My research in high-energy atmospheric physics focuses on terrestrial gamma-ray flashes (TGFs), gamma-ray glows, flickering gamma-ray flashes (FGFs) and terrestrial electron beams. I combine aircraft and spacecraft observations with Monte Carlo simulations to investigate how thunderstorms accelerate particles and produce high-energy radiation.

I work on instrument calibration, detector-response modelling and scientific data analysis for ASIM on the International Space Station and the ALOFT aircraft campaign. I participated in ALOFT in 2023, which revealed flickering gamma-ray flashes, reported in Nature in 2024. My subsequent work includes the spectral analysis of these flashes and modelling of relativistic runaway electron avalanches.

I am developing a gamma-ray pinhole camera to measure the spatial extent of gamma-ray glows during the planned ENLIGHTEN flight campaign in 2028.

I received my PhD from the University of Toulouse in 2015, worked on the TARANIS spacecraft as a postdoctoral researcher at Université Paris Diderot, and joined the University of Bergen in 2017.

I create scientific illustrations to explain high-energy phenomena in thunderstorms and the results of our research. These are available on my personal website, alongside the associated articles.

I co-supervise master’s and PhD students at the University of Bergen. I have taught energetic-particle propagation in the atmosphere at research schools in Leiden and Bergen (2019), and previously taught mathematics, thermodynamics and plasma physics at bachelor’s and master’s level in France.

2025

• Øystein Håvard Færder; Nikolai Grigorievich Lehtinen; David Alexandre Stephan Sarria et al. (2025). A parameter-space exploration of the Relativistic Discharge Model mapping for which conditions ALOFT’s Flickering Gamma-ray Flashes are produced. (ekstern lenke)
• Øystein Håvard Færder; Nikolai Grigorievich Lehtinen; David Alexandre Stephan Sarria et al. (2025). Systematic reproduction of hard radiation from thunderclouds including ALOFT’s Flickering Gamma-ray Flashes using an ODE model resembling a Lotka-Volterra predator-prey system. (ekstern lenke)
• David Alexandre Stephan Sarria; Nikolai Østgaard; Ingrid Bjørge-Engeland et al. (2025). Spectral Analysis of Flickering Gamma-Ray Flashes Observed During the ALOFT 2023 Campaign. (ekstern lenke)
• Timothy J. Lang; Nikolai Østgaard; Martino Marisaldi et al. (2025). Hunting for Gamma Rays above Thunderstorms: The ALOFT Campaign. (ekstern lenke)
• David Alexandre Stephan Sarria; Nikolai Østgaard; Ingrid Bjørge-Engeland et al. (2025). Evidence of gamma-ray glows observed in the relativistic feedback regime during the ALOFT 2023 flight campaign. (ekstern lenke)

2026

• Øystein Håvard Færder; Nikolai Grigorievich Lehtinen; D. Sarria et al. (2026). Numerical Parameter‐Space Studies of Various Types of Thundercloud Gamma‐Ray Emissions. (ekstern lenke)

2024

• David Alexandre Stephan Sarria (2024). Spectral analysis of Flickering Gamma Flashes observed during the ALOFT 2023 Campaign. (ekstern lenke)
• David Alexandre Stephan Sarria (2024). Results from the ALOFT-2023 mission: A flight campaign for TGF and gamma-ray glow observations over Central America and the Caribbean in July 2023. (ekstern lenke)
• Ingrid Bjørge-Engeland; Nikolai Østgaard; David Alexandre Stephan Sarria et al. (2024). Evidence of a New Population of Weak Terrestrial Gamma-Ray Flashes Observed From Aircraft Altitude. (ekstern lenke)
• Yuuki Wada; Philippe Laurent; Damien Pailot et al. (2024). On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS. (ekstern lenke)
• Nikolai Østgaard; Andrey Mezentsev; Martino Marisaldi et al. (2024). Flickering gamma-ray flashes, the missing link between gamma glows and TGFs. (ekstern lenke)
• Martino Marisaldi; Nikolai Østgaard; Andrey Mezentsev et al. (2024). Highly dynamic gamma-ray emissions are common in tropical thunderclouds. (ekstern lenke)
• Andrey Mezentsev; Nikolai Østgaard; Martino Marisaldi et al. (2024). Discerning TGF and Leader Current Pulse in ASIM Observation. (ekstern lenke)
• David Alexandre Stephan Sarria (2024). Spectral Analysis of High-Energy Radiation Events Observed during the ALOFT 2023 Campaign. (ekstern lenke)

2021

• A.J. Castro-Tirado; Nikolai Østgaard; E. Göǧüş et al. (2021). Very-high-frequency oscillations in the main peak of a magnetar giant flare. (ekstern lenke)
• David Alexandre Stephan Sarria; Nikolai Østgaard; Pavlo Kochkin et al. (2021). Constraining Spectral Models of a Terrestrial Gamma-Ray Flash From a Terrestrial Electron Beam Observation by the Atmosphere-Space Interactions Monitor. (ekstern lenke)
• Pavlo Kochkin; David Alexandre Stephan Sarria; Nikolai Grigorievich Lehtinen et al. (2021). A Rapid Gamma-Ray Glow Flux Reduction Observed From 20 km Altitude. (ekstern lenke)
• Anders Lindanger; Martino Marisaldi; David Alexandre Stephan Sarria et al. (2021). Spectral Analysis of Individual Terrestrial Gamma-ray Flashes Detected by ASIM. (ekstern lenke)
• Nikolai Østgaard; S.A. Cummer; Andrey Mezentsev et al. (2021). Simultaneous Observations of EIP, TGF, Elve, and Optical Lightning. (ekstern lenke)

2017

• Pavlo Kochkin; David Sarria; A.P.J. van Deursen et al. (2017). Positron annihilation in thunderstorms observed by ILDAS.. (ekstern lenke)
• Nikolai Østgaard; Hugh J. Christian; Eric Grove et al. (2017). Gamma-ray observations at 20 km altitude above thunderstorms. (ekstern lenke)
• David Sarria; Nikolai Østgaard; Pavlo Kochkin (2017). Modeling the 511 keV background enhancements observed by aircrafts in thunderstorms. (ekstern lenke)

2019

• Nikolai Østgaard; Torsten Neubert; Victor Reglero et al. (2019). First 10 Months of TGF Observations by ASIM. (ekstern lenke)
• David Sarria; Pavlo Kochkin; Nikolai Østgaard et al. (2019). The First Terrestrial Electron Beam Observed by the Atmosphere-Space Interactions Monitor. (ekstern lenke)
• David Sarria; Pavlo Kochkin; Nikolai Østgaard et al. (2019). Observation of a Terrestrial Electron Beam during the tropical cyclone Joaninha in March 2019. (ekstern lenke)
• Martino Marisaldi; Marcello Galli; C. Labanti et al. (2019). On the high-energy spectral component and fine time structure of terrestrial gamma ray flashes. (ekstern lenke)
• David Sarria; Nikolai Østgaard; Pavlo Kochkin et al. (2019). The First Terrestrial Electron Beam Observed by the Atmosphere‐Space Interactions Monitor (ASIM), EGU 2019 Presentation.. (ekstern lenke)
• Nikolai Østgaard; Hugh J. Christian; J. Eric Grove et al. (2019). Gamma Ray Glow Observations at 20-km Altitude. (ekstern lenke)

2022

• Ingrid Bjørge-Engeland; Nikolai Østgaard; Andrey Mezentsev et al. (2022). Terrestrial Gamma-Ray Flashes With Accompanying Elves Detected by ASIM. (ekstern lenke)
• Anders Lindanger; Chris Alexander Kallevik Skeie; Martino Marisaldi et al. (2022). Production of Terrestrial Gamma-Ray Flashes During the Early Stages of Lightning Flashes. (ekstern lenke)

2023

• David Alexandre Stephan Sarria (2023). Observation of Long and Intense sequences of Gamma-ray Glows during the 2023 ALOFT flight campaign. (ekstern lenke)
• M.D. Caballero-García; Rahul Gupta; S.B. Pandey et al. (2023). Multiwavelength study of the luminous GRB 210619B observed with Fermi and ASIM. (ekstern lenke)
• David Alexandre Stephan Sarria; Nikolai Østgaard; Martino Marisaldi et al. (2023). Library of Simulated Gamma-Ray Glows and Application to Previous Airborne Observations. (ekstern lenke)

2020

• Carolina Maiorana; Martino Marisaldi; Anders Lindanger et al. (2020). The 3rd AGILE Terrestrial Gamma-ray Flashes Catalog. Part II: Optimized Selection Criteria and Characteristics of the New Sample. (ekstern lenke)
• Anders Lindanger; Martino Marisaldi; Carolina Maiorana et al. (2020). The 3rd AGILE Terrestrial Gamma Ray Flash Catalog. Part I: Association to Lightning Sferics. (ekstern lenke)
• Chris Alexander Skeie; Nikolai Østgaard; Nikolai Lehtinen et al. (2020). Constraints on Recoil Leader Properties Estimated from X-ray Emissions in Aircraft-Triggered Discharges. (ekstern lenke)

2018

• David Sarria; Casper Rutjes; Gabriel Diniz et al. (2018). Evaluation of Monte Carlo tools for high-energy atmospheric physics II: relativistic runaway electron avalanches. (ekstern lenke)
• Pavlo Kochkin; David Sarria; Chris Alexander Skeie et al. (2018). In‐Flight Observation of Positron Annihilation by ILDAS. (ekstern lenke)

Se en fullstendig oversikt over publikasjoner i NVA.

Selected publications:

• Sarria, D., et al. (2025). Spectral analysis of flickering gamma-ray flashes observed during the ALOFT 2023 campaign. Journal of Geophysical Research: Atmospheres.
• Østgaard, N., et al. (2024). Flickering Gamma-Ray Flashes, the Missing Link between Gamma Glows and TGFs. Nature.
• Sarria, D., et al. (2023). Library of Simulated Gamma-Ray Glows and Application to Previous Airborne Observations. Journal of Geophysical Research: Atmospheres.
• Sarria, D., et al. (2018). Evaluation of Monte Carlo tools for high-energy atmospheric physics II: relativistic runaway electron avalanches. Geoscientific Model Development.

A full publication list, PDFs and links to research software are available on my personal website.

FGFF — What makes Flickering Gamma-ray Flashes Flicker? (2025–2029)
Project leader. Funded by the Research Council of Norway through FRIPRO (project 355149). The project investigates the mechanisms behind flickering gamma-ray flashes using multi-platform observations and computer simulations.

ASIM, ALOFT and ENLIGHTEN
Contributions include instrument calibration and modelling, analysis of high-energy radiation from thunderstorms, and development of a gamma-ray pinhole camera for the planned 2028 ENLIGHTEN flight campaign.