CAESAR Consultancy

Cambridge, United Kingdom

CAESAR Consultancy

Cambridge, United Kingdom
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Haldoupis C.,University of Crete | Rycroft M.,CAESAR Consultancy | Williams E.,Massachusetts Institute of Technology | Price C.,Tel Aviv University
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2017

This paper examines whether the Earth-ionosphere capacitor (EIC) model is correct, by comparing observed atmospheric electrical properties with those expected for a spherical capacitor, as defined in electrostatics. The comparisons suggest that the EIC concept cannot be reconciled with, and hence cannot account for, the observations, particularly the rapid reduction of the atmospheric electric field with height that is measured. This means that the spherical EIC concept is incorrect by being too simplistic; it is thus misleading. The reason for this flawed concept is simple: the model disregards the non-uniform conductivity of the atmosphere which requires the presence of a net positive charge in the lower atmosphere that equals in magnitude the Earth's negative charge. This positive charge shields the action of the Earth's negative charge from polarizing the ionosphere positively. Thus, the lower D region ionosphere remains electrically neutral, which makes the EIC concept inappropriate. © 2017 Elsevier Ltd

Fullekrug M.,University of Bath | Diver D.,University of Glasgow | Pincon J.-L.,Laboratoire Of Physique Et Chimie Of Lenvironnement Et Of Lespace | Phelps A.D.R.,University of Strathclyde | And 14 more authors.
Surveys in Geophysics | Year: 2013

The French government has committed to launch the satellite TARANIS to study transient coupling processes between the Earth's atmosphere and near-Earth space. The prime objective of TARANIS is to detect energetic charged particles and hard radiation emanating from thunderclouds. The British Nobel prize winner C. T. R. Wilson predicted lightning discharges from the top of thunderclouds into space almost a century ago. However, new experiments have only recently confirmed energetic discharge processes which transfer energy from the top of thunderclouds into the upper atmosphere and near-Earth space; they are now denoted as transient luminous events, terrestrial gamma-ray flashes and relativistic electron beams. This meeting report builds on the current state of scientific knowledge on the physics of plasmas in the laboratory and naturally occurring plasmas in the Earth's atmosphere to propose areas of future research. The report specifically reflects presentations delivered by the members of a novel Franco-British collaboration during a meeting at the French Embassy in London held in November 2011. The scientific subjects of the report tackle ionization processes leading to electrical discharge processes, observations of transient luminous events, electromagnetic emissions, energetic charged particles and their impact on the Earth's atmosphere. The importance of future research in this area for science and society, and towards spacecraft protection, is emphasized. © 2012 Springer Science+Business Media Dordrecht.

Pisa D.,ASCR Institute of Physics Prague | Pisa D.,French National Center for Scientific Research | Nemec F.,Charles University | Santolik O.,ASCR Institute of Physics Prague | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2013

We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two-step data-processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by ∼2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning-generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes. Key Points Additional attenuation of VLF waves observed prior seismic activity. Statistical study using data of the entire DEMETER mission. ©2013. American Geophysical Union. All Rights Reserved.

Rycroft M.J.,CAESAR Consultancy | Rycroft M.J.,University of Bath | Nicoll K.A.,University of Reading | Aplin K.L.,University of Oxford | Harrison R.G.,University of Reading
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2012

The global atmospheric electric circuit is driven by thunderstorms and electrified rain/shower clouds and is also influenced by energetic charged particles from space. The global circuit maintains the ionosphere as an equipotential at~+250 kV with respect to the good conducting Earth (both land and oceans). Its "load"is the fair weather atmosphere and semi-fair weather atmosphere at large distances from the disturbed weather "generator"regions. The main solar-terrestrial (or space weather) influence on the global circuit arises from spatially and temporally varying fluxes of galactic cosmic rays (GCRs) and energetic electrons precipitating from the magnetosphere. All components of the circuit exhibit much variability in both space and time. Global circuit variations between solar maximum and solar minimum are considered together with Forbush decrease and solar flare effects. The variability in ion concentration and vertical current flow are considered in terms of radiative effects in the troposphere, through infra-red absorption, and cloud effects, in particular possible cloud microphysical effects from charging at layer cloud edges. The paper identifies future research areas in relation to Task Group 4 of the Climate and Weather of the Sun-Earth System (CAWSES-II) programme. © 2012 Elsevier Ltd.

Harrison R.G.,University of Reading | Aplin K.L.,Clarendon Laboratory | Rycroft M.J.,CAESAR Consultancy | Rycroft M.J.,University of Bath
Natural Hazards and Earth System Sciences | Year: 2014

We illustrate how coupling could occur between surface air and clouds via the global electric circuit-through Atmospheric Lithosphere-Ionosphere Charge Exchange (ALICE) processes-in an attempt to develop a physical understanding of the possible relationships between earthquakes and clouds. © 2014 Author(s).

Rycroft M.J.,CAESAR Consultancy | Rycroft M.J.,University of Bath | Odzimek A.,University of Leicester | Odzimek A.,Polish Academy of Sciences
Journal of Geophysical Research: Space Physics | Year: 2010

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (∼1 kA) above thunderstorms and electrified rain/shower clouds raise the potential of the ionosphere (presumed to be an equipotential surface at 80 km altitude) to ∼250 kV with respect to the Earth's surface. The circuit is completed by currents flowing down through the fair-weather atmosphere in the land/sea surface and up to the cloud systems. Using a model for the atmospheric conductivity profile, the effects of both negative and positive cloud-to-ground (CG) lightning discharges on the ionospheric potential have been estimated. A large positive CG discharge creates an electric field that exceeds the breakdown field from the ionosphere down to ∼74 km, thereby forming a halo, a column sprite, and some milliseconds later, from ∼67 km down to ∼55 km at ∼60 ms after the discharge, a "carrot" sprite. Estimates are made of the return stroke current and the thundercloud charge moment change of a +CG discharge required to exceed the threshold breakdown field, or the threshold field for creating and sustaining negative or positive streamers. The values for breakdown at 80 km altitude are 35 kA and 350, (Coulomb.kilometers), respectively, and those at 70 km altitude are 45 kA and 360, respectively. The different temporal and spatial developments of the mesospheric electric field distinguishing between column and carrot sprites agree with the latest deductions from recent observations. The current flowing in the highly conducting sprite reduces the ionospheric potential by ∼1 V. Copyright © 2010 by the American Geophysical Union.

Harrison R.G.,University of Reading | Aplin K.L.,Rutherford Appleton Laboratory | Rycroft M.J.,CAESAR Consultancy | Rycroft M.J.,University of Bath
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2010

We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF "tweeks", the amplitude and phase of very low frequency radio waves in the Earth-ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density. © 2009 Elsevier Ltd.

Rycroft M.J.,CAESAR Consultancy | Harrison R.G.,University of Reading
Space Science Reviews | Year: 2012

A description is given of the global atmospheric electric circuit operating between the Earth's surface and the ionosphere. Attention is drawn to the huge range of horizontal and vertical spatial scales, ranging from 10 -9 m to 10 12 m, concerned with the many important processes at work. A similarly enormous range of time scales is involved from 10 -6 s to 10 9 s, in the physical effects and different phenomena that need to be considered. The current flowing in the global circuit is generated by disturbed weather such as thunderstorms and electrified rain/shower clouds, mostly occurring over the Earth's land surface. The profile of electrical conductivity up through the atmosphere, determined mainly by galactic cosmic ray ionization, is a crucial parameter of the circuit. Model simulation results on the variation of the ionospheric potential, ∼250 kV positive with respect to the Earth's potential, following lightning discharges and sprites are summarized. Experimental results comparing global circuit variations with the neutron rate recorded at Climax, Colorado, are then discussed. Within the return (load) part of the circuit in the fair weather regions remote from the generators, charge layers exist on the upper and lower edges of extensive layer clouds; new experimental evidence for these charge layers is also reviewed. Finally, some directions for future research in the subject are suggested. © 2011 Springer Science+Business Media B.V.

The last forty years have seen remarkable developments in our understanding of the Doppler-shifted cyclotron resonance interactions between ducted whistler-mode radio signals travelling in one direction along a dipolar geomagnetic fluxtube (1.5 < L < ~ 6) and Van Allen radiation belt electrons travelling in the other. These signals range from natural whistlers generated by lightning discharges and sweeping in frequency to (apparently) spontaneously generated hiss and chorus, and to single frequency signals from ground-based VLF radio transmitters. In these interactions, whistler-mode waves of audio frequency are amplified and the electrons' pitch angles are reduced, some being pushed into the loss cone to perturb the lower ionosphere at the foot of the flux tube where the interaction has taken place. The plasma instability is established at or close to the equatorial plane of the magnetosphere. With feedback mechanisms, cyclotron maser action, therefore, takes place. In many cases, this action produces signals of rising frequency (and occasionally of falling frequency). Observations have been made of aspects of these interactions on rockets and on Earth-orbiting satellites, complemented by radio observations made on the ground. Such observations are reviewed for naturally occurring whistlers, chorus and man-made signals, e.g. from the Siple transmitter in Antarctica and the NWC transmitter in Australia. Selfconsistent nonlinear theoretical analyses of these interactions, involving broad electron distribution functions, have been undertaken and numerical simulations performed. An overview of these recent developments is also provided.

Satori G.,Hungarian Academy of Sciences | Rycroft M.,CAESAR Consultancy | Bencze P.,Hungarian Academy of Sciences | Marcz F.,Hungarian Academy of Sciences | And 4 more authors.
Surveys in Geophysics | Year: 2013

This paper gives a resume of the papers written in English which (a) describe some of the recording instruments in use at the Nagycenk Observatory (NCK) since the International Geophysical Year (IGY 1957-1958) and up to the present time, (b) summarise the most important and different types of observations associated with thunderstorms which have been made there, and (c) discuss their various geophysical interpretations. The paper describes the main results which have been obtained in four areas of thunderstorm associated atmospheric and geospace science within the context of Earth system science. These relate to the following parameters of atmospheric electricity: the vertical electric potential gradient just above the Earth's surface and the air-Earth current as well as the point discharge current, Schumann resonance (SR) signals of the Earth-ionosphere cavity at 8, 14 and 20 Hz, transient luminous events (TLEs), and some aspects of the behaviour of the ionosphere. Deductions from these data sets are concerned with the global lightning activity and the conductivity of the air, with diurnal, seasonal, annual and long-term variations of the SR amplitudes and resonant frequencies in terms of migrating thunderstorm centres, with transient SR excitations and with sprites and other TLEs, and with ionospheric disturbances. The paper closes with some thoughts on future research directions based on the observations at NCK and Sopron and the results achieved since the IGY. © 2013 Springer Science+Business Media Dordrecht.

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