Thomas Gjesteland

• Zakariya, Yusuf F.; Berg, Morten Tellenes; Gjesteland, Thomas; Umahaba, Ramatu Ematum & Abanikannda, Mukhtar Oluwafemi (2025). From single to multiple assessments in a foundational mathematics course for engineering students: what do we gain? Frontiers in Education. 10. doi: 10.3389/feduc.2025.1544647. Full text in Research Archive Show summary

  Background: In response to high failure rates in foundational mathematics courses, the traditional single high-stakes final examination was replaced with four digital tests, with multiple attempts, and a hand-in project.Objectives: This study evaluates the impact of this reformed assessment strategy on a first-year calculus course for engineering students at a Norwegian university. We explored students' perceptions of the reformed assessment regarding their learning approaches, motivation, and the overall experience.Methods: We generated the data using semi-structured interviews of purposively selected engineering students and analyzed the data using thematic analysis.Results: The results showed that the multiple attempts on the examinations promoted consistent studying and reduced test anxiety. Additionally, students reported positive experience with collaborative learning, enhanced by peer learning and diverse perspectives during group work. Although students appreciated the flexibility of digital examinations, they noted limitations in feedback on minor errors.Conclusion: This research highlights the effectiveness of multiple low-stakes assessments in enhancing a supportive learning environment and suggests that digital tools can improve engagement and understanding in mathematics. The findings have implications for rethinking assessment practices in STEM education and offer insights into how digital assessments can mitigate the challenges students face in foundational courses.

• Zakariya, Yusuf F.; Midttun, Øystein; Nyberg, Svein Olav Glesaaen & Gjesteland, Thomas (2022). Reforming the Teaching and Learning of Foundational Mathematics Courses: An Investigation into the Status Quo of Teaching, Feedback Delivery, and Assessment in a First-Year Calculus Course. Mathematics. 10(13). doi: 10.3390/math10132164. Full text in Research Archive
• Gjesteland, Thomas & Vos, Pauline (2019). Affect and mathematical modeling assessment – A case study on students’ experience of challenge and flow during a compulsory mathematical modeling task by engineering students. In Chamberlin, Scott A. & Sriraman, Bharath (Ed.), Affect in Mathematical Modeling. Springer Publishing Company. ISSN 9783030044312. p. 257–272. doi: 10.1007/978-3-030-04432-9-16. Full text in Research Archive Show summary

  This chapter describes a study on engineering students’ affect while working on the Tracker Project Task, a group assessment task that asks students (1) to use digital tools (the camera in their smart phones and free tracker software) to capture the movement of an object, (2) to mathematically model that movement, and (3) to create a poster reporting on the video analysis of the movement. We applied an activity-based conceptualization of affect in mathematics (“do you like this activity?”), which differs from a subject-based conceptualization of affect (“do you like mathematics?”). A subject-based conceptualization has two drawbacks: (1) it does not distinguish among different aspects of mathematics, and (2) it draws in students’ bias and beliefs from earlier, often bad experiences of poor mathematics teaching. We found an activity-based operationalization of affect by using the concepts of challenge and flow. Flow is a state of absorption, in which people forget about time and experience feelings of happiness. We assessed n ¼ 346 students through the Tracker Project Task. To study affect, we developed an instrument of 10 items (Likert-type) to measure students’ experience of challenge and flow. We administered the survey through a web-based platform yielding a high response rate (n ¼ 239, 69%) and good reliability (Cronbach’s Alpha: 0,795). The results revealed that three out of five students experienced challenge and flow, which expresses students’ positive affect regarding a mathematical assessment activity. This can be ascribed to, on the one hand, the activity and the instrument not clearly being related to mathematics, and thus not being tainted by students’ earlier negative experiences with mathematics. On the other hand the Tracker Project Task had characteristics that can bring about flow: being open, offering ample time to submit the product, being accessible to all students (low floor), but also enabling the better students to challenge themselves further (high ceiling). Such characteristics may be better feasible within mathematical modeling assessment than canonical mathematics assessment.

• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2018). Mathematical modelling and activation – a study on a large class, a project-based task and students’ flow. International Network for Didactic Research in University Mathematics : INDRUM. Full text in Research Archive Show summary

  We studied how engineering students in a large class (n=346) can be activated by a project-based task, in which they have to model mathematically the motion of an object. The students had to throw an object, use (1) their smart phones for filming, and (2) tracker software for capturing the motion. Through a poster, they had to report their video analysis. We framed activation through the concept of flow, which is a state of being fully absorbed by an activity. We administered a web-based questionnaire (response rate 69%). The results show that such a project-based task is feasible with >300 students and activated them: three out of five experienced flow. Also, we validated the theory that for experiencing flow, a task must be perceived as challenging and that one’s skills should match that challenge.

• Albrechtsen, Kjetil; Østgaard, Nikolai; Berge, Nini & Gjesteland, Thomas (2018). Observationally Weak TGFs in the RHESSI Data. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 124(1), p. 287–298. doi: 10.1029/2018JD029272. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Bitzer, Phillip & Christian, Hugh J. (2017). On the timing between terrestrial gamma ray flashes, radio atmospherics, and optical lightning emission. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 122(7), p. 7734–7741. doi: 10.1002/2017JA024285. Full text in Research Archive Show summary

  On 25 October 2012 the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) and the Tropical Rainfall Measuring Mission (TRMM) satellites passed over a thunderstorm on the coast of Sri Lanka. RHESSI observed a terrestrial gamma ray flash (TGF) originating from this thunderstorm. Optical measurements of the causative lightning stroke were made by the lightning imaging sensor (LIS) on board TRMM. The World Wide Lightning Location Network (WWLLN) detected the very low frequency (VLF) radio emissions from the lightning stroke. The geolocation from WWLLN, which we also assume is the TGF source location, was in the convective core of the cloud. By using new information about both RHESSI and LIS timing accuracy, we find that the peak in the TGF light curve occurs 230 μs before the WWLLN time. Analysis of the optical signal from LIS shows that within the uncertainties, we cannot conclude which comes first: the gamma emission or the optical emission. We have also applied the new information about the LIS timing on a previously published event by Østgaard et al. (2012). Also for this event we are not able to conclude which signal comes first. More accurate instruments are needed in order to get the exact timing between the TGF and the optical signal.

• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2017). Students experiencing flow in a Physics lab task using mobile phones and free software. In Tveiten, Oddgeir (Eds.), Smart Universities: Education´s Digital Future. Logos Verlag Berlin. ISSN 9783832545956. p. 37–44. Full text in Research Archive Show summary

  In this paper we outline a study on an alternative to laboratory learning. Normally, lab learning is part of engineering students’ courses on Physics. Instead of making them work in a lab, we gave students an inquiry-based, open task: to model the movement of an object. The laboratory equipment consisted of their mobile phones for filming, and free available tracker software. Students worked in groups and reported their results on a poster. We studied the engagement of students with the task and whether it generated flow, a state in which one forgets about time. The results show that, indeed, students got into a flow, and this related to their perception of challenge. Also, the experiment shows that mobile and free technology can make Physics laboratory learning feasible beyond university campuses and opens new possibilities in inquiry-based laboratory learning, also for large numbers of students, distance education or within less affluent institutions.

• Mezentsev, Andrey; Østgaard, Nikolai; Gjesteland, Thomas; Albrechtsen, Kjetil; Lehtinen, Nikolai & Marisaldi, Martino [Show all 8 contributors for this article] (2016). Radio emissions from double RHESSI TGFs. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 121(13), p. 8006–8022. doi: 10.1002/2016JD025111. Full text in Research Archive
• Østgaard, Nikolai; Carlson, Brant Edward; Nisi, Ragnhild Schrøder; Gjesteland, Thomas; Grøndahl, Øyvind & Skeltved, Alexander Broberg [Show all 10 contributors for this article] (2016). Relativistic electrons from sparks in the laboratory. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 121(6), p. 2939–2954. doi: 10.1002/2015JD024394. Full text in Research Archive
• Marisaldi, Martino; Argan, Andrea; Ursi, Alessandro; Gjesteland, Thomas; Fuschino, Fabio & Labanti, Claudio [Show all 24 contributors for this article] (2015). Enhanced detection of terrestrial gamma-ray flashes by AGILE. Geophysical Research Letters. ISSN 0094-8276. 42(21), p. 9481–9487. doi: 10.1002/2015GL066100. Full text in Research Archive Show summary

  At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma-Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with lightning sferics detected by the World Wide Lightning Location Network. The new configuration provides the largest TGF detection rate surface density (TGFs/km2/yr) to date, opening prospects for improved correlation studies with lightning and atmospheric parameters on short spatial and temporal scales along the equatorial region.

• Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant Edward; Gjesteland, Thomas & Celestin, Sebastien (2015). Modeling the relativistic runaway electron avalanche and the feedback mechanism with GEANT4. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 119(11), p. 9174–9191. doi: 10.1002/2014JA020504. Full text in Research Archive Show summary

  This paper presents the first study that uses the GEometry ANd Tracking 4 (GEANT4) toolkit to do quantitative comparisons with other modeling results related to the production of terrestrial gamma ray flashes and high-energy particle emission from thunderstorms. We will study the relativistic runaway electron avalanche (RREA) and the relativistic feedback process, as well as the production of bremsstrahlung photons from runaway electrons. The Monte Carlo simulations take into account the effects of electron ionization, electron by electron (Møller), and electron by positron (Bhabha) scattering as well as the bremsstrahlung process and pair production, in the 250 eV to 100 GeV energy range. Our results indicate that the multiplication of electrons during the development of RREAs and under the influence of feedback are consistent with previous estimates. This is important to validate GEANT4 as a tool to model RREAs and feedback in homogeneous electric fields. We also determine the ratio of bremsstrahlung photons to energetic electrons Nγ/Ne. We then show that the ratio has a dependence on the electric field, which can be expressed by the avalanche time τ(E) and the bremsstrahlung coefficient α(ϵ). In addition, we present comparisons of GEANT4 simulations performed with a “standard” and a “low-energy” physics list both validated in the 1 keV to 100 GeV energy range. This comparison shows that the choice of physics list used in GEANT4 simulations has a significant effect on the results.

• Gjesteland, Thomas; Østgaard, Nikolai; Laviola, Sante; Miglietta, Mario Marcelli; Arnone, Enrico & Marisaldi, Martino [Show all 10 contributors for this article] (2015). Observation of intrinsically bright terrestrial gamma ray flashes from the Mediterranean basin. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 120(23), p. 12143–12156. doi: 10.1002/2015JD023704. Full text in Research Archive Show summary

  We present three terrestrial gamma ray flashes (TGFs) observed over the Mediterranean basin by the Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) satellite. Since the occurrence of these events in the Mediterranean region is quite rare, the characterization of the events was optimized by combining different approaches in order to better define the cloud of origin. The TGFs on 7 November 2004 and 16 October 2006 came from clouds with cloud top higher than 10–12 km where often a strong penetration into the stratosphere is found. This kind of cloud is usually associated with heavy precipitation and intense lightning activity. Nevertheless, the analysis of the cloud type based on satellite retrievals shows that the TGF on 27 May 2004 was produced by an unusual shallow convection. This result appears to be supported by the model simulation of the particle distribution and phase in the upper troposphere. The TGF on 7 November 2004 is among the brightest ever measured by RHESSI. The analysis of the energy spectrum of this event is consistent with a production altitude ≤12 km, which is in the upper part of the cloud, as found by the meteorological analysis of the TGF-producing thunderstorm. This event must be unusually bright at the source in order to produce such a strong signal in RHESSI. We estimate that this TGF must contain ∼3 × 1018 initial photons with energy >1 MeV. This is 1 order of magnitude brighter than earlier estimations of an average RHESSI TGF.

• Østgaard, Nikolai; Albrechtsen, Kjetil; Gjesteland, Thomas & Collier, Andrew B. (2015). A new population of terrestrial gamma-ray flashes in the RHESSI data. Geophysical Research Letters. ISSN 0094-8276. 42(24), p. 10937–10942. doi: 10.1002/2015GL067064. Full text in Research Archive Show summary

  Terrestrial gamma-ray flashes (TGFs) are the most energetic photon phenomenon occurring naturally on Earth. An outstanding question is as follows: Are these flashes just a rare exotic phenomenon or are they an intrinsic part of lightning discharges and therefore occurring more frequently than previously thought? All measurements of TGFs so far have been limited by the dynamic range and sensitivity of spaceborne instruments. In this paper we show that there is a new population of weak TGFs that has not been identified by search algorithms. We use the World Wide Lightning Location Network (WWLLN) to identify lightning that occurred in 2006 and 2012 within the 800 km field of view of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). By superposing 740,210 100 ms RHESSI data intervals, centered at the time of the WWLLN detected lightning, we identify at least 141 and probably as many as 191 weak TGFs that were not part of the second RHESSI data catalogue. This supports the suggestion that the global TGF production rate is larger than previously reported.

• Nisi, Ragnhild Schrøder; Østgaard, Nikolai; Gjesteland, Thomas & Collier, Andrew B. (2014). An altitude and distance correction to the initial fluence distribution of TGFs. Journal of Geophysical Research (JGR). ISSN 0148-0227. 119(10), p. 8698–8704. doi: 10.1002/2014JA019817. Full text in Research Archive Show summary

  The source fluence distribution of terrestrial gamma ray flashes (TGFs) has been extensively discussed in recent years, but few have considered how the TGF fluence distribution at the source, as estimated from satellite measurements, depends on the distance from satellite foot point and assumed production altitude. As the absorption of the TGF photons increases significantly with lower source altitude and larger distance between the source and the observing satellite, these might be important factors. We have addressed the issue by using the tropopause pressure distribution as an approximation of the TGF production altitude distribution and World Wide Lightning Location Network spheric measurements to determine the distance. The study is made possible by the increased number of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) TGFs found in the second catalog of the RHESSI data. One find is that the TGF/lightning ratio for the tropics probably has an annual variability due to an annual variability in the Dobson-Brewer circulation. The main result is an indication that the altitude distribution and distance should be considered when investigating the source fluence distribution of TGFs, as this leads to a softening of the inferred distribution of source brightness.

• Hansen, Ragnhild Schrøder; Østgaard, Nikolai; Gjesteland, Thomas & Carlson, Brant Edward (2013). How simulated fluence of photons from terrestrial gamma ray flashes at aircraft and balloon altitudes depends on initial parameters. Journal of Geophysical Research (JGR). ISSN 0148-0227. 118(5), p. 2333–2339. doi: 10.1002/jgra.50143. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward; Collier, Andrew B.; Cummer, Steven A. & Lu, Gaopeng [Show all 7 contributors for this article] (2013). Simultaneous observations of optical lightning and terrestrial gamma ray flash from space. Geophysical Research Letters. ISSN 0094-8276. 40(10), p. 2423–2426. doi: 10.1002/grl.50466. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Hansen, Ragnhild Schrøder; Collier, Andrew B. & Carlson, Brant Edward (2012). The true fluence distribution of terrestrial gamma flashes at satellite altitude. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 117. doi: 10.1029/2011JA017365. Full text in Research Archive
• Carlson, Brant Edward; Gjesteland, Thomas & Østgaard, Nikolai (2012). Connecting the terrestrial gamma-ray flash source strength and observed fluence distributions. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 117. doi: 10.1029/2011JA017122. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Collier, Andrew B.; Carlson, Brant Edward; Eyles, Chris J. & Smith, David M. (2012). A new method reveals more TGFs in the RHESSI data. Geophysical Research Letters. ISSN 0094-8276. 39. doi: 10.1029/2012GL050899. Full text in Research Archive
• Carlson, Brant Edward; Gjesteland, Thomas & Østgaard, Nikolai (2011). Terrestrial gamma-ray flash electron beam geometry, fluence, and detection frequency. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 116. doi: 10.1029/2011JA016812. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Collier, A. B.; Carlson, Brant Edward; Cohen, M. B. & Lehtinen, N. G. (2011). Confining the angular distribution of terrestrial gamma ray flash emission. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 116. doi: 10.1029/2011JA016716. Full text in Research Archive
• Collier, Andrew B.; Gjesteland, Thomas & Østgaard, Nikolai (2011). Assessing the power law distribution of TGFs. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 116. doi: 10.1029/2011JA016612. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Connell, Paul H.; Stadsnes, Johan & Fishman, Gerald J. (2010). Effects of dead time losses on terrestrial gamma ray flash measurements with the Burst and Transient Source Experiment. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 115. doi: 10.1029/2009JA014578. Full text in Research Archive
• Cohen, Morris B.; Inan, Umran S.; Said, Ryan K. & Gjesteland, Thomas (2010). Geolocation of terrestrial gamma-ray flash source lightning. Geophysical Research Letters. ISSN 0094-8276. 37. doi: 10.1029/2009GL041753. Full text in Research Archive

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• Larson, Niclas & Gjesteland, Thomas (2026). Consequences of a new assessment model in Mathematics 1 for engineering students. Skrifter från Svensk förening för matematikdidaktisk forskning. ISSN 1651-3274. 20, p. 225–226. doi: http:/matematikdidaktik.org/wp-content/uploads/2026/05/20_Madif15-Proceedings.pdf. Full text in Research Archive
• Larson, Niclas & Gjesteland, Thomas (2026). Consequences of a new assessment model in Mathematics 1 for engineering students. Full text in Research Archive Show summary

  Kort presentasjon på Madif-15 om lærere i ingeniøremner på bachelornivå sine erfaringer av ny vurderingsform av emnet Matematikk 1 i første semester på ingeniørutdanningen.

• Midttun, Øystein & Gjesteland, Thomas (2025). Portfolio assessment in mathematics promotes active learning. doi: https:/www.sefi.be/publication/mathematics-sig-seminar-2025-proceedings/. Full text in Research Archive Show summary

  This paper introduces a portfolio assessment in mathematics for first-year engineering students that was implemented at the University of Agder (UiA) in 2022. The portfolio consists of two key components, contributing 60% and 40% of the final grade, respectively: 1. Four computer-aided assessment (CAA) tests under supervision, providing immediate feedback on the students’ performance. The students can take each test up to four times, with their best attempt counting toward their final grade. 2. A written assignment, where students apply mathematical concepts from the curriculum to solve an engineering problem. We observe that the students take advantage of multiple test attempts, and that after each test, they organically form groups to discuss the problems with each other. Additionally, the university's math support center sees increased usage during test periods. Biggs et al. (2007) claim that learning is a result of what the student does and that active students foster deep learning. We argue that this assessment design encourages the students to become active in their own learning. The written assignment also helps students to relate mathematical competence to realistic engineering problems, thus making the subject more relevant to their studies. We claim that this competence is equally important for engineers as it is to solve difficult calculus problems by hand.

• Irgens, Børge; Opheim, Linda Gurvin; Huru, Hilja Lisa; Møllersen, Kajsa & Gjesteland, Thomas (2025). Studenters personvern: En diskusjon om etisk bruk av studentdata i forskning. Full text in Research Archive
• Larson, Niclas; Gjesteland, Thomas; Wæhle, Ingeborg; Bie, Eivind; Husebø, Sivert Espeland & Øvreås, Ole-Johan (2025). Student på UiA (del 2): Ingeniørutdanninger i Grimstad. doi: https:/podcasts.apple.com/us/podcast/student-p%C3%A5-uia-del-2-ingeni%C3%B8rutdanninger-i-grimstad/id1586322365?i=1000700047582. Full text in Research Archive Show summary

  Sesongens sjette episode av Spøkelser etter avdøde størrelser er den andre episoden med fokus på rekruttering til UiA, der vi framfor alt ser på programmene med mye matematikk. Episoden handler om ingeniørutdanningene på campus Grimstad. Først har Niclas Larson truffet to studenter på fornybar energi. De prater om utdanningen, men også om MatRIC Drop in og ENT3R, der det sistnevnte er et tilbud til elever i videregående skole. Deretter er det et møte med to som studerer kunstig intelligens, med prat om programmet, linjeforeningen og det fantastiske været i Grimstad. Til slutt kommer professor Thomas Gjesteland og forteller om tiltak i første matematikkurset på ingeniørutdanningen, noe som har gitt meget god effekt på ståprosenten. Medvirkende: Ingeborg Wæhle, Eivind Bie, Sivert Espeland Husebø, Ole-Johan Øvreås, Thomas Gjesteland, og programlederen Niclas Larson.

• Bakke, Jostein; Langford, Malcolm; Børrud, Elin; Cotner, Sehoya Harris; Engebretsen, Eivind & Graver, Fredrik (Georg Fredrik) [Show all 14 contributors for this article] (2023). Fremtidens høyere utdanning trenger en oppgradering - ikke budsjettkutt! Full text in Research Archive
• Gjesteland, Thomas & Sydnes, Magne Olav (2023). Editorial. Nordic Journal of STEM Education. 8(1). Full text in Research Archive
• Gjesteland, Thomas (2022). Scholarly approaches to Teaching and Learning. Full text in Research Archive
• Brekke, Morten; Gjesteland, Thomas & Landgärds, Ida Maria (2022). Erfarne studenter er løsningen for tidenes viktigste førstesemester 2022. Full text in Research Archive
• Gjesteland, Thomas (2022). Norge trenger senter for frem­ragende ut­danning. Full text in Research Archive
• Tranberg, Anders; Lurås, Inger Johanne; Jakobsen, Mette Mo; Siqveland, Arvid & Gjesteland, Thomas (2021). New Guidelines for the National Curriculum Regulations for Engineering Education in Norway(with emphasis on Mathematics). Full text in Research Archive
• Gjesteland, Thomas; Lima, Vegard; Lunøe-Nielsen, Sverre A; Radmehr, Farzad & Goodchild, Simon (2021). Gruppebasert prosjektoppgave i matematikk: Veiledernes erfaringer. Full text in Research Archive
• Langford, Malcolm; Larsen, Johanne Maria Rohde; Vandvik, Vigdis; Vabø, Ørjan Sørstrønen; Sindre, Guttorm & Gjesteland, Thomas [Show all 10 contributors for this article] (2020). Aune-utvalget vil gi bråstopp i utviklingen av gode vurderingsformer. Full text in Research Archive
• Eriksen, Marianne Hem; Gjesteland, Thomas & Bølstad, Jørgen (2020). «All forskning er vel ikke like bra?» En arkeolog, en fysiker og en statsviter svarer. Morgenbladet. ISSN 0805-3847. Full text in Research Archive
• Tjønndal, Anne Beret; Korsvoll, Nils Hallvard & Gjesteland, Thomas (2020). Er man hysterisk hvis man er redd for å bli smittet av koronaviruset her i Norge? Morgenbladet. ISSN 0805-3847. Full text in Research Archive
• Nilsen, Hans Kristian & Gjesteland, Thomas (2019). How do we get active students? Students enjoying transformed and improved learning experiences of mathematics in higher education. Full text in Research Archive
• Gjesteland, Thomas & Vos, Pauline (2017). Assessment of Physics laboratory skills of engineering students – project-based assessment with mobile phones and free tracker software. Full text in Research Archive
• Gjesteland, Thomas & Vos, Pauline (2017). The Physics Lab experiment: Students Experiencing Flow. Full text in Research Archive
• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2017). Students experiencing flow in a Physics lab task using mobile phones and free software. Full text in Research Archive
• Albrechtsen, Kjetil; Østgaard, Nikolai; Marisaldi, Martino; Gjesteland, Thomas & Berge, Nini (2017). Estimating the global production rate of TGFs. Full text in Research Archive
• Gjesteland, Thomas & Vos, Pauline (2017). Modelling motion by engineering students - getting into a flow. Full text in Research Archive
• Gjesteland, Thomas; Vos, Pauline & Wold, Margrethe (2016). Students Experiencing Flow in a Physic Laboratory Task using Mobile Phones and Free Software. Full text in Research Archive
• Mezentsev, Andrey; Østgaard, Nikolai; Gjesteland, Thomas; Albrechtsen, Kjetil; Marisaldi, Martino & Smith, David [Show all 7 contributors for this article] (2016). Radio emissions from double RHESSI TGFs. Full text in Research Archive
• Mezentsev, Andrey; Østgaard, Nikolai; Gjesteland, Thomas; Albrechtsen, Kjetil & Cummer, Steven A. (2016). Radio emissions from RHESSI TGFs. Full text in Research Archive
• Mezentsev, Andrey; Østgaard, Nikolai; Gjesteland, Thomas; Albrechtsen, Kjetil; Marisaldi, Martino & Smith, David [Show all 7 contributors for this article] (2016). Radio emissions from RHESSI TGFs. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Marisaldi, Martino; Briggs, M. S. & Smith, David M. (2016). Stereo Observations of Terrestrial Gamma-ray Flashes. Full text in Research Archive
• Aamodt, Vegard; Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward & Collier, Andrew B. (2015). Search for Terrestrial Electron Beams (TEBs) in SAMPEX data. Full text in Research Archive
• Gjesteland, Thomas; Christian, Hugh & Østgaard, Nikolai (2015). An observation of a TGF from the convective core of a thundercloud. Full text in Research Archive
• Mezentsev, Andrew; Østgaard, Nikolai; Gjesteland, Thomas; Skeltved, Alexander Broberg & Cummer, Steven A. (2015). VLF sferics associated with TGFs. Full text in Research Archive
• Skeltved, Alexander Broberg; Østgaard, Nikolai; Gjesteland, Thomas & Carlson, Brant Edward (2015). Modeling the production and acceleration of runaway electrons in strong inhomogeneous electric fields with GEANT4. Full text in Research Archive
• Østgaard, Nikolai; Carlson, Brant Edward; Gjesteland, Thomas; Grøndahl, Øystein; kochkin, pavlo & Nisi, Ragnhild Schrøder (2015). Search for relativistic electrons in laboratory discharge experiments. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward; Collier, Andrew B.; Cummer, Steven A. & Lu, Gaopeng [Show all 7 contributors for this article] (2015). Simultaneous observations of optical lightning and terrestrial gamma flash from space and radio signals on ground. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Christian, Hugh; Albrechtsen, Kjetil; Carlson, Brant Edward & Collier, Andrew B. [Show all 8 contributors for this article] (2015). The sequence of events in a lightning stroke: terrestrial gamma ray flash, radio signal and optical lightning. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward; Collier, Andrew B.; Cummer, Steven A. & Lu, Gang [Show all 7 contributors for this article] (2015). Simultaneous observations of optical lightning and terrestrial gamma flash and radio signals on ground. Full text in Research Archive
• Albrechtsen, Kjetil; Østgaard, Nikolai; Gjesteland, Thomas & Collier, Andrew B. (2015). Do all lightning produce TGFs? Approaching this question using data from RHESSI and WWLLN. Full text in Research Archive
• Montanya, J.; Fabro, F; Velde, O van der; Aranguren, David; Williams, E. & Morales, C [Show all 12 contributors for this article] (2014). Lightning activity and radar for a TGF case in Colombia. Full text in Research Archive
• Østgaard, Nikolai; Carlson, Brant Edward; Grøndahl, Øystein; Kochkin, P; Nisi, Ragnhild Schrøder & Gjesteland, Thomas (2014). Search for X-rays and relativistic electrons in laboratory discharge experiments. Full text in Research Archive
• Kelley, N. A.; Smith, David M.; Bowers, G. S.; Buzbee, P; Dwyer, J. R. & Cramer, E. S. [Show all 10 contributors for this article] (2014). Recent Results from ADELE and RHESSI. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward; Collier, Andrew B.; Cummer, Steven A. & Lu, Gaopeng [Show all 7 contributors for this article] (2014). First simultaneous observations of optical lightning and terrestrial gamma flash from space. Full text in Research Archive
• Infanger, Andrew; Smith, David M.; Gjesteland, Thomas & Østgaard, Nikolai (2014). Toward an optimized Third Catalog of RHESSI TGFs. Full text in Research Archive
• Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant Edward & Gjesteland, Thomas (2014). A study of the runaway relativistic electron avalanche and the feedback theory using GEANT4. Full text in Research Archive
• Østgaard, Nikolai; Carlson, Brant Edward; Grøndahl, Øystein; Nisi, Ragnhild Schrøder & Gjesteland, Thomas (2014). Search for X-rays and relativistic electrons in laboratory discharge experiments. Full text in Research Archive
• Nisi, Ragnhild Schrøder; Østgaard, Nikolai & Gjesteland, Thomas (2014). An altitude and distance correction to the initial fluence distribution of TGF. Full text in Research Archive
• Aamodt, Vegard; Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward & Collier, Andrew B. (2014). Search for Terrestrial Electron Beams (TEB) in SAMPEX data. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Nisi, Ragnhild Schrøder; Collier, Andrew B.; Smith, David M. & Cummer, Steven A. [Show all 7 contributors for this article] (2014). Twelve Years of RHESSI TGFs - The second RHESSI TGF catalog. Full text in Research Archive
• Skeltved, Alexander Broberg; Østgaard, Nikolai; Gjesteland, Thomas & Collier, Andrew B. (2014). Modelling the runaway electron avalanche and the feedback mechanism with GEANT4. Full text in Research Archive
• Kelley, N. A.; Smith, David M.; Bowers, G. S.; Dwyer, J. R.; Cummer, Steven A. & Gjesteland, Thomas [Show all 10 contributors for this article] (2013). Recent Results from ADELE and RHESSI. Full text in Research Archive
• Smith, David M.; Buzbee, P; Infanger, A; Cummer, Steven A.; Dwyer, J. R. & Lu, Gaopeng [Show all 8 contributors for this article] (2013). Results from the third RHESSI catalog of Terrestrial Gamma-ray Flashes. Full text in Research Archive
• Nisi, Ragnhild Schrøder; Østgaard, Nikolai; Carlson, Brant Edward & Gjesteland, Thomas (2013). Modeling of the Bremsstrahlung process in connection to Terrestrial gamma-ray flashes. Full text in Research Archive
• Gjesteland, Thomas (2013). Ser bak Lynet. Full text in Research Archive
• Gjesteland, Thomas (2013). Det Gåtefulle gammaglimtet. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Marisaldi, Martino; Fabio, Fushino; Sante, Laviola & Collier, Andrew B. (2013). Terrestrial Gamma ray Flashes observed over low clod tops. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Marisaldi, Martino; fuschino, f; arnona, e & laviola, s (2013). Unusual bright TGF from low cloud tops over the Mediterranean sea. Full text in Research Archive
• Skeltved, Alexander Broberg; Østgaard, Nikolai; Carlson, Brant Edward & Gjesteland, Thomas (2013). A study of the relativistiv runaway electron avalanche and the feedback theories to explain terrestrial gammaray production. Full text in Research Archive
• Gjesteland, Thomas (2013). Terrestrial Gamma ray Flashes, dark lightning and the dark side of dark lightning. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Collier, Andrew B.; Martino, Marisaldi; Fabio, Fushino & Arnona, Enrico [Show all 7 contributors for this article] (2013). Terrestrial Gamma ray Flashes observed over low clod tops. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Carlson, Brant Edward; Collier, Andrew B.; Cummer, Steven A. & Lu, Gaopeng [Show all 7 contributors for this article] (2013). First simultaneous observations of optical lightning and terrestrial gamma flash from space. Full text in Research Archive
• Collier, Andrew B.; Gjesteland, Thomas & Østgaard, Nikolai (2013). Intensity of Lightning Associated with TGFs. Full text in Research Archive
• Hansen, Ragnhild Schrøder; Østgaard, Nikolai; Gjesteland, Thomas & Carlson, Brant Edward (2012). Fluence of photons from Terrestrial Gamma ray flashes in aircraft and balloon altitudes - dependence of initial parameters in simulations. Full text in Research Archive
• Collier, Andrew B. & Gjesteland, Thomas (2011). Terrestrial Gamma-ray flash intensity distribution. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Collier, Andrew B.; Carlson, Brant Edward; Cohen, Morris B. & Lehtinen, Nikolai (2011). Confining the angular distribution of TGF emission. Full text in Research Archive
• Gjesteland, Thomas (2011). Jordiske Gammaglimt. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai & Collier, Andrew B. (2011). Constrains on the Terrestrial Gamma-ray Flashes Emission Cone by Spectral Analysis of Geolocated Events. EGU. Full text in Research Archive
• Gjesteland, Thomas; Østgaard, Nikolai; Collier, Andrew B.; Carlson, Brant Edward; Hansen, Ragnhild Schrøder & Eyles, C [Show all 8 contributors for this article] (2011). Are there more TGFs in the RHESSI data. Full text in Research Archive
• Carlson, Brant Edward; Gjesteland, Thomas & Østgaard, Nikolai (2011). The frequency of terrestrial gamma-ray flash electron beam observations. Full text in Research Archive
• Collier, Andrew B.; Gjesteland, Thomas & Østgaard, Nikolai (2011). Terrestrial Gamma-ray Flash Intensity Distribution. Full text in Research Archive
• Carlson, Brant Edward; Gjesteland, Thomas & Østgaard, Nikolai (2011). The TGF source luminosity distribution. Full text in Research Archive
• Østgaard, Nikolai; Hansen, Ragnhild Schrøder; Gjesteland, Thomas; Carlson, Brant Edward & Collier, Andrew B. (2011). Occurence frequency and fluence of TGFs. Full text in Research Archive
• Carlson, Brant Edward; Fishman, G; Briggs, M. S.; Cohen, M. B.; Østgaard, Nikolai & Said, R. K. [Show all 8 contributors for this article] (2011). Modeling TGF electron beams and constraints on the TGF source. Full text in Research Archive
• Østgaard, Nikolai; Carlson, Brant Edward; Hansen, Ragnhild Schrøder; Gjesteland, Thomas & Collier, Andrew B. (2011). The true distribution of TGF fluence measured from space. Full text in Research Archive
• Vaktdal, Siri M.; Østgaard, Nikolai; Gjesteland, Thomas; Hansen, Ragnhild Schrøder; Collier, Andrew B. & Carlson, Brant Edward (2011). TGF dependence on magnetic latitude and solar zenith angle. Full text in Research Archive
• Collier, Andrew B.; Gjesteland, Thomas & Østgaard, Nikolai (2011). Terrestrial Gamma-Ray Flash Intensity Distribution. Full text in Research Archive
• Østgaard, Nikolai; Hansen, Ragnhild Schrøder; Gjesteland, Thomas; Carlson, Brant Edward & Collier, Andrew B. (2011). Occurence frequency and fluence of TGFs. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Connell, Paul H. & Stadsnes, Johan (2009). Analysis of a subset of BATSE TGFs that do not suffer from instrumental limitations. Full text in Research Archive
• Østgaard, Nikolai; Gjesteland, Thomas; Connell, Paul H. & Stadsnes, Johan (2009). Production altitude, initial distributions and time delays for TGFs when instrumental deadtime effects are treated properly. Full text in Research Archive
• Gjesteland, Thomas (2012). Properties of Terrestrial Gamma ray Flashes. Modelling and Analysis of BATSE and RHESSI data. Universitetet i Bergen. ISSN 9788230820605. Full text in Research Archive Show summary

  This thesis objective is to study Terrestrial Gamma ray Flashes (TGFs), which are short burst (∼ 1 ms) of gamma-radiation from thunderstorms first discovered by Fishman et al. [1994]. The measured photons energies in TGFs are found to be up to several tens of MeV [Smith et al., 2005; Marisaldi et al., 2010a], which make them the most energetic natural photon phenomenon on Earth. The physics behind the production of TGFs are not well established. TGFs are assumed to be bremsstrahlung from relativistic electrons which are accelerated in strong electric fields related to thunderstorms. However, it is not known how frequent TGFs are, what are the altitude range in which they can be produced, the spatial extent of their source region, the angular distribution of the photons at the production altitude or to what kind of thunderstorms and lightning they are related to. There is a few suggested theories of how TGFs can be produced, but there are so far no consensus. The aim of this thesis is to study TGFs in order to understand what this recently discovered natural phenomenon is. In the papers presented in this thesis several questions regarding the nature of TGFs are addressed. The main contributions can be summarized in three points. 1) Determine the production altitude of TGFs. The production altitude will give constraints on the electric fields that produces TGF and which type of lightning and/or thunderstorms that produces TGFs. The production altitude is investigated by comparing Monte Carlo simulations with measurements from the Burst And Transient Source Experiment (BATSE). The conclusions of Paper I [Østgaard et al., 2008] and Paper II [Gjesteland et al., 2010] of this thesis is that the TGFs measured by BATSE are produced in ∼ 10−20 km altitude. 2) Determine the angular distribution of the photons produced in a TGF. The distribution of emitted photons will reflect the direction of the electric fields that produces the TGFs. Paper III [Gjesteland et al., 2011] argue that TGFs are emitted within a cone of 30◦−40◦ indicating that TGFs are produced in nearly vertical electric fields. 3) Examine how common TGFs are. When TGFs were discovered they were thought to be a rare phenomenon since they were only observed ∼ once a month [Fishman et al., 1994]. More recent results based on more sensitive instruments have observed ∼ 10 TGFs a month [Grefenstette et al., 2009], which is more frequent but still rare. Paper IV [Gjesteland et al., 2012] describes a method to lower the sensitivity threshold for the RHESSI satellite. Applying this method has more than double the number of identified TGFs. The increase of identified TGFs indicates that so far only the top of an ’iceberg’ of TGFs are observed. Paper V [Østgaard et al., 2012] use an analytical approach, by comparing the relative TGF count rates of the RHESSI and Fermi satellites, to show that one cannot reject the hypothesis that all lightning produce TGFs. If this is the case, then TGFs are a very common phenomenon which may have important impacts of the coupling between the lower atmosphere and space. This thesis starts with a historical walk trough the TGF research starting almost hundred years ago. Chapter 3 describes the two satellites instruments, BATSE and RHESSI, which are used in the studies of this thesis. Also, a brief overview of other experiments which have measured TGFs are presented. The same chapter also describes radio measurements of lightning which are found to be associated TGFs. Chapter 4 describes the basic theory behind TGFs. In chapter 5 present a brief summary of each of five papers, which is the scientific contribution in this thesis. The five papers are presented in chapter 6.

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