Nicu Barbu - Academia.edu (original) (raw)

Papers by Nicu Barbu

Research paper thumbnail of Radar-derived parameters in hail-producing storms and the estimation of hail occurrence in Romania using a logistic regression approach

Meteorological Applications

This study investigated the radar-derived parameters in hail-producing storms and compared two ha... more This study investigated the radar-derived parameters in hail-producing storms and compared two hail-detection approaches in order to select the optimal method for real-time hail detection for the southern part of Romania. A statistical analysis of radar parameters was made, and the thresholds for radar-deriver parameters in hailproducing storms were determined. In addition, the hail storms' life cycle and diurnal and seasonal cycles of hail occurrence were investigated. The first algorithm developed in this study was based on the logistic regression model (LRM); the second one on the vertically integrated liquid (VIL) density algorithm. These algorithms were tested for the convective seasons (May-September) of 2014 and 2015. For the construction of the LRM, the composite reflectivity (CR), VIL and echo-top high (ET) were used as predictors for the probability of hail occurrence determination for 43 hail events observed at the synoptic station located in the radar-coverage area. The obtained statistics showed a marked diurnal cycle of hail occurrence with a maximum in the afternoon hours (1500-1800 LT), and the highest occurrence frequency of hail falls was in June. The results revealed that 93% of hail events occurred with 60 dBZ CR, 87% with 13 km ET, 100% with 55 kg/m 2 VIL and 100% with 4.5 g/m 3 VIL density. For the two hail-detection methods' performance comparison, a twoby-two contingency table was constructed and several statistical scores calculated. The LRM algorithm performed better than the VIL density algorithm.

Research paper thumbnail of Aerosol type assessment at Magurele (Romania) based on remote sensing measurements and large scale circulation patterns

A qualitative evaluation of aerosols detected at Magurele (Romania) in correlation with air masse... more A qualitative evaluation of aerosols detected at Magurele (Romania) in correlation with air masses arriving to this region is presented. The aim of this study is to highlight the way the aerosols identified in the area of observation differ depending on its source and transport path. To establish the origin of atmospheric aerosols, two classification method were used, one based on Lagrangian approach (back trajectories analysis), and a second based on Eulerian approach (WLK COST733 catalogue). The analyzed period was from 2012 -2014 and the assessments were carried out both annual and seasonal evaluation. Additionally, the aerosols features within each circulation type had been evaluated in terms of mean aerosol optical depth (AOD) and Angstrom exponent (AE). The results emphasized the presence of aerosols within three main atmospheric layers: first one (between 0.5 and about 2 km) can be assimilated with the PBL, the second layer (between 2 and 4 km) has been detected in 44% of the analyzed cases, and the third layer (between 4 and 6 km) was identified only in 8% of cases. Occasionally (one case detected), the presence of a fourth layer has been noticed at heights of over 10 km. Within the first two layers the dominant types are continental, smoke and their mixture, while mineral aerosol particles dominate the third and fourth layers.

Research paper thumbnail of Analysis of Fog Events at Magurele – Romania Using Ground Based Equipments and Air Circulation

Research paper thumbnail of Heat waves in south-eastern europe - identification of synoptic patterns using COST733 catalogues

Seven of the twelve years at the beginning of 21st Century are considered to be among the driest ... more Seven of the twelve years at the beginning of 21st Century are considered to be among the driest years of all the meteorological record for South-Eastern Europe, since 1961. The study of the main causes and effects of this particular situation and of the subsequent impacts focuses on the analysis of connections between large scale circulation patterns and the last decade's heat waves and drought above mentioned area. Daily maximum temperatures and the Angot index were correlated with circulation patterns identified using COST733 catalogues. The results reveal that persistence, over the South-Eastern Europe, of high pressure synoptic systems having a strong Southern circulation component represents the main cause of extreme temperatures and prolonged drought episodes. keywords: heat wave, drought, circulation pattern, South-Eastern Europe, CLIMHYDEX

Research paper thumbnail of Drought Variability in Eastern Part of Romania and its Connection with Large-Scale Air Circulation

Drought is a phenomenon that appears due to precipitation deficit and it is intensified by strong... more Drought is a phenomenon that appears due to precipitation deficit and it is intensified by strong winds, high temperatures, low relative humidity and high insolation; in fact, all these factors lead to increasing of evapo-transpiration processes that contribute to soil water deficit. The Standardized Precipitation Evapotranspiration Index (SPEI) take into account all this factors listed above. The temporal variability of the drought in Eastern part of Romania for 50 years, during the period 1961-2010, is investigated. This study is focused on the drought variability related to large scale air circulation. The gridded dataset with spatial resolution of 0.5º lat/lon of SPEI, (https://digital.csic.es/handle/10261/72264) were used to analyze drought periods in connection with large scale air circulation determinate from the two catalogues (GWT – GrossWetter-Typen and WLK -WetterLargenKlassi-fikation) defined in COST733Action. The GWT catalogue uses at input dataset the sea level pressur...

Research paper thumbnail of Large-Scale Mechanisms Responsible for Heat Waves Occurrence in Romania

Romanian Journal of Physics

The heat waves, severe weather events, are generally associated with high pressure synoptic syste... more The heat waves, severe weather events, are generally associated with high pressure synoptic systems and tropical air mass advection. The study of the main causes and effects of these particular situations and their subsequent impacts focuses on the analysis of connections between heat waves and large-scale circulation. Daily maximum temperatures from 105 meteorological stations were used to identify the heat waves. The heat waves are identified by using thresholds imposed to the maximum temperature and to the duration of heat waves. After identification, heat waves were associated to circulation types established with GWT and WLK Catalogues developed within the COST733 Action. The most prolonged heat wave episode (18 days) was registered in 1994 at the Oradea synoptic station. The results reveal the persistence over the southeastern Europe of high pressure synoptic systems, having a northeastern circulation component at sea level and a northwestern or southwestern circulation compon...

Research paper thumbnail of Modeling the Precipitation Amounts Dynamics for Different Time Scales in Romania Using Multiple Regression Approach

Romanian Journal of Physics

Water resources are very important for ecosystems and water deficit may cause serious social and ... more Water resources are very important for ecosystems and water deficit may cause serious social and economical issues. The aim of this study is to analyze the performances of prediction procedure based on Multiple Linear Regression Model (MLRM), for the precipitation amounts for yearly and seasonal time scales, in Romania. For this purpose we have used as predictand annual and seasonal amount of precipitation and as predictors Mean Sea Level Pressure (MSLP), geopotential height at 300 hPa (HGT300), wind speed at 700 hPa (WS700), temperature at 850 hPa (T850) and Total Column Water (TCW). The selection of predictors is based on the collinearity and multicollinearity analysis. Multicollinearity problems occur only during winter. All data sets used in this study are reanalysis gridded data with a spatial resolution of 2º x 2º lat/lon and are obtained from 20th Century Reanalysis Version 2 (20CR V2) Project. The analysis is made for a period of 140 years between 1871 and 2010, the period 1...

Research paper thumbnail of Radar-derived parameters in hail-producing storms and the estimation of hail occurrence in Romania using a logistic regression approach

Meteorological Applications

This study investigated the radar-derived parameters in hail-producing storms and compared two ha... more This study investigated the radar-derived parameters in hail-producing storms and compared two hail-detection approaches in order to select the optimal method for real-time hail detection for the southern part of Romania. A statistical analysis of radar parameters was made, and the thresholds for radar-deriver parameters in hailproducing storms were determined. In addition, the hail storms' life cycle and diurnal and seasonal cycles of hail occurrence were investigated. The first algorithm developed in this study was based on the logistic regression model (LRM); the second one on the vertically integrated liquid (VIL) density algorithm. These algorithms were tested for the convective seasons (May-September) of 2014 and 2015. For the construction of the LRM, the composite reflectivity (CR), VIL and echo-top high (ET) were used as predictors for the probability of hail occurrence determination for 43 hail events observed at the synoptic station located in the radar-coverage area. The obtained statistics showed a marked diurnal cycle of hail occurrence with a maximum in the afternoon hours (1500-1800 LT), and the highest occurrence frequency of hail falls was in June. The results revealed that 93% of hail events occurred with 60 dBZ CR, 87% with 13 km ET, 100% with 55 kg/m 2 VIL and 100% with 4.5 g/m 3 VIL density. For the two hail-detection methods' performance comparison, a twoby-two contingency table was constructed and several statistical scores calculated. The LRM algorithm performed better than the VIL density algorithm.

Research paper thumbnail of Aerosol type assessment at Magurele (Romania) based on remote sensing measurements and large scale circulation patterns

A qualitative evaluation of aerosols detected at Magurele (Romania) in correlation with air masse... more A qualitative evaluation of aerosols detected at Magurele (Romania) in correlation with air masses arriving to this region is presented. The aim of this study is to highlight the way the aerosols identified in the area of observation differ depending on its source and transport path. To establish the origin of atmospheric aerosols, two classification method were used, one based on Lagrangian approach (back trajectories analysis), and a second based on Eulerian approach (WLK COST733 catalogue). The analyzed period was from 2012 -2014 and the assessments were carried out both annual and seasonal evaluation. Additionally, the aerosols features within each circulation type had been evaluated in terms of mean aerosol optical depth (AOD) and Angstrom exponent (AE). The results emphasized the presence of aerosols within three main atmospheric layers: first one (between 0.5 and about 2 km) can be assimilated with the PBL, the second layer (between 2 and 4 km) has been detected in 44% of the analyzed cases, and the third layer (between 4 and 6 km) was identified only in 8% of cases. Occasionally (one case detected), the presence of a fourth layer has been noticed at heights of over 10 km. Within the first two layers the dominant types are continental, smoke and their mixture, while mineral aerosol particles dominate the third and fourth layers.

Research paper thumbnail of Analysis of Fog Events at Magurele – Romania Using Ground Based Equipments and Air Circulation

Research paper thumbnail of Heat waves in south-eastern europe - identification of synoptic patterns using COST733 catalogues

Seven of the twelve years at the beginning of 21st Century are considered to be among the driest ... more Seven of the twelve years at the beginning of 21st Century are considered to be among the driest years of all the meteorological record for South-Eastern Europe, since 1961. The study of the main causes and effects of this particular situation and of the subsequent impacts focuses on the analysis of connections between large scale circulation patterns and the last decade's heat waves and drought above mentioned area. Daily maximum temperatures and the Angot index were correlated with circulation patterns identified using COST733 catalogues. The results reveal that persistence, over the South-Eastern Europe, of high pressure synoptic systems having a strong Southern circulation component represents the main cause of extreme temperatures and prolonged drought episodes. keywords: heat wave, drought, circulation pattern, South-Eastern Europe, CLIMHYDEX

Research paper thumbnail of Drought Variability in Eastern Part of Romania and its Connection with Large-Scale Air Circulation

Drought is a phenomenon that appears due to precipitation deficit and it is intensified by strong... more Drought is a phenomenon that appears due to precipitation deficit and it is intensified by strong winds, high temperatures, low relative humidity and high insolation; in fact, all these factors lead to increasing of evapo-transpiration processes that contribute to soil water deficit. The Standardized Precipitation Evapotranspiration Index (SPEI) take into account all this factors listed above. The temporal variability of the drought in Eastern part of Romania for 50 years, during the period 1961-2010, is investigated. This study is focused on the drought variability related to large scale air circulation. The gridded dataset with spatial resolution of 0.5º lat/lon of SPEI, (https://digital.csic.es/handle/10261/72264) were used to analyze drought periods in connection with large scale air circulation determinate from the two catalogues (GWT – GrossWetter-Typen and WLK -WetterLargenKlassi-fikation) defined in COST733Action. The GWT catalogue uses at input dataset the sea level pressur...

Research paper thumbnail of Large-Scale Mechanisms Responsible for Heat Waves Occurrence in Romania

Romanian Journal of Physics

The heat waves, severe weather events, are generally associated with high pressure synoptic syste... more The heat waves, severe weather events, are generally associated with high pressure synoptic systems and tropical air mass advection. The study of the main causes and effects of these particular situations and their subsequent impacts focuses on the analysis of connections between heat waves and large-scale circulation. Daily maximum temperatures from 105 meteorological stations were used to identify the heat waves. The heat waves are identified by using thresholds imposed to the maximum temperature and to the duration of heat waves. After identification, heat waves were associated to circulation types established with GWT and WLK Catalogues developed within the COST733 Action. The most prolonged heat wave episode (18 days) was registered in 1994 at the Oradea synoptic station. The results reveal the persistence over the southeastern Europe of high pressure synoptic systems, having a northeastern circulation component at sea level and a northwestern or southwestern circulation compon...

Research paper thumbnail of Modeling the Precipitation Amounts Dynamics for Different Time Scales in Romania Using Multiple Regression Approach

Romanian Journal of Physics

Water resources are very important for ecosystems and water deficit may cause serious social and ... more Water resources are very important for ecosystems and water deficit may cause serious social and economical issues. The aim of this study is to analyze the performances of prediction procedure based on Multiple Linear Regression Model (MLRM), for the precipitation amounts for yearly and seasonal time scales, in Romania. For this purpose we have used as predictand annual and seasonal amount of precipitation and as predictors Mean Sea Level Pressure (MSLP), geopotential height at 300 hPa (HGT300), wind speed at 700 hPa (WS700), temperature at 850 hPa (T850) and Total Column Water (TCW). The selection of predictors is based on the collinearity and multicollinearity analysis. Multicollinearity problems occur only during winter. All data sets used in this study are reanalysis gridded data with a spatial resolution of 2º x 2º lat/lon and are obtained from 20th Century Reanalysis Version 2 (20CR V2) Project. The analysis is made for a period of 140 years between 1871 and 2010, the period 1...