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Concept

Tornade

Publications associées (23)

Mountaintop Gamma Ray Observations of Three Terrestrial Gamma‐Ray Flashes at the Säntis Tower, Switzerland With Coincident Radio Waveforms

Farhad Rachidi-Haeri, Marcos Rubinstein, Antonio Sunjerga, Amirhossein Mostajabi

We report on the mountain top observation of three terrestrial gamma-ray flashes (TGFs) that occurred during the summer storm season of 2021. To our knowledge, these are the first TGFs observed in a mountaintop environment and the first published European ...

2024

Highly Hygroscopic Aerosols Facilitate Summer and Early‐Autumn Cloud Formation at Extremely Low Concentrations Over the Central Arctic Ocean

Julia Schmale, Andrea Baccarini

Arctic clouds are sensitive to atmospheric particles since these are sometimes in such low concentrations that clouds cannot always form under supersaturated water vapor conditions. This is especially true in the late summer, when aerosol concentrations ar ...

2024

Direct observations of X-rays produced by upward positive lightning

Farhad Rachidi-Haeri, Marcos Rubinstein, Antonio Sunjerga, Thomas Chaumont

X-rays have been observed in natural downward cloud-to-ground lightning for over 20 years and in rocket-triggered lightning for slightly less. In both cases, this energetic radiation has been detected during the stepped and dart leader phases of downward n ...

Nature Publishing Group2024

Expansion of the Materials Cloud 2D Database

Nicola Marzari, Giovanni Pizzi, Marco Gibertini, Davide Campi, Nicolas Frank Mounet

Two-dimensional(2D) materials are among the most promising candidatesfor beyond-silicon electronic, optoelectronic, and quantum computingapplications. Recently, their recognized importance sparked a pushto discover and characterize novel 2D materials. With ...

AMER CHEMICAL SOC2023

Supercell Thunderstorms in the Alpine Region - From Weather Radar Observations to Idealized Modeling

Monika Feldmann

The high-impact nature and increasing occurrence of severe weather phenomena pushes forward research on their occurrence and improving our understanding thereof. Supercell thunderstorms are the focus of much severe convective research, as they represent on ...

EPFL2023

Wind, Hail, and Climate Extremes: Modelling and Attribution Studies for Environmental Data

Ophélia Mireille Anna Miralles

This thesis presents work at the junction of statistics and climate science. We first provide methodology for use by climate scientists when performing fast event attribution using extreme value theory, and then describe two interdisciplinary projects in c ...

EPFL2023

Whirling instability of an eccentric coated fibre

François Gallaire, Edouard Boujo, Ludovic Pierre Gustave Keiser, Shahab Eghbali

We study a gravity-driven viscous flow coating a vertical cylindrical fibre. The destabilisation of a draining liquid column into a downward moving train of beads has been linked to the conjunction of the Rayleigh-Plateau and Kapitza instabilities in the l ...

Cambridge University Press2022

Estimating the non-dimensional energy of vortex rings by modelling their roll-up

Karen Ann J Mulleners, Guillaume de Guyon-Crozier

The non-dimensional energy of starting vortex rings typically converges to values around 0.33 when they are created by a piston-cylinder or a bluff body translating at a constant speed. To explore the limits of the universality of this value and to analyse ...

Cambridge University Press2022

A Characterisation of Alpine Mesocyclone Occurrence

Alexis Berne, Marco Gabella, Monika Feldmann

This work presents a characterisation of mesocyclone occurrence and frequency in the Alpine region, as observed from the Swiss operational radar network; 5 years of radar data are processed with a thunderstorm detection and tracking algorithm and subsequen ...

2021

An experimental study on the upper part-load elliptical vortex instability in a Francis turbine

François Avellan, Elena Vagnoni, Andres Müller, Arthur Tristan Favrel, Ali Amini

This paper presents preliminary results of an experimental study on the occurrence and development of the upper part-load instability in a reduced-scale Francis turbine. The study includes draft tube pressure measurements, high-speed flow visualization, an ...

IOP Publishing2021

Phenomenology and scaling of optimal flapping wing kinematics

Karen Ann J Mulleners, Alexander Gehrke

Biological flapping wing fliers operate efficiently and robustly in a wide range of flight conditions and are a great source of inspiration to engineers. The unsteady aerodynamics of flapping wing flight are dominated by large-scale vortical structures tha ...

IOP PUBLISHING LTD2021

Scaling of the translational velocity of vortex rings behind conical objects

Karen Ann J Mulleners, Guillaume de Guyon-Crozier

Ring vortices are efficient at transporting fluid across long distances. They can be found in nature in various ways: they propel squids, inject blood in the heart, and entertain dolphins. These vortices are generally produced by ejecting a volume of fluid ...

2021

Biomass burning aerosol as a modulator of the droplet number in the southeast Atlantic region

Athanasios Nenes

The southeastern Atlantic (SEA) and its associated cloud deck, off the west coast of central Africa, is an area where aerosol–cloud interactions can have a strong radiative impact. Seasonally, extensive biomass burning (BB) aerosol plumes from southern Afr ...

Copernicus Publications2020

Numerical Simulations of an Innovative Water Stirring Device for Fine Sediment Release: The Case Study of the Future Trift Reservoir

Pedro Filipe De Almeida Manso, Azin Amini

Reservoir sedimentation and consequently lack of storage volume and perturbation of the operation of intakes and bottom outlet is a key challenge affecting both hydropower production as well as dam safety and flood management. In the framework of a peer-re ...

Springer2020

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Julia Schmale, Sebastian Johannes Heinz-Josef Landwehr

At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near-surface turbulence. Therefore, processes related to near-surface turbulence and wave breaking, such as sea spray emission and ...

2020

Radar measurements of blowing snow off a mountain ridge

Michael Lehning, Wolf Hendrik Huwald, Benjamin Andreas Walter, Josué Etienne Gehring

Modelling and forecasting wind-driven redistribution of snow in mountainous regions with its implications on avalanche danger, mountain hydrology or flood hazard is still a challenging task often lacking in essential details. Measurements of drifting and b ...

2020

Cloud condensation nuclei activity of six pollenkitts and the influence of their surface activity

Athanasios Nenes

The role of surfactants in governing water interactions of atmospheric aerosols has been a recurring topic in cloud microphysics for more than two decades. Studies of detailed surface thermodynamics are limited by the availability of aerosol samples for ex ...

Copernicus Publications2019

Evaluation of global simulations of aerosol particle and cloud condensation nuclei number, with implications for cloud droplet formation

Athanasios Nenes, Julia Schmale

A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and ...

Copernicus Publications2019

A Study of a Large Bipolar Lightning Event Observed at the Säntis Tower

Farhad Rachidi-Haeri, Marcos Rubinstein, Davide Pavanello, Mohammad Azadifar

An unusual negative lightning flash was recorded at the Säntis Tower on June 15, 2012. The flash did not contain an initial continuous current typical of upward negative lightning, which is the most common type of event at the Säntis Tower. The flash conta ...

2019

Critical evolution of leading edge suction during dynamic stall

Karen Ann J Mulleners, Julien Dominique Claude Deparday

Dynamic stall dominates the aerodynamic performance, the robustness, and the wake dynamics of vertical axis wind turbines. To better assess the dynamic stall onset and its associated unsteady effects, this paper analyzes experimentally the evolution of the ...

IOP PUBLISHING LTD2018