Starting in 2016 August, the onboard software configuration of the Astrorivelatore Gamma ad Immagini LEggero (AGILE) MiniCALorimeter (MCAL) was modified in order to increase the instrument trigger ...capabilities for the detection of short duration high-energy transients, such as weak gamma-ray sub-threshold events and short gamma-ray bursts. MCAL is a nonimaging, all-sky detector, operating in the energy range 0.4-100 MeV. This change was carried out in order to make AGILE more competitive in the detection of electromagnetic counterparts to gravitational wave events revealed by the Laser Interferometer Gravitational-Wave Observatory/Virgo experiments. In the 22 months from 2016 August to 2018 May, the new adopted MCAL-GW configuration substantially enhanced the number of MCAL onboard triggers, increasing the total acquisition time of the instrument, and resulted in the detection of 52 bursts, 40 of which have been confirmed by the InterPlanetary Network.
Detection of terrestrial gamma-ray flashes with the AGILE/MCAL Ursi, Alessandro; Marisaldi, Martino; Tavani, Marco
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Volume:
30, Issue:
Suppl 1
Journal Article
Peer reviewed
Open access
AGILE is one of the satellites currently detecting terrestrial gamma-ray flashes (TGFs). In particular, the AGILE MiniCALorimeter detected more than 2000 events in 8 years activity, by exploiting a ...unique sub-millisecond timescale trigger logic and high-energy range. A change in the onboard configuration enhanced the trigger capabilities for the detection of these events, overcoming dead time issues and enlarging the detection rate of these events up to
>
50
TGFs/month, allowing to reveal shorter duration flashes. The quasi-equatorial low-inclination (
2
.
5
∘
) orbit of AGILE allows for the detection of repeated TGFs coming from the same storms, at the same orbital passage and throughout successive orbital overpasses, over the same geographic region. All TGFs detected by AGILE are fulfilling a database that can be used for offline analysis and forthcoming studies. The limited number of missions currently detecting these brief terrestrial flashes makes the understanding of this phenomenon very challenging and, in this perspective, the AGILE satellite played and still plays a major role, helping shedding light to many aspects of TGF science.
Terrestrial gamma ray flashes (TGFs) are brief bursts of energetic gammy‐ray photons generated during thunderstorms, which have been detected almost exclusively by satellite‐based instruments. Here ...we present three lines of evidence which includes the three out of three simultaneously observed pairs, the same occurrence contexts, and the consistent estimated occurrence rate, which indicate a direct relationship between a subset of TGFs and a class of energetic radio signal easily detectable by ground‐based sensors. This connection indicates that these gamma ray and radio emissions are two views of the same phenomenon and further enable detection of these TGFs from ground distant radio signals alone. Besides dramatically increasing the detection rate of TGFs, this ground detection approach can identify TGFs in continental and coastal areas that are at latitudes too high for present TGF‐detecting satellites and will provide more insights into the mechanism of TGF production.
Key Points
+EIPs and a subset of TGFs are intrinsically linked, and they are the two views of the same phenomenon
+EIPs can serve as a proxy for the ground detection of TGFs from distant electromagnetic radio signals
More measurements can be done on +EIP‐TGFs on land and thus deepen the insight into TGFs
Initial global extremes in lightning duration and horizontal distance were established in 2017 by an international panel of atmospheric lightning scientists and engineers assembled by the WMO. The ...subsequent launch of NOAA’s latest GOES-16/17 satellites with their Geostationary Lightning Mappers (GLMs) enabled extreme lightning to be monitored continuously over the western hemisphere up to 55⁰ latitude for the first time. Consequently, the former lightning extremes were more than doubled in 2019 to 709 km for distance and 16.730 s for duration. Continued detection and analysis of lightning “megaflashes” has now revealed two flashes that even exceed those 2019 records. As part of the ongoing work of the WMO in detection and documentation of global weather extremes, an international WMO evaluation committee was created to critically adjudicate these two GLM megaflash cases as new records for extreme lightning.
Abstract
The meteorological conditions required for the production of Terrestrial Gamma‐ray Flashes (TGFs) are not well understood. Particularly, the link between TGF production, meteorology, and ...weather severity is poorly characterized with most works focusing on only a small set of TGF events or isolated storms. This work is a further step toward understanding the general context of the meteorological conditions required for TGF production and if it differs from regular lightning production. We use TGFs observed from AGILE, ASIM, Fermi, and RHESSI to generate the largest catalog of TGFs with associated lightning sferics from either the World Wide Lightning Location Network (WWLLN) or Global Lightning Detection (GLD) combined with geostationary satellite images and meteorological conditions derived from ERA5 reanalysis data. In total we analyze 1582 TGF events and contextualize them in comparison to lightning flashes as characterized by ASIM. In our analysis we consider the proportion of TGFs and lightning coming from systems with overshooting tops as well as the Cloud Top Temperature (CTT) and the Convective Available Potential Energy (CAPE). Our results are consistent with previous studies, finding that TGFs observed from space come from primarily higher cloud tops than regular lightning flashes do. We find that CAPE and the proportion of cells with overshooting tops is similar for both TGF and lightning producing cells. It suggests that TGF observations from space are biased toward systems with higher cloud tops because the attenuation of the gamma‐rays from lower altitude TGFs reduce their intensity below the detection level of LEO instruments.
Plain Language Summary
Terrestrial Gamma‐ray Flashes (TGFs) are bursts of high energy radiation associated with only some lightning flashes. Here we seek to determine if the systems which generate TGFs are significantly different from those that generate only lightning flashes. While the general trend of TGF observations indicate that observable TGFs come from systems with higher cloud tops than other lightning, relatively little is understood about how the weather severity impacts the production of TGFs. To explore this we use geostationary satellite images and meteorological data to investigate the systems which generate TGFs compared to those that do not. We find that observed TGFs come from systems with higher cloud tops but not significantly more severe weather systems and that regional differences dominate over seasonal differences. It suggests that TGF observations from space are biased toward systems with higher cloud tops, because lower altitude TGFs cannot be detected from the space observatories.
Key Points
Global analysis of TGF cloud characteristics combining AGILE, ASIM, Fermi and RHESSI
TGF producing cells are higher than lightning producing cells but otherwise their weather severity is similar
Regional effects on the meteorological conditions for TGF production are more significant than seasonal effects
In this article, we report the first investigation over time of the atmospheric conditions around terrestrial gamma-ray flash (TGF) occurrences, using GPS sensors in combination with geostationary ...satellite observations and ERA5 reanalysis data. The goal is to understand which characteristics are favorable to the development of these events and to investigate if any precursor signals can be expected. A total of 9 TGFs, occurring at a distance lower than 45 km from a GPS sensor, were analyzed and two of them are shown here as an example analysis. Moreover, the lightning activity, collected by the World Wide Lightning Location Network (WWLLN), was used in order to identify any links and correlations with TGF occurrence and precipitable water vapor (PWV) trends. The combined use of GPS and the stroke rate trends identified, for all cases, a recurring pattern in which an increase in PWV is observed on a timescale of about two hours before the TGF occurrence that can be placed within the lightning peak. The temporal relation between the PWV trend and TGF occurrence is strictly related to the position of GPS sensors in relation to TGF coordinates. The life cycle of these storms observed by geostationary sensors described TGF-producing clouds as intense with a wide range of extensions and, in all cases, the TGF is located at the edge of the convective cell. Furthermore, the satellite data provide an added value in associating the GPS water vapor trend to the convective cell generating the TGF. The investigation with ERA5 reanalysis data showed that TGFs mainly occur in convective environments with unexceptional values with respect to the monthly average value of parameters measured at the same location. Moreover, the analysis showed the strong potential of the use of GPS data for the troposphere characterization in areas with complex territorial morphologies. This study provides indications on the dynamics of con-vective systems linked to TGFs and will certainly help refine our understanding of their production, as well as highlighting a potential approach through the use of GPS data to explore the lightning activity trend and TGF occurrences.
The Atmosphere‐Space Interactions Monitor was designed to monitor Terrestrial Gamma‐ray Flashes (TGFs) and Transient Luminous Events (TLEs) from space, enabling the study of how these phenomena are ...related. In this paper, we present observations of 17 TGFs with accompanying Elves. TGFs are short and highly energetic bursts of gamma photons associated with lightning discharges, whereas Elves are TLEs that are observed as concentric rings of ultraviolet (UV) and visible light at ionospheric altitudes, produced by the excitation of N2 molecules when an electromagnetic pulse hits the base of the ionosphere. Elves were identified when optical detections in the UV band could be clearly distinguished from other optical signals from lightning strokes. The TGFs they accompanied had short durations and were associated with particularly high peak current lightning. Lightning sferics associated with these events were detected by the global lightning network GLD360 and the World Wide Lightning Location Network, and they were, with the exception of one event, observed over ocean or coastal regions. It is likely that these events were associated with Energetic In‐cloud Pulses. We show that short duration TGFs tend to be associated with higher peak currents than long duration TGFs.
Key Points
We present a sample of 17 Terrestrial Gamma‐ray Flashes (TGFs) with accompanying Elves detected by Atmosphere‐Space Interactions Monitor
TGFs with Elves are short and associated with very high peak current lightning
The peak currents for these events are higher than for both lightning and TGFs in general
High Peak Current Lightning and the Production of Elves Bjørge‐Engeland, Ingrid; Østgaard, Nikolai; Marisaldi, Martino ...
Journal of geophysical research. Atmospheres,
28 February 2024, Volume:
129, Issue:
4
Journal Article
Peer reviewed
Open access
Elves are observed as expanding rings of light in the UV and visible optical bands. They are produced when electromagnetic pulses from lightning discharges interact with the lower parts of the ...ionosphere. Elves are well known to be associated with high peak current lightning discharges. Here, we use data from the Modular Multi‐spectral Imaging Array (MMIA) of the Atmosphere‐Space Interactions Monitor (ASIM), and search for observations of Elves when high peak current lightning discharges are detected by Vaisala's Global Lightning Detection network GLD360. We present two groups of events; high peak current detections associated with Elves and high peak current detections not associated with Elves. To understand why some current pulses with high peak currents do not produce observable Elves, we investigate and compare the lightning activity occurring before these two types of events, in terms of both the number of lightning discharges detected by GLD360 and the peak currents of the preceding discharges. Our results, using data from GLD360, suggest that current pulses with peak currents above |120| kA tend to produce Elves nearly always, regardless of the preceding lightning activity. For current pulses with peak currents between |70| and |120| kA, the number of observed Elves might be affected by the preceding lightning activity, or is the result of the characteristics of the storm cells that produce the Elve.
Plain Language Summary
There are many different phenomena that occur above active thunderstorms. Among these phenomena are Elves, which are observed as expanding rings of light (in UV and visible light) that are produced when powerful lightning pulses interact with the ionosphere at altitudes around 90 km. Elves are produced by strong electromagnetic waves from lightning pulses. We explore two sets of events in this study; strong lightning pulses that produce Elves, and strong lightning pulses that do not produce Elves. To understand why some strong pulses do not produce Elves, we investigate the lightning activity occurring before these events. We find that for lightning pulses with peak currents between |70| and |120| kA, the preceding lightning activity may affect whether an Elve is produced or not.
Key Points
We present two types of events; high peak current lightning associated with Elves, and high peak current lightning not associated with Elves
For peak currents >120 kA the probability of producing an Elve is more than 95%
For peak currents between 70 and 120 kA, previous lightning activity may influence whether an Elve is produced or not
AGILE is one of the satellites currently detecting terrestrial gamma-ray flashes (TGFs). In particular, the AGILE Mini-CALorimeter detected more than 2000 events in 8 years activity, by exploiting a ...unique sub-millisecond timescale trigger logic and high-energy range. A change in the onboard configuration enhanced the trigger capabilities for the detection of these events, overcoming dead time issues and enlarging the detection rate of these events up to \(>\)50 TGFs/month, allowing to reveal shorter duration flashes. The quasi-equatorial low-inclination ( 2.5\(^{\circ}\)) orbit of AGILE allows for the detection of repeated TGFs coming from the same storms, at the same orbital passage and throughout successive orbital overpasses, over the same geographic region. All TGFs detected by AGILE are fulfilling a database that can be used for offline analysis and forthcoming studies. The limited number of missions currently detecting these brief terrestrial flashes makes the understanding of this phenomenon very challenging and, in this perspective, the AGILE satellite played and still plays a major role, helping shedding light to many aspects of TGF science
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