A Mediterranean cyclone affecting North Africa and Libya was investigated through a set of numerical experiments designed to disentangle the roles of large-scale dynamics, air-sea interaction, and sea surface temperature (SST) structure. Simulations were performed with the WRF model, including an ocean mixed layer (OML) scheme with a prescribed depth of 40 m, consistent with observed conditions. Atmospheric initial and boundary conditions were provided by ECMWF IFS analyses at 6hrs intervals. The cyclone started as an extra tropical cyclone and developed as a warm seclusion system leeward of Tunisia, primarily driven by synoptic scale forcing and orographic effects rather than local thermodynamic feedbacks. Two baseline low-resolution simulations using global model SST were compared with four convection-permitting experiments (1.5 km grid spacing) forced by high-resolution CMEMS SST fields. These simulations, performed with and without spectral nudging, include sensitivity tests to the SST field (i.e., mesoscale SST anomaly removed). Results show that the cyclone track and propagation are largely controlled by the large-scale trough, with only limited local deviations associated with convective bursts. Spectral nudging exerts a secondary influence, slightly improving the alignment with the large-scale flow but inducing only minor changes in the trajectory and landfall timing. The role of air–sea interaction is primarily manifested in the cyclone morphology, propagation speed, and, to a lesser extent, intensity, with differences in minimum sea-level pressure of the order of 2-4 hPa across experiments. On the other hand precipitation is strongly modulated by SST structure. The presence of mesoscale SST anomalies enhances precipitation by more than 25%, highlighting the importance of fine scale air-sea interaction for convective processes. Removal of SST anomalies leads to reduced precipitation and a less organised convective system, despite relative limited impact on the overall cyclone path. These results indicate that, while the system exhibits some tropical-like features, its evolution is predominantly governed by large-scale dynamics, with air-sea interaction playing a secondary, but non-negligible role, particularly for precipitation processes.

On 18 August 2022, an exceptionally intense and fast-moving convective system crossed the western Mediterranean and parts of central Europe, causing widespread wind damage, large hail, and storm surges. Wind gusts exceeding 60 m/s were reported and the event exhibited the typical structure of a derecho, extending over 1000 km and resulting in 12 fatalities and over 100 injuries. This study provides a detailed analysis of the event's evolution and its impacts along the northwestern Italian coastal regions. The analysis is based on observational data, reports, and post-event surveys. The atmospheric characteristics conducive to the extreme event are reconstructed through high-resolution numerical simulations using the Weather Research and Forecasting (WRF) model, in a configuration that includes the assimilation of RADAR and lightning data (3DVAR). The simulations realistically reproduced the two main convective pulses that affected Liguria and northern Tuscany, capturing both the timing and the spatial distribution of maximum wind gusts (30-40 m/s) and rainfall. Post-event surveys documented wind damage up to EF2/IF2 intensity and confirmed the occurrence of downburst-like phenomena in Liguria. Soundings and model diagnostics indicated extreme instability (CAPE >4000 J/kg), strong low-level shear (> 40 m/s), and a dry mid-level layer favorable to intense downdrafts. A concurrent marine heatwave (SST anomalies up to +3 degrees C) likely enhanced low-level moisture fluxes and convective potential. The results emphasize that such marine heatwave-supported derechos represent a growing threat to Mediterranean coastal regions and highlight the need for improved short-term forecasting frameworks.

This study investigates Storm Samuel (Medicane JOLINA), a cyclone that developed over the central Mediterranean during March 2026 and subsequently affected North Africa and Libya. The system originated as a baroclinic cyclone in the lee of Tunisia, evolving through a warm-seclusion phase before acquiring tropical-like characteristics during the final stages of its life cycle. The event therefore provides an ideal framework for exploring the mechanisms governing the transition between extratropical and tropical-like structures in the Mediterranean environment. A hierarchy of numerical experiments is performed using the Weather Research and Forecasting (WRF) model at convection-permitting resolution. Simulations include configurations with and without spectral nudging, experiments using observed high-resolution SST fields and SST fields from which mesoscale anomalies have been removed, a suite of uniform SST perturbation experiments, and a pseudo-global-warming (PGW) simulation based on the ensemble-mean climate change signal derived from multiple future projections. An ocean mixed-layer parameterization is employed to account for air–sea coupling processes. The results indicate that cyclone genesis and propagation are primarily controlled by large-scale atmospheric forcing and regional orographic effects, while air–sea interactions exert a secondary influence on the storm trajectory. In contrast, SST structure plays a substantially larger role in modulating cyclone morphology, convective organisation and precipitation. Mesoscale SST anomalies favour enhanced diabatic activity and more organised convection, whereas their removal leads to a weaker and less coherent precipitation response. Sensitivity experiments further highlight a systematic thermodynamic response to SST changes, while the PGW simulation suggests an amplification of precipitation-producing processes under future climate conditions. Overall, the study highlights the hybrid nature of the event and emphasises how large-scale dynamics govern cyclone evolution, while mesoscale air–sea interactions critically modulate the intensity and hydrological impacts of Mediterranean tropical-like cyclones.

Carbon dioxide, CO2, and methane, CH4, variability in the atmosphere is important because it is the major driver of anthropogenic climate change, while carbon monoxide (CO) is an effective tracer for the combustion process. Knowing the atmospheric transport involved in the land-atmosphere-sea exchange can help to understand the sources of these gases. Measurements were made by a G2401 Picarro analyzer, at the permanent World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) observatory in Southern Italy: Lamezia Terme—LMT. This work presents a preliminary characterization of CO2, CH4, and CO variability in the central Mediterranean basin. The period of investigation includes eight years, i.e., 2015–2022, and has produced an important long-term dataset. A set of 3 primary standards of calibration from NOAA-GML is available at the LMT station: CB10928, CB11039, CB11164; also, secondary standards were used to calibrate the amount of greenhouse gases. Routine calibrations were performed using the observatory’s working standards to assess the possibility of drift and the calibration factors stability. Specifically, for each gas, two working standards with CH4, CO2, and CO mole fractions representing the lower and upper ranges of the expected ambient variability were used. Under the sea breeze regime, air masses more representative of the background atmospheric conditions could be observed, whereas the mole fraction of greenhouse gases was influenced by anthropogenic emissions when air masses flowed in from the interior of the land. This work would contribute significantly to a better understanding of tropospheric chemistry in the central Mediterranean region, which is known as a climate “hotspot.”

Abstract. The catastrophic flood that hit the Marche region (central Italy) on 15 September 2022 has been analyzed using high-resolution Weather Research and Forecasting (WRF) model simulations. The convective rainfall event responsible for the flood was favored by the passage of warm, moist air masses that interacted with the Central Apennines. The convective cells, triggered by the rough orography of the area, formed quasi-stationary bands that caused high rainfall accumulation in limited areas. The formation of these rainbands was sustained by the interaction between the low-level flow and the local topography, which generated a persistent low-level convergence line extending downwind from Mount Amiata northeastward towards the Apennines. The observed vertical profile upstream of the orography reveals that the instability was initially suppressed by an inversion layer and was released only when the humid air arrived at low levels and eroded the inhibition. Although the model somewhat underestimates a peak of rainfall (simulating 160–180 mm versus over 400 mm observed), it correctly reproduces the position of the storm and its evolution, confirming the key role of the orography in anchoring the system and making it quasi-stationary. Furthermore, the simulations suggest that gravity waves generated by the mountains helped to sustain the vertical motion of the impinging air, and highlight the role of upper-level dynamics (passage of a jet streak). Sensitivity experiments reveal a strong dependence on initial and boundary conditions. A comparison of the control run (forced with Global Data Assimilation System (GDAS) analysis/forecasts) with a European Centre for Medium-Range Weather Forecasts (ECMWF)-driven simulation shows a strong sensitivity in the low-level dynamics. Although the large-scale upper-level forcing is almost identical, the ECMWF-driven forecast fails to reproduce the correct amount and distribution of rainfall due to a weaker surface pressure gradient, reduced moisture advection, and lower instability at the time of the event. Specifically, the simulation forced with the ECMWF data anticipates the arrival of the moist air mass, determining a timing mismatch between the low-level supply of moist air (and the consequent release of instability) and the upper-level forcing. This lack of synchronization shifts the rainfall away from the observed area.

On July 10, 2019, a severe windstorm occurred in southeastern Italy, causing one fatality and severe damage. At approximately 17:10 UTC, the downburst crossed the port of Taranto, pushing an employee working on a crane in the Ilva steel plant under water. Unfortunately, the consequence of the event recalls that of an EF3 tornado that occurred on November 28, 2012, which was responsible for the death of another employee working exactly on the same crane. Observations suggest that the event was a microburst that crossed the Ionian coast of the Apulia region. The environment over the Ionian Sea, where the downburst developed, was characterized by intense deep-layer wind speed shear but limited directional shear and strong conditional instability. Mid-level humidity was reduced by dry air transported from the Sahara Desert toward southern Italy. Numerical simulations with a mesoscale model show that it is possible to produce a simulated windstorm with a trajectory and evolution like the real one. The genesis of the downburst was favored by some mesoscale meteorological features: the cold and dry low-level air following a cold front reduced the convective inhibition and initiated convection over the Ionian Sea, while the unidirectional wind profile favored the possibility of downburst development. Finally, the differences in environmental conditions with the case of November 2012 are discussed.

The aim of this research is the quantitative characterization of climate risk, in order to support spatial planners in choosing resilient adaptive actions at the urban and territorial scale. According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, climate risk is the combination of hazard, exposure, and vulnerability parameters. Vulnerability is a function of the climate sensitivity and the adaptive capacity. From the planners' point of view, climate sensitivity expresses the degree to which the study area is influenced by the climate variability. In this regard, the authors have implemented a GeoDataBase to quantify the climate sensitivity over a southern Italian region, analyzing long-term measured meteorological data (air temperature and precipitation) and subsequently generating synthetic maps by interpolating data. As a result, the authors present climate sensitivity maps of the Calabria region, providing useful physical and data-based identification of priority areas for planning purposes.

The radiative effects caused by a massive desert dust outbreak that took place in the Western Sahara Desert, in the proximity of the Atlantic Ocean, in June 2020 are studied. This outbreak featured two significant dust plumes, the second of which is the focus of the present study. For the identification of the dust plume, we adopted a multi-platform set of remote sensing data, including satellite retrievals from the sensors VIIRS, MODIS and SEVIRI onboard the NOAA-20, Aqua and MSG spacecrafts, respectively. The analysis of aerosol-radiation effects is based on a regional simulation with the WRF-Chem model, implementing the coupling between the aerosols of the GOCART speciation and the radiative modules defined in WRF-Chem model by the "New Goddard Shortwave and Longwave Schemes". In this context, two sets of simulations are proposed: the first one (CTL) without any feedback, and the second (CPL) adopting the fullycoupling strategy. From the comparison between the simulated and the observed (SEVIRI) incoming SW/LW radiation it follows that: (i) the presence of dust in the domain causes a reduction of the incoming SW radiation in the CPL runs; (ii) this reduction is fully in agreement with experimental data; (iii) conversely, the LW component appears to be insensitive to model coupling. Hence, the Goddard radiative coupling is effective in reducing the incoming SW radiation: the difference in terms of average daily values between model and SEVIRI is 123.7 vs 37.0 W m- 2 for CTL and CPL runs, respectively. The incoming longwave radiation seems to be less correlated with the coupling strategy, being the difference of 31.15 vs 15.8 W m- 2 for CTL and CPL runs, respectively. The dust radiative forcing (DRF), that characterises the aerosol-radiation interactions, results in an average surface cooling of -16.9 W m- 2 between the CPL and the CTL runs that could be attributed to a reduction of SW radiation absorbed and scattered by dust particles in the coupled run. At the top of the atmosphere (TOA), a warming, caused by the decrease in atmospheric transparency to the terrestrial thermal radiation, results in an average DRF of +1.5 W m- 2. Finally, the space- and time-averaged surface energy balance results in a difference (E(CPL) - E(CTL)) of about -7.5 W m- 2. Similarly, the dynamic response of the dust forcing within the Planetary Boundary Layer is characterised by a mean temperature difference (CPL-CTL) of about -0.7 K near the surface. Our findings strongly encourage the use of fully-coupled modelling strategy, between aerosols and meteorology, for regional-scale studies and in climate risk assessments.

A deep convective system affected the southern Mediterranean on 3-4 December 2022 causing heavy rains and wind gusts over three Italian regions (Sicily, Calabria, and Apulia) and a tornado in Calabria. We study the forecast sensitivity of this multi-hazard weather event to different physical parameterizations and configuration settings of the WRF (Weather Research and Forecasting) model, used at convection permitting horizontal resolution; in particular, we performed sensitivity tests on the role of the initial and boundary conditions, on the Sea Surface Temperature (SST), on the model horizontal resolution and on the cumulus parameterization. Moreover, a 6 h rapid update data assimilation analysis (3DVAR)/forecast cycle was investigated to further study the shortterm forecast capabilities of the modeling system. Most of the WRF configurations are able to well simulate the characteristics of the weather system, even if there are differences among the configurations, especially at the local scale, which causes differences in forecast performances. We found that the quality of the forecast is sensitive to the initial and boundary conditions with the best members having a probability of detection around 30-40 % for rainfall intensities of 40-50 mm/6 h. Most of the forecasts decrease their performance for larger precipitation thresholds, with few exceptions. Specifically, we found that increasing the horizontal resolution was beneficial for the case study as the probability of detection remains larger than 0.2 for rainfall thresholds larger than 60 mm/6 h and up to 100 mm/6 h. In addition, the forecast with lightning and radar reflectivity data assimilation has a probability of detection larger than 0.4 for the same intense thresholds; in both cases false alarms are not increased. For the tornado simulation, no improvement was found adopting 3DVAR. A possible forecasting strategy for severe weather events is outlined.

Unlike stratospheric ozone (O3), which is beneficial for Earth due to its capacity to screen the surface from solar ultraviolet radiation, tropospheric ozone poses a number of health and environmental issues. It has multiple effects that drive anthropogenic climate change, ranging from pure radiative forcing to a reduction of carbon sequestration potential in plants. In the central Mediterranean, which itself represents a hotspot for climate studies, multi-year data on surface ozone were analyzed at the Lamezia Terme (LMT) WMO/GAW coastal observation site, located in Calabria, Southern Italy. The site is characterized by a local wind circulation pattern that results in a clear differentiation between Western-seaside winds, which are normally depleted in pollutants and GHGs, and Northeastern-continental winds, which are enriched in these compounds. This study is the first detailed attempt at evaluating ozone concentrations at LMT and their correlations with meteorological parameters, providing new insights into the source of locally observed tropospheric ozone mole fractions. This research shows that surface ozone daily and seasonal patterns at LMT are “reversed” compared to the patterns observed by comparable studies applied to other parameters and compounds, thus confirming the general complexity of anthropogenic emissions into the atmosphere and their numerous effects on atmospheric chemistry. These observations could contribute to the monitoring and verification of new regulations and policies on environmental protection, cultural heritage preservation, and the mitigation of human health hazards in Calabria.

–WIND RISK is a research project dealing with measurement and modelling of wind fields within thunderstorm cumulonimbus clouds and outflows at the ground (i.e., downbursts and gust fronts). The general objective of the project is to advance the knowledge about the processes occurring inside thunderstorm clouds responsible for strong outflows, and the identification of the environmental (synoptic and meso-scale) conditions favourable to their development. The area under investigation is Northwestern Italy and the Ligurian Sea, which are among the most exposed regions to strong thunderstorms in Europe. Two measurement campaigns using Doppler weather radars and remote-sensing ground-based anemometry, and ad-hoc simulations using the WRF model are carried out to build a database of thunderstorm wind fields with special focus on downdraft and downburst characterization. All measurements and simulations are shared within the scientific community after the end of the project through datasets published on open access platforms.

This paper presents a model intercomparison study to improve the prediction and understanding of Mediterranean cyclone dynamics. It is based on a collective effort with five mesoscale models to look for a robust response among 10 numerical frameworks used in the community involved in the networking activity of the EU COST Action “MedCyclones”. The obtained multi-model, multi-physics ensemble is applied to the high-impact Medicane Ianos of September 2020 with a focus on the cyclogenesis phase, which was poorly forecast by numerical weather prediction systems. Models systematically perform better when initialised from operational IFS analysis data compared to the widely used ERA5 reanalysis. Reducing horizontal grid spacing from 10 km with parameterised convection to convection-permitting 2 km further improves the cyclone track and intensity. This highlights the critical role of deep convection during the early development stage. Higher resolution enhances convective activity, which improves the phasing of the cyclone with an upper-level jet and its subsequent intensification and evolution. This upscale impact of convection matches a conceptual model of upscale error growth in the midlatitudes, while it emphasises the crucial interplay between convective and baroclinic processes during medicane cyclogenesis. The 10 numerical frameworks show robust agreement but also reveal model specifics that should be taken into consideration, such as the need for a parameterisation of deep convection even at 2 km horizontal grid spacing in some models. While they require generalisation to other cases of Mediterranean cyclones, the results provide guidance for the next generation of global convection-permitting models in weather and climate.

In Southern Mediterranean regions, the issue of summer fires related to agriculture practices is a periodic recurrence. It implies a significant increase in carbon dioxide (CO2) emissions and other combustion-related gaseous and particles compounds emitted into the atmosphere with potential impacts on air quality and global climate. In this work, we performed an analysis of summer fire events that occurred on August 2021. Measurements were carried out at the permanent World Meteorological Organization (WMO)/Global Atmosphere Watch (GAW) station of Lamezia Terme (Code: LMT) in Calabria, Southern Italy. The observatory is equipped with greenhouse gases and black carbon analyzers, an atmospheric particulate impactor system, and a meteo-station for atmospheric parameters to characterize atmospheric mechanisms and transport for land and sea breezes occurrences. High mole fractions of carbon monoxide (CO) and carbon dioxide (CO2) coming from quadrants of inland areas were correlated with fire counts detected via the MODIS satellite (GFED-Global Fire Emissions Database) at 1 km of spatial resolution. In comparison with the typical summer values, higher CO and CO2 were observed in August 2021. Furthermore, the growth in CO concentration values in the tropospheric column was also highlighted by the analyses of the L2 products of the Copernicus SP5 satellite. Wind fields were reconstructed via a Weather Research and Forecasting (WRF) output, the latter suggesting a possible contribution from open fire events observed at the inland region near the observatory. So far, there have been no documented estimates of the effect of prescribed burning on carbon emissions in this region. This study suggested that data collected at the LMT station can be useful in recognizing and consequently quantifying emission sources related to open fires.

In this work, we analyzed the radiative effects caused by a giant Saharan dust intrusion that occurred in June 2020, transporting desert dust from the western Sahara to the Caribbean. Our analysis employs (i) remote sensing data from the VIIRS and SEVIRI sensors aboard the NOAA-20 and Meteosat spacecrafts, respectively, and (ii) a regional simulation using the WRF-Chem model, which integrates the aerosol speciation of GOCART with the New Goddard shortwave and longwave radiation schemes. Our results highlight a significant surface cooling effect, with a maximum reduction of shortwave radiation of about − 50 W m− 2, consistent with previous studies, while the longwave radiation component showed limited sensitivity to aerosol interactions. The analysis confirms the critical role of dust in reducing surface solar radiation through scattering and absorption processes. This study serves as an initial exploration of a more comprehensive work presented in a subsequent full paper, where additional simulations and detailed sensitivity analyses are provided. The results encourage the use of fully coupled aerosol-meteorology models in regional studies of dust-induced climate variability. However, limitations of the current study include the underestimation of aerosol optical depth in the early simulation period due to insufficient spin-up time, which may affect the accuracy of initial results.

In 2020, the Covid-19 outbreak led many countries across the globe to introduce lockdowns (LDs) that effectively caused most anthropic activities to either stop completely or be significantly reduced. In Europe, Italy played a pioneeristic role via the early introduction of a strict nationwide LD on March 9th. This study is aimed at evaluating, using both chemical and meteorological data, the environmental response to that occurrence as observed by the Lamezia Terme (LMT) GAW/WMO station in Calabria, Southern Italy. The first 2020 lockdown has therefore been used as a “proving ground” to assess CO, CO2, CH4, eBC, and NOx concentrations in a rather unique context by exploiting the location of LMT in the context of the Mediterranean Basin. In fact, its location on the Tyrrhenian coast of Calabria and local wind circulation both lead to daily cycles where western-seaside winds depleted in anthropogenic pollutants can be easily differentiated from northeastern-continental winds, enriched in anthropogenic outputs. Furthermore, the first Italian LD occurred during the seasonal transition from Winter to Spring and, consequently, Summer, thus providing new insights on emission outputs which are normally linked to domestic heating and other forms of season-specific activities.

In 2020, the COVID-19 outbreak led many countries across the globe to introduce lockdowns (LDs) that effectively caused most anthropic activities to either stop completely or be significantly reduced. In Europe, Italy played a pioneeristic role via the early introduction of a strict nationwide LD on March 9th. This study was aimed at evaluating, using both chemical and meteorological data, the environmental response to that occurrence as observed by the Lamezia Terme (LMT) GAW/WMO station in Calabria, Southern Italy. The first 2020 lockdown was therefore used as a “proving ground” to assess CO, CO2, CH4, BC, and NOx concentrations in a rather unique context by exploiting the location of LMT in the context of the Mediterranean Basin. In fact, its location on the Tyrrhenian coast of Calabria and local wind circulation both lead to daily cycles where western-seaside winds depleted in anthropogenic pollutants can be easily differentiated from northeastern-continental winds, enriched in anthropogenic outputs. In addition to this, the first Italian LD occurred during the seasonal transition from winter to spring and, consequently, summer, thus providing new insights on emission outputs correlated with seasons. The findings clearly indicated BC and, in particular, CO as strongly correlated with average daily temperatures, as well as possibly domestic heating. CO2’s reduction during the lockdown and consequent increase in the post-lockdown period, combined with wind data, allowed us to constrain the local source of emissions located northeast from LMT. NOx reductions during specific circumstances were consistent with hypotheses from previous research, which linked them to rush hour traffic and other forms of transportation emissions. CH4’s stable patterns were consistent with livestock, landfills, and other sources assumed to be nearly constant during LD periods.

Due to its high short-term global warming potential (GWP) compared to carbon dioxide, methane (CH4) is a considerable agent of climate change. This research is aimed at analyzing data on methane gathered at the GAW (Global Atmosphere Watch) station of Lamezia Terme (Calabria, Southern Italy) spanning seven years of continuous measurements (2016–2022) and integrating the results with key meteorological data. Compared to previous studies on detected methane mole fractions at the same station, daily-to-yearly patterns have become more prominent thanks to the analysis of a much larger dataset. Overall, the yearly increase of methane at the Lamezia Terme station is in general agreement with global measurements by NOAA, though local peaks are present, and an increase linked to COVID-19 is identified. Seasonal changes and trends have proved to be fully cyclic, with the daily cycles being largely driven by local wind circulation patterns and synoptic features. Outbreak events have been statistically evaluated depending on their weekday of occurrence to test possible correlations with anthropogenic activities. A cross analysis between methane peaks and specific wind directions has also proved that local sources may be deemed responsible for the highest mole fractions.

The key to a sustainable future is the reduction in humankind’s impact on natural systems via the development of new technologies and the improvement in source apportionment. Although days, years and seasons are arbitrarily set, their mechanisms are based on natural cycles driven by Earth’s orbital periods. This is not the case for weeks, which are a pure anthropic category and are known from the literature to influence emission cycles and atmospheric chemistry. For the first time since it started data gathering operations, CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane) and eBC (equivalent black carbon) values detected by the Lamezia Terme WMO/GAW station in Calabria, Southern Italy, have been evaluated via a two-pronged approach accounting for weekly variations in absolute concentrations, as well as the number of hourly averages exceeding select thresholds. The analyses were performed on seven continuous years of measurements from 2016 to 2022. The results demonstrate that the analyzed GHGs (greenhouse gasses) and aerosols respond differently to weekly cycles throughout the seasons, and these findings provide completely new insights into source apportionment characterization. Moreover, the results have been combined into a new parameter: the hereby defined WDWO (Weighed Distribution of Weekly Outbreaks) normalizes weekly trends in CO, CO2, CH4 and eBC on an absolute scale, with the scope of providing regulators and researchers alike with a new tool meant to better evaluate anthropogenic pollution and mitigate its effects on the environment and human health.

Volcanic emissions (ash, gas, aerosols) dispersed in the atmosphere during explosive eruptions generate hazards affecting aviation, human health, air quality, and the environment. We document for the first time the contamination of airspace by very fine volcanic ash due to sequences of transient ash plumes from Mount Etna. The atmospheric dispersal of sub-10 μm (PM10) ash is modelled using the WRF-Chem model, coupled online with meteorology and aerosols and offline with mass eruption rates (MERs) derived from near-vent Doppler radar measurements and inferred plume altitudes. We analyze two sequences of paroxysms with widely varied volcanological conditions and contrasted meteorological synoptic patterns in October–December 2013 and on 3–5 December 2015. We analyze the PM10 ash dispersal simulation maps in terms of time-averaged columnar ash density, concentration at specified flight levels averaged over the entire sequence interval, and daily average concentration during selected paroxysm days at these flight levels. The very fine ash from such eruption sequences is shown to easily contaminate the airspace around the volcano within a radius of about 1000 km in a matter of a few days. Synoptic patterns with relatively weak tropospheric currents lead to the accumulation of PM10 ash at a regional scale all around Etna. In this context, closely interspersed paroxysms tend to accumulate very fine ash more diffusively at a lower troposphere and in stretched ash clouds higher up in the troposphere. Low-pressure, high-winds weather systems tend to stretch ash clouds into ~100 km wide clouds, forming large-scale vortices 800–1600 km in diameter. Daily average PM10 ash concentrations commonly exceed the aviation hazard threshold, up to 1000 km downwind from the volcano and up to the upper troposphere for intense paroxysms. Vertical distributions show ash cloud thicknesses in the range 0.7–3 km, and PM10 sometimes stagnates at ground level, which represent a potential health hazard.