Journal of Applied Meteorology and Climatology, 2012
This work analyzes and classifies stratospheric airmass transport events (ST) detected at the Nep... more This work analyzes and classifies stratospheric airmass transport events (ST) detected at the Nepal Climate Observatory–Pyramid (NCO-P; 27°57′N, 86°48′E, 5079 m MSL) Global Atmospheric Watch–World Meteorological Organization station from March 2006 to February 2008. For this purpose, in situ ozone (O3), meteorological parameters (atmospheric pressure and relative humidity), and black carbon (BC) are analyzed. The paper describes the synoptic-scale meteorological scenarios that are able to favor the development of ST over the southern Himalaya, by analyzing the meteorological fields provided by the ECMWF model (geopotential height, wind speed, and potential vorticity), satellite Ozone Monitoring Instrument data (total column ozone), and three-dimensional back trajectories calculated with the Lagrangian Analysis Tool (LAGRANTO) model. The study, which represents the first “continuous” classification of ST in the southern Himalaya, permitted classification of 94% of ST days within four...
The pressing need for accurate and reliable precipitation measurements and forecasting poses theo... more The pressing need for accurate and reliable precipitation measurements and forecasting poses theoretical and technological problems. Remote-sensing instruments with increased coverage and sensitivity (such as space-borne and ground-based radar) are available; however, their full exploitation requires physical calibration and validation based on a deep knowledge of precipitation microphysics. This study reports a detailed analysis of the evidence of non-terminal velocities in a mid-latitude (Bologna, Italy) and a tropical location (Kolkata, India). The data from two identical disdrometers OTT-Parsivel2 were analyzed to shed light on the nature of the raindrops that fall at a velocity that is significantly higher (i.e., super-terminal drops) or lower (sub-terminal drops) than the terminal velocity expected for the raindrop sizes. The results show a significant fraction of super- and sub-terminal drops in both locations. The percentages of both super- and sub-terminal drops were higher...
The pressing need for accurate and reliable precipitation measurements and forecasting poses theo... more The pressing need for accurate and reliable precipitation measurements and forecasting poses theoretical and technological problems. Remote-sensing instruments with increased coverage and sensitivity (such as space-borne and ground-based radar) are available; however, their full exploitation requires physical calibration and validation based on a deep knowledge of precipitation microphysics. This study reports a detailed analysis of the evidence of non-terminal velocities in a mid-latitude (Bologna, Italy) and a tropical location (Kolkata, India). The data from two identical disdrometers OTT-Parsivel2 were analyzed to shed light on the nature of the raindrops that fall at a velocity that is significantly higher (i.e., super-terminal drops) or lower (sub-terminal drops) than the terminal velocity expected for the raindrop sizes. The results show a significant fraction of super- and sub-terminal drops in both locations. The percentages of both super- and sub-terminal drops were higher...
Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote se... more Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote sensing instruments with the necessary spatial coverage, resolution, and temporal sampling are essential for snowfall monitoring. Among such instruments, ground-radars have scanning capability and a resolution that make it possible to obtain a 3D structure of precipitating systems or vertical profiles when used in profiling mode. Radars from space have a lower spatial resolution, but they provide a global view. However, radar-based quantitative estimates of solid precipitation are still a challenge due to the variability of the microphysical, geometrical, and electrical features of snow particles. Estimations of snowfall rate are usually accomplished using empirical, long-term relationships between the equivalent radar reflectivity factor (Ze) and the liquid-equivalent snowfall rate (SR). Nevertheless, very few relationships take advantage of the direct estimation of the microphysical char...
In spite of the high relevance of the satellite data for collecting information regarding precipi... more In spite of the high relevance of the satellite data for collecting information regarding precipitation at global scale, validating satellite retrievals with measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only one able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters. In this study, we compare near surface GPM retrievals with almost 6 years of DSD parameters estimated by a laser disdrometer in Rome (Italy) since the launch of GPM mission. The comparison shows limited difference in performances of the different GPM algorithms, also with reference to the dual frequency algorithm with respect to the single frequency one. Furthermore, the agreement between satellite and ground based data depends on the considered precipitation variable as well as on the spatial and temporal scale matching constrains.
The high relevance of satellites for collecting information regarding precipitation at global sca... more The high relevance of satellites for collecting information regarding precipitation at global scale implies the need of a continuous validation of satellite products to ensure good data quality over time and to provide feedback for updating and improving retrieval algorithms. However, validating satellite products using measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only active sensor able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters from space. In this study, we compare near surface GPM retrievals with long time series of measurements collected by seven laser disdrometers in Italy since the launch of the GPM mission. The comparison shows limited differences in the performances of the different GPM algorithms, be they dual- or single-fr...
In spite of the high relevance of the satellite data for collecting information regarding precipi... more In spite of the high relevance of the satellite data for collecting information regarding precipitation at global scale, validating satellite retrievals with measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only one able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters. In this study, we compare near surface GPM retrievals with almost 6 years of DSD parameters estimated by a laser disdrometer in Rome (Italy) since the launch of GPM mission. The comparison shows limited difference in performances of the different GPM algorithms, also with reference to the dual frequency algorithm with respect to the single frequency one. Furthermore, the agreement between satellite and ground based data depends on the considered precipitation variable as well ...
The high relevance of satellites for collecting information regarding precipitation at global sca... more The high relevance of satellites for collecting information regarding precipitation at global scale implies the need of a continuous validation of satellite products to ensure good data quality over time and to provide feedback for updating and improving retrieval algorithms. However, validating satellite products using measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only active sensor able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters from space. In this study, we compare near surface GPM retrievals with long time series of measurements collected by seven laser disdrometers in Italy since the launch of the GPM mission. The comparison shows limited differences in the performances of the different GPM algorithms, be they dual- or single-fr...
. This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over South... more . This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over Southern Europe in late March 2020. This event was associated with an anomalous circulation pattern leading to several days of PM10 exceedances in connection with a dust source located in Central Asia a rare source of dust for Europe, more frequently affected by dust outbreaks from the Sahara desert. The synoptic meteorological configuration was analyzed in detail, while aerosol evolution during the transit of the dust cloud over Northern Italy was assessed at high time resolution by means of optical particle counting at three stations, namely Bologna, Trieste, and Mt. Cimone allowing to reveal transport timing among the three locations. Back-trajectory analyses supported by AOD (Aerosol Optical Depth) maps allowed to locate the mineral dust source area in the Aralkum region. The event was therefore analyzed through the observation of particle number size distribution with the support of chemical composition analysis. It is shown that PM10 exceedance recorded is associated with a large fraction of coarse particles in agreement with mineral dust properties. Both in-situ number size distribution and vertical distribution of the dust plume were cross-checked by Lidar Ceilometer and AOD data from two nearby stations, showing that the dust plume, differently from those originated in the Sahara desert, traveled close to the ground up to a height of about 2 km. The limited mixing layer height caused by high concentrations of absorbing and scattering aerosols caused the mixing of mineral dust with other locally-produced ambient aerosols, thereby potentially increasing its morbidity effects.
Low-cost sensors based on the optical particle counter (OPC) are increasingly being used to colle... more Low-cost sensors based on the optical particle counter (OPC) are increasingly being used to collect particulate matter (PM) data at high space and time resolution. In spite of their huge explorative potential, practical guidelines and recommendations for their use are still limited. In this work, we outline a few best practices for the optimal use of PM low-cost sensors based on the results of an intensive field campaign performed in Bologna (44°30′ N, 11°21′ E; Italy) under different weather conditions. Briefly, the performances of a series of sensors were evaluated against a calibrated mainstream OPC with a heated inlet, using a robust approach based on a suite of statistical indexes capable of evaluating both correlations and biases in respect to the reference sensor. Our results show that the sensor performance is sensibly affected by both time resolution and weather with biases maximized at high time resolution and high relative humidity. Optimization of PM data obtained is the...
Abstract Recently, the interest on snowfall remote sensing and quantitative precipitation estimat... more Abstract Recently, the interest on snowfall remote sensing and quantitative precipitation estimation is becoming a popular topic by both the scientific and operational communities. As a matter of fact, snow plays a key role in the hydrological cycle and Earth energy budget and clearly represents a meteorological hazard that can seriously compromise human activities and properties. In this study, we used a dual-polarization X-band weather radar to quantify the near-surface liquid equivalent snowfall rate, proposing a new parameterization based on the use of radar reflectivity factor and specific differential phase shift. This effort adds to several recent works, mainly focused on S-band weather radar systems, demonstrating that the use of the radar specific differential phase shift (Kdp) is able to enhance the estimation precision with respect to the more customary approaches making use of radar reflectivity factor alone. To demonstrate this concept also at X-band, some case studies were collected from December 2018 to May 2019 in the Southern Apennine Mountains in the area of Naples (Italy). They were used to compare the proposed radar based liquid equivalent snowfall rate estimations, based on Z and Kdp, with reference laser-optical disdrometer time series collected in the close reference site of Montevergine observatory. Findings show that also at X band the use of Kdp produces a better score between the radar-derived liquid equivalent snowfall rate and the reference one from the disdrometer.
Knowledge of the precipitation contribution to the Antarctic surface mass balance is essential fo... more Knowledge of the precipitation contribution to the Antarctic surface mass balance is essential for defining the ice-sheet contribution to sea-level rise. Observations of precipitation are sparse over Antarctica, due to harsh environmental conditions. Precipitation during the summer months (November–December–January) on four expeditions, 2015–16, 2016–17, 2017–18 and 2018–19, in the Terra Nova Bay area, were monitored using a vertically pointing radar, disdrometer, snow gauge, radiosounding and an automatic weather station installed at the Italian Mario Zucchelli Station. The relationship between radar reflectivity and precipitation rate at the site can be estimated using these instruments jointly. The error in calculated precipitation is up to 40%, mostly dependent on reflectivity variability and disdrometer inability to define the real particle fall velocity. Mean derived summer precipitation is ~55 mm water equivalent but with a large variability. During collocated measurements in...
Journal of Applied Meteorology and Climatology, 2012
This work analyzes and classifies stratospheric airmass transport events (ST) detected at the Nep... more This work analyzes and classifies stratospheric airmass transport events (ST) detected at the Nepal Climate Observatory–Pyramid (NCO-P; 27°57′N, 86°48′E, 5079 m MSL) Global Atmospheric Watch–World Meteorological Organization station from March 2006 to February 2008. For this purpose, in situ ozone (O3), meteorological parameters (atmospheric pressure and relative humidity), and black carbon (BC) are analyzed. The paper describes the synoptic-scale meteorological scenarios that are able to favor the development of ST over the southern Himalaya, by analyzing the meteorological fields provided by the ECMWF model (geopotential height, wind speed, and potential vorticity), satellite Ozone Monitoring Instrument data (total column ozone), and three-dimensional back trajectories calculated with the Lagrangian Analysis Tool (LAGRANTO) model. The study, which represents the first “continuous” classification of ST in the southern Himalaya, permitted classification of 94% of ST days within four...
The pressing need for accurate and reliable precipitation measurements and forecasting poses theo... more The pressing need for accurate and reliable precipitation measurements and forecasting poses theoretical and technological problems. Remote-sensing instruments with increased coverage and sensitivity (such as space-borne and ground-based radar) are available; however, their full exploitation requires physical calibration and validation based on a deep knowledge of precipitation microphysics. This study reports a detailed analysis of the evidence of non-terminal velocities in a mid-latitude (Bologna, Italy) and a tropical location (Kolkata, India). The data from two identical disdrometers OTT-Parsivel2 were analyzed to shed light on the nature of the raindrops that fall at a velocity that is significantly higher (i.e., super-terminal drops) or lower (sub-terminal drops) than the terminal velocity expected for the raindrop sizes. The results show a significant fraction of super- and sub-terminal drops in both locations. The percentages of both super- and sub-terminal drops were higher...
The pressing need for accurate and reliable precipitation measurements and forecasting poses theo... more The pressing need for accurate and reliable precipitation measurements and forecasting poses theoretical and technological problems. Remote-sensing instruments with increased coverage and sensitivity (such as space-borne and ground-based radar) are available; however, their full exploitation requires physical calibration and validation based on a deep knowledge of precipitation microphysics. This study reports a detailed analysis of the evidence of non-terminal velocities in a mid-latitude (Bologna, Italy) and a tropical location (Kolkata, India). The data from two identical disdrometers OTT-Parsivel2 were analyzed to shed light on the nature of the raindrops that fall at a velocity that is significantly higher (i.e., super-terminal drops) or lower (sub-terminal drops) than the terminal velocity expected for the raindrop sizes. The results show a significant fraction of super- and sub-terminal drops in both locations. The percentages of both super- and sub-terminal drops were higher...
Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote se... more Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote sensing instruments with the necessary spatial coverage, resolution, and temporal sampling are essential for snowfall monitoring. Among such instruments, ground-radars have scanning capability and a resolution that make it possible to obtain a 3D structure of precipitating systems or vertical profiles when used in profiling mode. Radars from space have a lower spatial resolution, but they provide a global view. However, radar-based quantitative estimates of solid precipitation are still a challenge due to the variability of the microphysical, geometrical, and electrical features of snow particles. Estimations of snowfall rate are usually accomplished using empirical, long-term relationships between the equivalent radar reflectivity factor (Ze) and the liquid-equivalent snowfall rate (SR). Nevertheless, very few relationships take advantage of the direct estimation of the microphysical char...
In spite of the high relevance of the satellite data for collecting information regarding precipi... more In spite of the high relevance of the satellite data for collecting information regarding precipitation at global scale, validating satellite retrievals with measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only one able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters. In this study, we compare near surface GPM retrievals with almost 6 years of DSD parameters estimated by a laser disdrometer in Rome (Italy) since the launch of GPM mission. The comparison shows limited difference in performances of the different GPM algorithms, also with reference to the dual frequency algorithm with respect to the single frequency one. Furthermore, the agreement between satellite and ground based data depends on the considered precipitation variable as well as on the spatial and temporal scale matching constrains.
The high relevance of satellites for collecting information regarding precipitation at global sca... more The high relevance of satellites for collecting information regarding precipitation at global scale implies the need of a continuous validation of satellite products to ensure good data quality over time and to provide feedback for updating and improving retrieval algorithms. However, validating satellite products using measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only active sensor able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters from space. In this study, we compare near surface GPM retrievals with long time series of measurements collected by seven laser disdrometers in Italy since the launch of the GPM mission. The comparison shows limited differences in the performances of the different GPM algorithms, be they dual- or single-fr...
In spite of the high relevance of the satellite data for collecting information regarding precipi... more In spite of the high relevance of the satellite data for collecting information regarding precipitation at global scale, validating satellite retrievals with measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only one able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters. In this study, we compare near surface GPM retrievals with almost 6 years of DSD parameters estimated by a laser disdrometer in Rome (Italy) since the launch of GPM mission. The comparison shows limited difference in performances of the different GPM algorithms, also with reference to the dual frequency algorithm with respect to the single frequency one. Furthermore, the agreement between satellite and ground based data depends on the considered precipitation variable as well ...
The high relevance of satellites for collecting information regarding precipitation at global sca... more The high relevance of satellites for collecting information regarding precipitation at global scale implies the need of a continuous validation of satellite products to ensure good data quality over time and to provide feedback for updating and improving retrieval algorithms. However, validating satellite products using measurements collected by sensors at ground is still a challenging task. To date, the Dual-frequency Precipitation Radar (DPR) aboard the Core Satellite of the Global Precipitation Measurement (GPM) mission is the only active sensor able to provide, at global scale, vertical profiles of rainfall rate, radar reflectivity, and Drop Size Distribution (DSD) parameters from space. In this study, we compare near surface GPM retrievals with long time series of measurements collected by seven laser disdrometers in Italy since the launch of the GPM mission. The comparison shows limited differences in the performances of the different GPM algorithms, be they dual- or single-fr...
. This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over South... more . This paper concerns an in-depth analysis of an exceptional incursion of mineral dust over Southern Europe in late March 2020. This event was associated with an anomalous circulation pattern leading to several days of PM10 exceedances in connection with a dust source located in Central Asia a rare source of dust for Europe, more frequently affected by dust outbreaks from the Sahara desert. The synoptic meteorological configuration was analyzed in detail, while aerosol evolution during the transit of the dust cloud over Northern Italy was assessed at high time resolution by means of optical particle counting at three stations, namely Bologna, Trieste, and Mt. Cimone allowing to reveal transport timing among the three locations. Back-trajectory analyses supported by AOD (Aerosol Optical Depth) maps allowed to locate the mineral dust source area in the Aralkum region. The event was therefore analyzed through the observation of particle number size distribution with the support of chemical composition analysis. It is shown that PM10 exceedance recorded is associated with a large fraction of coarse particles in agreement with mineral dust properties. Both in-situ number size distribution and vertical distribution of the dust plume were cross-checked by Lidar Ceilometer and AOD data from two nearby stations, showing that the dust plume, differently from those originated in the Sahara desert, traveled close to the ground up to a height of about 2 km. The limited mixing layer height caused by high concentrations of absorbing and scattering aerosols caused the mixing of mineral dust with other locally-produced ambient aerosols, thereby potentially increasing its morbidity effects.
Low-cost sensors based on the optical particle counter (OPC) are increasingly being used to colle... more Low-cost sensors based on the optical particle counter (OPC) are increasingly being used to collect particulate matter (PM) data at high space and time resolution. In spite of their huge explorative potential, practical guidelines and recommendations for their use are still limited. In this work, we outline a few best practices for the optimal use of PM low-cost sensors based on the results of an intensive field campaign performed in Bologna (44°30′ N, 11°21′ E; Italy) under different weather conditions. Briefly, the performances of a series of sensors were evaluated against a calibrated mainstream OPC with a heated inlet, using a robust approach based on a suite of statistical indexes capable of evaluating both correlations and biases in respect to the reference sensor. Our results show that the sensor performance is sensibly affected by both time resolution and weather with biases maximized at high time resolution and high relative humidity. Optimization of PM data obtained is the...
Abstract Recently, the interest on snowfall remote sensing and quantitative precipitation estimat... more Abstract Recently, the interest on snowfall remote sensing and quantitative precipitation estimation is becoming a popular topic by both the scientific and operational communities. As a matter of fact, snow plays a key role in the hydrological cycle and Earth energy budget and clearly represents a meteorological hazard that can seriously compromise human activities and properties. In this study, we used a dual-polarization X-band weather radar to quantify the near-surface liquid equivalent snowfall rate, proposing a new parameterization based on the use of radar reflectivity factor and specific differential phase shift. This effort adds to several recent works, mainly focused on S-band weather radar systems, demonstrating that the use of the radar specific differential phase shift (Kdp) is able to enhance the estimation precision with respect to the more customary approaches making use of radar reflectivity factor alone. To demonstrate this concept also at X-band, some case studies were collected from December 2018 to May 2019 in the Southern Apennine Mountains in the area of Naples (Italy). They were used to compare the proposed radar based liquid equivalent snowfall rate estimations, based on Z and Kdp, with reference laser-optical disdrometer time series collected in the close reference site of Montevergine observatory. Findings show that also at X band the use of Kdp produces a better score between the radar-derived liquid equivalent snowfall rate and the reference one from the disdrometer.
Knowledge of the precipitation contribution to the Antarctic surface mass balance is essential fo... more Knowledge of the precipitation contribution to the Antarctic surface mass balance is essential for defining the ice-sheet contribution to sea-level rise. Observations of precipitation are sparse over Antarctica, due to harsh environmental conditions. Precipitation during the summer months (November–December–January) on four expeditions, 2015–16, 2016–17, 2017–18 and 2018–19, in the Terra Nova Bay area, were monitored using a vertically pointing radar, disdrometer, snow gauge, radiosounding and an automatic weather station installed at the Italian Mario Zucchelli Station. The relationship between radar reflectivity and precipitation rate at the site can be estimated using these instruments jointly. The error in calculated precipitation is up to 40%, mostly dependent on reflectivity variability and disdrometer inability to define the real particle fall velocity. Mean derived summer precipitation is ~55 mm water equivalent but with a large variability. During collocated measurements in...
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Papers by Alessandro Bracci