Andrew Mezentsev - Academia.edu (original) (raw)

Papers by Andrew Mezentsev

Slides of the presentation held during the 2018 AGU Fall Meeting in Washington, D.C. . See full i... more Slides of the presentation held during the 2018 AGU Fall Meeting in Washington, D.C. . See full information here. The associated journal article is available here. <strong>Abstract :</strong> In the spring of 2017 the «GOES-R Validation Flight Campaign» was undertaken with an ER-2 aircraft over the continental United States. The plane, flying at a cruise altitude of 20km, had a scientific payload designed to detect optical signals, electric fields and gamma rays from thunderstorms. On May 8, 2017, the on-board gamma-ray spectrometers could detect a gamma-ray glow event lasting for about 4 minutes over Colorado. It was detected by several spectrometers, including three BGO-based detectors, similar to the ones on-board of the ASIM instrument docked to the international space station. The glow showed a gamma-ray count increase on top of the background of 10 to 40 %, which was rather unexpected from such high altitude (20 km). We present a detailed analysis and modeling of t...

Journal of Geophysical Research: Atmospheres, 2019

In the spring of 2017 an ER-2 aircraft campaign was undertaken over continental United States to ... more In the spring of 2017 an ER-2 aircraft campaign was undertaken over continental United States to observe energetic radiation from thunderstorms and lightning. The payload consisted of a suite of instruments designed to detect optical signals, electric fields, and gamma rays from lightning. Starting from Georgia, USA, 16 flights were performed, for a total of about 70 flight hours at a cruise altitude of 20 km. Of these, 45 flight hours were over thunderstorm regions. An analysis of two gamma ray glow events that were observed over Colorado at 21:47 UT on 8 May 2017 is presented. We explore the charge structure of the cloud system, as well as possible mechanisms that can produce the gamma ray glows. The thundercloud system we passed during the gamma ray glow observation had strong convection in the core of the cloud system. Electric field measurements combined with radar and radio measurements suggest an inverted charge structure, with an upper negative charge layer and a lower positive charge layer. Based on modeling results, we were not able to unambiguously determine the production mechanism. Possible mechanisms are either an enhancement of cosmic background locally (above or below 20 km) by an electric field below the local threshold or an enhancement of the cosmic background inside the cloud but then with normal polarity and an electric field well above the Relativistic Runaway Electron Avalanche threshold.

Terrestrial gamma-ray flashes (TGFs) are sub-millisecond bursts of energetic photons up to severa... more Terrestrial gamma-ray flashes (TGFs) are sub-millisecond bursts of energetic photons up to several tens of MeV produced in the atmosphere. The energy spectra of TGFs are compatible with the Relativistic Runaway Electron Avalanche (RREA) process followed by bremsstrahlung emissions (

Terrestrial Gamma-ray Flashes (TGFs) are short (~10 us to ~2 ms) flashes of high energy (< 40 MeV... more Terrestrial Gamma-ray Flashes (TGFs) are short (~10 us to ~2 ms) flashes of high energy (< 40 MeV) photons, produced by thunderstorms When interacting with the atmosphere, the TGF's photons produce relativistic electrons and positrons at higher altitudes, and a fraction is able to escape the atmosphere [1,2,3]. The electrons/positrons are then bounded to Earth's magnetic field lines and can travel large distances inside the ionosphere and the magnetosphere. This phenomenon is called a Terrestrial Electron Beam (TEB). The Atmosphere-Space Interactions Monitor (ASIM), dedicated to the study of TGF and associated events, started to operate in June 2018. ASIM contains an optical instrument (MMIA) made of micro-cameras and photometers, as well the Modular X and Gamma-ray Sensor (MXGS) for high energy radiation. MXGS is composed of the low energy detector (LED, 50 keV to 400 keV) and the High Energy detector (HED, 300 keV to 40 MeV). This presentation is focused on a new event which was detected on March 24, 2019. The TEB originated from rainbands produced by the tropical cyclone Joaninha, in the Indian Ocean, close to Madagascar. This observation shows, for the first time to our knowledge: (1) the low energy part (>50 keV) of the TEB spectrum, using the LED, (2) an estimate of the incoming direction of the electron Beam from recorded data.

A detailed analysis of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial ... more 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 μs. 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 sf...

Terrestrial Gamma ray Flashes (TGFs) are short bursts of high energy (<40 MeV) photons, produced ... more Terrestrial Gamma ray Flashes (TGFs) are short bursts of high energy (<40 MeV) photons, produced during thunderstorms. A review of TGFs theory and observations is presented by Dwyer et al. (2012). TGFs were first detected using the BATSE experiment on-board the CGRO spacecraft (Fishman et al., 1994). Later, TGFs were recorded by the satellites RHESSI (

• We present the first statistical analysis of emissions at 180-230 nm, 337 nm and 777 nm coincid... more • We present the first statistical analysis of emissions at 180-230 nm, 337 nm and 777 nm coincident with TGFs as measured by a single platform • 90% of TGFs occur at the onset of large-amplitude optical pulses supporting the streamer-leader mechanism for TGF generation • The sources of the emissions are estimated to be 1-5 km below the cloud tops

Journal of Geophysical Research: Atmospheres, 2018

We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from ... more We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from terrestrial gamma ray flashes (TGFs) with the energy spectral density of VLF radio sferics recorded by Duke VLF receiver simultaneously with those TGFs. In total, six events with world wide lightning location network (WWLLN) defined locations were analyzed to exhibit a good fit between the modeled and observed energy spectral densities. In VLF range the energy spectral density of the TGF source current moment is found to be dominated by the contribution of secondary low-energy electrons and independent of the relativistic electrons which play their role in low-frequency (LF) range. Additional spectral modulation by the multiplicity of TGF peaks was found and demonstrated a good fit for two TGFs whose VLF sferics consist of two overlapping pulses each. The number of seeding pulses in TGF defines the spectral shape in VLF range, which allows to retrieve this number from VLF sferics, assuming they were radiated by TGFs. For two events it was found that the number of seeding pulses is small, of the order of 10. For the rest of the events the lower boundary of the number of seeding pulses was found to be between 10 to 10 3 .

• Flying over an area with no nearby lightning activity, the ASIM-MXGS instrument detected a four... more • Flying over an area with no nearby lightning activity, the ASIM-MXGS instrument detected a four ms long event with a soft spectrum. • Observations coupled with simulations suggest that more than 90% of the counts come from a TEB, and the rest from the associated TGF. • A source TGF with a broad angular distribution and 10 17 to 10 19 photons can explain the observation.

Journal of Geophysical Research: Atmospheres, 2016

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Journal of Geophysical Research: Atmospheres, 2017

Several computer models exist to explain the observation of terrestrial gamma-ray flashes (TGFs).... more Several computer models exist to explain the observation of terrestrial gamma-ray flashes (TGFs). Some of these models estimate the electric field ahead of lightning leaders and its effects on electron acceleration and multiplication. In this paper, we derive a new set of constraints to do more realistic modeling. We determine initial conditions based on in situ measurements of electric field and vertical separation between the main charge layers of thunderclouds. A maximum electric field strength of 50 kV/cm at sea level is introduced as the upper constraint for the leader electric field. The threshold for electron avalanches to develop of 2.86 kV/cm at sea level is introduced as the lower value. With these constraints, we determine a region where acceleration and multiplication of electrons occur. The maximum potential difference in this region is found to be ∼52 MV, and the corresponding number of avalanche multiplication lengths is ∼3.5. We then quantify the effect of the ambient electric field compared to the leader field at the upper altitude of the negative tip. Finally, we argue that only leaders with the highest potential difference between its tips (∼600 MV) can be candidates for the production of TGFs. However, with the assumptions we have used, these cannot explain the observed maximum energies of at least 40 MeV. Open questions with regard to the temporal development of the streamer zone and its effect on the shape of the electric field remain.

Journal of geophysical research. Atmospheres : JGR, Jan 16, 2016

Radio Science, 2019

Lightning discharges and radio transmitters emit low-frequency (∼3-300 kHz) electromagnetic waves... more Lightning discharges and radio transmitters emit low-frequency (∼3-300 kHz) electromagnetic waves with large electric field strengths and stable phases. This phase stability makes it possible to map the source locations of lightning and transmitters in the sky. Electromagnetic waves with smaller electric field strengths generally exhibit a reduced phase stability, caused by numerous simultaneous physical processes that blend into an underlying continuum radiation trapped inside the Earth-ionosphere cavity. It is therefore currently not known whether the source locations of continuum radiation can be determined. Here we show the first map of coherent continuum radiation in the sky above an array of high-precision radio receivers. The source locations of the coherent continuum radiation are found at elevation angles ∼30 ∘ − 60 ∘ above the horizon. The identified source locations are attributed to intermittent radio transmitters that emit electromagnetic waves with electric field strengths ∼2 orders of magnitude below the instrumental noise floor. The results demonstrate that it is possible to simultaneously map the signals from coherent continuum radiation, lightning discharges, and radio transmitters in the sky. This work thereby lays the foundation toward the discovery of many more coherent source locations of low-frequency electromagnetic waves in the sky. It is expected that the identified source locations vary with time as a result of the impact of solar variability on the D-region ionosphere. Future studies have therefore the potential to contribute to a novel remote sensing and an improved understanding of the D-region ionosphere, influenced by the near-Earth space environment.

Radio Science, 2018

The electromagnetic spectrum at low frequencies from ∼3 to 300 kHz is dominated by impulses from ... more The electromagnetic spectrum at low frequencies from ∼3 to 300 kHz is dominated by impulses from lightning discharges and anthropogenic radio transmissions used for communication. Electromagnetic waves generated in near-Earth space exhibit generally smaller amplitudes that are attenuated when travelling through the ionosphere before they can be observed at high and midlatitudes. Electromagnetic waves with yet smaller amplitudes contribute to the overall electromagnetic energy trapped within the Earth-ionosphere cavity. At this point, the electromagnetic waves from all possible sources blend into an unstructured continuum radiation near the instrumental noise floor, which is often considered to be a fundamental limit to scientific discovery. As a result, the sources of continuum radiation have been little studied and are essentially unknown. Here we show how low-frequency continuum radiation is detected and discriminated against known radio sources and instrumental noise by use of rigorous criteria inferred from novel precision measurements with an array of radio receivers. In particular, it is found that coherent continuum radiation from intermittent radio transmitters exhibits electric field strengths 0.5-0.7 μV/m, which are almost 2 orders of magnitude smaller when compared to the noise floor of the radio receivers ∼25 μV/m. Another part of the continuum radiation is found at local zenith above the array when it is caused by random instrumental noise. The results exemplify the possibility to extract sources from continuum radiation to study their origin and physical properties, which can contribute to an improved understanding of the impact of space weather and solar variability on the Earth's upper atmosphere.

E3S Web of Conferences, 2016

Sprites are Transient Luminous Events (TLEs) that can extend vertically from 40 to 90 km and hori... more Sprites are Transient Luminous Events (TLEs) that can extend vertically from 40 to 90 km and horizontally over several tens of km to form clusters of individual or multiple column or/and carrot-shaped luminous elements. They can even extend over more than 100 km in the form of sequential luminous emissions that are called "dancing sprites". Their optical detection and other parameters describing the storm and the lightning activity associated allow us to understand the conditions of their production and their links with the lightning activity. Our observations confirm some characteristics of the sprites and put forward others: (i) the sprites are essentially produced above the stratiform region of the Mesoscale Convective Systems after positive cloud-to-ground lightning flashes that produce large Charge Moment Change (CMC), with a shorter delay if the impulsive CMC (iCMC) is larger. (ii) The dancing sprites reflect the timing and the location of the successive lightning strokes that generate them. (iii) The sprite elements can be shifted from the stroke location when their delay is large. (iv) Bright sprites produce current signatures in ELF radiation a few milliseconds (<5 ms) after the positive strokes that generate them.

Radio Science, 2016

The electromagnetic wave propagation velocity at low radio frequencies is an important input para... more The electromagnetic wave propagation velocity at low radio frequencies is an important input parameter for lightning location systems that use time of arrival (TOA) method. This velocity is normally fixed at or near the speed of light. However, this study finds that the radio waves from two submarine communication transmitters at 20.9 kHz and 23.4 kHz exhibit phase propagation velocities that are~0.51% slower and~0.64% faster than the speed of light as a result of sky wave contributions and ground effects. Therefore, a novel technique with a variable phase propagation velocity is implemented for the first time in the TOA method and applied to electric field recordings with a long-baseline lightning location system that consists of four radio receivers in western Europe. The lightning locations inferred from variable velocities improve the accuracy of locations inferred from a fixed velocity by~0.89-1.06 km when compared to the lightning locations reported by the UK MetOffice. The normal distributions of the observed phase propagation velocities in small geographic areas are not centered at the speed of light. Consequently, representative velocities can be calculated for many small geographic areas to produce a velocity map over central France where numerous lightning discharges occurred. This map reflects the impact of sky waves and ground effects on the calculation of lightning locations as a result of the network configuration. It is concluded that the use of variable phase propagation velocities mitigates the influence of sky waves and ground effects in long-range lightning location networks.