Numerical Simulation on Physical and Chemical Processes in Convective Clouds

Vlado Spiridonov,Mladjen Curic 한국기상학회 2009 Asia-Pacific Journal of Atmospheric Sciences Vol.45 No.1

Examination of Physical Processes of Convective Cell Evolved from a MCS - Using a Different Model Initialization

Vlado Spiridonov,Mladjen Ćurić 한국기상학회 2016 Asia-Pacific Journal of Atmospheric Sciences Vol.52 No.3

The present study is focused on examination of the physical processes of convective cell evolved from a MCS occurred on 4 November 2011 over Genoa, Italy. The Quantitative Precipitation Forecasts (QPF) have been performed using WRF v3.6 model under different configurations and cloud permitting simulations. The results indicate underestimation of the amount of precipitation and spatial displacement of the area with a peak 24-h accumulated rainfall in (mm). Our main objective in the research is to test the cloud model ability and performance in simulation of this particular case. For that purpose a set of sensitivity experiments under different model initializations and initial data have been conducted. The results also indicate that the merging process apparently alters the physical processes through low- and middle-level forcing, increasing cloud depth, and enhancing convection. The examination of the microphysical process simulated by the model indicates that dominant production terms are the accretion of rain by graupel and snow, probabilistic freezing of rain to form graupel and dry and wet growth of graupel. Experiment under WRF v3.6 model initialization has shown some advantage in simulation of the physical processes responsible for production and initiation of heavy rainfall compared to other model runs. Most of the precipitation came from ice-phase particles-via accretion processes and the graupel melting at temperature T0 ≥ 0oC. The rainfall intensity and accumulated rainfall calculated by the model closely reflect the amount of rainfall recorded. Thus, the main benefit is to better resolve convective showers or storms which, in extreme cases, can give rise to major flooding events. In such a way, this model may become major contributor to improvements in weather analysis and small-scale atmospheric predictions and early warnings of such subscale processes.

Examination of Sulfate Chemistry Sensitivity in a Mid-latitude and Tropical Storm Using a Cloud Resolving Model

Vlado Spiridonov,Mladjen Curic 한국기상학회 2012 Asia-Pacific Journal of Atmospheric Sciences Vol.48 No.4

We examine the sensitivities of heterogeneous sulfate chemistry in a mid-latitude and tropical storm using a cloud resolving model. Both thermodynamic environments show unstable conditions favorable for development of intensive convection, with more CAPE in tropical compared to mid-latitude storm. Compared with the observed severe storms, modeled results show a relatively good agreement with the radar and surface chemical observations. Microphysical evaluation indicates that the accretion and autoconversion appear to be most important processes in such considered clouds. This sensitivity simulation is an upper bound for conversion of S (IV) to sulfate. The tropical convective storm produces for about 2.5 times more sulfate compared to mid-latitude storm and converts more SO2 to sulfate, increasing wet deposition of sulfur. The results for a midlatitude run indicate that aerosol nucleation and impact scavenging account for between 18.9% and 28.9% of the in-cloud sulfate ultimately deposited. As a result of greater rainfall efficiency, tropical storm shows about two times higher sub-cloud scavenging rate than mid-latitude storm. The oxidation of S (IV) to SO4−2 in cloud droplets and in precipitation is found to be dominant in both convective storms accounting almost with the same percentage contribution of 45.4% and 46.3% to sulfur deposition, respectively. In-cloud oxidation contribute a larger fraction of the total amount of sulfur deposited in tropical case (29.2%) when compared to the mid-latitude case (11.8), respectively. Neglecting aqueous-phase chemistry in ice-phase hydrometeors in both convective clouds led to overpredict deposition of about 40% to 33% relative to the base runs.

A Storm Modeling System as an Advanced Tool in Prediction of Well Organized Slowly Moving Convective Cloud System and Early Warning of Severe Weather Risk

Vlado Spiridonov,Mladjen Curic 한국기상학회 2015 Asia-Pacific Journal of Atmospheric Sciences Vol.51 No.1

Short-range prediction of precipitation is a critical input toflood prediction and hence the accuracy of flood warnings. Sincemost of the intensive processes come from convective clouds-theprimary aim is to forecast these small-scale atmospheric processes. One characteristic pattern of organized group of convective cloudsconsist of a line of deep convection resulted in the repeated passageof heavy-rain-producing convective cells over NW part of Macedoniaalong the line. This slowly moving convective system producedextreme local rainfall and hailfall in urban Skopje city. A 3-d cloudmodel is used to simulate the main storm characteristic (e.g.,structure, intensity, evolution) and the main physical processesresponsible for initiation of heavy rainfall and hailfall. The modelshowed a good performance in producing significantly more realisticand spatially accurate forecasts of convective rainfall event than ispossible with current operational system. The output results give agood initial input for developing appropriate tools such as floodingindices and potential risk mapping for interpreting and presenting thepredictions so that they enhance operational flood predictioncapabilities and warnings of severe weather risk of weather services. Convective scale model-even for a single case used has provedsignificant benefits in several aspects (initiation of convection, stormstructure and evolution and precipitation). The storm-scale model(grid spacing-1 km) is capable of producing significantly morerealistic and spatially accurate forecasts of convective rainfall eventsthan is possible with current operational systems based on modelwith grid spacing 15 km.

Numerical Simulation of Airborne Cloud Seeding over Greece, Using a Convective Cloud Model

Vlado Spiridonov,Theodore Karacostas,Dimitrios Bampzelis,Ioannis Pytharoulis 한국기상학회 2015 Asia-Pacific Journal of Atmospheric Sciences Vol.51 No.1

An extensive work has been done by the Department ofMeteorology and Climatology at Aristotle University of Thessalonikiand others using a three-dimensional cloud resolving model tosimulate AgI seeding by aircraft of three distinct hailstorm casesoccurred over Greece in period 2007-2009. The seeding criterion forsilver iodide glaciogenic seeding from air is based on the beneficialcompetition mechanism. According to thermodynamic analysis andclassification proposed by Marwitz (1972a, b, and c) and based ontheir structural and evolutionary properties we classified them inthree groups as singlecell, multicell and supercell hailstorms. Theseeding optimization for each selected case is conducted by analysisof the thermodynamic characteristics of the meteorological environmentas well as radar reflectivity fields observed by the state of theart Thunderstorm Identification, Tracking, Analysis and Nowcasting(TITAN) software applied in the Greek National Hail SuppressionProgram (GNHSP). Results of this comprehensive study have shownpositive effects with respect to hailfall decrease after successfulseeding as our primarily objective. All three cases have illustrated15-20% decrease in accumulated hailfall at the ground Seededclouds have exhibited earlier development of precipitation and slightdynamical enhancement of the updraft and rainfall increase of ~10-12.5%. The results have emphasized a strong interaction betweencloud dynamics and microphysics, especially the subgrid scaleprocesses that have impact on agent transport and diffusion in acomplex environment. Comparisons between modelled and observedradar reflectivity also show a relatively good agreement. Simulatedcloud seeding follows the operational aircraft seeding for hailsuppression. The ability of silver-iodide particles to act as ice nucleihas been used to perform airborne cloud seeding, under controlledconditions of temperature and humidity. The seeding effects dependupon applying the seeding methodology in proper seeding time, rightplacement and agent dose rate.

Evaluation of Supercell Storm Triggering Factors Based on a Cloud Resolving Model Simulation

Vlado Spiridonov,Mladjen Ćurić 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

An attempt has been made in this study to examine the conditional instability parameters in the selected area and to determine the main ingredients responsible for initiation and evolution of supercell storm over Skopje, Macedonia on 6 August 2016. WRF model forecasts provide the basic meteorological parameters for cloud model initialization and the detail information about atmospheric instability potential as triggering factor for severe convection. The cloud model simulation has been performed with very fine spatial and temporal resolution capable to resolve the detail aspects of convection. The results utilizing this novel method suggest that, upper level lifting, moisture advection, large CAPE, near surface convergence and increased potential vortices in the selected area play substantial role in early assessment of the atmospheric status, convective instability and storm potential. In addition the directional wind shear (veering) at the near surface layer, high storm helicity index, differential heating induced by the strong local forcing environment serve as triggering factors for initiation of supercell storm with rotational updrafts-mesocyclone. The cloud model simulation with fine resolution allows more detail insight into the storm dynamics and the mechanism of generation of rotational updrafts and mesocyclone, a hook echo signature and the presence of bounded weak echo region as ingredients for supercellular structure and evolution. The overshooting top of 15 km, peak updraft speed of 40 m/s, wind gust of 35 m/s and reflectivity which exceeds 70 dBZ indicates to the occurrence of a very severe storm. A longer live cycle of storm and the intense water production, with extreme rainfall rate of 38 mm/5 min, contribute to formation of excessive torrential rainfall and local catastrophic flooding.

Novel Thunderstorm Alert System (NOTHAS)

Vlado Spiridonov,Mladjen Curic,Nedim Sladic,Boro Jakimovski 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.3

A “ No vel Th understorm A lert S ystem” (NOTHAS) has been developed and extensively tested for forecast and warnings of mid-latitude and tropical convective events. The design of the system showed some potential advantages compared to earlier alert systems, mainly in reducing uncertainties in predictions by taking the given maximum hourly local-scale signal. It represents a dynamic tool which allows the use of the probability concept of multivariate distribution and integrating it into general function by taking all convective parameters. It utilizes the latest developed microphysical parameterization scheme using a scale and aerosol awareness convective scheme and the sharpest criteria for mid-latitude storms. NOTHAS shows consistency and some kind of flexibility in post-processing applications, regardless of different parameterizations used in the ensemble or deterministic forecasts. The scientific verification shows a high level of accuracy in all significant scores which indicates that severe weather outlooks produced by NOTHAS for several hours ahead are in good alignment with observed thunderstorm activity. This novel tool shows a good performance which has sufficient merit for further additional testing and system evaluation of different severe mid-latitude and tropical storms, tropical cyclones and other severe weather cases across regions.