scholarly journals Ice particles in stratiform clouds in the Arctic and possible mechanisms for the production of high ice concentrations

2001 ◽  
Vol 106 (D14) ◽  
pp. 15065-15075 ◽  
Author(s):  
Arthur L. Rangno ◽  
Peter V. Hobbs
Keyword(s):  
The Arctic ◽  
Ice Particles ◽  
Stratiform Clouds

Combined effect of the Weber-Bergeron-Findeisen mechanism and large eddies on microphysics of mixed-phase stratiform clouds

2021 ◽  
Author(s):  
A. Khain ◽  
M. Pinsky ◽  
A. Korolev
Keyword(s):  
Mixed Phase ◽  
Combined Effect ◽  
The Arctic ◽  
Cloud Base ◽  
Statistical Parameters ◽  
Arctic Boundary Layer ◽  
Ice Particles ◽  
Ice Concentration ◽  
Stratiform Clouds ◽  
Large Eddies

AbstractThe process of glaciation in mixed-phase stratiform clouds was investigated by a novel Lagrangian-Eulerian model (LEM) in which thousands of adjoining Lagrangian parcels moved within a turbulent-like velocity field with statistical parameters typical of the Arctic boundary layer. We used detailed bin microphysics to describe the condensation/evaporation processes in each parcel, in which droplets, aerosols, and ice particles were described using size distributions of 500 mass bins. The model also calculated aerosol mass inside droplets and ice particles. Gravitational sedimentation of droplets and ice particles was also accounted for. Assuming that droplet freezing is the primary source of ice particles, the Arctic clouds observed in ISDAC were successfully simulated. The model showed that at a low ice particle concentration typical of ISDAC, large vortices (eddies) led to a quasi-stationary regime, in which mixed-phase St existed for a long time. The large eddies controlled the water partitioning in the mixed-phase clouds. Droplets formed and grew in updrafts, typically reaching the cloud top, and evaporated in downdrafts. Ice particles grew in updrafts and downdrafts. The Wegener-Bergeron-Findeisen (WBF) mechanism was efficient in downdrafts and some parts of updrafts, depending on ice concentration and vertical velocity. At low ice concentrations, the effect of ice on the phase partitioning was negligible. In this regime, liquid droplets were found near the cloud top, whereas ice particles precipitated through the cloud base. When ice concentration exceeded about 10 per liter, the WBF mechanism led to glaciation of almost the entire cloud, with the exception of narrow cloud regions associated with strong updrafts. At ice particle concentrations of a few tens per liter, the oscillatory regime took place due to the ice-liquid interaction. The microphysical structure of mixed-phase St forms as a combined effect of cloud dynamics (large eddies) and the WBF mechanism

scholarly journals Long-lifetime ice particles in mixed-phase stratiform clouds: Quasi-steady and recycled growth

2015 ◽  
Vol 120 (22) ◽  
pp. 11,617-11,635 ◽  
Author(s):  
Fan Yang ◽  
Mikhail Ovchinnikov ◽  
Raymond A. Shaw
Keyword(s):  
Mixed Phase ◽  
Ice Particles ◽  
Stratiform Clouds ◽  
Long Lifetime

scholarly journals Arctic stratospheric dehydration – Part 1: Unprecedented observation of vertical redistribution of water

2013 ◽  
Vol 13 (22) ◽  
pp. 11503-11517 ◽  
Author(s):  
S. M. Khaykin ◽  
I. Engel ◽  
H. Vömel ◽  
I. M. Formanyuk ◽  
R. Kivi ◽  
...  
Keyword(s):  
Water Vapour ◽  
Stratospheric Ozone ◽  
Measurement Techniques ◽  
Thick Layer ◽  
Satellite Observation ◽  
The Arctic ◽  
Ice Particles ◽  
Climate Interactions ◽  
Stratospheric Clouds

Abstract. We present high-resolution measurements of water vapour, aerosols and clouds in the Arctic stratosphere in January and February 2010 carried out by in situ instrumentation on balloon sondes and high-altitude aircraft combined with satellite observations. The measurements provide unparalleled evidence of dehydration and rehydration due to gravitational settling of ice particles. An extreme cooling of the Arctic stratospheric vortex during the second half of January 2010 resulted in a rare synoptic-scale outbreak of ice polar stratospheric clouds (PSCs) remotely detected by the lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The widespread occurrence of ice clouds was followed by sedimentation and consequent sublimation of ice particles, leading to vertical redistribution of water inside the vortex. A sequence of balloon and aircraft soundings with chilled mirror and Lyman- α hygrometers (Cryogenic Frostpoint Hygrometer, CFH; Fast In Situ Stratospheric Hygrometer, FISH; Fluorescent Airborne Stratospheric Hygrometer, FLASH) and backscatter sondes (Compact Optical Backscatter Aerosol Detector, COBALD) conducted in January 2010 within the LAPBIAT (Lapland Atmosphere-Biosphere Facility) and RECONCILE (Reconciliation of Essential Process Parameters for an Enhanced Predictability of Arctic Stratospheric Ozone Loss and its Climate Interactions) campaigns captured various phases of this phenomenon: ice formation, irreversible dehydration and rehydration. Consistent observations of water vapour by these independent measurement techniques show clear signatures of irreversible dehydration of the vortex air by up to 1.6 ppmv in the 20–24 km altitude range and rehydration by up to 0.9 ppmv in a 1 km thick layer below. Comparison with space-borne Aura MLS (Microwave Limb Sounder) water vapour observations allow the spatiotemporal evolution of dehydrated air masses within the Arctic vortex to be derived and upscaled.

scholarly journals Synergistic radar and sub-millimeter radiometer retrievals of ice hydrometeors in mid-latitude frontal cloud systems

2021 ◽  
Author(s):  
Simon Pfreundschuh ◽  
Stuart Fox ◽  
Patrick Eriksson ◽  
David Duncan ◽  
Stefan A. Buehler ◽  
...  
Keyword(s):  
Climate Models ◽  
Single Scattering ◽  
Gas Absorption ◽  
The Arctic ◽  
Retrieval Algorithm ◽  
Sensor Calibration ◽  
Cloud Systems ◽  
Microphysical Properties ◽  
Ice Particles ◽  
Increased Sensitivity

Abstract. Accurate measurements of ice hydrometeors are required to improve the representation of clouds and precipitation in weather and climate models. In this study, a newly developed, synergistic retrieval algorithm that combines radar with passive millimeter and sub-millimeter observations is applied to observations of three frontally-generated, mid-latitude cloud systems in order to validate the retrieval and asses its capabilities to constrain the properties of ice hydrometeors. To account for uncertainty in the assumed shapes of ice particles, the retrieval is run multiple times while the assumed shape is varied. Good agreement with in situ measurements of ice water content and particle concentrations for particle maximum diameters larger than 200 μm is found for one of the flights for the Large Plate Aggregate and the 6-Bullet Rosette shapes. The variational retrieval fits the observations well although small systematic deviations are observed for some of the sub-millimeter pointing towards issues with the sensor calibration or the modeling of gas absorption. We find that the quality of the fit to the observations is independent of the assumed ice particle shape, indicating that the employed combination of observations is insufficient to constrain the shape of ice particles in the observed clouds. Compared to a radar-only retrieval, the results show an improved sensitivity of the synergistic retrieval to the microphysical properties of ice hydrometeors at the base of the cloud. Our findings indicate that the synergy between active and passive microwave observations improve remote-sensing measurements of ice hydrometeors and may thus help to reduce uncertainties that affect currently available data products. Due to the increased sensitivity to their microphysical properties, the retrieval may also be a valuable tool to study ice hydrometeors in field campaigns. The good fits obtained to the observations increases confidence in the modeling of clouds in the Atmospheric Radiative Transfer Simulator and the corresponding single scattering database, which were used to implement the retrieval forward model. Our results demonstrate the suitability of these tools to produce realistic simulations for upcoming sub-millimeter sensors such as the Ice Cloud Image or the Arctic Weather Satellite.

From Egg-Code to Actual Ice Field Flow Definition

2014 ◽  
Author(s):  
Solange van der Werff ◽  
Clemens van der Nat ◽  
Ed Wiersema ◽  
Gus Cammaert ◽  
Wim Jolles
Keyword(s):  
Numerical Modelling ◽  
Size Distribution ◽  
Open Water ◽  
The Arctic ◽  
Additional Parameter ◽  
Ice Particles ◽  
Starting Point ◽  
Distribution Parameters ◽  
Ice Field ◽  
Ice Floes

The Arctic Operations Handbook JIP [1] is an initiative of the Dutch offshore industry to investigate available existing standards and guidelines related to typical offshore contractor operations in Arctic conditions. The JIP identified that guidelines are required for the evaluation of the flow of ice around floating structures, and eventually to predict the resulting ice loads as input to workability studies. A pilot study called IceStream was set up as a first step towards developing guides and tools for ice flow behaviour prediction. This paper describes ice field definition and visualization as conducted within this pilot project. In the process of developing guides and tools, the objective of IceStream is to obtain a description of the geometry of an ice field, similar to open water conditions. These definitions, indicating the severity of the conditions, are needed as a basis for the determination of operational limits, and serve as an input for numerical prediction models. The ‘egg-code’ [2] principle is identified to be a good starting point when focussing on level ice, as it contains a limited but sufficient number of parameters to indicate the ice field characteristics. The applicability of the egg-code in numerical modelling is demonstrated by the development of an algorithm which translates egg-code parameters together with floe size distribution parameters into an ice field visualisation that complies with these parameters. The floe size distribution parameters are established from field observation studies. The ice field is defined by a set of ice particles, each particle represented by its area and ice thickness. Other properties (such as bending and crushing strength) can be assigned to the ice particles as well. Based on the ice field definition, Voronoi Treemapping is used to visualize the ice field. An additional parameter in this treemapping is required to indicate the distribution of ice floes over the domain (or ice cluster formation). Sea ice fields with any ice concentration between open water and 10/10th can be generated in this way. The result is an ice field consisting of random shaped (convex) ice particles with individual properties that comply with the given egg-code. The generated set of ice floes has shown to be a suitable input in the numerical modelling of an ice field approaching a floating structure.

scholarly journals Vertical Structure of Ice Clouds and Vertical Air Motion from Vertically Pointing Cloud Radar Measurements

2021 ◽  
Vol 13 (21) ◽  
pp. 4349
Author(s):  
Bo-Young Ye ◽  
GyuWon Lee
Keyword(s):  
Vertical Structure ◽  
Cirrus Clouds ◽  
Doppler Velocity ◽  
Upward Motion ◽  
Fall Velocity ◽  
Ice Clouds ◽  
Cloud Radar ◽  
Ice Particles ◽  
Stratiform Clouds ◽  
Air Motion

The vertical structure of ice clouds and vertical air motion (Vair) were investigated using vertically pointing Ka-band cloud radar. The distributions of reflectivity (Z), Doppler velocity (VD), and spectrum width (SW) were analyzed for three ice cloud types, namely, cirrus, anvil, and stratiform clouds. The radar parameters of the cirrus clouds showed narrower distributions than those of the stratiform and anvil clouds. In the vertical structures, the rapid growth of Z and VD occurred in the layer between 8 and 12 km (roughly a layer of −40 °C to −20 °C) for all ice clouds. The prominent feature in the stratiform clouds was an elongated “S” shape in the VD near 7–7.5 km (at approximately −16 °C to −13 °C) due to a significant decrease in an absolute value of VD. The mean terminal fall velocity (Vt) and Vair in the ice clouds were estimated using pre-determined Vt–Z relationships (Vt = aZb) and the observed VD. Although the cirrus clouds demonstrated wide distributions in coefficients a and exponents b depending on cloud heights, they showed a smaller change in Z and Vt values compared to that of the other cloud types. The anvil clouds had a larger exponent than that of the stratiform clouds, indicating that the ice particle density of anvil clouds increases at a faster rate compared with the density of stratiform clouds for the same Z increment. The significant positive Vair appeared at the top of all ice clouds in range up to 0.5 m s−1, and the anvil clouds showed the deepest layer of upward motion. The stratiform and anvil clouds showed a dramatic increase in vertical air motion in the layer of 6–8 km as shown by the rapid decrease of VD. This likely caused increase of supersaturation above. A periodic positive Vair linked with a significant reduction in VD appeared at the height of 7–8 km (approximately −15 °C) dominantly in the stratiform clouds. This layer exhibited a bi-modal power spectrum produced by pre-existing larger ice particles and newly formed numerous smaller ice particles. This result raised a question on the origins of smaller ice particles such as new nucleation due to increased supersaturation by upward motion below or the seeder-feeder effect. In addition, the retrieved Vair with high-resolution data well represented a Kelvin-Helmholtz wave development.

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 Impact of particle shape on the morphology of noctilucent clouds

2015 ◽  
Vol 15 (22) ◽  
pp. 12897-12907 ◽  
Author(s):  
J. Kiliani ◽  
G. Baumgarten ◽  
F.-J. Lübken ◽  
U. Berger
Keyword(s):  
Particle Shape ◽  
Middle Atmosphere ◽  
Mass Density ◽  
Optical Measurements ◽  
The Arctic ◽  
Noctilucent Clouds ◽  
Axis Ratio ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Ice Particles

Abstract. Noctilucent clouds (NLCs) occur during summer in the polar region at altitudes around 83 km. They consist of ice particles with a typical size around 50 nm. The shape of NLC particles is less well known but is important both for interpreting optical measurements and modeling ice cloud characteristics. In this paper, NLC modeling of microphysics and optics is adapted to use cylindrical instead of spherical particle shape. The optical properties of the resulting ice clouds are compared directly to NLC three-color measurements by the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) Rayleigh/Mie/Raman (RMR) lidar between 1998 and 2014. Shape distributions including both needle- and disc-shaped particles are consistent with lidar measurements. The best agreement occurs if disc shapes are 60 % more common than needles, with a mean axis ratio of 2.8. Cylindrical particles cause stronger ice clouds on average than spherical shapes with an increase of backscatter at 532 nm by &amp;approx; 30 % and about 20 % in ice mass density. This difference is less pronounced for bright than for weak ice clouds. Cylindrical shapes also cause NLCs to have larger but a smaller number of ice particles than for spherical shapes.

scholarly journals Arctic Mixed-Phase Cloud Properties from AERI Lidar Observations: Algorithm and Results from SHEBA

2005 ◽  
Vol 44 (4) ◽  
pp. 427-444 ◽  
Author(s):  
D. D. Turner
Keyword(s):  
Liquid Water ◽  
Heat Budget ◽  
Single Layer ◽  
Precipitable Water ◽  
Mixed Phase ◽  
The Arctic ◽  
Retrieval Algorithm ◽  
Cloud Optical Depth ◽  
Microphysical Properties ◽  
Ice Particles

Abstract A new approach to retrieve microphysical properties from mixed-phase Arctic clouds is presented. This mixed-phase cloud property retrieval algorithm (MIXCRA) retrieves cloud optical depth, ice fraction, and the effective radius of the water and ice particles from ground-based, high-resolution infrared radiance and lidar cloud boundary observations. The theoretical basis for this technique is that the absorption coefficient of ice is greater than that of liquid water from 10 to 13 μm, whereas liquid water is more absorbing than ice from 16 to 25 μm. MIXCRA retrievals are only valid for optically thin (τvisible &lt; 6) single-layer clouds when the precipitable water vapor is less than 1 cm. MIXCRA was applied to the Atmospheric Emitted Radiance Interferometer (AERI) data that were collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment from November 1997 to May 1998, where 63% of all of the cloudy scenes above the SHEBA site met this specification. The retrieval determined that approximately 48% of these clouds were mixed phase and that a significant number of clouds (during all 7 months) contained liquid water, even for cloud temperatures as low as 240 K. The retrieved distributions of effective radii for water and ice particles in single-phase clouds are shown to be different than the effective radii in mixed-phase clouds.

scholarly journals Lagrangian simulation of ice particles and resulting dehydration in the polar winter stratosphere

2019 ◽  
Vol 19 (1) ◽  
pp. 543-563 ◽  
Author(s):  
Ines Tritscher ◽  
Jens-Uwe Grooß ◽  
Reinhold Spang ◽  
Michael C. Pitts ◽  
Lamont R. Poole ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Michelson Interferometer ◽  
Ice Nucleation ◽  
The Arctic ◽  
Orthogonal Polarization ◽  
Satellite Orbits ◽  
Lagrangian Simulation ◽  
Ice Particles ◽  
The Antarctic ◽  
Good Agreement

Abstract. Polar stratospheric clouds (PSCs) and cold stratospheric aerosols drive heterogeneous chemistry and play a major role in polar ozone depletion. The Chemical Lagrangian Model of the Stratosphere (CLaMS) simulates the nucleation, growth, sedimentation, and evaporation of PSC particles along individual trajectories. Particles consisting of nitric acid trihydrate (NAT), which contain a substantial fraction of the stratospheric nitric acid (HNO3), were the focus of previous modeling work and are known for their potential to denitrify the polar stratosphere. Here, we carried this idea forward and introduced the formation of ice PSCs and related dehydration into the sedimentation module of CLaMS. Both processes change the simulated chemical composition of the lower stratosphere. Due to the Lagrangian transport scheme, NAT and ice particles move freely in three-dimensional space. Heterogeneous NAT and ice nucleation on foreign nuclei as well as homogeneous ice nucleation and NAT nucleation on preexisting ice particles are now implemented into CLaMS and cover major PSC formation pathways. We show results from the Arctic winter 2009/2010 and from the Antarctic winter 2011 to demonstrate the performance of the model over two entire PSC seasons. For both hemispheres, we present CLaMS results in comparison to measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), and the Microwave Limb Sounder (MLS). Observations and simulations are presented on season-long and vortex-wide scales as well as for single PSC events. The simulations reproduce well both the timing and the extent of PSC occurrence inside the entire vortex. Divided into specific PSC classes, CLaMS results show predominantly good agreement with CALIOP and MIPAS observations, even for specific days and single satellite orbits. CLaMS and CALIOP agree that NAT mixtures are the first type of PSC to be present in both winters. NAT PSC areal coverages over the entire season agree satisfactorily. However, cloud-free areas, next to or surrounded by PSCs in the CALIOP data, are often populated with NAT particles in the CLaMS simulations. Looking at the temporal and vortex-averaged evolution of HNO3, CLaMS shows an uptake of HNO3 from the gas into the particle phase which is too large and happens too early in the simulation of the Arctic winter. In turn, the permanent redistribution of HNO3 is smaller in the simulations than in the observations. The Antarctic model run shows too little denitrification at lower altitudes towards the end of the winter compared to the observations. The occurrence of synoptic-scale ice PSCs agrees satisfactorily between observations and simulations for both hemispheres and the simulated vertical redistribution of water vapor (H2O) is in very good agreement with MLS observations. In summary, a conclusive agreement between CLaMS simulations and a variety of independent measurements is presented.

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