A representation of the collisional ice break-up process in the two-moment microphysics LIMA v1.0 scheme of Meso-NH

Abstract. The paper describes a switchable parameterization of collisional ice break-up (CIBU), an ice multiplication process that fits in with the two-moment microphysical Liquid Ice Multiple Aerosols (LIMA) scheme. The LIMA scheme with three ice types (pristine cloud ice crystals, snow aggregates, and graupel hail) was developed in the cloud-resolving mesoscale model (Meso-NH). Here, the CIBU parameterization assumes that collisional break-up is mostly efficient for the small and fragile snow aggregate class of particles when they are hit by large, dense graupel particles. The increase of cloud ice number concentration depends on a prescribed number (or a random number) of fragments being produced per collision. This point is discussed and analytical expressions of the newly contributing CIBU terms in LIMA are given. The scheme is run in the cloud-resolving mesoscale model (Meso-NH) to simulate a first case of a three-dimensional deep convective event with heavy production of graupel. The consequence of dramatically changing the number of fragments produced per collision is investigated by examining the rainfall rates and the changes in small ice concentrations and mass mixing ratios. Many budgets of the ice phase are shown and the sensitivity of CIBU to the initial concentration of freezing nuclei is explored. The scheme is then tested for another deep convective case where, additionally, the convective available potential energy (CAPE) is varied. The results confirm the strong impact of CIBU with up to a 1000-fold increase in small ice concentrations, a reduction of the rainfall or precipitating area, and an invigoration of the convection with higher cloud tops. Finally, it is concluded that the efficiency of the ice crystal fragmentation needs to be tuned carefully. The proposed parameterization of CIBU is easy to implement in any two-moment microphysics scheme. It could be used in this form to simulate deep tropical cloud systems where anomalously high concentrations of small ice crystals are suspected.

Download Full-text

A representation of the collisional ice break-up process in the two-moment microphysics scheme LIMA v1.0 of Meso-NH

10.5194/gmd-2017-287 ◽

2017 ◽

Author(s):

Thomas Hoarau ◽

Jean-Pierre Pinty ◽

Christelle Barthe

Keyword(s):

Mesoscale Model ◽

Convective Cloud ◽

Ice Crystals ◽

Three Dimension ◽

Microphysics Scheme ◽

Multiplication Process ◽

Break Up ◽

High Concentrations ◽

Ice Multiplication ◽

Cloud Ice

Abstract. The paper describes a switchable parameterization of CIBU (Collisional Ice Break-Up), an ice multiplication process that fits in with the two-moment microphysical scheme LIMA (Liquid Ice Multiple Aerosols). The LIMA scheme with three ice types (pristine cloud ice crystals, snowaggregates and graupel-hail) was developed in the cloud-resolving mesoscale model Meso-NH. Here the CIBU process assumes that collisional break-up is mostly efficient for small snowaggregate class of particles with a fragile structure when hit by large and dense graupel particles. The increase of cloud ice number concentration depends on a prescribed number of fragments being produced per collision. This point is discussed and analytical expressions of the newly contributing CIBU terms in LIMA are given. The scheme is run in Meso-NH for the case of a three-dimension deep convective cloud with a heavy production of graupel. The consequence of dramatically changing the number of fragments produced per collision is explored in particular to estimate an upper bound of the CIBU effect. The case of a random number of fragments is also proposed to illustrate the consequence of the uncertainty of this parameter. Finally it is concluded that the assessment of CIBU certainly needs accurate laboratory experiments to check the conditions and to tune the efficiency of the process of ice crystal fragmentation. However the proposed parameterization which can be easily implemented in many two-moment microphysics schemes, could be used in this form to simulate the case of real deep tropical clouds where anomalously high concentrations of small ice crystals are suspected to occur.

Download Full-text

Application of holography and automated image processing for laboratory experiments on mass and fall speed of small cloud ice crystals

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-14889-2020 ◽

2020 ◽

Vol 20 (23) ◽

pp. 14889-14901

Author(s):

Maximilian Weitzel ◽

Subir K. Mitra ◽

Miklós Szakáll ◽

Jacob P. Fugal ◽

Stephan Borrmann

Keyword(s):

Three Dimensional ◽

Ice Crystals ◽

Local Cooling ◽

Ice Cloud ◽

Before And After ◽

Data Points ◽

Melting Crystal ◽

Cloud Ice ◽

Automated Image Processing ◽

The Relationship

Abstract. An ice cloud chamber was developed at the Johannes Gutenberg University of Mainz for generating several thousand data points for mass and sedimentation velocity measurements of ice crystals with sizes less than 150 µm. Ice nucleation was initiated from a cloud of supercooled droplets by local cooling using a liquid nitrogen cold finger. Three-dimensional tracks of ice crystals falling through the slightly supersaturated environment were obtained from the reconstruction of sequential holographic images, automated detection of the crystals in the hologram reconstructions, and particle tracking. Through collection of the crystals and investigation under a microscope before and after melting, crystal mass was determined as a function of size. The experimentally obtained mass versus diameter (m(D)) power law relationship resulted in lower masses for small ice crystals than from commonly adopted parameterizations. Thus, they did not support the currently accepted extrapolation of relationships measured for larger crystal sizes. The relationship between Best (X) and Reynolds (Re) numbers for columnar crystals was found to be X=15.3 Re1.2, which is in general agreement with literature parameterizations.

Download Full-text

LIMA (v1.0): a two-moment microphysical scheme driven by a multimodal population of cloud condensation and ice freezing nuclei

Geoscientific Model Development Discussions ◽

10.5194/gmdd-8-7767-2015 ◽

2015 ◽

Vol 8 (9) ◽

pp. 7767-7820 ◽

Cited By ~ 1

Author(s):

B. Vié ◽

J.-P. Pinty ◽

S. Berthet ◽

M. Leriche

Keyword(s):

Mesoscale Model ◽

Cloud Condensation Nuclei ◽

Three Dimensional ◽

Single Equation ◽

Ice Crystals ◽

Growth Mode ◽

Squall Line ◽

Complex Nature ◽

Cloud Droplets ◽

Ice Clouds

Abstract. The paper describes the 2-moment microphysical scheme LIMA (Liquid Ice Multiple Aerosols), which relies on the prognostic evolution of a three-dimensional (3-D) aerosol population, and the careful description of the nucleating properties that enable cloud droplets and pristine ice crystals to form. LIMA uses the aerosol nucleating properties to form cloud droplets and pristine ice crystals. Several modes of Cloud Condensation Nuclei (CCN) and Ice Freezing Nuclei (IFN) are considered individually. A special class of partially soluble IFN is also introduced. These "aged" IFN act first as CCN and then as IFN by immersion nucleation at low temperatures. All the CCN modes are in competition with each other, as expressed by the single equation of maximum supersaturation. The IFN are insoluble aerosols that nucleate ice in several ways (condensation, deposition and immersion freezing) assuming the singular hypothesis. The scheme also includes the homogeneous freezing of cloud droplets, the Hallett–Mossop ice multiplication process and the freezing of haze at very low temperature. LIMA assumes that water vapour is in thermodynamic equilibrium with the population of cloud droplets (adjustment to saturation in warm clouds). In ice clouds, the prediction of the number concentration of the pristine ice crystals is used to compute explicit deposition and sublimation rates (leading to free under/supersaturation over ice). The formation of hydrometeors is standard. The autoconversion, accretion and self-collection processes shape the raindrop spectra. The initiation of the large crystals and aggregates category is the result of the depositional growth of large crystals beyond a critical size. Aggregation and riming are computed explicitly. Heavily rimed crystals (graupel) can experience a dry or wet growth mode. An advanced version of the scheme includes a separate hail category of particles forming and growing exclusively in the wet growth mode. The sedimentation of all particle types is included. The LIMA scheme is inserted in the cloud-resolving mesoscale model Meso-NH. The flexibility of LIMA is illustrated by two 2-D experiments. The first one highlights the sensitivity of orographic ice clouds to IFN types and IFN concentrations. Then a squall line case discusses the microstructure of a mixed-phase cloud and the impacts of pure CCN and IFN polluting plumes. The experiments show that LIMA captures the complex nature of aerosol-cloud interactions leading to different pathways for cloud and precipitation formation.

Download Full-text

Application of holography and automated image processing for laboratory experiments on mass and fall speed of small cloud ice crystals

10.5194/acp-2020-339 ◽

2020 ◽

Author(s):

Maximilian Weitzel ◽

Subir K. Mitra ◽

Miklós Szakáll ◽

Jacob P. Fugal ◽

Stephan Borrmann

Keyword(s):

Three Dimensional ◽

Ice Crystals ◽

Local Cooling ◽

Ice Cloud ◽

Before And After ◽

Data Points ◽

Melting Crystal ◽

Cloud Ice ◽

Automated Image Processing ◽

The Relationship

Abstract. An ice cloud chamber was developed at the Johannes Gutenberg University of Mainz for generating several thousand data points for mass and sedimentation velocity measurements of ice crystals with sizes less than 150 μm. Ice nucleation was initiated from a cloud of supercooled droplets by local cooling using a liquid nitrogen cold finger. Three-dimensional tracks of ice crystals falling through the slightly supersaturated environment were obtained from the reconstruction of sequential holographic images, automated detection of the crystals in the hologram reconstructions, and particle tracking. Through collection of the crystals and investigation under a microscope before and after melting, crystal mass was determined as a function of size. The experimentally obtained mass versus diameter (m(D)) power law relationship resulted in lower masses for small ice crystals than from commonly adopted parameterizations. Thus, they did not support the currently accepted extrapolation of relationships measured for larger crystal sizes. The relationship between Best (X) and Reynolds (Re) numbers for columnar crystals was found to be X = 15.3Re1.2, which is in general agreement with literature parameterizations.

Download Full-text

Secondary ice production processes in wintertime alpine mixed-phase clouds

10.5194/acp-2021-760 ◽

2021 ◽

Author(s):

Paraskevi Georgakaki ◽

Georgia Sotiropoulou ◽

Étienne Vignon ◽

Anne-Claire Billault-Roux ◽

Alexis Berne ◽

...

Keyword(s):

Mixed Phase ◽

Ice Crystals ◽

Swiss Alps ◽

Blowing Snow ◽

Production Processes ◽

Break Up ◽

Ice Production ◽

Cloud Ice ◽

Droplet Shattering ◽

Mixed Phase Clouds

Abstract. Observations of orographic mixed-phase clouds (MPCs) have long shown that measured ice crystal number concentrations (ICNCs) can exceed the concentration of ice nucleating particles by orders of magnitude. Additionally, model simulations of alpine clouds are frequently found to underestimate the amount of ice compared with observations. Surface-based blowing snow, hoar frost and secondary ice production processes have been suggested as potential causes, but their relative importance and persistence remains highly uncertain. Here we study ice production mechanisms in wintertime orographic MPCs observed during the Cloud and Aerosol Characterization Experiment (CLACE) 2014 campaign at the Jungfraujoch site in the Swiss Alps with the Weather Research and Forecasting model (WRF). Simulations suggest that droplet shattering is not a significant source of ice crystals at this specific location – but break-up upon collisions between ice particles is quite active, elevating the predicted ICNCs by up to 3 orders of magnitude, which is consistent with observations. The initiation of the ice-ice collisional break-up mechanism is primarily associated with the occurrence of seeder-feeder events from higher precipitating cloud layers. The enhanced aggregation of snowflakes is found to drive secondary ice formation in the simulated clouds, the role of which is strengthened when the large hydrometeors interact with the primary ice crystals formed in the feeder cloud. Including a constant source of cloud ice crystals from blowing snow, through the action of the break-up mechanism, can episodically enhance ICNCs. Increases in secondary ice fragment generation can be counterbalanced by enhanced orographic precipitation, which seems to prevent explosive multiplication and cloud dissipation. These findings highlight the importance of secondary ice and "seeding" mechanisms – primarily falling ice from above and to a lesser degree blowing ice from the surface – which frequently enhance primary ice and determine the phase state and properties of MPCs.

Download Full-text

Simulation and Analysis of Floodlighting Based on 3D Computer Graphics

Energies ◽

10.3390/en14041042 ◽

2021 ◽

Vol 14 (4) ◽

pp. 1042

Author(s):

Rafał Krupiński

Keyword(s):

Computer Graphics ◽

External Surface ◽

Geometric Model ◽

Three Dimensional ◽

Fold Increase ◽

Luminance Level ◽

Object Model ◽

Geometric Mesh ◽

Average Luminance ◽

To Receive

The paper presents the opportunities to apply computer graphics in an object floodlighting design process and in an analysis of object illumination. The course of object floodlighting design has been defined based on a virtual three-dimensional geometric model. The problems related to carrying out the analysis of lighting, calculating the average illuminance, luminance levels and determining the illuminated object surface area are also described. These parameters are directly tied with the calculations of the Floodlighting Utilisation Factor, and therefore, with the energy efficiency of the design as well as the aspects of light pollution of the natural environment. The paper shows how high an impact of the geometric model of the object has on the accuracy of photometric calculations. Very often the model contains the components that should not be taken into account in the photometric calculations. The research on what influence the purity of the geometric mesh of the illuminated object has on the obtained results is presented. It shows that the errors can be significant, but it is possible to optimise the 3D object model appropriately in order to receive the precise results. For the example object presented in this paper, removing the planes that do not constitute its external surface has caused a two-fold increase in the average illuminance and average luminance. This is dangerous because a designer who wants to achieve a specific average luminance level in their design without optimizing the model will obtain the luminance values that will actually be much higher.

Download Full-text

NAM Model Forecasts of Warm-Season Quasi-Stationary Frontal Environments in the Central United States

Weather and Forecasting ◽

10.1175/2010waf2222394.1 ◽

2010 ◽

Vol 25 (4) ◽

pp. 1281-1292 ◽

Cited By ~ 3

Author(s):

Shih-Yu Wang ◽

Adam J. Clark

Keyword(s):

United States ◽

Mesoscale Model ◽

Convective Available Potential Energy ◽

Warm Season ◽

Correlation Coefficients ◽

Precipitable Water ◽

Wind Fields ◽

Vapor Flux ◽

Convective Systems ◽

Central United States

Abstract Using a composite procedure, North American Mesoscale Model (NAM) forecast and observed environments associated with zonally oriented, quasi-stationary surface fronts for 64 cases during July–August 2006–08 were examined for a large region encompassing the central United States. NAM adequately simulated the general synoptic features associated with the frontal environments (e.g., patterns in the low-level wind fields) as well as the positions of the fronts. However, kinematic fields important to frontogenesis such as horizontal deformation and convergence were overpredicted. Surface-based convective available potential energy (CAPE) and precipitable water were also overpredicted, which was likely related to the overprediction of the kinematic fields through convergence of water vapor flux. In addition, a spurious coherence between forecast deformation and precipitation was found using spatial correlation coefficients. Composite precipitation forecasts featured a broad area of rainfall stretched parallel to the composite front, whereas the composite observed precipitation covered a smaller area and had a WNW–ESE orientation relative to the front, consistent with mesoscale convective systems (MCSs) propagating at a slight right angle relative to the thermal gradient. Thus, deficiencies in the NAM precipitation forecasts may at least partially result from the inability to depict MCSs properly. It was observed that errors in the precipitation forecasts appeared to lag those of the kinematic fields, and so it seems likely that deficiencies in the precipitation forecasts are related to the overprediction of the kinematic fields such as deformation. However, no attempts were made to establish whether the overpredicted kinematic fields actually contributed to the errors in the precipitation forecasts or whether the overpredicted kinematic fields were simply an artifact of the precipitation errors. Regardless of the relationship between such errors, recognition of typical warm-season environments associated with these errors should be useful to operational forecasters.

Download Full-text

Pericyte contractility controls endothelial cell cycle progression and sprouting: insights into angiogenic switch mechanics

AJP Cell Physiology ◽

10.1152/ajpcell.00185.2014 ◽

2014 ◽

Vol 307 (9) ◽

pp. C878-C892 ◽

Cited By ~ 21

Author(s):

Jennifer T. Durham ◽

Howard K. Surks ◽

Brian M. Dulmovits ◽

Ira M. Herman

Keyword(s):

Cell Cycle Progression ◽

Network Formation ◽

Rho Gtpase ◽

Three Dimensional ◽

Rho Kinase ◽

Leading Edge ◽

Fold Increase ◽

Cycle Progression ◽

Interacting Protein ◽

Angiogenic Switch

Microvascular stability and regulation of capillary tonus are regulated by pericytes and their interactions with endothelial cells (EC). While the RhoA/Rho kinase (ROCK) pathway has been implicated in modulation of pericyte contractility, in part via regulation of the myosin light chain phosphatase (MLCP), the mechanisms linking Rho GTPase activity with actomyosin-based contraction and the cytoskeleton are equivocal. Recently, the myosin phosphatase-RhoA-interacting protein (MRIP) was shown to mediate the RhoA/ROCK-directed MLCP inactivation in vascular smooth muscle. Here we report that MRIP directly interacts with the β-actin-specific capping protein βcap73. Furthermore, manipulation of MRIP expression influences pericyte contractility, with MRIP silencing inducing cytoskeletal remodeling and cellular hypertrophy. MRIP knockdown induces a repositioning of βcap73 from the leading edge to stress fibers; thus MRIP-silenced pericytes increase F-actin-driven cell spreading twofold. These hypertrophied and cytoskeleton-enriched pericytes demonstrate a 2.2-fold increase in contractility upon MRIP knockdown when cells are plated on a deformable substrate. In turn, silencing pericyte MRIP significantly affects EC cycle progression and angiogenic activation. When MRIP-silenced pericytes are cocultured with capillary EC, there is a 2.0-fold increase in EC cycle entry. Furthermore, in three-dimensional models of injury and repair, silencing pericyte MRIP results in a 1.6-fold elevation of total tube area due to EC network formation and increased angiogenic sprouting. The pivotal role of MRIP expression in governing pericyte contractile phenotype and endothelial growth should lend important new insights into how chemomechanical signaling pathways control the “angiogenic switch” and pathological angiogenic induction.

Download Full-text

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

10.5194/acp-2017-754 ◽

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.

Download Full-text

Initiation and Maintenance Mechanisms for Heavy Precipitation System over a Mountainous Island under a Prevailing Monsoon Current

Earth Science Research ◽

10.5539/esr.v5n2p90 ◽

2016 ◽

Vol 5 (2) ◽

pp. 90

Author(s):

Y.-L. Lin ◽

K.-Y. Lee ◽

C.-S. Chen ◽

F.-Y. Cheng ◽

P.-L. Lin ◽

...

Keyword(s):

Heavy Rainfall ◽

Mesoscale Model ◽

Convective Available Potential Energy ◽

Leading Edge ◽

Western Slope ◽

Mountain Range ◽

Unstable Flow ◽

Near Surface ◽

Precipitation System ◽

Early Afternoon

In this study, the initiation and maintenance mechanisms of two long-lived, summer heavy rainfall systems over Taiwan are investigated by performing observational data analyses and numerical simulations using a mesoscale model. For both cases of 9-10 July 2008 (Case A) and 18-19 August 2006 (Case B), the heavy rainfall system developed over the western slope of the Central Mountain Range (CMR) under low-level prevailing southwesterly and westerly flows in early afternoon, respectively. These heavy rainfall systems were moving westward toward Taiwan Strait from CMR, while the embedded individual cells were moving in the opposite direction, behaving like a multicell storm. It was also found these individual cells were initiated, enhanced, and then maintained at the leading edge of the near-surface cool outflow and merged with the heavy rainfall systems which became long-lived. These heavy rainfall systems were classified as an upstream propagating precipitation system in a low Froude-number, conditionally unstable flow with high convective available potential energy (CAPE) or Regime I as proposed in a previous study.

Download Full-text