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Journal ArticleDOI

On the cloud microphysical processes during the November 2, 1994 hazardous storm in the southeastern Mediterranean as simulated with a mesoscale model

01 Mar 2000-Atmospheric Research (Elsevier)-Vol. 53, pp 63-89

AbstractA mesoscale model (CSU RAMS) model with cloud microphysics is used for analysis of the November 1–2, 1994 weather developments over the eastern Mediterranean (EM). The hazardous weather processes of the period are successfully simulated. According to observations, as well as the modeling results, the main areas with very intensive precipitation were located over Egypt and southern Israel. Results of the simulation are used to evaluate the role of the cloud microphysics of the storm. Analysis of time variations of the model, derived from microphysical characteristics, is made at several locations along the path of the storm. The processes at the locations represent different stages of the storm development. The results show that during this intense storm, cloud microphysical processes experienced at least two phases of development. During the first phase, which was associated with initiation and intensification of the mesoscale convective system (MCS), the condensate, mainly composed of cloud water, existed in the deep layer from 3 to 10 km. It was evidently formed by condensation and collection processes in the slowly developing updrafts. During the second phase, associated mainly with frontal type cloud developments, the clouds were much less vertically developed and were characterized by less intense cloud processes. Pristine ice particles were found at about 10 km during most of the period. Vertical development of the clouds was less active than during the first stage. Observed rapid decrease of the rain intensity over Israel was mainly a consequence of the transformation process. At the same time, the increase in dustiness of the air over the region during this time could also have contributed to this decrease although the role of this factor is not completely clear.

Topics: Mesoscale convective system (58%), Cloud physics (57%), Storm (56%), Mesoscale meteorology (56%), Thunderstorm (55%)

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Journal ArticleDOI
Abstract: . This report addresses the effects of pollution on the development of precipitation in clean ("pristine") and polluted ("hazy") environments in the Eastern Mediterranean by using the Integrated Community Limited Area Modeling System (ICLAMS) (an extended version of the Regional Atmospheric Modeling System, RAMS). The use of this model allows one to investigate the interactions of the aerosols with cloud development. The simulations show that the onset of precipitation in hazy clouds is delayed compared to pristine conditions. Adding small concentrations of GCCN to polluted clouds promotes early-stage rain. The addition of GCCN to pristine clouds has no effect on precipitation amounts. Topography was found to be more important for the distribution of precipitation than aerosol properties. Increasing by 15% the concentration of hygroscopic dust particles for a case study over the Eastern Mediterranean resulted in more vigorous convection and more intense updrafts. The clouds that were formed extended about three kilometers higher, delaying the initiation of precipitation by one hour. Prognostic treatment of the aerosol concentrations in the explicit cloud droplet nucleation scheme of the model, improved the model performance for the twenty-four hour accumulated precipitation. The spatial distribution and the amounts of precipitation were found to vary greatly between the different aerosol scenarios. These results indicate the large uncertainty that remains and the need for more accurate description of aerosol feedbacks in atmospheric models and climate change predictions.

102 citations


Journal ArticleDOI
Abstract: [1] In the framework of the European Union-funded project “Investigation of Cloud by Ground-based and Airborne Radar and Lidar” (CARL) the Regional Atmospheric Modeling System (RAMS) was used in order to study ice crystal formation and evolution in a cold cloud formation during a field program over Palaiseau, France. Sensitivity tests were performed so as to bind the uncertainty from various factors controlling model results. Emphasis is given to the sensitivity of the model with respect to the shape parameter of gamma distribution in the cloud microphysics module. Sensitivity analysis of the model was also performed in relation to the initialization of the simulation. The results are compared to in situ and remote sensing observations of the cloud formation. The analysis revealed that the model was able to reproduce the cloud characteristics (e.g., the spatial and temporal variability of the phenomena and the cloud geometry) in a satisfactory way. A detailed comparison of the model results with aircraft data showed that the model-calculated water content and number concentration deviate significantly for the small-size particle bin (2–47 microns) but are in good agreement for the medium- (25–800 microns) and large-size (200–6400 microns) bins. The differences for the smaller particles can partially be attributed to both poor performance of the microphysical algorithms and instrument inaccuracies. Some differences for the larger particles can be attributed either to the definition of the cloud boundaries by the model or to disturbances caused by the ascent path of the aircraft or both. The time of model initialization is also an important factor affecting cloud formation during the first few hours of the simulation. The performed simulations and model/data intercomparisons showed that RAMS is able to reproduce most of the microphysical parameters of cold cloud formations satisfactorily while utilizing conventional meteorological fields and observations for initial and boundary conditions.

6 citations


Cites background or methods from "On the cloud microphysical processe..."

  • ...Larger values of the shape parameter affect the microphysical characteristics of the precipitation process [Krichak and Levin, 2000]....

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  • ...(2) The convective dynamics are represented in the coarser grid by the Kuo-type cumulus parameterization scheme [Kuo, 1974] modified by Tremback [1990], while in all grids the explicit microphysics parameterization was activated....

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Journal ArticleDOI
Abstract: A three-dimensional numerical model (Regional Atmospheric Modeling System—-RAMS) was used to study the formation and evolution of water forms in a two-layer cloud structure observed during a field campaign over Brest (France). The model performance in regular operations, using conventional meteorological data as initial and lateral boundary conditions, was also examined. Remote sensing observations of the cloud system and in-situ aircraft data, selected during the campaign, were used to validate the model outputs. The model simulations showed that the lower cloud formation was characterized by high number concentration of pristine ice and snow, while the concentration of aggregates, graupel and hail were considerably lower. Hydrometeors in liquid phase appeared demonstrating high number concentration and water content on the top of this layer. The upper cloud layer consisted only of frozen water substances in lower amounts. The qualitative and quantitative comparison of the model-calculated meteorological and microphysical fields to the available observational data revealed that the model reflected fairly well the cloud structure (e.g., the spatio-temporal variability of the cloud parameters, the geometry of the cloud system). However, there were deviations as far as the model underestimating the ice water content (IWC) and number concentration (Nt) fields is concerned, especially at the atmospheric layer between 2.5 and 4 km of altitude. These deviations of the model simulated quantities from the measured ones may be attributed either to the performance of the model’s microphysics scheme, to instrument inaccuracies and to the local disturbance caused by the aircraft.

6 citations


Cites background from "On the cloud microphysical processe..."

  • ...It has been reported that increased values of the shape parameter affect the microphysical characteristics of the precipitation process (Krichak and Levin [42])....

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Journal ArticleDOI
Abstract: A fractional study of the factor separation (FS) approach is performed. A fractional version of the FS method is discussed. The revised approach allows a determination of role of the acting physical mechanisms as well as that of potential nonlinearity of the modeling system responses. Application of the approach is demonstrated based on the simulations of an eastern Mediterranean weather development during 1‐2 November 1994, performed with the Florida State University global spectral model. Thirteen model simulations with varying intensity of the turbulent surface fluxes in the runs were performed for the analysis. Two locations selected for sensitivity analysis of the model results represent the processes over the Red Sea and the Mediterranean Sea. It is shown that the variation of the FS results obtained in the experiments with different intensity of factors may be in some cases significant. The degree of variability of the FS results obtained in the experiments with varying intensity of the factors under the analysis provides useful information on sufficiency (or insufficiency) of available simulation results for an improved evaluation of the role of the acting factors in a meteorological process.

6 citations


Cites methods from "On the cloud microphysical processe..."

  • ...Krichak and Alpert (2000) and Krichak and Levin (2000) successfully used the FSU GSM simulation results for organization of the mesoscale downscaling of the development....

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  • ...The case has already been studied using both the large- and mesoscale atmospheric models (Krichak and Alpert 1998; Krichak et al. 2000; Krichak and Levin 2000)....

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  • ...A detailed discussion of the synoptic developments and the high-resolution modeling results are available in Krichak and Alpert (1998), Krichak and Levin (2000), and Krichak et al. (2000)....

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Journal ArticleDOI
Abstract: [1] Forward trajectories of the air masses from the Arabian Sea area were computed for each day from February 1 to April 10, 1999. This allowed the determination of the episodes characterized by the air mass transport to Africa and the Mediterranean region. Numerical simulation of one of such episodes, also characterized by intense cyclone and dust plume development, was performed using the Eta weather and dust predicting system. The simulation allowed an evaluation of the vertical distribution of the pollutants in the cyclone. Backward trajectories, ending in the area of the cyclone development point to the origin of a part of its air masses over the Arabian Sea. Potential role of the eastern Mediterranean weather systems in the transport to Europe of the polluted air masses from the INDOEX area is discussed.

5 citations


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Journal ArticleDOI

3,290 citations


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774 citations


"On the cloud microphysical processe..." refers background in this paper

  • ...Such areas can coincide with developing cloud systems, for instance, in the cases of the early stages of development of the MCS....

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Journal ArticleDOI
Abstract: A new cloud microphysical parameterization is described. Features of this new scheme include: the use of generalized gamma distributions as the basis function for all hydrometeor species; the use of a heat budget equation for hydrometeor classes, allowing heat storage and mixed phase hydrometears; partitioning hydrometeors into seven classes (including separate graupel and hail categories) ; the use of stochastic collection rather than continuous accretion approximations and extension of the ice nucleation scheme to include homogeneous nucleation of ice from haze particles and cloud droplets. The versatility and credibility of the new scheme is explored, using sensitivity experiments for a simple two-dimensional convective cloud simulation.

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"On the cloud microphysical processe..." refers background or methods in this paper

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Journal ArticleDOI
Abstract: Measurements of aerosol composition in the eastern Mediterranean reveal that sulfate is found in most aerosol particles. Some of the large particles contain mixtures of chemicals such as sulfate and sea salt. The most striking observation is the discovery that mineral dust particles often get coated with sulfate and other soluble materials. The amount of soluble material on these particles is found to be related to their surface area, suggesting that the deposition process could be surface dependent. The mechanism by which sulfate is found on some of the mineral dust particles is believed to originate from evaporating cloud drops, which were originally nucleated on sulfate cloud condensation nuclei (CCN) and subsequently collected dry interstitial mineral dust particles. The presence of soluble material on mineral dust particles, converts the latter into effective giant CCN. This is further corroborated by the fact that the few large drops near the bases of convective clouds near the coast of Isr...

507 citations


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