Abstract
The 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 Indirect and Semi-Direct Aerosol Campaign (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 L
−1
, 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.
Most atmospheric motions of different spatial scales and precipitation are closely related to phase transitions in clouds. The continuously increasing resolution of large‐scale and mesoscale ...atmospheric models makes it feasible to treat the evolution of individual clouds. The explicit treatment of clouds requires the simulation of cloud microphysics. Two main approaches describing cloud microphysical properties and processes have been developed in the past four and a half decades: bulk microphysics parameterization and spectral (bin) microphysics (SBM). The development and utilization of both represent an important step forward in cloud modeling. This study presents a detailed survey of the physical basis and the applications of both bulk microphysics parameterization and SBM. The results obtained from simulations of a wide range of atmospheric phenomena, from tropical cyclones through Arctic clouds using these two approaches are compared. Advantages and disadvantages, as well as lines of future development for these methods are discussed.
Key Points
Review of concepts of microphysical methods
Analysis of errors in representation of microphysical processes
Comparison of results obtained by different methods
Stochastic parameters are introduced into a model of network games with production and knowledge externalities. The model was formulated by V. Matveenko and A. Korolev and generalizes Romer’s ...two-period model. The agents’ productivities have both deterministic and Wiener components. The research represents the dynamics of a single agent and the dynamics in a triangle that occurs in the process of combining the agents. Explicit expressions for the dynamics of a single agent and dyad agents are obtained in the form of Brownian random processes. Solutions of stochastic equations and systems are analyzed qualitatively.
Shattering presents a serious obstacle to current airborne in situ methods of characterizing the microphysical properties of ice clouds. Small shattered fragments result from the impact of natural ...ice crystals with the forward parts of aircraft-mounted measurement probes. The presence of these shattered fragments may result in a significant overestimation of the measured concentration of small ice crystals, contaminating the measurement of the ice particle size distribution (PSD). One method of identifying shattered particles is to use an inter-arrival time algorithm. This method is based on the assumption that shattered fragments form spatial clusters that have short inter-arrival times between particles, relative to natural particles, when they pass through the sample volume of the probe. The inter-arrival time algorithm is a successful technique for the classification of shattering artifacts and natural particles. This study assesses the limitations and efficiency of the inter-arrival time algorithm. The analysis has been performed using simultaneous measurements of two-dimensional (2-D) optical array probes with the standard and antishattering "K-tips" collected during the Airborne Icing Instrumentation Experiment (AIIE). It is shown that the efficiency of the algorithm depends on ice particle size, concentration and habit. Additional numerical simulations indicate that the effectiveness of the inter-arrival time algorithm to eliminate shattering artifacts can be significantly restricted in some cases. Improvements to the inter-arrival time algorithm are discussed. It is demonstrated that blind application of the inter-arrival time algorithm cannot filter out all shattered aggregates. To mitigate against the effects of shattering, the inter-arrival time algorithm should be used together with other means, such as antishattering tips and specially designed algorithms for segregation of shattered artifacts and natural particles.
•norbornene-based polymers with different lengths of n-alkyl substituents have been synthesized and tested as stationary phases in GC.•the retention of n-alkanes on new stationary phases was ...correlated with carbon numbers derived from both the structure of the solute and the structure of the polymer.•correlations with the polymer carbon number revealed two inflection points, one of which is associated with a phase transition in the polymer, and the other with a change in the sorption mechanism.•the retention of n-alkanes increases with a decrease in the length of hydrocarbon substituents in the polymers and is accompanied by an increase in enthalpy and a decrease of entropy of sorption.
Polymerization of 5-n-alkyl-substituted 2-norbornenes synthesized a series of polymers having the same structure of the main polymer chain, but differing in the length of the alkyl substituent (up to 14 methylene units). The obtained polymers were studied by the capillary IGC method as a stationary phase during separation of a mixture of normal hydrocarbons C6-C10. Retention data in the form of a logarithm of the retention factor lnk were correlated with the size of the sorbate (via the carbon number of the alkane ZS) and with the size of the n-alkyl substituent in the polymer chain (via the carbon number of the polymer ZP). Correlation of lnk vs. ZS turned out to be linear for all polymers, but the angle of the slope of linear dependence dlnk/dZS increases with a decrease in the carbon number of the polymer ZP. Dependency of dlnk/dZS vs. ZP is not linear and indicates an increase in the retention of sorbates by the stationary phase with a decrease in the length of the alkyl substituent in the polymer chain. The correlation of the retention of lnk analytes with the carbon number of the polymer ZP is not linear and indicates an increase in the sorbate/sorbent interaction with a decrease in the length of the alkyl substituent. Inflection points were found at both correlations with ZP in the region of ZP = 8, which indicates a possible change in the sorption mechanism or a change in the phase state of the polymer. In polymer chemistry, the phase state of a polymer is characterized by the glass transition temperature Tg, the dependence of which vs. ZP turned out to be nonlinear with an inflection point at ZP ∼11. Thus, a decrease in the length of the alkyl substituent leads to the transition of the polymer from a rubbery state to a glassy one at ZP ∼ 11, which in turn, with a further decrease in the carbon number of the polymer to ZP ∼ 8, causes a change in the sorption mechanism from bulk sorption to surface sorption. The change in the sorption mechanism is accompanied by an increase in the interaction of the sorbate with the stationary phase, which manifests itself both in an increase in the retention time of analytes and in an increase in the enthalpy and entropy of sorption. The reason for this increase can be seen in the formation of a microporous structure in 5-alkyl-substituted polynorbornenes in a glassy state.
A new type of donor–acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3, they react as sources of even‐numbered 1,2‐ and 1,4‐dipoles instead of the classical ...odd‐numbered 1,3‐dipoles due to migration of positive charge from the benzyl center. This type of reactivity has been demonstrated for new reactions, namely, cyclodimerizations of donor–acceptor cyclopropanes that occur as 2+2‐, 3+2‐, 4+2‐, 5+2‐, 4+3‐, and 5+4‐annulations. The 4+2‐annulation of 2‐arylcyclopropane‐1,1‐dicarboxylates to give polysubstituted 2‐aryltetralins has been developed in a preparative version that provides exceedingly high regio‐ and diastereoselectivity and high yields. The strategy for selective hetero‐combination of donor–acceptor cyclopropanes was also been developed. The mechanisms of the discovered reactions involving the formation of a comparatively stable 1,2‐ylide intermediate have been studied.
Old ring, new reactivity: A new type of donor–acceptor cyclopropane reactivity has been discovered. On treatment with anhydrous GaCl3, they react as sources of even‐numbered 1,2‐ and 1,4‐dipoles instead of the classical odd‐numbered 1,3‐dipoles owing to the migration of positive charge from the benzyl center.
The process of collective diffusional growth of droplets in an adiabatic parcel ascending or descending with the constant vertical velocity is analyzed in the frame of the regular condensation ...approach. Closed equations for the evolution of liquid water content, droplet radius, and supersaturation are derived from the mass balance equation centered with respect to the adiabatic water content. The analytical expression for the maximum supersaturation formed near the cloud base is obtained here. Similar analytical expressions for the height and liquid water mixing ratio corresponding to the level where occurs have also been obtained. It is shown that all three variables , , and are linearly related to each other and all are proportional to , where w is the vertical velocity and N is the droplet number concentration. Universal solutions for supersaturation and liquid water mixing ratio are found here, which incorporates the dependence on vertical velocity, droplet concentration, temperature, and pressure into one dimensionless parameter. The actual solutions for and can be obtained from the universal solutions with the help of appropriate scaling factors described in this study. The results obtained in the frame of this study provide a new look at the nature of supersaturation formation in liquid clouds. Despite the fact that the study does not include a detailed treatment of the activation process, it is shown that this work can be useful for the parameterization of cloud microphysical processes in cloud models, especially for the parameterization of cloud condensation nuclei (CCN) activation.
The sizes and shapes of ice crystals influence the radiative properties of clouds, as well as precipitation initiation and aerosol scavenging. However, ice crystal growth mechanisms remain only ...partially characterized. We present the growth processes of two complex ice crystal habits observed in Arctic mixed‐phase clouds during the Ny‐Ålesund AeroSol Cloud ExperimeNT campaign. First, are capped‐columns with multiple columns growing out of the plates' corners that we define as columns on capped‐columns. These ice crystals originated from cycling through the columnar and plate temperature growth regimes, during their vertical transport by in‐cloud circulation. Second, is aged rime on the surface of ice crystals having grown into faceted columns or plates depending on the environmental conditions. Despite their complexity, the shapes of these ice crystals allow to infer their growth history and provide information about the in‐cloud conditions. Additionally, these ice crystals exhibit complex shapes and could enhance aggregation and secondary ice production.
Plain Language Summary
Snowflakes formed in the atmosphere have a wide variety of shapes and sizes and no two snowflakes are identical. The reason for this infinite number of shapes is that the environmental temperature and relative humidity prevailing during the snowflakes' growth determine their exact aspects. Thus, the prevailing environmental conditions can be determined from the shape of snowflakes, and become more complicated with increased shape complexity. During a measurement campaign in the Arctic, we identified two complex snowflake types and the history of environmental conditions in which they grew in. We inferred that some snowflakes were recirculating to higher or lower parts of the clouds and that others had collided with cloud droplets that froze on their surface at the early stage of their growth. These snowflakes may enhance the formation of new snowflakes and the initiation of precipitation.
Key Points
A large variety of ice crystal sizes and shapes were observed in Arctic mixed‐phase clouds with a holographic imager
The growth history of two types of complex ice crystals was inferred from their shapes
These ice crystals could enhance aggregation and secondary ice production
Airborne measurements of ice water content (IWC) in both ice and mixed-phase clouds remain one of the long-standing problems in experimental cloud physics. For nearly three decades, IWC has been ...measured with the help of the Nevzorov hot-wire total water content (TWC) sensor, which had an inverted cone shape. It was assumed that ice particles would be captured inside the cone and then completely melt and evaporate. However, wind tunnel experiments conducted with the help of high-speed video recordings showed that ice particles may bounce out of the TWC cone, resulting in the underestimation of the measured IWC. The TWC sensor was modified to improve the capture efficiency of ice particles. The modified sensor was mounted on the National Research Council (NRC) Convair-580 and its measurements in ice clouds were compared with the measurements of the original Nevzorov TWC sensor, a Droplet Measurement Technologies (DMT) counterflow virtual impactor (CVI), and IWC calculated from the particle size distribution measured by optical array probes (OAPs). Results indicated that the IWC measured by the modified TWC hot-wire sensor as well as the CVI and that deduced from the OAP size distributions agreed reasonably well when the maximum size of ice particles did not exceed 4 mm. However, IWC measured by the original TWC sensor was approximately 3 times lower than that measured by the other three techniques. This result can be used for the retrieval of the past IWC measurements obtained with this TWC sensor. For clouds with ice particles larger than 4 mm, the IWC measured by the modified TWC sensor and CVI exhibited diverging measurements.
•Two solid solutions: Sr2-xLaxMnSbO6 (x = 0.25, 0.50. 0.67 and 0.75) and Sr1.5La0.5Mn1+xSb1-xO6 (x = 0.25 and 0.50) were prepared through solid state synthesis at ordinary condition.•The chemical ...composition, crystal structure and magnetic properties of SS were studied based on mixed Mn2+/Mn3+ and Mn3+/Mn4+ oxidation states, respectively.•The structure of first group samples was characterized by the monoclinic space group P21/n containing alternating MnO6 and SbO6 octahedra with unit cell volume increasing with × and prevailing antiferromagnetic exchange interaction at low temperatures.•The result of change of a ratio of Mn/Sb in Sr1.5La0.5Mn1+xSb1-xO6 in favor of Mn (x = 0.25 and 0.5) is phase separation of system on the orthorhombic Pnma and ferromagnetic rhombohedral Rc phases.
Solid solutions (SS) based on Sr2MnSbO6 and SrLaMnSbO6 with mixed oxidation states of Mn have been prepared by solid state synthesis under standard conditions. The structural and magnetic properties of Sr2-xLaxMnSbO6 and Sr1.5La0.5Mn1+ySb1-yO6 have been studied using X-ray diffraction data and magnetic susceptibility χ and magnetization σ measurements at 2–400 K. The samples of the first group crystallize in the monoclinic space group P21/n, their unit cell volume increases with × due to the formation of mixed Mn3+/Mn2+ valence. The change of the Weiss constant Θ sign from positive to negative with variation of ×, as well as the divergence between FC and ZFC dependences χ(T) below 40 K and spin-glass behavior indicate that the dominant exchange interactions between Mn3+ and Mn2+ cations in Sr2-xLaxMnSbO6 are of antiferromagnetic nature. The samples of the second group (at y = 0.25 and 0.50) were characterized as non-uniform, containing apparently two phases with a mixed Mn3+/Mn4+ state. The composition of the phases was established approximately by studying their structural and magnetic characteristics. The composition and crystal structure of the main phases are similar to those of the monoclinic samples described above. The secondary phases are identified as rhombohedral (space group R3¯c) with ferromagnetic properties with TC of 304.2 K (y = 0.25) and 365 K (y = 0.50).
PDF
