Fall Velocity Research Articles

PEAKO and peakTree: tools for detecting and interpreting peaks in cloud radar Doppler spectra – capabilities and limitations

Abstract. Cloud radar Doppler spectra are of particular interest for investigating cloud microphysical processes, such as ice formation, riming and ice multiplication. When hydrometeor types within a cloud radar observation volume have different terminal fall velocities, they can produce individual Doppler spectrum peaks. The peaks of different particle types can overlap and be further broadened and blended by turbulence and other dynamical effects. If these (sub-)peaks can be separated, properties of the underlying hydrometeor populations can potentially be estimated, such as their fall velocity, number, size and to some extent their shape. However, this task is complex and dependent on the operation settings of the specific cloud radar, as well as atmospheric dynamics and hydrometeor characteristics. As a consequence, there is a need for adjustable tools that are able to detect peaks in cloud radar Doppler spectra to extract the valuable information contained in them. This paper presents the synergistic use of two algorithms used for analyzing the peaks in Doppler spectra: PEAKO and peakTree. PEAKO is a supervised machine learning tool that can be trained to obtain the optimal parameters for detecting peaks in Doppler spectra for specific cloud radar instrument settings. The learned parameters can then be applied by peakTree, which is used to detect, organize and interpret Doppler spectrum peaks. The application of the improved PEAKO–peakTree toolkit is demonstrated in two case studies. The interpretation is supported by forward-simulated cloud radar Doppler spectra by the Passive and Active Microwave TRAnsfer tool (PAMTRA), which are also used to explore the limitations of the algorithm toolkit posed by turbulence and the number of spectral averages chosen in the radar settings. From the PAMTRA simulations, we can conclude that a minimum number of n = 20–40 spectral averages is desirable for Doppler spectrum peak discrimination. Furthermore, small liquid peaks can only be reliably separated for eddy dissipation rate values up to approximately 0.0002 m2 s−3 in the simulation setup which we tested here. The first case study demonstrates that the methods work for different radar systems and settings by comparing the results for two cloud radar systems which were operated simultaneously at a site in Punta Arenas, Chile. Detected peaks which can be attributed to liquid droplets agree well between the two systems, as well as with an independent liquid-predicting neural network. The second case study compares PEAKO–peakTree-detected cloud radar Doppler spectrum peaks to in situ observations collected by a balloon-based holographic imager during a campaign in Ny-Ålesund, Svalbard. This case demonstrates the algorithm toolkit's ability to identify different hydrometeor types but also reveals its limitations posed by strong turbulence and a low n. Despite these challenges, the algorithm toolkit offers a powerful means of extracting comprehensive information from cloud radar observations. In the future, we envision PEAKO–peakTree applications on the one hand for interpreting cloud microphysics in case studies. The identification of liquid cloud peaks emerges as a valuable asset, e.g., in studies on cloud radiative effects, in seeder–feeder processes, or for tracing vertical air motions. Furthermore, the computation of the moments for each subpeak enables the tracking of hydrometeor populations and the observation of growth processes along fallstreaks. On the other hand, PEAKO–peakTree applications could be extended to statistical evaluations of longer data sets. Both algorithms are openly available on GitHub, offering accessibility for the scientific community.

Influence of flow discharge and minibasin shape on the flow behavior and depositional mechanics of ponded turbidity currents

The interplay between seafloor sediment-laden density-driven flows, turbidity currents, and topography helps to shape continental margins. However, these interactions are poorly understood, especially those within enclosed depressions termed minibasins. In this study, novel experiments quantify the three-dimensional (3-D) dynamics of turbidity currents interacting with a range of minibasin geometries that, for the first time, scale within the parameter space of natural systems. Controls on flow dynamics are quantified by measuring the evolving velocity and sediment transport fields, in addition to maps of bathymetry. This study focuses on three aspects of turbidity current interactions with minibasins. First, the results suggest that sediment transport and deposition in minibasins is likely dominated by evolving flow conditions. Contrary to earlier studies in two-dimensional (2-D) flumes, this study supports a time-to-flow equilibrium in minibasins that scales with the time to replace ambient fluid with turbid influx, and this replacement time likely takes days to achieve in many field-scale minibasins. Second, in all experiments, horizontal flow circulation is observed, which is critical for distributing sediment throughout minibasins. However, the strength of the horizontal circulation reduces as the ratio of minibasin length to width increases, which leads to stagnant or even upstream-directed flow near the bed, elevated height of the velocity maximum in flows, the lowering of near-bed shear stresses, and more homogeneous deposits through a reduction in bed reworking. Finally, the results indicate that fluid detrainment from minibasins significantly reduces sediment fall velocities, severely lowering the sediment-trapping efficiency for small or light particles. This reduction in effective fall velocities of sediments suggests a mechanism that fractionates fine particulates (e.g., clays), nutrients (e.g., organic carbon), and pollutants (e.g., microplastics) along transport paths down topographically complex margins.

Dynamics of Barred Coast at Different Temporal Scales (by the Example of Vistula Spit in the Baltic Sea)

According to fundamental concepts, the morphodynamic system of an accumulative sandy coast with underwater bars exhibits cyclic behavior across various time scales. This raises the question: which factor is more significant for the dynamics of a given coast—individual storms or seasonal changes in wave activity? While observations and studies addressing this issue have primarily been conducted on oceanic coasts, there is a lack of comparable data for fetch-limited areas. Monitoring of the bottom topography along the west coast of Vistula Spit (Baltic Sea) revealed a cyclic behavior in morphology, transitioning from a straightened external bar to its connection with the shore. Analysis of field measurement results indicated that seasonal variations in wave intensity do not significantly impact coastal relief. Furthermore, it was found that the complete cycle of underwater bar evolution lasts approximately two years, during which the coast profile maintains a stable shape at the stage of the straightened external bar. The identification of the primary factor influencing coastal evolution can be characterized by the Dean number (Ω), which combines wave parameters (wave height and period) with sediment fall velocity. Utilizing ERA5 wave reanalysis data, we compared the variability of Ω values on both annual and monthly scales. The analysis revealed that for the section of the coast under consideration, there is no clearly dominant evolutionary factor; rather, the coast is influenced approximately equally by individual storm events and seasonal fluctuations in wave energy. Modeling storm-induced bed profile deformations using the CROSS-PB model demonstrated that the position of the external underwater bar remains nearly constant even during intense and prolonged storms. It is concluded that under specific conditions—determined by a combination of sediment size, coastal slope, and wave regime characteristics—the coast can remain stable, exhibiting minimal response to relatively strong storms and seasonal variations in wave energy. Such coasts are characterized by an absence of a dominant evolutionary factor as indicated by fluctuations in the Dean parameter, allowing their morphodynamic cycles to span several seasons. This type of morphodynamics in coastal accumulative relief appears to be typical for conditions found in fetch-limited areas, such as regional and semi-closed seas.

On the evaluation of accretion process near a quantum-improved charged black hole

This paper deals with astrophysical accretion onto the quantum-improved charged black hole. An accretion process does not depend on time; it is a stationary process. In this analysis, we explore the physical quantities like energy density, radial velocity, sonic speed, and accretion mass rate for quantum-improved charged black holes and compare them with the existing outcomes corresponding to the Schwarzschild black hole. Following the Michel and Babichev approaches, we investigate the quantities mentioned above by taking into account different equations of state. These fundamental approaches and black hole parameters are responsible for decreasing the fluid's radial infalling velocity during the accretion process and, for others, as a gravitational enhancer, increasing the fluid flow into the black hole horizon. The polytropic fluid's accretion process is also discussed. All the quantities are analyzed graphically with a contour structure. It is observed that the maximum accretion rate is achieved for different values of the considered black hole parameters. From this analysis, we may be able to understand the physical mechanism of accretion onto a quantum-improved charged black hole.

Analyzing sedimentation patterns in the Naumure Multipurpose Project (NMP) reservoir using 1D HEC-RAS modeling

Naumure Multipurpose Project (NMP) featuring a 169 m high Concrete Face Rock Filled Dam (CFRD) is the proposed reservoir project in the West Rapti River with an installed capacity of 218.34 MW. Most of the rivers in Nepal carry significant sediment loads that will consequently catalyze reservoir sedimentation. This phenomenon prevails as the primary factor in reducing reservoirs useful life, making ineffective for both flood control and hydroelectricity generation. Ultimately, such process of sedimentation has adverse impacts on projects economic feasibility and long-term sustainability. Therefore, the objective of this research was to examine the expected sediment deposition pattern in the NMP reservoir throughout its operational period by employing 1D HEC-RAS model to simulate the sedimentation process. The model was simulated for 10, 20, 30, 40 and 50 years. Yang’s equation as a sediment transport function, Active layer as a bed sorting method and Toffaleti as a fall velocity method were best suited for the river reach. The delta deposition was formed between 11 km and 22 km upstream of the dam region in the Jhimruk river, with the sediment deposition depth reaching peaks of about 23 m, 38 m, 39 m, 41 m and 49 m in 10, 20, 30, 40 and 50 years, respectively. Similarly, the delta deposition was formed between 13 km and 33 km upstream of dam region in the Madi river, with the sediment deposition depth reaching peaks of about 47 m, 62 m, 60 m, 68 m and 75 m in 10, 20, 30, 40 and 50 years respectively. Headcutting of delta deposition occurred between 20 and 30 year due to high flood during low stage of reservoir. Furthermore, the study revealed that about 6.22%, 11.61%, 15.94%, 22.96% and 25.65% of the storage capacity of NMP reservoir will be depleted in 10, 20, 30, 40 and 50 years respectively.

Designing Corrugated Board Properties to Mitigate Puncturing Impacts Occurring in E‐Commerce or Other Demanding Parcel Handling Distribution Chains

ABSTRACTThe growth of e‐commerce trade has led to more parcel shipments, causing an increase in corrugated board box packaging. Individually shipped boxes often sustain more damage, like crushing or puncturing, compared to pallet‐transported boxes. In contrast to the known relationships between containerboard properties and box compressive strength, there is no standard method for designing corrugated board against puncturing, which can result in damages, customer dissatisfaction and costly returns. A hole is typically seen as a severe compromise to package integrity, whereas some crushed boxes can be acceptable for nonfragile items. Addressing this, this research has focused on developing design equations linking containerboard and corrugated board properties to resistance against puncturing. These equations give the energy loss of an impacting object that would cause a hole and define the energy absorbance limit of the material. The equations enable material design aimed at minimizing puncturing risks based on specific distribution chain conditions, like fall heights and velocities.

In Search of Infall Motion in Molecular Clumps. V. HCO+ (1–0) and HCN (1–0) Observations toward 210 Infall Candidates

We have carried out HCO+(J = 1–0) and HCN (J = 1–0) line observations towards 210 infall candidates selected from the CO blue-profile catalog by Jiang et al., using the Purple Mountain Observatory 13.7 m telescope. Out of the 210 targets, 42 sources are further confirmed to have infall signatures in HCO+ and/or HCN lines, with a confirmation rate of ∼20%. According to the line profiles, we classify them into two categories: double-peaked and peak-shoulder. Some physical properties are estimated through profile fitting using the RATRAN model. We find that the two types are separated in parameter space, indicating they may be of different properties. The median values of kinetic temperature, infall velocity, and mass infall rate for the two types are 10.5 K and 40.8 K, 0.40 km s−1 and 1.00 km s−1, and 4.6 × 10−5 M ⊙ yr−1 and 3.5 × 10−4 M ⊙ yr−1, respectively. The infall velocities and mass-infall rates of peak-shoulder sources are slightly larger than those of double-peaked ones, suggesting they tend to form more massive stars. We also discuss the association of the 42 confirmed sources with other star formation activities such as maser and outflow, which supports this result.

Scour at the rear side of rubble mound revetments due to random wave overtopping: Laboratory experiments

This study presents the physical model experiments on the wave overtopping induced bed level changes at an unprotected rear side of a rubble mound revetment with a crown wall. In the experiments, the wave conditions, the backfill material size, and the backfill depth (vertical distance from the crest level to the rear side bed level) are varied. Two mobility parameters, namely the densimetric overtopping discharge and the relative fall velocity, are introduced to represent the initiation of motion and suspension of the backfill material, respectively. The temporal evolution of scour depth at the rear side is related to the mobility parameter, the number of waves and the backfill depth utilizing regression analyses. The effect of the backfill depth on the scour is found very limited for the available data set. However, the time scale of the scour is found to be related with the backfill depth only. For the present data set, it varied within a range of 1500–16000 number of waves approximately, with an average of 5600 waves. An equilibrium scour profile is reached 3 to 4 times the time scale. The geometry of the scour profile is expressed in terms of the scour depth, based on the equilibrium scour profile data.

Prediction of rain erosion damage progression using disdrometer rain data: The importance of liquid water content

Wind turbine blade erosion poses a significant challenge to the durability and performance of wind turbines. Modeling of rain erosion damage, considering atmospheric conditions, improves our understanding of the progression of leading-edge erosion on wind turbine blades. In this study, we investigate the impact of varying raindrop characteristics on rain erosion damage development. We analyse 2.5 years of data from a disdrometer, which measures the size and velocity of falling rain droplets, at Risø campus. Various post-processing methods of the disdrometer data are used for estimating representative droplet diameters and fall velocities for each rain event. We compare measured droplet fall velocities with theoretical terminal velocities, revealing a necessity for revising theoretical approaches to raindrop fall velocity for erosion damage modeling. The measured rain rates and representative fall velocities are used to calculate the liquid water content in the air. We introduce a bin-wise summation method for estimating the liquid water content, circumventing the need for representative droplet assumptions. As this method provides the most accurate input for the damage model, we benchmark the other post-processing methods against it and employ it to evaluate bias estimates of associated damage predictions. The largest bias (22%) in accumulated damage is found with an arithmetic mean droplet diameter approach and the smallest bias (-2%) with the median volume estimation method for damage model input. Furthermore, we demonstrate that, for a given rainfall volume, smaller droplets contribute to larger accumulated damage compared to larger droplets.

Protostellar disk accretion in turbulent filaments

Context. Recent observations of protostellar cores suggest that most of the material in the protostellar phase is accreted along streamers. Streamers in this context are defined as velocity coherent funnels of denser material potentially connecting the large-scale environment to the small scales of the forming accretion disk. Aims. Using simulations that simultaneously resolve the driving of turbulence on the filament scale as well as the collapse of the core down to protostellar disk scales, we aim to understand the effect of the turbulent velocity field on the formation of overdensities in the accretion flow. Methods. We performed a three-dimensional numerical study on a core collapse within a turbulent filament using the RAMSES code and analysed the properties of overdensities in the accretion flow. Results. We find that overdensities are formed naturally by the initial turbulent velocity field inherited from the filament and subsequent gravitational collimation. This leads to streams that are not really filamentary but show a sheet-like morphology. Moreover, they have the same radial infall velocities as the low density material. As a main consequence of the turbulent initial condition, the mass accretion onto the disk does not follow the predictions for solid body rotation. Instead, most of the mass is funneled by the overdensities to intermediate disk radii.

Impact of Microphysics Parameterization Schemes on the Assimilation of GOES‐16 ABI All‐Sky Infrared Radiances for a Bow Echo Analysis and Prediction

AbstractThis study aims to investigate how assimilating GOES‐16 ABI infrared brightness temperature (BT) with different microphysics schemes affects the convection‐allowing analysis and prediction of the 3 May 2020 bow echo case. The Gridpoint Statistical Interpolation‐based Ensemble Kalman Filter (GSI‐EnKF) system and Weather Research and Forecasting (WRF) model are utilized to conduct data assimilation (DA) experiments using Thompson, WDM6, NSSL, and Morrison microphysics schemes. Correlation structures between BT and model state variables indicate that assimilating infrared BT can adjust bowing MCS dynamics via latent cooling and the rear inflow jet. Such corrections during DA cycling enhance the rear inflow jet and bow echo size, primarily for microphysics schemes featuring faster hydrometeor fall velocity and stronger latent cooling. The improved analyses lead to better forecasts of the bow echo's shape, size, timing of the bowing process, and wind speeds. Substituting a larger microphysics‐dependent effective radius for a constant default value increases prior BT, the magnitude of BT innovations, and accumulated impact on the rear inflow jet, especially for the WDM6 and Morrison schemes. In the subsequent forecasts, incorporating microphysics‐dependent effective radius further improves the experiment using the Morrison scheme but degrades it when using the WDM6 scheme.

Quantifying uncertainty in simulations of the West African monsoon with the use of surrogate models

Abstract. Simulating the West African monsoon (WAM) system using numerical weather and climate models suffers from large uncertainties, which are difficult to assess due to nonlinear interactions between different components of the WAM. Here we present a fundamentally new approach to the problem by approximating the behavior of a numerical model – here the Icosahedral Nonhydrostatic (ICON) model – through a statistical surrogate model based on universal kriging, a general form of Gaussian process regression, which allows for a comprehensive global sensitivity analysis. The main steps of our analysis are as follows: (i) identify the most important uncertain model parameters and their probability density functions, for which we employ a new strategy dealing with non-uniformity in the kriging process. (ii) Define quantities of interest (QoIs) that represent general meteorological fields, such as temperature, pressure, cloud cover and precipitation, as well as the prominent WAM features, namely the tropical easterly jet, African easterly jet, Saharan heat low (SHL) and intertropical discontinuity. (iii) Apply a sampling strategy with regard to the kriging method to identify model parameter combinations which are used for numerical modeling experiments. (iv) Conduct ICON model runs for identified model parameter combinations over a nested limited-area domain from 28° W to 34° E and from 10° S to 34° N. The simulations are run for August in 4 different years (2016 to 2019) to capture the peak northward penetration of rainfall into West Africa, and QoIs are computed based on the mean response over the whole month in all years. (v) Quantify sensitivity of QoIs to uncertain model parameters in an integrated and a local analysis. The results show that simple isolated relationships between single model parameters and WAM QoIs rarely exist. Changing individual parameters affects multiple QoIs simultaneously, reflecting the physical links between them and the complexity of the WAM system. The entrainment rate in the convection scheme and the terminal fall velocity of ice particles show the greatest effects on the QoIs. Larger values of these two parameters reduce cloud cover and precipitation and intensify the SHL. The entrainment rate primarily affects 2 m temperature and 2 m dew point temperature and causes latitudinal shifts, whereas the terminal fall velocity of ice mostly affects cloud cover. Furthermore, the parameter that controls the evaporative soil surface has a major effect on 2 m temperature, 2 m dew point temperature and cloud cover. The results highlight the usefulness of surrogate models for the analysis of model uncertainty and open up new opportunities to better constrain model parameters through a comparison of the model output with selected observations.

Investigation of the Effect of Physical Ability on the Fall Mitigation Motion Using the Combination of Experiment and Simulation

The simulation of fall plays a critical role in estimating injuries caused by fall. However, implementing human fall mitigation motions on a simulator proves challenging due to the complexity and variability of fall movement. Our simulator estimates fall motion by extrapolating the motion observed in fall experiments. By incorporating actual fall motion data for the upper limbs, we enhanced the realism of the fall simulation. The application of forward dynamics control to the lower limbs allowed for the adjustment of mitigation motions, taking into account individual physical capabilities. In this study, fall simulations were conducted under the constraints of maximum joint torque and maximum torque change rate, emulating the physical capabilities of both the elderly and young adults. Our results successfully demonstrated the mitigation motion facilitated by the stance leg reduced the descent velocity of the center of mass by 0.75 m/s for elderly individuals and by 1.25 m/s for young adults, compared to a zero torque condition. This indicates that our study introduced a novel method for quantifying the impact of the lower limbs’ physical capabilities on fall velocity. Such a method represents a significant advancement in understanding how mitigation motions can influence fall injury simulations.

Magnetic field amplification in massive primordial halos

Context. The potential importance of magnetic fields during structure formation and gravitational collapse in the early Universe has been shown in several studies. In particular, magnetic field amplification by the small-scale dynamo plays an important role in addition to the pure amplification expected from gravitational collapse. Aims. In this paper we study the small-scale dynamo for halos of ≳107 M⊙ collapsing at z ≳ 12, under different ambient conditions due to the strength of the Lyman-Werner background. Additionally, we estimate the approximate saturation level by varying the initial magnetic field strength. Methods. We performed cosmological magnetohydrodynamical simulations for three distinct halos of ∼107 M⊙ at z ≥ 12 by varying the Jeans resolution from 32 − 256 cells and employed Lyman Werner background flux of strengths 102 − 105 in units of J21, where J21 = 10−21 erg cm−2 sr−1 s−1Hz−1. To follow the chemical and thermal evolution of the gas, we made use of the KROME package. Results. In addition to the compression by collapse, we find magnetic field amplification via the dynamo in the regimes of atomic and molecular hydrogen cooling. Moreover, we find a lower saturation level in the molecular hydrogen cooling regime. This behaviour can be understood in terms of the generally reduced radial infall velocities and vorticities in this regime, as well as the higher Mach numbers of the gas, which give rise to a smaller saturation ratio. Conclusions. Our results overall suggest that the dynamo operates over a large range of conditions in the collapsing gas.

Seasonal Variation in Vertical Structure for Stratiform Rain at Mêdog Site in Southeastern Tibetan Plateau

Mêdog is located at the entrance of the water vapor channel of the Yarlung Tsangpo Great Canyon on the southeastern Tibetan Plateau (TP). In this study, the seasonal variation in the microphysical vertical structure of stratiform precipitation at the Mêdog site in 2022 was investigated using micro rain radar (MRR) observations, as there is a lack of similar studies in this region. The average melting layer height is the lowest in February, after which it gradually increases, reaches its peak in August, and then gradually decreases. For lower rain categories, the vertical distribution of small drops remains uniform in winter below the melting layer. The medium-sized drops show slight increases, leading to negative gradients in the microphysical profiles. Slight or evident decreases in concentrations of small drops are observed with decreasing height in the premonsoon, monsoon, and postmonsoon seasons, likely due to significant evaporation. The radar reflectivity, rain rate, and liquid water content profiles decrease with decreasing height according to the decrease in concentrations of small drops. With increasing rain rate, the drop size distribution (DSD) displays significant variations in winter, and the fall velocity decreases rapidly with decreasing height. In the premonsoon, monsoon, and postmonsoon seasons, the concentrations of large drops significantly decrease below the melting layer because of the breakup mechanism, leading to the decreases in the fall velocity profiles with decreasing height during these seasons. Raindrops with sizes ranging from 0.3–0.5 mm are predominant in terms of the total drop number concentration in all seasons. Precipitation in winter and postmonsoon seasons is mainly characterized by small raindrops, while that in premonsoon and monsoon seasons mainly comprises medium-sized raindrops. Understanding the seasonal variation in the vertical structure of precipitation in Mêdog will improve the radar quantitative estimation and the use of microphysical parameterization schemes in numerical weather forecast models over the TP.

Numerical simulation of the cloud seeding operation of a convective rainfall event occurred in Beijing

Observation-validated cloud seeding simulation is valuable in assisting in evaluating seeding effect, but its sensitivity to microphysics schemes and cloud seeding parameterizations is rarely investigated. In this research three cloud seeding parameterizations (the Hsie, Demott and Xue parameterizations) are coupled with two microphysics schemes (the Thompson and Milbrandt schemes), to perform simulations of the rainfall suppression cloud seeding operation on a convective rainfall event occurred in North China on 1 July 2021, aiming to evaluate the seeding effect and investigate its sensitivity to microphysics schemes and seeding parameterizations. The differences of rainfall suppression effect between three seeding parameterizations are smaller than those between two microphysics schemes. The rainfall suppression ratios produced by the simulations configured with the Milbrandt scheme range from 16.3% to 24.7%, while those with the Thompson scheme range from 0.47% to 1.38%. The difference of the seeding effect between these two microphysics schemes arises from their different method in parameterizing the snow deposition growth process. In addition, in the seeding simulations with the Milbrandt scheme, the surface rainfall decrease region is followed by a rainfall increase region. This rainfall decrease-increase pattern is caused by the fact that the reduced graupel particles caused by cloud seeding falls to the ground earlier with its larger fall velocity, while the seeding-increased snow particle falls to the ground later due to its smaller fall velocity. This result suggests there is an ephemeral cloud seeding window for rainfall suppression operation.

Turbulence as a Key Driver of Ice Aggregation and Riming in Arctic Low‐Level Mixed‐Phase Clouds, Revealed by Long‐Term Cloud Radar Observations

AbstractTurbulence in clouds is known to enhance particle collision rates, as widely demonstrated for warm rain formation. A similar impact on ice growth processes is expected but a solid observational basis is missing. A statistical analysis of a 15‐month data set of cloud radar observations allows for the first time to quantify the impact of turbulence on ice aggregation and riming in Arctic low‐level mixed‐phase clouds. Increasing eddy dissipation rate (EDR), from below 10−4 to above 10−3 m2 s−3, yields larger ice aggregates, and higher particle concentration, likely caused by increasing fragmentation. In conditions more favorable to riming, higher EDR is associated with dramatically higher particle fall velocities (by up to 125%), under similar liquid water paths, indicative of markedly higher degrees of riming. Our findings thus reveal the key role of turbulence for cold precipitation formation, and highlight the need for an improved understanding of turbulence‐hydrometeor interactions in cold clouds.

Vertical structures and microphysical mechanisms of winter precipitation over the southwestern mountainous area of China

The vertical structures and microphysical processes of winter precipitation were investigated using comprehensive observations of three PARSIVELs and one MRR during January–March 2022 over the southwestern mountainous area of China. Twelve precipitation events were classified into four precipitation categories, including solid-phase precipitation, mixed-phase precipitation, light liquid-phase precipitation and heavy liquid-phase precipitation. Statistics reveal that, the majority of winter precipitation originates from snowflakes, with significantly higher precipitation top altitudes in liquid-phase precipitation compared to solid-phase and mixed-phase precipitation. Among the four different precipitation categories, there are distinct layers in which different microphysical processes dominate. For solid-phase precipitation, there is single solid-phase layer with few phase-type transitions, increased reflectivity (Ze) and precipitation rate (R) above 2.1 km altitude are likely affected by deposition and aggregation growth of snowflakes, increased fall velocity (Vf) and dispersed spectral width (Vsw) below 2.1 km altitude might suggest that most snowflakes rime into graupel and a few snowflakes melt. For mixed-phase precipitation, there are two distinct phase-type layers with weak phase-type transitions; in solid-phase layer (above 2.1 km altitude), accompanied by decreased Ze and R, decreased (increased) proportion of liquid-phase/mixed-phase hydrometeors above (below) 4.5 km altitude is likely attributed to refreezing/sublimation with fragmentation (sublimation); in mixed-phase layer (below 2.1 km altitude), significantly increased Vf and more dispersed Vsw suggest that snowflakes rime/melt into graupel, mixed-phase and liquid-phase hydrometeors. Although both light and heavy liquid-phase precipitation are divided into three distinct phase-type layers with remarkable phase-type transitions, significant differences exist in their vertical structures: first, heavy liquid-phase precipitation exhibits substantially higher precipitation top altitudes and a greater abundance of supercooled hydrometeors, resulting more active microphysical processes and noticeable increases of Ze and R at all altitudes; second, in melting layer, Ze in light liquid-phase precipitation initially increases and then decreases, known as bright band signature, however, Ze in heavy liquid-phase precipitation continuously increases due to enhanced melting and collision processes; third, in liquid-phase layer, both Ze and R in light liquid-phase precipitation show decreasing trends due to evaporation or break-up process, while Ze and R in heavy liquid-phase precipitation show remarkable increasing trends attributed to collision coalescence processes. Moreover, there are significant differences in ground particle size distributions, with small-size high-concentration hydrometeors in solid-phase precipitation, medium-size medium-concentration hydrometeors in mixed-phase precipitation, small-size low-concentration hydrometeors in light liquid-phase precipitation, and large-size high-concentration hydrometeors in heavy liquid-phase precipitation, resulting different Z-R relationships among the four precipitation categories.

The splashback radius and the radial velocity profile of galaxy clusters in IllustrisTNG

We used 1697 clusters of galaxies from the TNG300-1 simulation (mass M200c > 1014 M⊙ and redshift range 0.01 ≤ z ≤ 1.04) to explore the physics of the cluster infall region. We used the average radial velocity profile derived from simulated galaxies, vrad(r), and the average velocity dispersion of galaxies at each redshift, σv(r), to explore cluster-centric dynamical radii that characterize the cluster infall region. We revisited the turnaround radius, the limiting outer radius of the infall region, and the radius where the infall velocity has a well-defined minimum. We also explored two new characteristic radii: (i) the point of inflection of vrad(r) that lies within the velocity minimum, and (ii) the smallest radius where σv(r) = |vrad(r)|. These two, nearly coincident, radii mark the inner boundary of the infall region where radial infall ceases to dominate the cluster dynamics. Both of these galaxy velocity based radii lie within 1σ of the observable splashback radius. The minimum in the logarithmic slope of the galaxy number density is an observable proxy for the apocentric radius of the most recently accreted galaxies, the physical splashback radius. The two new dynamically derived radii relate the splashback radius to the inner boundary of the cluster infall region.

Performance of the Thies Clima 3D Stereo Disdrometer: Evaluation during Rain and Snow Events.

Imaging disdrometers are widely used in field campaigns to provide information on the shape of hydrometeors, together with the diameter and the fall velocity, which can be used to derive information on the shape-size relations of hydrometeors. However, due to their higher price compared to laser disdrometers, their use is limited to scientific research purposes. The 3D stereo (3DS) is a commercial imaging disdrometer recently made available by Thies Clima and on which there are currently no scientific studies in the literature. The most innovative feature of the 3DS is its ability in capturing images of the particles passing through the measurement volume, crucial to provide an accurate classification of hydrometeors based on information about their shape, especially in the case of solid precipitation. In this paper. the performance of the new device is analyzed by comparing 3DS with the Laser Precipitation Monitor (LPM) from the same manufacturer, which is a known laser disdrometer used in many research works. The data used in this paper were obtained from measurements of the two instruments carried out at the Casale Calore site in L'Aquila during the CORE-LAQ (Combined Observations of Radar Experiments in L'Aquila) campaign. The objective of the comparison analysis is to analyze the differences between the two disdrometers in terms of hydrometeor classification, number and falling speed of particles, precipitation intensity, and total cumulative precipitation on an event basis. As regards the classification of precipitation, the two instruments are in excellent agreement in identifying rain and snow; greater differences are observed in the case of particles in mixed phase (rain and snow) or frozen phase (hail). Due to the different measurement area of the two disdrometers, the 3DS generally detects more particles than the LPM. The performance differences also depend on the size of the hydrometeors and are more significant in the case of small particles, i.e., D < 1 mm. In the case of rain events, the two instruments are in agreement with respect to the terminal velocity in still air predicted by the Gunn and Kinzer model for drops with a diameter of less than 3 mm, while, for larger particles, terminal velocity is underestimated by both the disdrometers. The agreement between the two instruments in terms of total cumulative precipitation per event is very good. Regarding the 3DS ability to capture images of hydrometeors, the raw data provide, each minute, from one to four images of single particles and information on their size and type. Their number and coarse resolution make them suitable to support only qualitative analysis of the shape of precipitating particles.