New Empirical Formulation for the Sublimational Breakup of Graupel and Dendritic Snow

2021 ◽  
Author(s):  
Akash Deshmukh ◽  
Vaughan T. J. Phillips ◽  
Aaron Bansemer ◽  
Sachin Patade ◽  
Deepak Waman
Keyword(s):  
Dynamic Equilibrium ◽  
Thought Experiment ◽  
Atmospheric Model ◽  
Scaling Analysis ◽  
Quasi Equilibrium ◽  
Ice Particles ◽  
Ice Multiplication ◽  
Bin Microphysics ◽  
Ice Production ◽  
New Formulation

AbstractIce fragments are generated by sublimation of ice particles in subsaturated conditions in natural clouds. Conceivably, such sublimational breakup would be expected to cause ice multiplication in natural clouds. Any fragment that survives will grow to become ice precipitation that may sublimate and fragment further.As a first step towards assessing this overlooked process, a formulation is proposed for the number of ice fragments from sublimation of ice particles for an atmospheric model. This is done by amalgamating laboratory observations from previously published studies. The concept of a ‘sublimated mass activity spectrum’ for the breakup is applied to the dataset. The number of ice fragments is determined by the relative humidity over ice and the initial size of the parent ice particles. The new formulation applies to dendritic crystals and heavily rimed particles only.Finally, a thought experiment is performed for an idealized scenario of subsaturation with in-cloud descent. Scaling analysis yields an estimate of an ice enhancement ratio of about 5 (50) within a weak deep convective downdraft of about 2 m s-1, for an initial monodisperse population of dendritic snow (graupel) particles of 3 L-1 and 2 mm . During descent, there is a dynamic equilibrium between continual emission of fragments and their depletion by sublimation. A simplified bin microphysics parcel model exhibits this dynamical quasi-equilibrium, consistent with the thought experiment. The fragments have average lifetimes of around 90 and 240 seconds for dendrites and graupel respectively. Sublimational breakup is predicted to cause significant secondary ice production.

The Microphysics of Ice and Precipitation Development in Tropical Cumulus Clouds

2015 ◽  
Vol 72 (6) ◽  
pp. 2429-2445 ◽  
Author(s):  
R. Paul Lawson ◽  
Sarah Woods ◽  
Hugh Morrison
Keyword(s):  
High Speed ◽  
Cloud Model ◽  
Supercooled Liquid ◽  
High Speed Photography ◽  
Cumulus Clouds ◽  
Cloud Particle ◽  
Ice Particles ◽  
Aircraft Observations ◽  
Bin Microphysics ◽  
Ice Production

Abstract The rapid glaciation of tropical cumulus clouds has been an enigma and has been debated in the literature for over 60 years. Possible mechanisms responsible for the rapid freezing have been postulated, but until now direct evidence has been lacking. Recent high-speed photography of electrostatically suspended supercooled drops in the laboratory has shown that freezing events produce small secondary ice particles. Aircraft observations from the Ice in Clouds Experiment–Tropical (ICE-T), strongly suggest that the drop-freezing secondary ice production mechanism is operating in strong, tropical cumulus updraft cores. The result is the production of small ice particles colliding with large supercooled drops (hundreds of microns up to millimeters in diameter), producing a cascading process that results in rapid glaciation of water drops in the updraft. The process was analyzed from data collected using state-of-the-art cloud particle probes during 54 Learjet penetrations of strong cumulus updraft cores over open ocean in a temperature range from 5° to −20°C. Repeated Learjet penetrations of an updraft core containing 3–5 g m−3 supercooled liquid showed an order-of-magnitude decrease in liquid mass concentration 3 min later at an elevation 1–1.5 km higher in the cloud. The aircraft observations were simulated using a one-dimensional cloud model with explicit bin microphysics. The model was initialized with drop and ice particle size distributions observed prior to rapid glaciation. Simulations show that the model can explain the observed rapid glaciation by the drop-freezing secondary ice production process and subsequent riming, which results when large supercooled drops collide with ice particles.

scholarly journals Cloud Conditions Favoring Secondary Ice Particle Production in Tropical Maritime Convection

2014 ◽  
Vol 71 (12) ◽  
pp. 4500-4526 ◽  
Author(s):  
Andrew Heymsfield ◽  
Paul Willis
Keyword(s):  
Liquid Water ◽  
Particle Production ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Virgin Islands ◽  
Complex Interactions ◽  
Ice Particles ◽  
Ice Multiplication ◽  
The Many ◽  
Ice Production

Abstract Progress in understanding the formation of ice in lower-tropospheric clouds is slowed by the difficulties in characterizing the many complex interactions that lead to ice initiation and to the dynamic, non-steady-state nature of the clouds. The present study characterizes the conditions where secondary ice particles, specifically identified as needle or thin columnar types, are observed in tropical maritime convection with modest liquid water contents during the Ice in Clouds Experiment-Tropical (ICE-T), based out of St. Croix, U.S. Virgin Islands, and the NASA African Monsoon Multidisciplinary Analyses (NAMMA) in 2006 sampling from Cape Verde, Africa. The properties of the cloud droplet populations relevant to the secondary ice production process and the ice particle populations are characterized as a function of temperature and vertical velocity. These secondary ice particles are observed primarily in regions of low liquid water content and weak vertical velocities. Two situations are examined in detail. First, ice formation is examined by following the tops of a group of ICE-T chimney clouds as they ascend and cool from a temperature of +7° to −8°C, examining the production of the first ice. Then, using the data from a cloud system sampled during NAMMA, the authors elucidate a process that promotes ice multiplication. The intention is that this study will lead both to a better understanding of how secondary ice production proceeds in natural clouds and to more realistic laboratory studies of the processes involved.

A laboratory and model investigation of secondary ice production during to supercooled drop collisions with ice surfaces 

2021 ◽  
Author(s):  
Paul Connolly ◽  
Rachel James ◽  
Vaughan Phillips
Keyword(s):  
Laboratory Data ◽  
Ice Formation ◽  
Atmospheric Sciences ◽  
Ice Particles ◽  
Cold Room ◽  
Mode 2 ◽  
Rain Drops ◽  
Break Up ◽  
Ice Surfaces ◽  
Ice Production

<p>This work presents new laboratory data investigating collisions between supercooled drops and ice particles as a source of secondary ice particles in natural clouds. Furthermore we present numerical model simulations to put the laboratory measurements into context.</p><p>Secondary ice particles form during the breakup of freezing drops due to so-called “spherical freezing” (or Mode 1), where an ice shell forms around the freezing drop. This process has been studied and observed for drops in free-fall in laboratory experiments since the 1960s, and also more recently by Lauber et al. (2018) with a high-speed camera. Aircraft field measurements (Lawson et al. 2015) and lab data (Kolomeychuk et al. 1975) suggest that such a process is dependent on the size of drops, with larger drops being more effective at producing secondary ice.  Collision induced break-up of rain drops has been well studied with pioneering investigations in the mid-1980s, and numerous modelling studies showing that it is responsible for observed trimodal rain drop size distributions in the atmosphere, which can be well approximated by an exponential distribution.</p><p> </p><p>In mixed-phase clouds we know that rain-drops can collide with more massive ice particles. This, depending on the type of collision, may lead to the break-up of the supercooled drop (e.g. as hinted by Latham and Warwicker, 1980), potentially stimulating secondary ice formation (Phillips et al. 2018 - non-spherical, Mode 2).  There is a dearth of laboratory data investigating this mechanism.  This mechanism is the focus of the presentation.</p><p>Here we present the results of recent experiments where we make use of the University of Manchester (UoM) cold room facility. The UoM cold room facility consists of 3 stacked cold rooms that can be cooled to temperatures below -55 degC. A new facility has been built to study secondary ice production via Mode 2 fragmentation. We generate supercooled drops at the top of the cold rooms and allow them to interact with different ice surfaces near the bottom. This interaction is filmed with a new camera setup.</p><p>Our latest results will be presented at the conference.</p><p>References</p><p>Kolomeychuk, R. J., D. C. McKay, and J. V. Iribarne. 1975. “The Fragmentation and Electrification of Freezing Drops.” <em>Journal of the Atmospheric Sciences</em> 32 (5): 974–79. https://doi.org/10.1175/1520-0469(1975)032<0974>2.0.CO;2.</p><p>Latham, J., and R. Warwicker. 1980. “Charge Transfer Accompanying the Splashing of Supercooled Raindrops on Hailstones.” Quarterly Journal of the Royal Meteorological Society 106 (449): 559–68. https://doi.org/10.1002/qj.49710644912.</p><p>Lauber, Annika, Alexei Kiselev, Thomas Pander, Patricia Handmann, and Thomas Leisner. 2018. “Secondary Ice Formation during Freezing of Levitated Droplets.” Journal of the Atmospheric Sciences 75 (8): 2815–26. https://doi.org/10.1175/JAS-D-18-0052.1.</p><p>Lawson, R. Paul, Sarah Woods, and Hugh Morrison. 2015. “The Microphysics of Ice and Precipitation Development in Tropical Cumulus Clouds.” Journal of the Atmospheric Sciences 72 (6): 2429–45. https://doi.org/10.1175/JAS-D-14-0274.1.</p><p> </p><p> </p>

Empirical Formulation for number of ice crystal fragments by sublimational breakup

2020 ◽  
Author(s):  
Akash Deshmukh ◽  
Vaughan Phillips
Keyword(s):  
Relative Humidity ◽  
Cloud Model ◽  
Experimental Studies ◽  
Ice Crystal ◽  
Initial Size ◽  
Sublimation Process ◽  
Numerical Formulation ◽  
High Concentrations ◽  
Ice Multiplication ◽  
Ice Production

<p>There is much uncertainty about high concentrations of ice observed in clouds and their origins. In the literature, there have been previous experimental studies reported about the sublimation process of an ice crystal causes emission of fragments by breakup.   Such sublimational breakup is a type of secondary ice production, which in natural clouds can cause ice multiplication. </p><p>To represent this process of sublimation breakup in any cloud model, the present study proposes a numerical formulation of the number of ice fragments generated by sublimation of pristine ice crystal. This is done by amalgamating laboratory observations from previous published studies. The number of ice fragments determined by relative humidity (RH) and initial size of the ice particle were measured in the published experiments, and by simulating them we are able to infer parameters of a sublimation breakup scheme.   At small initial sizes, the dependency on size prevails, whereas at larger sizes both dependencies are comparable. This formulation is compared with observations to see the behaviour of it.</p>

Bin-Emulating Hail Melting in Three-Moment Bulk Microphysics

2020 ◽  
Vol 77 (10) ◽  
pp. 3361-3385 ◽  
Author(s):  
Edward R. Mansell ◽  
Daniel T. Dawson II ◽  
Jerry M. Straka
Keyword(s):  
Substantial Effect ◽  
Size Spectrum ◽  
Dependent Manner ◽  
Particle Spectrum ◽  
Microphysics Scheme ◽  
Ice Particles ◽  
Distribution Shape ◽  
Mean Size ◽  
The Mean ◽  
Bin Microphysics

AbstractA three-moment bulk microphysics scheme is modified to treat melting in a size-dependent manner that emulates results from a spectral bin scheme. The three-moment bulk framework allows the distribution shape to change and accommodate some direct effects of melting on both the hail and raindrop size distributions. Reflectivity changes and shed raindrop sizes are calculated over discrete size ranges of the hail particle spectrum. Smaller ice particles are treated as melting into drops of the same mass, whereas large particles shed drops as they melt. As small ice particles are lost, the size spectrum naturally becomes narrower and the mean size of small hail can increase. Large hail with a narrow spectrum, however, can decrease in size from melting. A substantial effect is seen on the rain median volume diameter when small drops are shed from large melting hail. The NSSL bulk scheme is compared with bin microphysics in steady-state hail shafts and in a supercell storm case. It is also shown that melting (or any substantial removal of mass) induces gravitational size sorting in bulk microphysics to increase hail size despite the design of the process rates to maintain the mean size of the melting ice. This unintended side effect can be a correct behavior for small hail, but not for large hail with a narrow distribution, when mean hail size should decrease by melting.

Secondary Ice Production upon Freezing of Freely Falling Drizzle Droplets

2020 ◽  
Vol 77 (8) ◽  
pp. 2959-2967 ◽  
Author(s):  
Alice Keinert ◽  
Dominik Spannagel ◽  
Thomas Leisner ◽  
Alexei Kiselev
Keyword(s):  
Pure Water ◽  
Free Fall ◽  
Terminal Velocity ◽  
Sea Salt ◽  
Ice Formation ◽  
Formation Mechanisms ◽  
Ice Multiplication ◽  
Ice Production ◽  
Droplet Shattering ◽  
Droplet Fragmentation

Abstract Ice multiplication processes are known to be responsible for the higher concentration of ice particles versus ice nucleating particles in clouds, but the exact secondary ice formation mechanisms remain to be quantified. Recent in-cloud observations and modeling studies have suggested the importance of secondary ice production upon shattering of freezing drizzle droplets. In one of our previous studies, four categories of secondary ice formation during freezing of supercooled droplets have been identified: breakup, cracking, jetting, and bubble bursts. In this work, we extend the study to include pure water and an aqueous solution of analog sea salt drizzle droplets moving at terminal velocity with respect to the surrounding cold humid air. We observe an enhancement in the droplet shattering probability as compared to the stagnant air conditions used in the previous study. Under free-fall conditions, bubble bursts are the most common secondary ice production mode in sea salt drizzle droplets, while droplet fragmentation controls the secondary ice production in pure water droplets.

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.

Numerical Analysis of Electro-Thermal Phenomena in Metal by Boltzmann Transport Equation for Electron

2005 ◽  
Author(s):  
Kohei Ito ◽  
Ryohei Muramoto ◽  
Isamu Shiozawa ◽  
Yasushi Kakimoto ◽  
Takashi Masuoka
Keyword(s):  
Transport Equation ◽  
Equilibrium Distribution ◽  
Boltzmann Transport Equation ◽  
Quasi Equilibrium ◽  
Boltzmann Transport ◽  
Simulation Based ◽  
Far From Equilibrium ◽  
New Formulation ◽  
Thermal Phenomena ◽  
Non Equilibrium

By the development of micro-fabrication technology, much smaller-size electronic devices will be soon available. In such a smaller device, a non-equilibrium state might appear in metal and/or semiconductor. In this case, it is difficult to estimate the device performance by the macroscopic transport equations that assume quasi-equilibrium distribution. We are developing a numerical simulation based on Boltzmann transport equation (BTE), which can analyze thermal and electric phenomena even when the state is far from equilibrium. In this study, we show a new formulation of BTE for free electron in metal and its calculation result: the thermoelectric power obtained agreed with that of experimental value: the heat flux derived by the non-equilibrium distribution was two-orders small than that estimated by thermal conductivity.

scholarly journals Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

2015 ◽  
Vol 15 (18) ◽  
pp. 25647-25694 ◽  
Author(s):  
R. J. Farrington ◽  
P. J. Connolly ◽  
G. Lloyd ◽  
K. N. Bower ◽  
M. J. Flynn ◽  
...  
Keyword(s):  
Wrf Model ◽  
Surface Flux ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Field Campaign ◽  
Orographic Clouds ◽  
Ice Multiplication ◽  
Ice Production ◽  
Surface Ice ◽  
Mixed Phase Clouds

Abstract. This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between the 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nuclei (IN) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing IN concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A surface flux of hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

Laboratory experiments on secondary ice production upon free falling drizzle droplets observed by high speed video and thermal imaging

2021 ◽  
Author(s):  
Alice Keinert ◽  
Judith Kleinheins ◽  
Alexei Kiselev ◽  
Thomas Leisner
Keyword(s):  
High Resolution ◽  
High Speed ◽  
Video Microscopy ◽  
Freezing Process ◽  
Crack Open ◽  
High Speed Video ◽  
Pressure Release ◽  
Ice Particles ◽  
Ice Production ◽  
Ice Shell

<p>During the freezing of supercooled drizzle droplets, the ice shell forms at the droplet surface and propagates inwards, causing a pressure rise in the droplet core. If the pressure exceeds the mechanical stability of the ice shell, the shell can crack open and eject secondary ice particles or cause the full disintegration of the ice shell leading to droplet shattering. Recent in-cloud observations and modeling studies have suggested the importance of secondary ice production upon shattering of freezing drizzle droplets. The details of this process are poorly understood and the number of secondary ice particles produced during freezing remains to be quantified.</p><p>Here we present insight into experiments with freezing drizzle droplets levitated in electrodynamic balance under controlled conditions with respect to temperature, humidity and airflow velocity. Individual droplets are exposed to a flow of cold air from below, simulating free fall conditions. The freezing process is observed with high-speed video microscopy and a high-resolution infrared thermal measuring system. We show the observed frequencies for various events associated with the production of secondary ice particles during freezing for pure water droplets and aqueous solution of analogue sea salt droplets (300 µm in diameter) and report a strong enhancement of the shattering probability as compared to our previous study (Lauber et al., 2018) conducted in stagnant air. Analysis of pressure release events recorded by high-resolution infrared thermography suggest that pressure release events associated with the possible ejection of secondary ice particles occur far more frequent than previously quantified with observations by high speed video microscopy only.</p><p> </p><p>Lauber, A., A. Kiselev, T. Pander, P. Handmann, and T Leisner (2018). “Secondary Ice Formation during Freezing of Levitated Droplets”, Journal of the Atmospheric Sciences 75, pp. 2815–2826. </p>

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