bluuebunny/crossref_metadata_2025 huggingface dataset:
La ville, espace des tensions de la modernité
Authors: FERGUSON Yann
Published: March 2023

La perception de la ville moderne renvoie la question de ses différents moments sociologiques qui la constituent, à savoir, la différenciation sociale, l’individualisation et la rationalisation. A ce titre, la ville abrite des activités humaines qui en font un tout traversés par de multiples tensions. Il en résulte des interrogations notamment des citadins sur leur capacité à accepter une vie en société et un destin collectif.
Crise territoriale, éléments de définition
Authors: LAGANIER Richard , VEYRET Yvette
Published: March 2023

Comment définir une crise ? À partir de quels critères peut-on définir la crise, comment classer les différents types de crise ? Quelle différence peut-on faire entre crise et catastrophe ? La territorialisation des crises et des catastrophes permet de proposer une typologie. La notion de crise recouvre des réalités multiples. Chaque crise est unique. Si l’événement déclencheur peut être d’origine variée, il révèle surtout des vulnérabilités dormantes, propres aux territoires concernés : vulnérabilités matérielles, fonctionnelles et structurelles.
Crise fondatrice du renouveau territorial
Authors: VEYRET Yvette , LAGANIER Richard
Published: March 2023

L’augmentation des événements catastrophiques d’origine industrielle ou naturelle est le révélateur d’une intégration insuffisamment pensée du risque en ville. Retrouver un environnement de qualité est un enjeu, en termes d’images et d’appropriation territoriale. Renouveler les territoires en intégrant les leçons tirées des crises passées et des risques revient à prendre en compte différentes temporalités d’action et à concevoir des projets urbains qui considèrent la complexité des systèmes territoriaux et leur dynamique. Cela suppose une vision globale, multidimensionnelle, fondée à la fois sur la protection, la prévention et l’adaptation de l’habitat, des quartiers, des villes, des infrastructures urbaines (réseaux, infrastructures critiques, etc.) aux dangers. Plusieurs exemples d’adaptation sont ainsi présentés.
Les problèmes inverses pour la reconstruction d’image en holographie
Authors: SOULEZ Ferréol , THIÉBAUT Éric
Published: March 2023

Ce chapitre est une introduction aux principes des méthodes inverses avec une attention particulière au cas de la reconstruction d'image en holographie numérique qui sert d'exemple d'application et de fil conducteur. Sont abordés les problèmes liés au modèle de formation des données (non-linéarité, troncature du champ, bruits de mesure,...) ainsi que les différents a priori permettant de résoudre ces problèmes.
Une introduction à l’imagerie computationnelle monodétecteur
Authors: DUCROS Nicolas
Published: March 2023

L’imagerie computationnelle monodétecteur permet d’acquérir une image au moyen d’un détecteur ponctuel, ce qui en fait une méthode de choix pour l’imagerie spectrale dans le visible ou l’infrarouge. Ce chapitre donne un aperçu de l’évolution de cette approche au cours des dernières décennies, notamment en ce qui concerne les algorithmes de reconstruction.
Sedimentary blue carbon dynamics based on chronosequential observations in a tropical restored mangrove forest
Authors: Ray Raghab , Suwa Rempei , Miyajima Toshihiro , Munar Jeffrey , Yoshikai Masaya , San Diego-McGlone Maria Lourdes , Nadaoka Kazuo
Published: March 2023

Abstract. Among the many ecosystem services provided by mangroves, the
sequestration of large amounts of organic carbon (OC) in marine ecosystems
(also known as “blue carbon”) has given these unique ecological environments
enormous global attention. While there are many studies on the blue carbon
potential of intact mangroves (i.e., naturally growing), there have been
very few studies on restored mangroves (i.e., planted). This study aims to
address this knowledge gap by examining the sediment development process
during the early colonization (rehabilitation) of mangroves in an OC-poor
estuary in Panay Island, Philippines. Based on source apportionment of
multiple end-members in the sedimentary organic matter, the contribution of
mangrove plant material was higher at the older sites compared to the
younger sites or bare sediments where there is a higher contribution of riverine
input. A clear increasing gradient according to mangrove development was
observed for bulk OC (0.06–3.4 µmol g−1), porewater OC
(292–2150 µmol L−1), sedimentary OC stocks (3.13–77.4 Mg C ha−1), and OC loading per surface area (7–223 µmol m−2).
The estimated carbon accumulation rates (6–33 mol m−2 yr−1) based
on chronosequence are within the global ranges and show an increasing
pattern with the age of mangroves. Hence, the sediments of relatively young
mangrove forests appear to be a significant potential C sink, and short-term
chronosequence-based observations can efficiently define the importance of
mangrove restoration programs as a potential carbon sequestration pathway.
Nowcasting severe weather using geostationary satellite data and GLM-based lightning trends of thunderstorm cells
Authors: Erdmann Felix , Poelman Dieter R.
Published: March 2023

In December 2022, the third generation of Meteosat (MTG) is launched to provide geostationary imagery over Europe and other parts of the world. MTG also carries a Lightning Imager (LI) to locate lightning discharges from space. A similar instrument, the Geostationary Lightning Mapper (GLM), operationally monitors lightning on the GOES-R series satellites.

This work uses EUMETSAT’s NWCSAF nowcasting software to identify and track thunderstorms from space. GLM lightning history for each storm track can be analyzed in order to identify abrupt changes in the storm’s flash rate, e.g., lightning jumps (LJs) and lightning dives (LDs). Severe weather reports from the NOAA Storm Prediction Center (SPC) archive are used as ground truth to verify the retrieved LJs, to determine leadtimes, and to investigate the potential of those lightning trends to nowcast severe weather. As a first step, three different LJ-algorithms are tested and their parameters are optimized for the GLM records. Under the hypothesis that lightning trends are correlated to severe weather occurrences, contingency tables are created and evaluated with well-known scores, e.g., the Critical Success Index (CSI). Overall, more than 45,000 thunderstorms are analyzed in this work. About 5% of the thunderstorms exhibit a LJ and/or SPC severe weather report. It is found that a modification of the so-called sigma-LJ algorithm and a novel Relative Increase Level (RIL) LJ algorithm show the most promising results when using moderately strict parameters. Leadtimes are highly variable with LJs occurring on average 36 minutes before the SPC report. Further research filters the LJs based on thresholds of the storm’s convective rain rates and overshooting top detection to improve the CSI when correlating LJs and SPC reports.
Two Archetypes of Tornadic Quasilinear Convective Systems in the United Kingdom: Vortex Genesis and Maintenance
Authors: J. Buckingham Ty , M. Schultz David , M. Markowski Paul , J. Trapp Robert
Published: March 2023

Nine tornado outbreaks (days with three or more tornadoes) have occurred in the United Kingdom from quasi-linear convective systems in the 16 years between 2004 and 2019. Of the nine outbreaks, eight can be classified into two archetypes: type 1 and type 2. Simulations of each archetype were performed to determine vortex genesis mechanisms. In a type 1 event, a vortex sheet broke down into near-equally spaced misovortices, whereas in a type 2 event, disorganized, elongated cyclonic–anticyclonic couplets evolved into a small number of misovortices. The assessment of Rayleigh's and Fjörtoft's instability criteria, along with misovortices having a wavelength of about 7.5 times the width of the shear zone, implied horizontal shearing instability (HSI) was the initial mechanism for the amplification of perturbations along the vortex sheet in the type 1 event. Vorticity-tendency analysis also revealed near-equally spaced localized horizontal advection maxima prior to the growth of perturbations in the type 1 event, further reinforcing HSI as a plausible mechanism. Deformation was not strong enough to suppress vortex growth. In contrast, the type 2 event did not satisfy either criteria. Parcels acquired vertical vorticity differently dependent on the location and the height that they entered the misovortex. In the type 1 event, parcels entering the misovortex at lower heights experienced varying magnitudes of stretching and tilting, whereas tilting was considerably stronger at greater heights. In the type 2 event, parcels entering the misovortex from the leading edge of the misovortex acquired the majority of their vertical vorticity via both tilting and stretching, and parcels entering the misovortex from the trailing edge acquired the majority of their vertical vorticity via stretching. These results suggest two possible mechanisms for misovortex genesis in UK tornado outbreaks: type 1 where HSI initiates the vortices and type 2 that form from vorticity couplets along the front not formed from HSI.
Impact of mountains on environments and estimated precipitation intensity of supercells
Authors: Kvak Robert , Zacharov Petr , Okon Luboslav , Bliznak Vojtech , Meri Ladislav , Kaspar Marek
Published: March 2023

For decades, the role of mountains in influencing both a supercell environment during initiation stage and later storm dynamics was poorly understood. Since the consequences of terrain-induced effects on supercells seem to play a crucial part in the distribution of convective precipitation at least in mountainous regions, several topic-focused papers have already been published particularly in the last fifteen years. Our contribution to the issue is based on the examination of two-dimensional radar data of 62 supercells that initiated over the western part of the Carpathian Mountains in Central Europe in the years 2015–2019. To investigate the basic spatiotemporal characteristics and estimated precipitation intensity of storms, mainly Doppler and pseudo-CAPPI products from the Slovak weather radar network were employed in the study. Potential impact of terrain asymmetry on supercells precipitation intensity through their lifetime was evaluated by the relationship between morphometric variables of the terrain and radar reflectivity factor within the proximity (5, 10, 15-km radius) of detected mesocyclones in 5-min radar scans. Subsequently, atmospheric conditions along with convective parameters during the events were simulated in the COSMO model. Initial environments were compared with actual radar reflectivity properties (e.g., area of reflecting radar pixels >50 dBZ) of storms and their propagation qualities such as translation speed, duration, and track length. Although no general connection of radar reflectivity to underlying terrain even with a time shift up to 30 min was found, increasing reflectivity of some supercells showed preferences to more unstable environments which clearly were related to orographic modification. Besides, the poster highlights several other intriguing findings of supercells behavior over complex terrain.
Revisiting the unusual period of F4/F5 tornadoes in Europe from 1965 to 1971
Authors: Schyns Jerome , Gatzen Christoph , Schielicke Lisa
Published: March 2023

In the six-year period of 1965 to 1971, an unusually high number of violent tornadoes of category F4 and F5 was observed in Europe including six F4 tornadoes in Switzerland, France (2), Italy (2) and Germany as well as one F5 tornado in France. We use this tornado series to analyze the conditions present in violent European tornadoes.

ESWD (European Severe Weather Database) data, ERA5 reanalysis data and historic weather maps are used to classify the large-scale weather patterns with respect to the strength of synoptic-scale forcing, the position of the jet stream across Europe and relative to the tornadic thunderstorms, location of fronts including drylines, coastal fronts, and pre-frontal convergence zones that could have influenced the thunderstorms development. We use an ingredients-based method to analyze the large-scale flow, focusing on the origin and advection of lapse rates, low-level moisture, zones of lift, and vertical wind shear. For example, we distinguish between situations with a large area affected by an overlap of CAPE and strong vertical wind shear and situations where only a small “sweet spot” could have influenced the development and organization of the thunderstorms.

The vertical profile close to the convective storms are analyzed in ERA5 data that are compared with observation data. Here, we concentrate on the profile of vertical wind shear and the occurrence of low-level streamwise vorticity, expected cloud base, and expected cold pool potential due to evaporative cooling. Additionally, we estimate the motion vectors of supercells.

Proximity soundings serve to initialize supercell simulations using cloud model 1 (CM1, using the pre-configured, idealized supercell set-ups). We discuss the development of convection in the idealized model simulation and characterize the thunderstorms with respect to the lifted condensation level, the height of the mesocyclone, storm motion vector, and col pool potential. The results are compared to findings from the literature.
Observations of Severe-Wind Driven and other Wildfires with DOWs
Authors: Wurman Joshua , Kosiba Karen
Published: March 2023

Doppler On Wheels (DOW) mobile / targetable truck-borne radars have deployed to collect fine-scale observations in several wildfires, one, recently, causing widespread destruction in an urban area.   DOW measurements in wildfires permit the mapping of the windfields, hydrometeors, and airborne particles in the fire plumes, and characterization of the near-fire environment.  DOWs can collect windfield and other data below the observing horizon of more distant radars, and at much finer-scale spatial resolution, revealing otherwise unmappable aspects of low-level and small scale structure and evolution. 

 

Observations of three wildfires will be discussed: 

In 2020, two DOWs deployed in the mountains of Colorado and collected dual-Doppler vector wind data primarily in the fire environment.  

During another fire in 2020, the DOWs were deployed close to wildfires  which destroyed many homes.  Small-scale vortices and other features are resolvable due to the close proximity of the  deployed radars to the wildfires.  Dual-Doppler DOW analysis, the first fine-scale dual-Doppler analysis of this type,  will be presented.  

In 2021, a DOW deployed in South Boulder, Colorado in the metropolitan Boulder wildfire / extreme wind event where winds exceeding 45 m/s enhanced fires which destroyed many homes and businesses in the south Boulder area.  The evolution of the wind field was mapped.
Using convection-permitting simulations to assess future changes in lightning and hail in Europe 
Authors: Kahraman Abdullah , Kendon Elizabeth , Fowler Hayley , Wilkinson Jonathan
Published: March 2023

How lightning and hail will change in the future with global warming is highly uncertain, mainly due to the small space and time scales of these phenomena, which requires high-resolution climate simulations for their accurate representation. Recently km-scale climate simulations have become available that are ‘convection-permitting’ and give the possibility of studying how convective storms may change. We use a pan-European convection-permitting (2.2km grid spacing) model to analyse future changes in deep moist convection, lightning, and hail across Europe under a high emissions-scenario. This includes a physically based lightning prediction scheme, that uses graupel and ice-fluxes that are explicitly represented within the model. It also provides convective-scale outputs, not previously available from conventional climate models, exploited here to study future changes using an ingredients-based approach inherited from severe storm forecasting.

For hail, we derive a new severe hail potential metric that represents the likelihood of hail >2cm at the surface, accounting for hail growth and subsequent melting. Overall, we find an increasing frequency of deep moist convection across Europe mainly due to more instability with warming, but partially limited by greater convective inhibition. However, the increase in storms does not directly translate to an increase in lightning, mainly due to much higher melting level heights resulting in less cloud ice and hence less electrification. Weaker circulation and a northward shift of favourable weather regimes in the future simulation also affects the results, which vary regionally. While lightning increases in future over the mountains (due to enhanced Alpine Pumping) and in the north, lightning decreases over much of central Europe and over the sea. The potential for severe hail generally decreases in future, although storms locally produce higher amounts of graupel in the south. We also identify a new, warmer type of thunderstorms in the future, which may have important implications for changes to the frequency of the largest hailstones.
Mobile S-band and Bistatic Networks for Severe Storms
Authors: Wurman Joshua , Kosiba Karen
Published: March 2023

A next-generation long wavelength adaptable/targetable research radar network, comprising an array of truck-borne quickly-deployable scanning 10-cm radars, S-band On Wheels (SOW), incorporating a Bistatic Adaptable Radar Network (BARN), can provide fine-scale S-band dual-polarization observations of the atmospheric boundary layer, convective, and other precipitating systems while simultaneously measuring dynamically meaningful fine-scale vector wind fields. 

 

SOW is a new paradigm for long-wavelength research radars, replacing large cumbersome expensive singular radars with a network of several smaller, nimbler, less expensive systems. 

 

SOW and BARN  will fill critical gaps in current observing systems, providing broadly and inexpensively available long wavelength, dual-polarimetric, near-ground, fine-scale, vector wind observations.   

 

When implemented, a network of 4 SOWs, SOWNET, will replace single 10-cm large 10-cm 1° radars with an array of smaller, 5.5 m (18’) antenna, quickly-deployable, 1.5° beamwidth truck-borne radars. 

With multiple SOWs, typical ranges to targets are much shorter, resulting in improved resolution compared to single 1° 10-cm radars. 

1,2,3, or 4 SOWs can comprise a SOWNET deployment, customizing for small or large missions.   Inexpensive deployments of 1-2 SOWs qualitatively broaden access to this critical observational capability

BARN enables multiple-Doppler vector wind measurements over targeted regions.

SOWNET provides  moderate-resolution multiple-Doppler measurements, BARN provides  finer-scale over smaller domains. 

BARN units are coupled with single or multiple SOWS, COW, or DOWs.  

Stationary BARN units are unattended, low power, and similar to deployable weather stations

Highly redundant BARN units provide extreme reliability of multiple-Doppler operation.
Tornado Thermodynamics Observations and the Boundary-layer Evolution and Structure of Tornadoes (BEST) Study 
Authors: Kosiba Karen , Wurman Josh
Published: March 2023

Our knowledge of tornadogenesis, evolution, and structure has advanced substantially with the increase in computing resources and the availability of fine temporal- and spatial- scale observations.  Even so, many questions/hypotheses remain observationally unconfirmed/untested.  These include: the role of secondary rear-flank downdraft surges in the tornado genesis/maintenance process, the mechanisms of the generation of horizontal vorticity (ωh) and its transformation into tornado-strength near-surface vertical vorticity (ζ), how the evolution of the low-level mesocyclone relates to tornadogenesis, evolution and dissipation, the variability of tornado wind speeds with height and time, and how tornado intensity, propagation speed and structure, including variations in wind with height and time, affect human-impacting damage.  The degree to which the answers to these questions vary depending on the strength, size, structure, and persistence/duration of tornadoes is unknown.  

Answering these critical questions relating to the evolution of ζ, the role of downdrafts, updrafts, and baroclinic zones depends on the diagnosis of kinematically important quantities involving vector wind fields such as Div(V), vertical velocity (w), ωh and ζ, and tilting/stretching of ωh and ζ.  In tandem with DOW radar deployments, surface weather stations (Pods) have been utilized in many DOW tornado missions for well over a decade, obtaining not only surface wind data, but surface thermodynamic data, as well.  These integrated observations have been collected over a wide range of tornado structures and at various times in tornado evolution.  Results will be presented from analyses of multiple cases with both low-level DOW radar and surface thermodynamic data.  Preliminary observations suggest that there is a distinct and localized change in the near-field thermodynamics during tornado evolution over short time and spatial scales, which suggest changes in storm processes.     

Plans for the proposed 2023-2024 BEST (Boundary-layer Evolution and Structure of Tornadoes) project, focusing on characterizing the thermodynamic and kinematic structure of tornadoes below 100 m AGL, especially below 50 m AGL, using proximate DOW radars, PODNet, and Driftersondes from the University of Illinois Flexible Array of Radars and Mesonets (FARM) will be presented.

 
Selective simulated seeding on hailstorms – a summertime case study over Switzerland
Authors: Papaevangelou Nikolaos , Lohmann Ulrike , Ferrachat Sylvaine
Published: March 2023

Abstract Ice Nucleating Particles (INPs) are known to affect the microphysical properties of hailstorms. However, their role on surface precipitation amount and hail size distribution is still unclear. The reason is that hailstorms are rare events that consist of many non–linear interacting processes. In this study, we are analyzing the effect of INPs perturbations on hailstorms observed on 6th of July 2019 over the Swiss plateau in terms of precipitation and hail size distribution. The simulations are performed by the regional weather and climate model COSMO(Consortium for Small-Scale Modeling) (Steppeler et al., 2003; Baldauf et al., 2011) on a rotated latitude-longitude grid with 0.01° horizontal resolution (which corresponds to approximately 1.1km grid spacing), 80 hybrid vertical levels with the upper limit being at approximately 23 km and  6 s temporal resolution. One prerequisite of our experiment is to create a thunderstorm that is in agreement with one of the observed thunderstorms, using initial and boundary conditions of the given day. We define this agreement when the following two conditions are met: i) the simulated cell is within 40 km and 3 hours of the observed cell and ii) when the hail diameter of the simulated cell is larger than 1 cm at the cloud base in one or more grid points. When this is achieved, we seed these hailstorms the time period that they are at the cumulus until the early mature stage (onset of precipitation). The seeding is conducted in the updraft close to the cloud base. The additional INPs from the seeding are treated as a prognostic variable following the studies by Possner et al. (2017) and Eirund et al. (2018). In order to go back in time and locate the wider area in which the hailstorm was at these stages, we use the mean updraft 700-500 hPa and precipitation rate. The mean updraft indicates the area where there is upward motion until 3 m/s while the precipitation rate assures the existence of a deep convective cloud which doesn’t precipitate heavily -- higher than 5 mm/hr.  The whole process is repeated 10 times following the time-lagged ensemble approach (Vogel et al. 2013), in order to analyze the effect of seeding and its significance in the context of model variability.
Derechos in Finland
Authors: Rauhala Jenni
Published: March 2023

Derechos are long-lived convective wind events that cause damage in vast areas. Since little was known before about derecho occurrence in Finland, the purpose of this study was to search for previously unidentified derecho events and describe derecho occurrence and characteristics in Finland. Derechos were identified by comparing radar reflectivity development of convective storms to the maximum wind gust measurements and reported wind damage. Based on results of this study, derechos are not as rare events in Finland as has been previously assumed. In the preliminary dataset derechos have been observed in Finland from June to October. Compared to other types of convective severe weather, derechos are long lasting events, with their duration in Finland ranging in our dataset from 4h 30 min to 9h 30 min. The length of the observed derecho tracks in Finland varied between 400 km and 660 km. The often-used criteria to search and classify derecho cases based on wind gust measurements of 25 m/s or more, seem not to be very effective in Finland. Even many of the major events, with vast wind damage areas identified by emergency reports of wind damage, would end up having few if any ≥25 m/s gusts measured. The challenge of identifying events that cross country borders, move over open sea or low population areas, is also discussed.
Climatology of derechos and wind squalls in Czechia during the last 25 years
Authors: Rýva David
Published: March 2023

Derechos are well known as originators of widespread and significant damage associated with larger convective storms. Damage caused by derechos can be comparable with damage produced by tornadoes, locally even with strong tornadoes, but an affected area is much larger. As a result, derechos are able to cause significant damage to property, crops, forests etc. They are also able to cause numerous injuries and even fatalities. The research activities of some authors in Europe during the last two decades have shown that derechos are not rare in Central Europe.This study presents detailed results of our research on the occurence and characteristics of derechos and other large scale convectively induced wind squalls in the Czech Republic during warm seasons of the last 25 years (1998 - 2022). We have used our own software tools to identify all convectively indiced wind events. Newly we also used GIS software tools to create better and more complete spatial analyses and climatology of derechos and occurence of convective wind storms. Cold season events were rejected from our study because they usually are a part of a large, synoptic scale, wind storms and it is not easy to distinguish between convective or nonconvective wind gusts. The comparison with the US climatology shows that derechos here in the heart of the Central Europe are almost as frequent as in the continental US and that they definitely should be taken into account in weather forecasts and also in a weather risk assessment.
The risk of lightning strikes in stadiums: the example of football
Authors: Schmitt Stéphane
Published: March 2023

A previous study on lightning-related human accidents in Europe (2010-2019), estimates that 10% of lightning victims were in a stadium, sports or leisure facility and the vast majority were playing football.

An in-depth analysis of 10 remarkable cases provides information on the thunderstorms responsible for these events: these were not sudden (in 7 out of 10 cases, the thunderstorm has been visible for more than 40 minutes), and the victims were not struck by exceptionally severe thunderstorms (in 6 out of 10 cases, there were less than 10 cloud-to-ground flashes within 10km of the victim) or by intense peak current (in 6 out of 10 cases, the flash was less than the 20kA which is the average value of CG current).

While the victims were children in 5 out of 10 cases, raising questions about the responsibility of adults, the analysis of post-accident declarations reveals at least the ineffectiveness of human judgement in ensuring safety, even though all these events could technically have been the subject of an early warning.

Above all, this fatalism can be counterproductive to any effective awareness-raising by wrongly considering these events as fateful...in the manner of a divine character that we would still attribute to lightning after ages...

 
Towards a deeper understanding of the scale interactions between cold fronts and convection during the European warm-season
Authors: Pacey George , Pfahl Stephan , Schielicke Lisa
Published: March 2023

While convection commonly initiates along synoptic-scale cold fronts during the European warm-season, rarely does convection initiate along the entirety of the boundary. This indicates smaller-scale processes, e.g., solar heating, outflow boundaries and topography, are likely responsible for the spatial and temporal onset of convective initiation. Interactions between the frontal circulation and such smaller-scale processes are not currently well-understood. Our cold-frontal convective cell climatology highlighted convective cells are most frequent marginally ahead of the surface front. On the other hand, pre-surface-frontal cells have the largest fraction associated with mesocyclones, intense convective cores and lightning. Pre-surface-frontal convergence lines, which have been observed to be linked to the western edge of elevated mixed layer plumes, could play a role in these larger cell intensity fractions.

Here we train a logistic regression model for cold-frontal convective cells based on thermodynamic and dynamic variables derived from ERA5 and assess its performance based on the area under the ROC curve (AUC). The logistic regression model exhibits high skill (AUC~0.90) but the model performance is not consistent across the cold-frontal environment. The highest model skill is for cells in the drier and cooler post-frontal airmass, whereas the lowest is for cells near the surface front. This highlights the complexity of smaller-scale processes favouring the development of convective cells near to the surface front. To further understand the underlying processes and multi-scale interactions responsible for convection initiation and cell evolution in cold-frontal environments we analyse case studies of interest in the Central European domain. We will also use these case studies to study up-scale feedbacks on the frontal structure caused by convective cells. This is an important step towards a more comprehensive understanding of scale interactions between cold fronts and convection.
Combining GNSS meteorology and Instability Indices for derivation of classification functions in South Central Bulgaria.
Authors: Slavchev Martin , Guerova Guergana , Dimitrova Tsvetelina
Published: March 2023

Severe weather events, such as intense precipitation, hail and thunderstorms, are common summer phenomena in Bulgaria and are associated with large economic losses. An active hail suppression is taking place in North West and South Central Bulgaria over the dense agricultural regions from May to September. A joint venture between Sofia University "St. Kliment Ohridski'' and the Bulgarian Hail Suppression Agency contributed to the project “Balkan-Mediterranean real-time severe weather service” (BeRTISS, 2017-2020). As part of the BeRTISS project, a pilot operational service was established by exploiting GNSS tropospheric products in support of safety, quality of life and environmental protection in the region. To facilitate the service, in 2018 a GNSS network with 12 reference stations was installed and since February 2020, the Sofia University GNSS Analysis Center provides operational near-real time products. First results of combining GNSS derived Integrated Water Vapour (IWV) and Instability Indices (InI) are reported for Sofia plain for the period May-September (2010 - 2015). Based on statistical regression analysis, classification functions are obtained that contribute to the thunderstorm forecasting skill. The majority of the classification functions combining IWV and InI are reported with the best performance in May, followed by June and September. In this work, IWV and InI classification functions are presented for South Central Bulgaria. The first results for the period May-September 2020-2021 indicate the probability of detection 0.71 for IWV, 0.85 for InI, and 0.89 for IWV and InI combined. While false alarms decreased from 0.42 for IWV to 0.39 for InI and 0.28 for IWV and InI combined. These results will be implemented in the GNSS Strom Demonstrator web portal.  
Tornadic, hail and wind storms in Central Europe – when to expect what: a case study of the severe weather outbreak on 20 May 2022 
Authors: Beyer Marcus , Wapler Kathrin
Published: March 2023

An understanding of historical events, e.g. regarding the occurrence and characteristics of severe storms, may help to improve the situational awareness of future events. Thus, an example case is used to show typical setups for the occurrence and characteristics of severe convective storms. This case is also used for internal forecasters training.

 

The case is analysed regarding its synoptic and mesoscale environment as well as storm characteristics. It is discussed in which region to expect which phenomena based on available data. The case study will be presented as poster in a way to allow the conference participants to (re)forecast and (re)nowcast themselves the location, intensity and type of storms.

 

On 20 May 2022, a severe weather outbreak took place, influencing parts of Central Europe: heavy precipitation, large hail, severe windstorm and at least eight tornadoes occurred according to the European Severe Weather Database.

 

 

A pronounced short-wave trough was moving from Western Europe into Germany. The trough led to an intensification of a downstream surface low that was moving from Benelux into Northern Germany during the day.

 

Radar radial wind data showed persistent rotation tracks. Individual storms show tracks of higher VIL and VII values. The lighting activity of many storms was high including lightning jumps.
Radar-based Hail Detection and Hail Size Estimation at DWD
Authors: Schultze Markus , Wilke Tabea , Berndt Christian
Published: March 2023

Hail is a pronounced natural hazard in Germany. Nevertheless, major hail events are quite rare and there is a lack of information in hail occurrence and size and its spatiotemporal distribution. Measurement sensors that are able to detect hail (e.g. disdrometers) are in principle available in Germany, but the spatial density of those stations is far lower than the typical spatial extent of hail events. Furthermore, sensors for hail size estimation are still in evaluation stage and currently only located at a few selected places. Hail reports based on professional and particularly amateurish eyewitness become increasingly important. But besides a certain degree of subjectivity in the reported hail size, highly populated areas might be overrepresented compared to rural and sparsely populated areas. Areal information from weather radar networks can overcome this issue with a high spatiotemporal resolution. Because of the high update frequency and fast availability of radar data, an automatic hail detection and hail size estimation might provide valuable hints to forecasters and supports the warning decision process.       
The Deutscher Wetterdienst (DWD) utilizes a C-Band dual-polarimetric weather radar network consisting of 17 radar stations that provide ten volume scans and a terrain-following low-elevation scan every five minutes. The operationally used hydrometeor classification algorithm HYMEC processes data of reflectivity, differential reflectivity and co-polar correlation coefficient to distinguish between hail and other hydrometeors. With this classification a hail distribution over Germany can already be derived. For the analysis of hail sizes, the Maximum Expected Size of Hail (MESH) and a method based on Vertical Integrated Ice (VII) are used. The latter method is motivated by a linear relation between maximum hail size and VII proposed by our forecasters based on their practical experience.        
This contribution will give an overview on the statistics of hail occurrence and hail size using the aforementioned algorithms in Germany during the convective seasons 2021 and 2022. Also, selected case studies are discussed in more detail. The results are compared against hail observations from manned and automatic weather stations, reports from the European Severe Weather Database and user reports from DWD’s WarnWetter-App.
Influence of orography on supercells in Slovakia
Authors: Šinger Miroslav
Published: March 2023

The spatial distribution of supercells is strongly inhomogeneous across Slovakia with a higher frequency of occurrence in several regions in the eastern part of the country. The main aim of the work was to find reasons for this inhomogeneity. This is done by running high-resolution simulations of the ALARO model with a grid spacing of 1 km for all supercell cases in eastern Slovakia between 2017 and 2020. We studied the evolution of pre-convective environments, as well as the lower tropospheric flow patterns to establish the typical scenarios, in which supercells occur in Slovakia. The most important factor was found to be an interaction of large-scale flow with local orography, which affected a whole range of processes in the troposphere. As a result of the various orographic effects, such as blocking, wrapping, gap wind, lee cyclogenesis, and upslope flow, we have detected zones of enhanced convergence and spatial anomalies of ingredients important for the development of deep moist convection. In most of the analyzed cases, we noted a local increase in the vertical wind shear in the lee of the mountains, which increased the probability of supercell formation. In the cases with the prevailing southerly flow and warm-air advection regime, supercells typically formed to the south and east of the Western Carpathians. Convergence lines and upslope flow initiated convection and local enhancement of vertical wind shear was essential for the genesis of supercells. In the cases with the prevailing northerly flow and cold-air advection, blocking allowed for the maintenance of a warm and humid air mass (with non-zero CAPE values) and a generation of convergence zone on the southern flank of Western Carpathians.
A derecho in northern Europe
Authors: Rauhala Jenni
Published: March 2023

A mesoscale convective system (MCS) producing a derecho impacted four European countries 16-17 October 2022. The MCS produced high wind gusts and wind damage that started over Denmark, continued over Sweden, Estonia and Finland, along 1300 km long path. The MCS formed a large-scale bow echo that travelled through dense observation network over southern coastal waters of Finland resulting in detailed measurements of storm passage over surface observation stations, an observation mast and three radars. In Finland the maximum gust observed was 39,2 m/s, and storm-scale (≥25 m/s) wind gusts were observed on 16 surface observation stations. Wind measurements showed that the duration of storm-scale wind gusts were approximately 18 minutes and the maximum wind gusts (above 30 m/s) lasted approximately 10 minutes as the bow echo moved over observation stations. This unique observation data gives us insight to wind speeds and their duration in a derecho. The focus of this study is on comparison of radar observations of the MCS to the measurements from the surface observation network such as maximum wind gusts, temperature and cold pool strength, and change in the surface pressure. The synoptic and mesoscale environment is also described. The unusual seasonal time of the event caused extra challenge in its forecasting.
Risk Assessment for Hail Damages to Buildings and Cars in Switzerland: Current Risk and Future Projections
Authors: Schmid Timo , Bresch David N.
Published: March 2023

Hail is a severe meteorological hazard that can cause significant damage to both buildings and cars. Here, we present the first-ever open-source risk model for hail damages, provided within the CLIMADA framework. The availability of high-resolution radar-based hail intensity measures and detailed damage and exposure data from local insurance companies in Switzerland allows for a spatially explicit calibration of vulnerability functions for buildings and cars. The model is able to provide climatological evaluations of hail risk and real-time hail damage estimates based on any user-provided exposure data. Furthermore, combined with crowd-sourced hail reports, the detailed damage data allows for an evaluation and uncertainty quantification of different radar-based hail intensity measures. Results highlight the limitation of radar-based state-of-the-art hail size estimates, such as Maximum Expected Severe Hail Size (MESHS), for accurate risk assessments of hail damages. In a second step, the model will be expanded to use high-resolution convection resolving simulations with the hail growth module HAILCAST as hazard variable. This enables the assessment of hail risk under climate change, when driven by 2-km nested climate simulations following a pseudo global warming approach. This submission is part of the scClim project (https://scclim.ethz.ch/), which seamlessly couples kilometer-resolution weather predictions and climate simulations with hail impact assessments for multiple sectors.
Comparing CMIP6 Future Projections for Severe Convective Environments in a Warmed Climate over Australia, Europe and North America
Authors: Allen John , Gopalakrishnan Deepak , Cuervo-Lopez Carlos , Trapp Robert , Robinson Eric
Published: March 2023

Severe thunderstorms are a global phenomena, producing a variety of hazards that include hail, tornadoes, damaging winds lightning and heavy precipitation. In the present climate, these events produce large losses to property and life. The warming climate is expected to influence these storm attributes, primarily through increasing thermodynamic instability driven by increased atmospheric moisture as warming occurs to near-surface temperatures. However, while a number of studies have explored how the climate system modulates these hazards through changes to favorable environmental conditions, these projections have generally been latitudinally biased away from the subtropics and focused on potentially aggressive warming scenarios. This presents a challenge to our understanding, as many parts of the world that currently regularly experience severe thunderstorms exist in different climate regimes or latitudes, and which exhibit non-linear responses to the warming climate.  Hence what is known for some latitudes and warming scenarios may not reflect a complete picture of the expected changes to hazards on a global level.

This presentation seeks to share newly developed insights into the frequency at which environments favorable to severe convection occur in particular regions, with a focus on identifying potential model biases. Extending from historical frequency, how these environments will evolve in response to moderately and strongly warmed scenarios in terms of both climate variability and change as projected using the latest generation of Coupled-Model Intercomparison Project Version 6 (CMIP6) data is explored. Results highlight that increases over the Northern and Western hemispheres are not necessarily reflective of changes in the subtropics and Southern hemisphere, and may respond differently depending on the environmental proxy used. While the driving mechanism of these changes are strong increases in CAPE, these changes can be modulated by local processes, and are often accompanied by factors that either resist convection (CIN), or seasonally may coincide with high likelihood of storm organization (S06, SRH).
ACCuReSy Project- targeting the aerosol-cloud interactions within convective environments in Romania
Authors: Andrei Simona , Pîrloagă Răzvan , Adam Mariana , Tudor Alexandru , Piticar Adrian , Antonescu Bogdan
Published: March 2023

Understanding the macrophysical and microphysical processes within a convective environment is highly important to strengthen the resilience and adaptation to severe weather. The ACCuReSy project targets a topic a topic under debate within the international scientific community but less tackled in Romania: the aerosol-cloud interactions. By using state-of-the-art remote sensing instruments from new exploratory platforms placed within relevant two locations chosen by their relevance for the environmental factors that meet the conditions for observing convective development either thermal and dynamical, the project aims to perform advanced research on the atmospheric environment before, during and shortly after the convective events and to investigate the aerosol-cloud interactions with special attention on the factors that contribute to the hail formation. Here we present briefly the work performed during the first phase of the project and the future steps in achieving our goals.

Key words: aerosol-clouds interactions, cloud macro- and microphysics, convective clouds, severe weather

Acknowledgment: This work is funded by a grant of the Ministry of Research, Innovation and Digitization, CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2021-1938, ctr. No. 713PED, and partially supported by the Romanian National Core Program Contract No.11N/03.01 2023 and by the Romanian Ministry of Research, Innovation and Digitalization, through Program 1- Development of the national research-development system, Subprogram 1.2 - Institutional performance - Projects to finance the excellent RDI, Contract no. 18PFE/30.12.2021
Microphysical evolution of thunderstorms in tropical environments associated with gigantic jet production using CM1
Authors: van der Velde Oscar , Montanyà Joan , López Jesús , Mansell Ted
Published: March 2023

Low-light cameras installed in different locations in Colombia have recorded a total of 70 Gigantic Jets (GJ), mainly between 2016 and 2022. These are spectacular cloud-to-ionosphere lightning discharges reaching 90 km altitude and are mostly a tropical phenomenon. However, there are many more thunderstorms in the tropics that do not produce them.

We summarize the results of a statistical study of ERA5 profiles of 48 gigantic jet nights and 83 null cases in northern and western Colombia in a work published in Atmospheric Research (van der Velde et al. 2022). The main conclusion was that the environment of gigantic jet producing storms is characterized by greater warm cloud depth (to -10°C), weak low-level shear, weak lapse rates and reduced updraft and downdraft buoyancies, while no evidence was found for cloud top shear effects. It was hypothesized that warm cloud processes and secondary ice processes may result in a temporary low rime accretion rate, which could reverse the charging polarity and temporarily cause a highly negatively charged balance in the storm.

Mean vertical profiles have been constructed for null events and GJ events. They have minimal CIN (-10 J/kg) and were not modified. These are used to initiate Cloud Model 1 simulations at 0.25 km grid spacing or better and the NSSL microphysics scheme (other models and schemes may be considered). A sensitivity study was done to see the effect of initial lifting mechanism on the storm evolution. With default settings a very fragile storm was simulated. Here, we compare against satellite evolution of GJ producing storms, which tend to be rather strong. A setting of updraft nudging was selected that reproduces the storm well, while not causing unrealistically strong converging winds at the surface in response. The effect of cloud condensation nuclei is also tested.

The purpose of the simulations is to find differences to the microphysical particle distributions and densities, between GJ and null and in GJ case ERA5 profiles, which can affect the electrical charging efficiency and polarity. In a preliminary study with CM1+NSSL microphysics, we confirmed that there are indeed differences e.g. in graupel – ice/snow density overlap, but effects on charging and typical timing of the gigantic jets relative to the storm evolution are in need of further investigation.