-CM). Both C-AC and C-CM are based on classical nucleation theory. The freezing rate with VF is found to be greater in downdraft regions than in updraft regions due to the downdraft having a higher number concentration of large droplets. The C-AC cases show active freezing of small droplets near cloud top, whereas in the C-CM cases, mainly the 8–32-μm-sized droplets freeze in updraft regions near the cloud base. Because the initial crystal size is assumed to affect the axis ratio of hexagonal plates, the VF cases produce crystals with larger axis ratios, resulting in smaller mode radii than the C-AC cases. In all cases, irregular polycrystals dominate near cloud top and a band-like structure develops within the cloud, which qualitatively agrees with previous observations. In the VF and C-CM cases, unactivated large droplets arising from coarse-mode aerosol particles contributed significantly to the freezing rate, producing an important influence on crystal habit.

Download Full-text

Impacts of Secondary Ice Production on Arctic Mixed-Phase Clouds based on ARM Observations and CESM2

10.5194/acp-2020-1276 ◽

2020 ◽

Author(s):

Xi Zhao ◽

Xiaohong Liu ◽

Vaughan T. J. Phillips ◽

Sachin Patade

Keyword(s):

Global Climate Model ◽

Single Layer ◽

Ice Nucleation ◽

Number Concentration ◽

Mixed Phase ◽

Department Of Energy ◽

Cloud Base ◽

Ice Crystal ◽

Ice Production ◽

Mixed Phase Clouds

Abstract. For decades, measured ice crystal number concentrations have been found to be orders of magnitude higher than measured ice nucleating particles in moderately cold clouds. This observed discrepancy reveals the existence of secondary ice production (SIP) in addition to the primary ice nucleation. However, the importance of SIP relative to primary ice nucleation remains highly unclear. Furthermore, most weather and climate models do not represent well the SIP processes, leading to large biases in simulated cloud properties. This study demonstrates a first attempt to represent different SIP mechanisms (frozen raindrop shattering, ice-ice collisional break-up, and rime splintering) in a global climate model (GCM). The model is run in the single column mode to facilitate comparisons with the Department of Energy (DOE)'s Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We show the SIP importance in the four types of clouds during M-PACE (i.e., multilayer, and single-layer stratus, transition, and front clouds), with the maximum enhancement in ice crystal number concentration by up to 4 orders of magnitude in the moderately-cold clouds. We reveal that SIP is the dominant source of ice crystals near the cloud base for the long-lived Arctic single-layer mixed-phase clouds. The model with SIP improves the occurrence and phase partitioning of the mixed-phase clouds, reverses the vertical distribution pattern of ice number concentration, and provides a better agreement with observations. The findings of this study highlight the importance of considering the SIP in GCMs.

Download Full-text

An Analytic Scaling Law for the Depositional Growth of Snow in Thin Mixed-Phase Layer Clouds

Journal of the Atmospheric Sciences ◽

10.1175/2009jas3021.1 ◽

2009 ◽

Vol 66 (9) ◽

pp. 2620-2639 ◽

Cited By ~ 2

Author(s):

Vincent E. Larson ◽

Adam J. Smith

Keyword(s):

Scaling Laws ◽

Scaling Law ◽

Power Laws ◽

Mixed Phase ◽

Crystal Habit ◽

Cloud Base ◽

Mixing Ratio ◽

Phase Layer ◽

Snow Crystals ◽

Mixed Phase Clouds

Abstract In various practical problems, such as assessing the threat of aircraft icing or calculating radiative transfer, it is important to know whether mixed-phase clouds contain significant liquid water content. Some mixed-phase clouds remain predominantly liquid for an extended time, whereas others glaciate quickly. The glaciation rate of mixed-phase layer clouds is thought to depend on various factors, including number concentration of snow crystals, terminal velocity of snow crystals, and crystal habit type. This paper attempts to quantify some of these factors by deriving scaling laws (i.e., power laws) for the mixing ratio and sedimentation flux of snow at cloud base. The scaling laws are derived from the governing equation for snow mixing ratio. They neglect aggregation of snow crystals and accretion of supercooled liquid by snow crystals. The scaling laws permit arbitrary exponents and prefactors of the mass–diameter and fall speed–diameter power laws, allowing flexibility in crystal habit properties. The scaling laws are tested using idealized large-eddy simulation (LES) of three thin, midlevel layer clouds. The scaling laws agree adequately with the LES over one order of magnitude for snow flux and over two orders of magnitude for snow mixing ratio. They indicate, for instance, that in the present LES, cloud-base snow flux and snow mixing ratio increase faster than linearly with increasing cloud thickness and supersaturation with respect to ice. By varying the exponents and prefactors of the scaling laws, one may explore the sensitivity of glaciation rate to habit type. The relationship is complex, but, for the cloud cases examined, dendrites tend to glaciate cloud more rapidly than plates.

Download Full-text

The ice nucleating ability of macromolecules in immersion freezing decreases in the presence of salts: Implications for freezing point depression calculations

10.5194/egusphere-egu21-5914 ◽

2021 ◽

Author(s):

Jon F. Went ◽

Jeanette D. Wheeler ◽

François J. Peaudecerf ◽

Nadine Borduas-Dedekind

Keyword(s):

Sea Water ◽

Freezing Point ◽

Pure Water ◽

Salt Content ◽

Mixed Phase ◽

Cloud Formation ◽

Sea Spray ◽

Freezing Point Depression ◽

Immersion Freezing ◽

Mixed Phase Clouds

Cloud formation represents a large uncertainty in current climate predictions. In particular, ice in mixed-phase clouds requires the presence of ice nucleating particles (INPs) or ice nucleating macromolecules (INMs). An influential population of INPs has been proposed to be organic sea spray aerosols in otherwise pristine ocean air. However, the interactions between INMs present in sea water and their freezing behavior under atmospheric immersion freezing conditions warrants further research to constrain the role of sea spray aerosols on cloud formation. Indeed, salt is known to lower the freezing temperature of water, through a process called freezing point depression (FPD). Yet, current FPD corrections are solely based on the salt content and assume that the INMs&#8217; ice nucleation abilities are identical with and without salt. Thus, we measured the effect of salt content on the ice nucleating ability of INMs, known to be associated with marine phytoplankton, in immersion freezing experiments in the Freezing Ice Nuclei Counter (FINC) (Miller et al., AMTD, 2020). We measured eight INMs, namely taurine, isethionate, xylose, mannitol, dextran, laminarin, and xanthan as INMs in pure water at temperatures relevant for mixed-phase clouds (e.g. 50% activated fraction at temperatures above &#8211;23 &#176;C at 10 mM concentration). Subsequently, INMs were analyzed in artificial sea water containing 36 g salt L-1. Most INMs, except laminarin and xanthan, showed a loss of ice activity in artificial sea water compared to pure water, even after FPD correction. Based on our results, we hypothesize sea salt has an inhibitory effect on the ice activity of INMs. This effect influences our understanding of how INMs nucleate ice as well as challenges our use of FPD correction and subsequent extrapolation to ice activity under mixed-phase cloud conditions.

Download Full-text

Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-31079-2013 ◽

2013 ◽

Vol 13 (11) ◽

pp. 31079-31125 ◽

Cited By ~ 2

Author(s):

J. Sedlar ◽

M. D. Shupe

Keyword(s):

Vertical Velocity ◽

Vertical Mixing ◽

Vertical Motion ◽

Temperature Inversion ◽

Arctic Sea Ice ◽

Cloud Layer ◽

Mixed Phase ◽

The Arctic ◽

Cloud Base ◽

Mixed Phase Clouds

Abstract. Over the Arctic Ocean, little is known, observationally, on cloud-generated buoyant overturning vertical motions within mixed-phase stratocumulus clouds. Characteristics of such motions are important for understanding the diabatic processes associated with the vertical motions, the lifetime of the cloud layer and its micro- and macrophysical characteristics. In this study, we exploit a suite of surface-based remote sensors over the high Arctic sea ice during a week-long period of persistent stratocumulus in August 2008 to derive the in-cloud vertical motion characteristics. In-cloud vertical velocity skewness and variance profiles are found to be strikingly different from observations within lower-latiatude stratocumulus, suggesting these Arctic mixed-phase clouds interact differently with the atmospheric thermodynamics (cloud tops extending above a stable temperature inversion base) and with a different coupling state between surface and cloud. We find evidence of cloud-generated vertical mixing below cloud base, regardless of surface-cloud coupling state, although a decoupled surface-cloud state occurred most frequently. Detailed case studies are examined focusing on 3 levels within the cloud layer, where wavelet and power spectral analyses are applied to characterize the dominant temporal and horizontal scales associated with cloud-generated vertical motions. In general, we find a positively-correlated vertical motion signal across the full cloud layer depth. The coherency is dependent upon other non-cloud controlled factors, such as larger, mesoscale weather passages and radiative shielding of low-level stratocumulus by multiple cloud layers above. Despite the coherency in vertical velocity across the cloud, the velocity variances were always weaker near cloud top, relative to cloud mid and base. Taken in combination with the skewness, variance and thermodynamic profile characteristics, we observe vertical motions near cloud-top that behave differently than those from lower within the cloud layer. Spectral analysis indicates peak cloud-generated w variance timescales slowed only modestly during decoupled cases relative to coupled; horizontal wavelengths only slightly increased when transitioning from coupling to decoupling. The similarities in scales suggests that perhaps the dominant forcing for all cases is generated from the cloud layer, and it is not the surface forcing that characterizes the time and space scales of in-cloud vertical velocity variance. This points toward the resilient nature of Arctic mixed-phase clouds to persist when characterized by thermodynamic regimes unique to the Arctic.

Download Full-text

Ice Particle Production in Mid-level Stratiform Mixed-phase Clouds Observed with Collocated A-Train Measurements

10.5194/acp-2017-927 ◽

2017 ◽

Author(s):

Damao Zhang ◽

Zhien Wang ◽

Pavlos Kollias ◽

Andrew M. Vogelmann ◽

Kang Yang ◽

...

Keyword(s):

Northern Hemisphere ◽

Particle Production ◽

Climate Models ◽

Global Scale ◽

Number Concentration ◽

Mixed Phase ◽

Liquid Water Path ◽

Lidar Measurements ◽

Dust Events ◽

Mixed Phase Clouds

Abstract. Collocated CloudSat radar and CALIPSO lidar measurements between 2006 and 2010 are analyzed to study primary ice particle production characteristics in mid-level stratiform mixed-phase clouds on a global scale. For similar clouds in terms of cloud top temperature and liquid water path, Northern Hemisphere latitude bands have layer-maximum radar reflectivity (ZL) that is ~1 to 8 dBZ larger than their counterparts in the Southern Hemisphere. The systematically larger ZL under similar cloud conditions suggests larger ice number concentrations in mid-level stratiform mixed-phase clouds over the Northern Hemisphere, which is possibly related to higher background aerosol loadings. Furthermore, we show that northern mid- and high-latitude springtime has ZL that is larger by up to 8 dBZ (a factor of 6 higher ice number concentration) than other seasons, which might be related to more dust events that provide effective ice nucleating particles. Our study suggests that aerosol-dependent ice number concentration parameterizations are required in climate models to improve mixed-phase cloud simulations, especially over the Northern Hemisphere.

Download Full-text

Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-3461-2014 ◽

2014 ◽

Vol 14 (7) ◽

pp. 3461-3478 ◽

Cited By ~ 20

Author(s):

J. Sedlar ◽

M. D. Shupe

Keyword(s):

Vertical Velocity ◽

Vertical Motion ◽

Temperature Inversion ◽

Arctic Sea Ice ◽

Cloud Layer ◽

Mixed Phase ◽

The Arctic ◽

Lower Latitude ◽

Cloud Base ◽

Mixed Phase Clouds

Abstract. Over the Arctic Ocean, little is known on cloud-generated buoyant overturning vertical motions within mixed-phase stratocumulus clouds. Characteristics of such motions are important for understanding the diabatic processes associated with the vertical motions, the lifetime of the cloud layer and its micro- and macrophysical characteristics. In this study, we exploit a suite of surface-based remote sensors over the high-Arctic sea ice during a weeklong period of persistent stratocumulus in August 2008 to derive the in-cloud vertical motion characteristics. In-cloud vertical velocity skewness and variance profiles are found to be strikingly different from observations within lower-latitude stratocumulus, suggesting these Arctic mixed-phase clouds interact differently with the atmospheric thermodynamics (cloud tops extending above a stable temperature inversion base) and with a different coupling state between surface and cloud. We find evidence of cloud-generated vertical mixing below cloud base, regardless of surface–cloud coupling state, although a decoupled surface–cloud state occurred most frequently. Detailed case studies are examined, focusing on three levels within the cloud layer, where wavelet and power spectral analyses are applied to characterize the dominant temporal and horizontal scales associated with cloud-generated vertical motions. In general, we find a positively correlated vertical motion signal amongst vertical levels within the cloud and across the full cloud layer depth. The coherency is dependent upon other non-cloud controlled factors, such as larger, mesoscale weather passages and radiative shielding of low-level stratocumulus by one or more cloud layers above. Despite the coherency in vertical velocity across the cloud, the velocity variances were always weaker near cloud top, relative to cloud middle and base. Taken in combination with the skewness, variance and thermodynamic profile characteristics, we observe vertical motions near cloud top that behave differently than those from lower within the cloud layer. Spectral analysis indicates peak cloud-generated w variance timescales slowed only modestly during decoupled cases relative to coupled; horizontal wavelengths only slightly increased when transitioning from coupling to decoupling. The similarities in scales suggests that perhaps the dominant forcing for all cases is generated from the cloud layer, and it is not the surface forcing that characterizes the time- and space scales of in-cloud vertical velocity variance. This points toward the resilient nature of Arctic mixed-phase clouds to persist when characterized by thermodynamic regimes unique to the Arctic.

Download Full-text

The efficiency of secondary organic aerosol particles to act as ice nucleating particles at mixed-phase cloud conditions

10.5194/acp-2017-1223 ◽

2018 ◽

Author(s):

Wiebke Frey ◽

Dawei Hu ◽

James Dorsey ◽

M. Rami Alfarra ◽

Aki Pajunoja ◽

...

Keyword(s):

Secondary Organic Aerosol ◽

Aerosol Particles ◽

Organic Aerosol ◽

Ice Nucleation ◽

Mixed Phase ◽

Dust Particles ◽

Ice Cloud ◽

Liquid Saturation ◽

Reference Experiment ◽

Mixed Phase Clouds

Abstract. Secondary Organic Aerosol (SOA) particles have been found to be efficient ice nucleating particles under the cold conditions of (tropical) upper tropospheric cirrus clouds. Whether they also are efficient at initiating freezing at slightly warmer conditions as found in mixed phase clouds remains undetermined. Here, we study the ice nucleating ability of photo-chemically produced SOA particles with the combination of the Manchester Aerosol and Ice Cloud Chambers. Three SOA systems were tested resembling biogenic/anthropogenic particles and particles of different phase state. After the aerosol particles were formed, they were transferred into the cloud chamber where subsequent quasi-adiabatic cloud evacuations were performed. Additionally, the ice forming abilities of ammonium sulfate and kaolinite were investigated as a reference to test the experimental setup. Clouds were formed in the temperature range of −20 °C to −28.6 °C. Only the reference experiment using dust particles showed evidence of ice nucleation. No ice particles were observed in any other experiment. Thus, we conclude that SOA particles produced under the conditions of the reported experiments are not efficient ice nucleating particles starting at liquid saturation under mixed-phase cloud conditions.

Download Full-text

Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-28845-2014 ◽

2014 ◽

Vol 14 (21) ◽

pp. 28845-28883

Author(s):

N. S. Umo ◽

B. J. Murray ◽

M. T. Baeza-Romero ◽

J. M. Jones ◽

A. R. Lea-Langton ◽

...

Keyword(s):

Hydrological Cycle ◽

Coal Fly Ash ◽

Aerosol Particles ◽

Bottom Ash ◽

Ice Nucleation ◽

Mixed Phase ◽

Dust Particles ◽

Cloud Properties ◽

Mixed Phase Clouds ◽

The Impact

Abstract. Ice nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice nucleating particles, but the ice nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

Download Full-text

On-line single particle analysis of ice particle residuals from mountain-top mixed-phase clouds using laboratory derived particle type assignment

10.5194/acp-2016-365 ◽

2016 ◽

Author(s):

S. Schmidt ◽

J. Schneider ◽

T. Klimach ◽

S. Mertes ◽

L. P. Schenk ◽

...

Keyword(s):

Single Particle ◽

Aerosol Particles ◽

Mixed Phase ◽

Particle Analysis ◽

Single Particle Analysis ◽

Particle Type ◽

Industrial Emissions ◽

Anthropogenic Aerosol ◽

Outcome Instrument ◽

Mixed Phase Clouds

Abstract. In-situ single particle analysis of ice particle residuals (IPR) and out-of-cloud aerosol particles was conducted by means of laser ablation mass spectrometry during the intensive INUIT-JFJ/CLACE campaign at the high alpine research station Jungfraujoch (3580 m a.s.l.) in January/February 2013. During the four week campaign more than 70000 out-of-cloud aerosol particles and 595 IPR were analyzed covering a particle size diameter range from 100 nm to 3 µm. The IPR were sampled during 273 hours while the station was covered by mixed-phase clouds at ambient temperatures between −27 °C and −6 °C. The identification of particle types is based on laboratory studies of different types of biological, mineral and anthropogenic aerosol particles. As outcome instrument specific marker peaks for the different investigated particle types were obtained and applied to the field data. The results show that the sampled IPR contain a larger relative amount of natural, primary aerosol, like soil dust (13 %) and minerals (11 %), in comparison to out-of-cloud aerosol particles (2 % and < 1 %, respectively). Additionally, anthropogenic aerosol particles, like particles from industrial emissions and lead-containing particles, were found to be more abundant in the IPR than in the out-of-cloud aerosol. The out-of-cloud aerosol contained a large fraction of aged particles (30 %, including organic material and secondary inorganics), whereas this particle type was much less abundant (3 %) in the IPR. In a selected subset of the data where a direct comparison between out-of-cloud aerosol particles and IPR in air masses with similar origin was possible, a pronounced enhancement of biological particles was found in the IPR.

Download Full-text

The microphysical characters of wintertime mixed-phase clouds in North China.

10.5194/egusphere-egu21-3691 ◽

2021 ◽

Author(s):

Xuexu Wu ◽

Minghuai Wang ◽

Daniel Rosenfeld ◽

Delong Zhao ◽

Deping Ding

Keyword(s):

Water Content ◽

North China ◽

Particle Number ◽

Number Concentration ◽

Mixed Phase ◽

Ice Crystals ◽

Particle Number Concentration ◽

Aggregation Process ◽

Higher Temperature ◽

Mixed Phase Clouds

We use aircraft observation data to investigate the microphysical characters of wintertime mixed-phase clouds in North China, including the cloud particle number concentration (Nc), the liquid water content (LWC), the ice particle number concentration (Ni), the ice water content (IWC), the particle spectrum distributions (PSDs) and the effective diameter (De). For wintertime mixed-phase clouds, the average Nc and Ni were 170&#177;154 cm-3 and 26&#177;39 L-1, respectively; the average LWC and IWC were 0.05&#177;0.06 and 0.07&#177;0.09g/m3, respectively; the De for cloud particles was 10&#177;4 &#956;m. When compared to the results from other regions, including East Europe, North America, Southern Ocean and Tibetan Plateau, we found that the wintertime mixed-phase cloud in North China has larger Nc, smaller LWC, IWC and De, and narrower PSDs. The main reason might be the larger aerosol loading and smaller water content in the atmosphere in winter in North China. With increasing temperature, Nc and LWC increased, but Ni and De decreased. The dominate physical processes in wintertime mixed-phase cloud were aggregation process and riming process. As the temperature increased, the peak concentration of ice PSD decreased, but Ni increased and the ice PSD became wider, indicating more ice crystals and the ice crystals became larger at higher temperature. With temperature increasing, the ice habit also changed, and the amount of plates, irregular crystals and their aggregates increased. What&#8217;s more, with the existence of larger LWC at higher temperature, the ice crystals gradually tightened and their surface became more complicated as well. Therefore, both aggregation process and riming process were more active at higher temperature, but riming process changed much more. This work fills the gap in the observation of wintertime mixed-phase clouds in north China, and the results suggest that the wintertime mixed-phase clouds have some unique microphysical characters.<div>&#160;</div>

Download Full-text