Reactor like TGE model

EGUGA, 2018

Terrestrial Gamma Ray Flashes (TGFs) are extraordinarily bright events of gamma radiation originating from thunderclouds [Fishman et al., 1994]. These events have been further investigated by several satellites devoted to high-energy astrophysics, such as the Reuven Ramaty High-Energy Spectroscopic Imager (RHESSI) [Grefenstette et al., 2009], the Astrorivelatore gamma ad Immagini Leggero (AGILE) [Marisaldi et al., 2010a; Tavani et al., 2010; Marisaldi et al., 2014] and the Fermi Space Telescope [Briggs et al., 2010]. Despite the recognition from their discovery that TGFs originate from thunderstorms (Fishman et al. 1994), relatively little is known about the TGF-producing storms. In order to understand if they can exhibit any distinct characteristics and to start a long term of research with the aim to create a link between TGF and meteorological events, we examined a population of 78 TGF and corresponding WWLLN lightning data in the spatial and temporal proximity of TGFs detected by AGILE from 2015 April to 2015 June. The analysis of satellites (both LEO and GEO) observations' coincidence makes us able to study convective characteristics and precipitation structures related to TGF occurrence. In particular, we use the frequent GEO satellites data to follow the cloud system dynamics, and passive microwave sensors on polar orbiting satellites to study the inner cloud structure. When possible, this is further improved using the Dual-frequency Precipitation Radar (DPR) observations provided by the Global Precipitation Measurement (GPM). Finally, we carried on a statistical analysis for the whole population of TGF in order to study the temporal evolution of the cloud electrical activity in relation with TGF occurrence. The analysis of the spatial and temporal distribution of flashes shows that most of TGFs occur during the peak of flash production.

Journal of Atmospheric and Solar-Terrestrial Physics, 2014

In the beginning of last century C.T.R. Wilson proposed that strong electric field of the thunderclouds might accelerate electrons to very high energies. However, this and many other electromagnetic processes in our atmosphere are poorly understood till now; the key questions about the thundercloud electrification and lightning initiation remain unanswered. During recent decades several observations of gamma ray, electron and neutron fluxes correlated with thunderstorms were reported. Nonetheless, the origin of these fluxes is under debate till now. The direct registration of the particle showers initiated by the runaway electrons (the most popular theory) was missing. We present the experimental evidence of the microsecond duration electron bursts originated from runaway electrons accelerated in thunderclouds. The electron acceleration downward becomes possible after creation of the Lower Positive Charged Region below the main negative charged layer in the middle of the thundercloud. Our analysis is based on the vast thunderstorm data from the Aragats Mountain in Armenia, 3200 m above sea level. Varieties of particle detectors located at Aragats Space Environmental Center are registering neutral and charged particle fluxes correlated with thunderstorms, so-called Thunderstorm Ground Enhancements. Simultaneously the electric mills and lightning detectors are monitoring the near-surface electric field and lightning flashes. In the paper we present the model of TGE initiation. We demonstrate the necessity of the Lower positive charge region development for the lower dipole operation and TGE initiation. Our observations establish direct relationship of the negative electric field strength and rain rate with TGE.

Journal of Geophysical Research: Space Physics, 2013

Terrestrial gamma-ray flashes (TGFs) have been correlated with an early development stage of high altitude positive intracloud (+IC) flashes in which the negative leader propagates up toward the upper positive charge region, while the positive leader propagates down toward the lower negative charge region. The resultant bidirectional leaders develop electrical potential differences in the vicinity of their heads with respect to the ambient potential distribution created by the thundercloud charges. These potential differences are believed to be of essential importance for the generation of TGFs. Using electrostatic calculations and a three-dimensional Cartesian fractal model, we quantify these potential differences produced in a developing +IC lightning discharge for given thunderstorm electric configurations. We present a case of a +IC lightning discharge in a realistic thunderstorm configuration that leads to a very high ($300 MV) potential difference and show how a delay in the development of the negative leader with respect to the positive one in a bidirectional leader system can facilitate a high potential difference in the negative leader head region.

Bulletin of the American Meteorological Society, 2015

Gamma-ray Flashes (TGFs) from a sample of 2279 TGFs detected with the Fermi Gamma-ray Burst Monitor (GBM). From these accurate geolocations, 24 TGFs are found within the NEXRAD weather radar operational range, in the Gulf of Mexico, the Caribbean and in the Pacific near Guam. NEXRAD Enhanced Echo Top (EET) data show that these 24 TGFs are consistently adjacent to high altitude regions of the storms. The high EET values suggest that there is likely a detection-selection effect, in which the gamma rays from lower-altitude TGFs are attenuated by the atmosphere so that such TGFs fall below the detection threshold of current space-based detectors. The Vertical Integrated Liquid Density (VILD) values and the volume scan reflectivities (Z) show that these 24 TGFs originate from storms of a wide range of convective strengths. Convective Available Potential Energy (CAPE) values from reanalysis also vary widely, providing additional evidence of the range of convection in these TGF-producing storms. 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 3 Capsule Summary Twenty-four Terrestrial Gamma-ray Flashes (TGFs) detected with Fermi 42 GBM have accurate geolocations and NEXRAD observations. The TGF-producing storms have a 43 wide range of convective strengths and the GBM-detected TGFs are located near the high portions 44 of the storms.

The relationship of lightning and elementary particle fluxes in the thunderclouds is not fully understood to date. Using the particle beams (the so-called Thunderstorm Ground Enhancements – TGEs) as a probe we investigate the characteristics of the interrelated atmospheric processes. The well-known effect of the TGE dynamics is the abrupt termination of the particle flux by the lightning flash. With new precise electronics, we can see that particle flux decline occurred simultaneously with the rearranging of the charge centers in the cloud. The analysis of the TGE energy spectra before and after the lightning demonstrates that the high-energy part of the TGE energy spectra disappeared just after lightning. The decline of particle flux coincides on millisecond time scale with first atmospheric discharges and we can conclude that Relativistic Runaway Electron Avalanches (RREA) in the thundercloud assist initiation of the negative cloud to ground lightning. Thus, RREA can provide enough ionization to play a significant role in the unleashing of the lightning flash. Among top unanswered questions in lightning research 1 state as number one: " By what physical mechanism or mechanisms is lightning initiated in the thundercloud? " and-number two: " What physical mechanisms govern the propagation of the different types of lightning leaders? ". They also mentioned that " The problem of how lightning is initiated inside thunderclouds is not only one of the biggest unsolved problems in lightning physics; it is also probably one of the biggest mysteries in the atmospheric sciences ". One of the candidates related to initiation and propagation of lightning is considered to be energetic runaway electrons. Electron acceleration in the thunderstorm atmospheres was first recognized by CTR Wilson 2 ; then Gurevich et al. 3 introduced the electron runaway concept (named Runaway Breakdown-RB, now mostly referred as Relativistic Electron Runaway Avalanche – RREA); in 2003 J. Dwyer 4 developed the feedback model of intracloud electron-gamma ray avalanches exponentially enhancing electron number. Recent observations of hundreds of the Thunderstorm ground enhancements (TGE, an abrupt enhancement of the secondary cosmic rays measured on the Earth's surface in correlation with thunderstorms) on Aragats provide an extensive source for the development of models of particle acceleration and multiplication in thunderclouds 5, 6. The electric field strength and spatial extent required for the RB/RREA development was measured during balloon flights in thunderstorm atmospheres at New Mexico. A 1.87 kV/cm field extended 1 km downwards from the height of 5.77 km would give an RREA multiplication factor of about 650 7. In situ measurements of the RREA by the network of particle detectors on Aragats allow retrieving the RREA parameters and developing a TGF initiation model 8, 9. Estimated multiplication factor was ~330, e-folding length ~250–300 m and maximum energy of RREA electrons in the cloud-40–50 MeV. The strength of the uniform vertically downward field of 1.5 km elon-gation expected to be 1.8–2.0 kV/cm. For the both observed cases, RREA electron flux will significantly increase the electrical conductivity in the cloud and possibly would not only introduce an additional leakage current but also can assist propagation of the lightning leader. In this study, we analyze a special kind of TGEs, i.e. TGEs abruptly terminated by lightning flashes. To our knowledge, first reports on the particle flux abruptly terminated by lightning flash come from measurements made on board of NASA STORM Hazard Project F-106 aircraft. The X-ray flux is sometimes seen to increase prior to observed lightning discharge and then return to background level 10. The balloon flights near Norman, Oklahoma in the spring of 1995 reveals an increase in X-ray intensity of 2 orders of magnitude lasting for approximately 1 min. The X-ray intensity returned to background level at the time of a lightning flash that reduced the electric field strength measured at the balloon 11. The Baksan group reported the first TGEs of this kind 12. They