Martin Füllekrug

Unusually intense continuing current in lightning produces delayed mesospheric breakdown

Ultra low frequency magnetic eld measure- mentsmade500{2000 kmfrom positivelightningdischarges show a signature that is consistent with unusually high am- plitude cloud-to-ground continuing lightning current. The magnitudeofthisnearlyconstantcurrentmomentisaslarge as 60 kA km and can last at half this amplitude for longer than 150 ms, thereby moving 640 C or more (assuming a 7 km vertical channel length) to the ground after the return stroke. This total charge transfer is more than an order of magnitudegreaterthanmostpreviouslyreportedcontinuing currents in positive discharges. Three cases analyzed show thisstrongcontinuingcurrentflowsbefore,during,andafter spritesthatinitiatemorethan40msafterthereturnstroke. Accounting for this continuing current, quantitative analy- sis shows that the total vertical lightning charge moment changes are large enough to produce mesospheric electrical breakdown and long-delayed sprites.

Global triangulation of intense lightning discharges

A global network of three electromagnetic measurement instruments is used to simultaneously record time series of globally observable Extremely-Low-Frequency (ELF) magnetic field disturbances which propagate with little attenuation around the globe within the Earth-ionosphere cavity. The triangulation of individual lightning flashes results in a picture of the temporal evolution of intense lightning discharge occurrences on the planetary scale during April 1998. The lightning flash charge moments are calculated with the short pulse approximation of the normal mode expansion. The majority of the triangulated lightning discharges exhibit charge moments with a potential to excite mesospheric sprites and ∼5–20% may account for air breakdown at sprite altitudes in ∼50–70 km height.

Sprites, elves and intense lightning discharges

Contributing Authors. Preface.- Introduction to the Physics of Sprites, Elves and Intense Lightning Discharges M.J. Rycroft. 1.1 Basic Properties of the Atmosphere. 1.2 Risk Theory of Electrical Phenomena Occurring in the Atmosphere. 1.3 The Properties of Sprites, Elves and Intense Lightning Discharges. 1.4 Introduction to Theories and Numerical Modelling of Sprites. 1.5 Conclusions. Acknowledgements.- The Meteorology of Transient Luminous an Introduction and Overview W.A. Lyons. 2.1 Introduction. 2.2 Observations of Convective Phenomena. 2.3 A Brief History of TEE Observations. 2.4 Characteristics of TLE-Parent Lightning and Storms. 2.5 Research Frontiers Acknowledgments.- The Microphysical and Electrical Properties of Sprite-Producing Thunderstorms E.Williams and Y. Yair. 3.1 Introduction. 3.2 The Non-Inductive Charging Process in Thunderclouds. 3.3 Cloud Scale Charge Structure Possible with the Non-Inductive Mechanism. 3.4 The Electrical Structure Inside Sprite-Producing Storms in Summer-time. 3.5 The Electrical Structure inside Sprite-Producing Storms in Wintertime. 3.6 Gaps in Knowledge and Future Needs. Acknowledgments.- Global Thunderstorm Activity C. Price. 4.1 The Earths Energy Balance. 4.2 The General Circulation of the Atmosphere. 4.3 Frontal Thunderstorms in Mid-Latitude Regions. 4.4 Global Observations of Lightning. 4.5 The Global Atmospheric Electric Circuit. 4.6 Future Directions.- Imaging Systems in the Research Thomas H. Allin et al. 5.1 Introduction to Low Light Imaging. 5.2 The Spritewatch Systems. 5.3 Conclusions.- Spacecraft Based Studies of Transient Luminous Events S.B. Mende et al. 6.1 Introduction. 6.2 FORMOSAT-2 Satellite and the ISUAL Instrument. 6.3 Initial Observations with ISUAL. 6.4 Summary. Acknowledgments.- Observations of Sprites From Space at the Nadir: The LSO (Lightning and Sprite Observations) Experiment on Board of the International Space Station E. Blanc et al. 7.1 Introduction. 7.2 Spectral Differentiation of Sprite and Lightning Emissions. 7.3 Experiment. 7.4 Observations. 7.5 Perspectives.- Remote Sensing of the Upper Atmosphere by VLF C.J. Rodger and R.J. McCormick. 8.1 Ionospheric Conductivity. 8.2 Sources of VLF Electromagnetic (EM) Waves. 8.3 VLF Propagation in the Earth-Ionosphere Waveguide. 8.4 Relaxation of High-Altitude Ionospheric Modifications. 8.5 Summary.- Measurements of Lightning Parameters from Remote Electromagnetic Fields S.A. Cummer. 9.1 Background and Motivation. 9.2 Remote Lightning Parameter Measurements. 9.3 Data Analysis Techniques. 9.4 Summary.- Location and Electrical Properties of Sprite-Producing Lightning from a Single Elf Site Y. Hobara et al. 10.1 Introduction. 10.2 Locating Distant ELF Sources and Quantifying their Electrical Properties. 10.3 Winter TLEs and Associated Electromagnetic Phenomena in Japan. 10.4 Conclusion. Acknowledgments.- Calibrated Radiance Measurements with an Air-Filled Glow Discharge Tube: Applicat

Schumann resonance parameter changes during high‐energy particle precipitation

A systematic study of Schumann resonance parameters during high-energy particle precipitation events is presented. Protons and electrons with energies above 1 MeV ionize the upper boundary of the Earth-ionosphere cavity, leading to an increase of the resonance frequency and a decrease of the damping of the first Schumann resonance, as derived from measurements at Arrival Heights, Antarctica. The study uses the nine strongest solar proton events of the past solar cycle 22 and high-energy electrons emitted periodically from corotating interaction regions in the solar wind during 1994–1995. The variation of the Schumann resonance parameters is in qualitative agreement with current theories of Schumann resonances. The study also shows that high-energy particle precipitation is not the only relevant source affecting Schumann resonance parameters. The reported findings constitute a so far little-explored aspect of solar terrestrial relations.

Mesospheric sprite current triangulation

A network of three time-synchronized high-precision induction coil magnetometers is installed in North America to measure sprite-associated lightning flash waveforms in the frequency range 0.1–1000 Hz during the Energetics of Upper Atmosphere Excitation by Lightning, 1998, sprite campaign in July 1998. Simultaneous intensified video observations on board an aircraft are used to investigate 16 sprites with long time delays >33.33 ms relative to the parent lightning discharge reported by the National Lightning Detection Network. Three different long-delayed sprite-associated waveforms can be distinguished: 38% do not exhibit any significant magnetic intensity variation, 25% exhibit slow variations ∼100 ms, and 25% exhibit short pulses ∼4 ms. The source locations of the sprite-associated short pulses are triangulated by use of arrival time difference analysis. One source location exhibits a substantial spatial displacement ∼60 km relative to the parent lightning discharge, in agreement with the azimuths of sprite luminosity edges determined from the corresponding background star field of the video observations on board the aircraft. It is concluded from the temporal and spatial coincidence of the secondary short pulse and the sprite luminosity that this particular sprite is associated with current in the mesosphere.

The Manifestation of the Madden–Julian Oscillation in Global Deep Convection and in the Schumann Resonance Intensity

Abstract This study determines the relationship between intraseasonal oscillations observed in two independent measures of global lightning activity: a global mean convective index (a proxy for deep convection) derived from the Goddard Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) Pathfinder infrared cloud observations, and Schumann resonance magnetic intensity recorded at Arrival Heights, Antarctica. The study was initiated when previous results indicated a possible link between intraseasonal variations in Schumann resonances and variability of sunspot numbers on the timescale of the solar rotation period. The authors used seven years (1989–95) of daily records, though the Schumann resonance record had a number of gaps. Results of cross-spectrum and composite analysis show that intraseasonal oscillations in deep convection modulate the global variations in the Schumann resonance intensity. In the Tropics, the intraseasonal wave in deep convection has a wavenumber...

The planetary rate of sprite events

We propose a new formula to calculate the planetary rate of sprite events, based on observations with sprite detectors. This formula uses the number of detected sprites, the detection efficiency and the false alarm rate of the detector and spatial and temporal effectiveness functions. The role of these elements in the formula is discussed for optical and non-optical recordings. We use the formula to calculate an average planetary rate of sprite events of similar to 2.8 per minute with an accuracy of a factor similar to 2 - 3 by use of observations reported in the literature. The proposed formula can be used to calculate the occurrence rate of any physical event detected by remote sensing.

Wideband digital low-frequency radio receiver

A wideband digital low-frequency radio receiver for scientific applications is described. The portable battery-powered instrument has the capability to record electric field strengths in the frequency range from ~4 Hz to ~400 kHz with a sampling frequency of 1 MHz, an amplitude resolution of ~35 µV and a timing accuracy of ~12 ns whilst performing continuous digital waveform recordings for several days. The instrument strictly follows a modular design such that it can be extended to higher frequencies and timing accuracy when the corresponding digital technology becomes available. The low-cost radio receiver can be developed into an interferometric network by synchronizing individual radio receivers to map the low-frequency radio sky. The first measurements of atmospheric electric fields are carried out at Exmoor National Park in Southwest England to illustrate the capabilities of the novel instrument.

The contribution of anisotropic conductivity in the ionosphere to lightning flash bearing deviations in the ELF/ULF range

Lightning flash bearing deviations in the ELF/ULF range are monitored at two independently operating measurement instruments in Hollister, California, and Silberborn, Germany. The lightning flash bearing deviation at Hollister exhibits a rotational dependence ∼12°, associated with the conductivity contrast between the Earths crust and the nearby Pacific Ocean. The bearing deviations at both stations exhibit a pronounced diurnal local time variation ∼11°. This diurnal variation is attributed to the anisotropic conductivity in the ionosphere during day- and nighttime conditions. No bearing deviation dependency from the source-receiver distance can be distinguished. Correction for the mean rotational dependence at Hollister and the mean diurnal variation at both locations results in residual bearing deviations ∼ ±10° which are related to the variability of anisotropic conductivity in the ionosphere on a subdiurnal time scale.

The contribution of sprites to the global atmospheric electric circuit

The global static electric field in the global atmospheric electric circuit resulting from mesospheric sprite discharges is inferred from a coupled model for the global static and dynamic electric fields derived from Maxwell’s equations. It is found that the global atmospheric electric field from individual sprites is ≲ 44 mV/m, which can be measured with conventional ULF/ELF radio wave antennas at frequencies ≲ 4 Hz.