On the timing between terrestrial gamma ray flashes, radio atmospherics, and optical lightning emission

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 $\mu$s 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 {\O}stgaard 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

Radio emissions from double RHESSI TGFs

A detailed analysis of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flashes (TGFs) is performed in association with World Wide Lightning Location Network (WWLLN) sources and very low frequency (VLF) sferics recorded at Duke University. RHESSI clock offset is evaluated and found to experience changes on the 5 August 2005 and 21 October 2013, based on the analysis of TGF-WWLLN matches. The clock offsets were found for all three periods of observations with standard deviations less than 100 {\mu}s. This result opens the possibility for the precise comparative analyses of RHESSI TGFs with the other types of data (WWLLN, radio measurements, etc.) In case of multiple-peak TGFs, WWLLN detections are observed to be simultaneous with the last TGF peak for all 16 cases of multipeak RHESSI TGFs simultaneous with WWLLN sources. VLF magnetic field sferics were recorded for two of these 16 events at Duke University. These radio measurements also attribute VLF sferics to the second peak of the double TGFs, exhibiting no detectable radio emission during the first TGF peak. Possible scenarios explaining these observations are proposed. Double (multipeak) TGFs could help to distinguish between the VLF radio emission radiated by the recoil currents in the +IC leader channel and the VLF emission from the TGF producing electrons

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

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Properties of Terrestrial Gamma ray Flashes. Modelling and Analysis of BATSE and RHESSI data

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

Affect and Mathematical Modeling Assessment : A Case Study on Engineering Students’ Experience of Challenge and Flow During a Compulsory Mathematical Modeling Task

Author's accepted version (postprint).Available from 05/06/2020.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 = 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 = 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.acceptedVersio

Effects of dead time losses on terrestrial gamma ray flash measurements with the Burst and Transient Source Experiment

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Mathematical modelling and activation – a study on a large class, a project-based task and students' flow

International audienceWe 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

Mathematical modelling and activation – a study on a large class, a project-based task and students' flow

International audienceWe 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

Production altitude and time delays of the terrestrial gamma flashes: Revisiting the Burst and Transient Source Experiment spectra

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The true fluence distribution of terrestrial gamma flashes at satellite altitude

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