The Sensitivity of Simulated Convective Storms to Variations in Prescribed Single-Moment Microphysics Parameters that Describe Particle Distributions, Sizes, and Numbers

2006 ◽  
Vol 134 (9) ◽  
pp. 2547-2565 ◽  
Author(s):  
Charles Cohen ◽  
Eugene W. McCaul
Keyword(s):  
Shape Parameter ◽  
Deep Convection ◽  
Cloud Water ◽  
Atmospheric Modeling ◽  
Number Concentration ◽  
Cloud Droplets ◽  
Low Level ◽  
Single Moment ◽  
Mean Size ◽  
The Mean

Abstract The sensitivity of cloud-scale simulations of deep convection to variations in prescribed microphysics parameters is studied, using the single-moment scheme in the Regional Atmospheric Modeling System (RAMS) model. Realistic changes were made to the shape parameters in the gamma distributions of the diameters of precipitating hydrometeors and of cloud droplets, in the number concentration of cloud droplets, and in the mean size of the hail and graupel. Simulations were performed with two initial soundings that are identical except for their temperature. The precipitation rate at the ground is not very sensitive to changes in the value of the shape parameter used for all precipitating hydrometeors (rain, hail, graupel, snow, and aggregates) or to the mean size of the hail and graupel, owing to counteracting effects. For example, with a larger shape parameter value, there is a greater production of precipitation by collection of cloud water, but also a larger rate of evaporation of the liquid precipitation. However, with a larger shape parameter value, the greater production of precipitation by collection and the increased evaporation result in more low-level cooling by the downdraft. Specifying larger hail and graupel results in less low-level cooling by the downdraft. The simulation with the cold initial sounding showed a change in storm propagation velocity when the specified sizes of hail and graupel were increased, but this did not occur when the warm initial sounding was used. With a larger shape parameter for cloud water or with a larger number concentration of cloud droplets, there is less autoconversion and less collection of cloud water and, consequently, much less precipitation at the ground and denser cirrus anvils. While the number concentration of cloud droplets can be forecast in some models with parameterized microphysics, at present the shape parameter for cloud water cannot and must, therefore, be carefully selected.

scholarly journals Observational Study of the Entrainment-Mixing Process in Warm Convective Clouds

2007 ◽  
Vol 64 (6) ◽  
pp. 1995-2011 ◽  
Author(s):  
Frédéric Burnet ◽  
Jean-Louis Brenguier
Keyword(s):  
Number Concentration ◽  
Mixing Process ◽  
Cumulus Clouds ◽  
Cloud Droplets ◽  
Mixing Processes ◽  
Convective Clouds ◽  
Droplet Distribution ◽  
Homogenization Time ◽  
Mean Size ◽  
Entrainment Mixing

Thermodynamical and microphysical measurements collected in convective clouds are examined within the frame of the homogeneous/inhomogeneous mixing concept, to determine how entrainment-mixing processes affect cloud droplets, their number concentration, and their mean size. The three selected case studies—one stratocumulus layer and two cumulus clouds—exhibit very different values of the cloud updraft intensity, of the adiabatic droplet mean volume diameter, and of the saturation deficit in the environment, all three parameters that are expected to govern the microphysical response to entrainmentmixing. The results confirm that the observed microphysical features are sensitive to the droplet response time to evaporation and to the turbulent homogenization time scale, as suggested by the inhomogeneous mixing concept. They also reveal that an instrumental artifact due to the heterogeneous spatial droplet distribution may be partly responsible for the observed heterogeneous mixing features. The challenge remains, however, to understand why spatially homogeneous cloud volumes larger than the instrument resolution scale (10 m) are so rarely observed. The analysis of the buoyancy of the cloud and clear air mixtures suggests that dynamical sorting could also be efficient for the selection, among all possible mixing scenarios, of those that minimize the local buoyancy production.

scholarly journals Sensitivity of Warm-Frontal Processes to Cloud-Nucleating Aerosol Concentrations

2013 ◽  
Vol 70 (6) ◽  
pp. 1768-1783 ◽  
Author(s):  
Adele L. Igel ◽  
Susan C. van den Heever ◽  
Catherine M. Naud ◽  
Stephen M. Saleeby ◽  
Derek J. Posselt
Keyword(s):  
Vapor Deposition ◽  
The United States ◽  
Cloud Water ◽  
Phase Region ◽  
Atmospheric Modeling ◽  
Cloud Droplets ◽  
Colorado State University ◽  
Pollution Levels ◽  
Warm Front ◽  
Ice Production

Abstract An extratropical cyclone that crossed the United States on 9–11 April 2009 was successfully simulated at high resolution (3-km horizontal grid spacing) using the Colorado State University Regional Atmospheric Modeling System. The sensitivity of the associated warm front to increasing pollution levels was then explored by conducting the same experiment with three different background profiles of cloud-nucleating aerosol concentration. To the authors’ knowledge, no study has examined the indirect effects of aerosols on warm fronts. The budgets of ice, cloud water, and rain in the simulation with the lowest aerosol concentrations were examined. The ice mass was found to be produced in equal amounts through vapor deposition and riming, and the melting of ice produced approximately 75% of the total rain. Conversion of cloud water to rain accounted for the other 25%. When cloud-nucleating aerosol concentrations were increased, significant changes were seen in the budget terms, but total precipitation remained relatively constant. Vapor deposition onto ice increased, but riming of cloud water decreased such that there was only a small change in the total ice production and hence there was no significant change in melting. These responses can be understood in terms of a buffering effect in which smaller cloud droplets in the mixed-phase region lead to both an enhanced vapor deposition and decreased riming efficiency with increasing aerosol concentrations. Overall, while large changes were seen in the microphysical structure of the frontal cloud, cloud-nucleating aerosols had little impact on the precipitation production of the warm front.

A Multimoment Bulk Microphysics Parameterization. Part I: Analysis of the Role of the Spectral Shape Parameter

2005 ◽  
Vol 62 (9) ◽  
pp. 3051-3064 ◽  
Author(s):  
J. A. Milbrandt ◽  
M. K. Yau
Keyword(s):  
Growth Rates ◽  
Moment Method ◽  
Shape Parameter ◽  
Number Concentration ◽  
Spectral Shape ◽  
Size Spectrum ◽  
Atmospheric Models ◽  
Size Sorting ◽  
The Mean

Abstract With increasing computer power, explicit microphysics schemes are becoming increasingly important in atmospheric models. Many schemes have followed the approach of Kessler in which one moment of the hydrometeor size distribution, proportional to the mass content, is predicted. More recently, the two-moment method has been introduced in which both the mass and the total number concentration of the hydrometeor categories are independently predicted. In bulk schemes, the size spectrum of each hydrometeor category is often described by a three-parameter gamma distribution function, N(D) = N0Dαe−λD. Two-moment schemes generally treat N0 and λ as prognostic parameters while holding α constant. In this paper, the role of the spectral shape parameter, α, is investigated by examining its effects on sedimentation and microphysical growth rates. An approach is introduced for a two-moment scheme where α is allowed to vary diagnostically as a function of the mean-mass diameter. Comparisons are made between calculations using various bulk approaches—a one-moment, a two-moment, and a three-moment method—and an analytic bin model. It is found that the size-sorting mechanism, which exists in a bulk scheme when different fall velocities are applied to advect the different predicted moments, is significantly different amongst the schemes. The shape parameter plays an important role in determining the rate of size sorting. Likewise, instantaneous growth rates related to the moments are shown to be significantly affected by this parameter.

scholarly journals Investigation of Aerosol-Cloud Interactions under Different Absorptive Aerosol Regimes using ARM SGP Ground-Based Measurements

2019 ◽  
Author(s):  
Xiaojian Zheng ◽  
Baike Xi ◽  
Xiquan Dong ◽  
Timothy Logan ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Cloud Droplet ◽  
The United States ◽  
Number Concentration ◽  
Department Of Energy ◽  
Strong Light ◽  
Low Level ◽  
Aerosol Cloud ◽  
Aerosol Loading ◽  
The Mean ◽  
Absorbing Aerosols

Abstract. The physicochemical properties of aerosols and their impacts on cloud microphysical properties are examined using data collected from the Department of Energy Atmospheric Radiation Measurement (ARM) facility over the Southern Great Plains region of the United States (ARM-SGP). A total of 16 low-level stratus cloud cases under daytime coupled boundary layer conditions are selected. The aerosol-cloud interaction index (ACIr) is used to quantify the aerosol impacts with respect to cloud-droplet effective radius. The mean value of ACIr calculated from all selected samples is 0.145 ± 0.05 and ranges from 0.09 to 0.24 at a range of cloud liquid water paths (LWP = 20–300 g m−2). The magnitude of ACIr decreases with increasing LWP which suggests a cloud microphysical response to diminished aerosol loading presumably due to enhanced collision-coalescence processes and enlarged particle size. In the presence of weak light-absorbing aerosols, the low-level clouds feature a higher number concentration of cloud condensation nuclei (NCCN) and smaller effective radii (re) while the opposite is true for strong light-absorbing aerosols. Furthermore, the mean activation ratio of aerosols to CCN (NCCN / Na) for weakly (strongly) absorbing aerosols is 0.54 (0.45), owing to the different hygroscopic abilities associated with the dominant aerosol species. In terms of the sensitivity of cloud droplet number concentration (Nd) to aerosol loading, the conversion ratio of Nd / NCCN for weakly (strongly) absorptive aerosols is 0.68 (0.54). Consequently, we expect larger shortwave radiative cooling effect from clouds influenced by weakly absorbing aerosols than strongly absorbing aerosols.

scholarly journals Ensemble Statistics Accessed through Proxies: Range Heuristic and Dependence on Low-Level Properties in Variability Discrimination

2018 ◽  
Author(s):  
Jonas Sin-Heng Lau ◽  
Timothy F. Brady
Keyword(s):  
Visual Information ◽  
Low Level ◽  
Ensemble Statistics ◽  
Mean Size ◽  
Systematic Biases ◽  
Size Variability ◽  
The Mean ◽  
Per Se ◽  
Parallel Access

People can quickly and accurately compute not only the mean size of a set of items but also the size variability of the items. However, it remains unknown how these statistics are estimated. Here we show that neither parallel access to all items nor random subsampling of just a few items is sufficient to explain participants' estimations of size variability. In three experiments, we had participants compare two arrays of circles with different variability in their sizes. In the first 2 experiments, we manipulated the congruency of the range and variance of the arrays. The arrays with congruent range and variability information were judged more accurately, indicating the use of range as a proxy for variability. Experiments 2B and 3 showed that people also are not invariant to low- or mid-level visual information in the arrays, as comparing arrays with different low-level characteristics (filled vs. outlined circles) led to systematic biases. Together, these experiments indicate that range and low- or mid-level properties are both utilized as proxies for variability discrimination, and people are flexible in adopting these strategies. These strategies are at odds with the claim of parallel extraction of ensemble statistics per se and random subsampling strategies previously proposed in the literature.

Batch Precipitation of Lead Iodide

1994 ◽  
Vol 59 (6) ◽  
pp. 1301-1304
Author(s):  
Jaroslav Nývlt ◽  
Stanislav Žáček
Keyword(s):  
Aqueous Solution ◽  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Crystal Size ◽  
Lead Nitrate ◽  
Lead Iodide ◽  
Constant Rate ◽  
Mean Size ◽  
The Mean

Lead iodide was precipitated by a procedure in which an aqueous solution of potassium iodide at a concentration of 0.03, 0.10 or 0.20 mol l-1 was stirred while an aqueous solution of lead nitrate at one-half concentration was added at a constant rate. The mean size of the PbI2 crystals was determined by evaluating the particle size distribution, which was measured sedimentometrically. The dependence of the mean crystal size on the duration of the experiment exhibited a minimum for any of the concentrations applied. The reason for this is discussed.

scholarly journals Mesoscale Features Associated with Tropical Cyclone Formations in the Western North Pacific

2008 ◽  
Vol 136 (6) ◽  
pp. 2006-2022 ◽  
Author(s):  
Cheng-Shang Lee ◽  
Kevin K. W. Cheung ◽  
Jenny S. N. Hui ◽  
Russell L. Elsberry
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Synoptic Patterns ◽  
The Mean

Abstract The mesoscale features of 124 tropical cyclone formations in the western North Pacific Ocean during 1999–2004 are investigated through large-scale analyses, satellite infrared brightness temperature (TB), and Quick Scatterometer (QuikSCAT) oceanic wind data. Based on low-level wind flow and surge direction, the formation cases are classified into six synoptic patterns: easterly wave (EW), northeasterly flow (NE), coexistence of northeasterly and southwesterly flow (NE–SW), southwesterly flow (SW), monsoon confluence (MC), and monsoon shear (MS). Then the general convection characteristics and mesoscale convective system (MCS) activities associated with these formation cases are studied under this classification scheme. Convection processes in the EW cases are distinguished from the monsoon-related formations in that the convection is less deep and closer to the formation center. Five characteristic temporal evolutions of the deep convection are identified: (i) single convection event, (ii) two convection events, (iii) three convection events, (iv) gradual decrease in TB, and (v) fluctuating TB, or a slight increase in TB before formation. Although no dominant temporal evolution differentiates cases in the six synoptic patterns, evolutions ii and iii seem to be the common routes taken by the monsoon-related formations. The overall percentage of cases with MCS activity at multiple times is 63%, and in 35% of cases more than one MCS coexisted. Most of the MC and MS cases develop multiple MCSs that lead to several episodes of deep convection. These two patterns have the highest percentage of coexisting MCSs such that potential interaction between these systems may play a role in the formation process. The MCSs in the monsoon-related formations are distributed around the center, except in the NE–SW cases in which clustering of MCSs is found about 100–200 km east of the center during the 12 h before formation. On average only one MCS occurs during an EW formation, whereas the mean value is around two for the other monsoon-related patterns. Both the mean lifetime and time of first appearance of MCS in EW are much shorter than those developed in other synoptic patterns, which indicates that the overall formation evolution in the EW case is faster. Moreover, this MCS is most likely to be found within 100 km east of the center 12 h before formation. The implications of these results to internal mechanisms of tropical cyclone formation are discussed in light of other recent mesoscale studies.

scholarly journals Effects of topical gel formulation of Ficus carica latex on cutaneous leishmaniasis induced by Leishmania major in BALB/c mice

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Ali Pouryousef ◽  
Erfan Eslami ◽  
Sepehr Shahriarirad ◽  
Sina Zoghi ◽  
Mehdi Emami ◽  
...  
Keyword(s):  
Cutaneous Leishmaniasis ◽  
Murine Model ◽  
Leishmania Major ◽  
Considerable Effect ◽  
Ficus Carica ◽  
Control Group ◽  
Topical Gel ◽  
The Third ◽  
Mean Size ◽  
The Mean

Abstract Objectives The current study aimed to evaluate the effects of Ficus carica latex on the treatment of cutaneous leishmaniasis (CL), induced by Leishmania major. A 5% topical gel with F. carica latex was prepared. BALB/c mice were infected by inoculation of amastigotes form of L. major. Thirty BALB/c mice were divided into five groups, where the first group was treated daily, the second group twice per day, and the third group every other day with the 5% topical gel, for 3 weeks. The sizes of the lesions were measured before and during the course of treatment. Results Although the mean size of lesions in the mice group treated with the 5% F. carica gel, especially in the group receiving daily treatment, was less than the mean size of the lesions in the control group, yet, the differences was not statistically significant (p > 0.05). The findings of the current study demonstrated that the 5% F. carica latex with a 3-week course of treatment had no considerable effect in recovery or control of CL induced by L. major in the murine model. Using higher concentration of F. carica latex and with longer treatment lengths may increase its efficacy in the treatment of CL.

scholarly journals Mudrock Microstructure: A Technique for Distinguishing between Deep-Water Fine-Grained Sediments

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 653
Author(s):  
Shereef Bankole ◽  
Dorrik Stow ◽  
Zeinab Smillie ◽  
Jim Buckman ◽  
Helen Lever
Keyword(s):  
Grain Size ◽  
Deep Water ◽  
Sedimentary Facies ◽  
X Ray Diffraction ◽  
Weak Current ◽  
Large Area ◽  
Fine Grained ◽  
Mean Size ◽  
The Mean ◽  
Water Facies

Distinguishing among deep-water sedimentary facies has been a difficult task. This is possibly due to the process continuum in deep water, in which sediments occur in complex associations. The lack of definite sedimentological features among the different facies between hemipelagites and contourites presented a great challenge. In this study, we present detailed mudrock characteristics of the three main deep-water facies based on sedimentological characteristics, laser diffraction granulometry, high-resolution, large area scanning electron microscopy (SEM), and the synchrotron X-ray diffraction technique. Our results show that the deep-water microstructure is mainly process controlled, and that the controlling factor on their grain size is much more complex than previously envisaged. Retarding current velocity, as well as the lower carrying capacity of the current, has an impact on the mean size and sorting for the contourite and turbidite facies, whereas hemipelagite grain size is impacted by the natural heterogeneity of the system caused by bioturbation. Based on the microfabric analysis, there is a disparate pattern observed among the sedimentary facies; turbidites are generally bedding parallel due to strong currents resulting in shear flow, contourites are random to semi-random as they are impacted by a weak current, while hemipelagites are random to oblique since they are impacted by bioturbation.

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