scholarly journals Multiyear statistics of columnar ice production in stratiform clouds over Hyytiälä, Finland

2021 ◽  
Author(s):  
Haoran Li ◽  
Ottmar Möhler ◽  
Tuukka Petäjä ◽  
Dmitri Moisseev
Keyword(s):  
Single Layer ◽  
Number Concentration ◽  
Ice Crystals ◽  
Liquid Water Path ◽  
Ice Particles ◽  
Stratiform Clouds ◽  
Shallow Clouds ◽  
Linear Depolarization Ratio ◽  
Generation Mechanisms ◽  
Ice Production

Abstract. Formation of ice particles in clouds at the temperatures of −10 °C or warmer was documented by using ground-based remote sensing observations. At these temperatures, the number concentration of ice nucleating particles (INP) is not only expected to be small, but also this number is highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations, indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify the formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiälä station for more than two years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, spectral LDR was utilized to identify newly formed ice particles. Our results indicate that that the columnar ice production took place in 5 to 13 % of clouds, where cloud top temperatures were −12 °C or higher. For colder clouds, this percentage can be as high as 33 %. 40 ~ 50 % of columnar-ice-producing events last less than 1 hour, while 5 ~ 15 % can persist for more than 6 hours. By comparing clouds where columnar crystals were produced with the ones where these crystals were absent, we found that the columnar-ice-producing clouds tend to have larger values of liquid water path and precipitation intensity. The columnar-ice-producing clouds were subdivided into subcategories, using the temperature difference, Δ T, between the altitudes where columns are first detected and the cloud top altitude. The cases where Δ T  is less than 2 °C are typically single-layer shallow clouds where needles are produced at the cloud top. In multilayered clouds, where Δ T > 2 °C, columns are produced in a layer that is seeded by ice particles falling from above. This classification allows to study potential impacts of various SIP mechanisms, such as Hallet-Mossop process or freezing breakup, on columnar ice production. To answer the question whether the observed ice particles are generated by SIP in the observed single-layer shallow clouds, ice particle number concentrations were retrieved and compared to several INP parameterizations. It was found that the ice number concentrations tend to be 1 ~ 3 orders of magnitude higher than the expected INP concentrations.

scholarly journals Two-year statistics of columnar-ice production in stratiform clouds over Hyytiälä, Finland: environmental conditions and the relevance to secondary ice production

2021 ◽  
Vol 21 (19) ◽  
pp. 14671-14686
Author(s):  
Haoran Li ◽  
Ottmar Möhler ◽  
Tuukka Petäjä ◽  
Dmitri Moisseev
Keyword(s):  
Single Layer ◽  
Number Concentration ◽  
Ice Crystals ◽  
Liquid Water Path ◽  
Ice Particles ◽  
Stratiform Clouds ◽  
Shallow Clouds ◽  
Linear Depolarization Ratio ◽  
Generation Mechanisms ◽  
Ice Production

Abstract. Formation of ice particles in clouds at temperatures of −10 ∘C or warmer was documented by using ground-based radar observations. At these temperatures, the number concentration of ice-nucleating particles (INPs) is not only expected to be small, but this number is also highly uncertain. In addition, there are a number of studies reporting that the observed number concentration of ice particles exceeds expected INP concentrations, indicating that other ice generation mechanisms, such as secondary ice production (SIP), may play an important role in such clouds. To identify formation of ice crystals and report conditions in which they are generated, W-band cloud radar Doppler spectra observations collected at the Hyytiälä station for more than 2 years were used. Given that at these temperatures ice crystals grow mainly as columns, which have distinct linear depolarization ratio (LDR) values, the spectral LDR was utilized to identify newly formed ice particles. It is found that in 5 %–13 % of clouds, where cloud top temperatures are −12 ∘C or warmer, production of columnar ice is detected. For colder clouds, this percentage can be as high as 33 %; 40 %–50 % of columnar-ice-producing events last less than 1 h, while 5 %–15 % can persist for more than 6 h. By comparing clouds where columnar crystals are produced and to the ones where these crystals are absent, the columnar-ice-producing clouds tend to have larger values of liquid water path and precipitation intensity. The columnar-ice-producing clouds were subdivided into three categories, using the temperature difference, ΔT, between the altitudes where columns are first detected and cloud top. The cases where ΔT is less than 2 K are typically single-layer shallow clouds where needles are produced at the cloud top. In multilayered clouds where 2 K < ΔT, columns are produced in a layer that is seeded by ice particles falling from above. This classification allows us to study potential impacts of various SIP mechanisms, such as the Hallet–Mossop process or freezing breakup, on columnar-ice production. To answer the question whether the observed ice particles are generated by SIP in the observed single-layer shallow clouds, ice particle number concentrations were retrieved and compared to several INP parameterizations. It was found that the ice number concentrations tend to be 1–3 orders of magnitude higher than the expected INP concentrations.

scholarly journals Some effects of ice crystals on the FSSP measurements in mixed phase clouds

2012 ◽  
Vol 12 (19) ◽  
pp. 8963-8977 ◽  
Author(s):  
G. Febvre ◽  
J.-F. Gayet ◽  
V. Shcherbakov ◽  
C. Gourbeyre ◽  
O. Jourdan
Keyword(s):  
Particle Size ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Crystal Surfaces ◽  
Hexagonal Ice ◽  
Ice Particles ◽  
Second Mode ◽  
Ice Production ◽  
Bulk Parameters ◽  
Mixed Phase Clouds

Abstract. In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD). The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the FSSP) and the concentration of (natural) ice particles (CPI data). In mixed cloud, a simple estimation of the number of ice crystals impacting the FSSP inlet shows that the ice crystal shattering effect is the main factor in observed ice production.

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

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.

Secondary Ice Production – development of a new experimental set-up

2021 ◽  
Author(s):  
Susan Hartmann ◽  
Alice Keinert ◽  
Alexei Kiselev ◽  
Frank Stratmann
Keyword(s):  
Particle Number ◽  
Number Concentration ◽  
Mixed Phase ◽  
Sugar Solution ◽  
Particle Number Concentration ◽  
Ice Particles ◽  
Thin Carbon ◽  
Set Up ◽  
Ice Production ◽  
Mixed Phase Clouds

&lt;p&gt;Mixed-phase clouds are essential elements in Earth&amp;#8217;s weather and climate system. Aircraft measurements of mixed-phase clouds demonstrated a strong discrepancy between the observed ice particle and ice nucleating particle number concentration of one to four orders of magnitude [1-4]. Different secondary ice production (SIP) mechanisms have been hypothesized which can increase the total ice particle number concentration by multiplication of primary ice particles and hence might explain the observed discrepancy [5-7].&lt;/p&gt;&lt;p&gt;In a joint project of KIT and Tropos, we focus on the investigation two SIP processes: shattering of large freezing droplets (KIT) and SIP as a result of droplet-ice collisions (Tropos), commonly known as Hallett-Mossop [9] or rime-splintering process. Thereby, we aim at a quantitative understanding of the SIP underlying physical mechanisms, utilizing a newly developed experimental set-up (Ice Droplets splintEring on FreezIng eXperiment, IDEFIX). &amp;#160;&lt;/p&gt;&lt;p&gt;IDEFIX is based on a modular concept and consists of three modules, i.e., the SIP chamber, the growth section, and the ice particle detector. We developed two different versions of the SIP chamber: in the KIT-SIP chamber a freezing drizzle droplet is levitated in electrodynamic balance; and in the TROPOS-SIP chamber quasi-monodisperse droplets collide with an ice particle which is fixed on thin carbon fibers. IDEFIX is designed to match realistic fall or impact velocities and collision rates of the droplets with the ice particle. The SIP process will be observed with high-speed video microscopy and an infrared measuring system. In the growth section, which features supersaturated conditions with respect to ice, the presumably small secondarily produced ice particles will be grown to detectable sizes. Finally, to count the number of secondarily produced ice particles either an optical particle spectrometer will be used for distinguishing between droplets and ice particles, or the ice particles will be impacted on a metastable sugar solution. Currently, we characterize velocity, temperature and humidity fields of the TROPOS-collision chamber and determine droplet-ice particle collision rates.&lt;/p&gt;

scholarly journals A new look at the environmental conditions favorable to secondary ice production

2019 ◽  
Author(s):  
Alexei Korolev ◽  
Ivan Heckman ◽  
Mengistu Wolde ◽  
Andrew S. Ackerman ◽  
Ann M. Fridlind ◽  
...  
Keyword(s):  
Ice Crystals ◽  
Liquid Drops ◽  
Melting Layer ◽  
Convective Systems ◽  
Spatially Correlated ◽  
Ice Particles ◽  
Mesoscale Convective ◽  
In Situ Observations ◽  
Ice Production

Abstract. This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals (hexagonal plates or columns) with characteristic sizes smaller than 100 μm. Due to their young age, such small ice crystals can be used as tracers for identifying the conditions for SIP. Observations reported here were conducted in oceanic tropical mesoscale convective systems (MCS) and mid-latitude frontal clouds in the temperature range from 0 °C to −15 °C heavily seeded by aged ice particles. It was found that both in MCSs and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. It is proposed that the initiation of SIP above the melting layer is related to the circulation of liquid drops through the melting layer. Liquid drops formed via melting ice particles are advected by the convective updrafts above the melting layer, where they impact with aged ice, freeze and shatter. The ice splinters generated by shattering initiate the chain reaction of SIP. The size of the splinters generated during SIP were estimated as 10 μm or less. In most SIP cases, small secondary ice particles spatially correlated with liquid phase, vertical updrafts and aged rimed ice particles. However, in many cases neither graupel nor liquid drops were observed in the SIP regions, and therefore, the conditions for an active Hallett-Mossop process were not met. A principal conclusion of this work is that the freezing drop shattering mechanism is alone among established SIP mechanisms is plausibly accounting for the measured ice concentrations in the observed conditions. No other SIP mechanisms could be confidently identified from the airborne in-situ observations.

scholarly journals Observations of cloud microphysics and ice formation during COPE

2016 ◽  
Vol 16 (2) ◽  
pp. 799-826 ◽  
Author(s):  
J. W. Taylor ◽  
T. W. Choularton ◽  
A. M. Blyth ◽  
Z. Liu ◽  
K. N. Bower ◽  
...  
Keyword(s):  
Vapour Deposition ◽  
Cell Formation ◽  
Cloud Microphysics ◽  
Ice Crystals ◽  
Convective Precipitation ◽  
Cumulus Clouds ◽  
Ice Particles ◽  
Early Afternoon ◽  
Ice Production ◽  
The Uk

Abstract. We present microphysical observations of cumulus clouds measured over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) in August 2013, which are framed into a wider context using ground-based and airborne radar measurements. Two lines of cumulus clouds formed in the early afternoon along convergence lines aligned with the peninsula. The lines became longer and broader during the afternoon due to new cell formation and stratiform regions forming downwind of the convective cells. Ice concentrations up to 350 L−1, well in excess of the expected ice nuclei (IN) concentrations, were measured in the mature stratiform regions, suggesting that secondary ice production was active. Detailed sampling focused on an isolated liquid cloud that glaciated as it matured to merge with a band of cloud downwind. In the initial cell, drizzle concentrations increased from  ∼ 0.5 to  ∼ 20 L−1 in around 20 min. Ice concentrations developed up to a few per litre, which is around the level expected of primary IN. The ice images were most consistent with freezing drizzle, rather than smaller cloud drops or interstitial IN forming the first ice. As new cells emerged in and around the cloud, ice concentrations up to 2 orders of magnitude higher than the predicted IN concentrations developed, and the cloud glaciated over a period of 12–15 min. Almost all of the first ice particles to be observed were frozen drops, while vapour-grown ice crystals were dominant in the latter stages. Our observations are consistent with the production of large numbers of small secondary ice crystals/fragments, by a mechanism such as Hallett–Mossop or droplets shattering upon freezing. Some of the small ice froze drizzle drops on contact, while others grew more slowly by vapour deposition. Graupel and columns were seen in cloud penetrations up to the −12 °C level, though many ice particles were mixed habit due to riming and growth by vapour deposition at multiple temperatures. Our observations demonstrate that the freezing of drizzle/raindrops is an important process that dominates the formation of large ice in the intermediate stages of cloud development. As these frozen drops were the first precipitation observed, interactions between the warm-rain and secondary ice production processes appear to be key to determining the timing and location of precipitation.

scholarly journals Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions

2021 ◽  
Vol 21 (5) ◽  
pp. 3855-3870
Author(s):  
Annika Lauber ◽  
Jan Henneberger ◽  
Claudia Mignani ◽  
Fabiola Ramelli ◽  
Julie T. Pasquier ◽  
...  
Keyword(s):  
Number Concentration ◽  
Ice Crystals ◽  
Radiation Budget ◽  
Ice Crystal ◽  
High Concentration ◽  
Melting Layer ◽  
Mountainous Regions ◽  
Order Of Magnitude ◽  
Ice Production ◽  
Droplet Fragmentation

Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between −3 and −8 ∘C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 ∘C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.

scholarly journals Continuous secondary ice production initiated by updrafts through the melting layer in mountainous regions

2020 ◽  
Author(s):  
Annika Lauber ◽  
Jan Henneberger ◽  
Claudia Mignani ◽  
Fabiola Ramelli ◽  
Julie T. Pasquier ◽  
...  
Keyword(s):  
Number Concentration ◽  
Ice Crystals ◽  
Radiation Budget ◽  
Ice Crystal ◽  
High Concentration ◽  
Melting Layer ◽  
Mountainous Regions ◽  
Ice Production ◽  
Droplet Fragmentation ◽  
Precipitation Formation

Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice nucleating particle concentration in clouds. The Hallett-Mossop process is active between −3 °C and −8 °C and has been implemented into several models while all other secondary ice processes are poorly constrained and lack a well-founded quantification. During two hours of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 °C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at high temperatures when primary ice nucleation is basically absent and the first ice is initiated by collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary ice crystals when it fragments upon freezing. The application of the parametrization to our measurements shows high uncertainties, but the estimated number of splinters produced per fragmenting droplet (18–43) lies within the range of uncertainty if we assume that all droplets larger than 40 µm fragment when they freeze.

scholarly journals Probing ice clouds by broadband mid-infrared extinction spectroscopy: case studies from ice nucleation experiments in the AIDA aerosol and cloud chamber

2006 ◽  
Vol 6 (12) ◽  
pp. 4775-4800 ◽  
Author(s):  
R. Wagner ◽  
S. Benz ◽  
O. Möhler ◽  
H. Saathoff ◽  
U. Schurath
Keyword(s):  
Size Distribution ◽  
Particle Number ◽  
Ice Nucleation ◽  
Number Concentration ◽  
Cloud Chamber ◽  
Ice Crystals ◽  
Ice Clouds ◽  
Number Size Distribution ◽  
Ice Particles ◽  
Infrared Extinction

Abstract. Series of infrared extinction spectra of ice crystals were recorded in the 6000–800 cm−1 wavenumber regime during expansion cooling experiments in the large aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe. Either supercooled sulphuric acid solution droplets or dry mineral dust particles were added as seed aerosols to initiate ice formation after having established ice supersaturated conditions inside the chamber. The various ice nucleation runs were conducted at temperatures between 237 and 195 K, leading to median sizes of the nucleated ice particles of 1–15 µm. The measured infrared spectra were fitted with reference spectra from T-matrix calculations to retrieve the number concentration as well as the number size distribution of the generated ice clouds. The precise evaluation of the time-dependent ice particle number concentrations, i.e., the rates of new ice particle formation, is of particular importance to quantitatively analyse the ice nucleation experiments in terms of nucleation rates and ice activation spectra. The ice particles were modelled as finite circular cylinders with aspect ratios ranging from 0.5 to 3.0. Benefiting from the comprehensive diagnostic tools for the characterisation of ice clouds which are available at the AIDA facility, the infrared retrieval results with regard to the ice particle number concentration could be compared to independent measurements with various optical particle counters. This provided a unique chance to quantitatively assess potential errors or solution ambiguities in the retrieval procedure which mainly originate from the difficulty to find an appropriate shape representation for the aspherical particle habits of the ice crystals. Based on these inter-comparisons, we demonstrate that there is no standard retrieval approach which can be routinely applied to all different experimental scenarios. In particular, the concept to account for the asphericity of the ice crystals, the a priori constraints which might be imposed on the unknown number size distribution of the ice crystals (like employing an analytical distribution function), and the wavenumber range which is included in the fitting algorithm should be carefully adjusted to each single retrieval problem.

scholarly journals A new look at the environmental conditions favorable to secondary ice production

2020 ◽  
Vol 20 (3) ◽  
pp. 1391-1429 ◽  
Author(s):  
Alexei Korolev ◽  
Ivan Heckman ◽  
Mengistu Wolde ◽  
Andrew S. Ackerman ◽  
Ann M. Fridlind ◽  
...  
Keyword(s):  
Ice Crystals ◽  
Liquid Drops ◽  
Melting Layer ◽  
Convective Systems ◽  
Spatially Correlated ◽  
Ice Particles ◽  
Mesoscale Convective ◽  
In Situ Observations ◽  
Ice Production

Abstract. This study attempts a new identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals (hexagonal plates or columns) with typical sizes smaller than 100 µm. Due to their young age, such small ice crystals can be used as tracers for identifying the conditions for SIP. Observations reported here were conducted in oceanic tropical mesoscale convective systems (MCSs) and midlatitude frontal clouds in the temperature range from 0 to −15 ∘C and heavily seeded by aged ice particles. It was found that in both MCSs and frontal clouds, SIP was observed right above the melting layer and extended to higher altitudes with colder temperatures. The roles of six possible mechanisms to generate the SIP particles are assessed using additional observations. In most observed SIP cases, small secondary ice particles spatially correlated with liquid-phase, vertical updrafts and aged rimed ice particles. However, in many cases, neither graupel nor liquid drops were observed in the SIP regions, and therefore, the conditions for an active Hallett–Mossop process were not met. In many cases, large concentrations of small pristine ice particles were observed right above the melting layer, starting at temperatures as warm as −0.5 ∘C. It is proposed that the initiation of SIP above the melting layer is stimulated by the recirculation of large liquid drops through the melting layer with convective turbulent updrafts. After re-entering a supercooled environment above the melting layer, they impact with aged ice, freeze, and shatter. The size of the splinters generated during SIP was estimated as 10 µm or less. A principal conclusion of this work is that only the freezing-drop-shattering mechanism could be clearly supported by the airborne in situ observations.

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