AE53A-01 13:40h
Creation of a New, Public Global Circuit Database
For over a century, atmospheric electricity data has been collected from all over the world, as well as from space. For the last thirty years, Antarctica has been the observatory site of choice for atmospheric electricity studies. The primary difficulties researchers have faced when analyzing these data are both data collection, and acquiring data collected by others in formats easily used. Recently, a project was undertaken to consolidate all these data and make them easily available to the general public in a few "universal" formats via the Internet. A poll was taken to determine what format(s) would be the best ``universal'' formats to use. It was determined ASCII and NetCDF formats would best suit likely researchers. FLATDBMS, (an old but still used format appreciated by old-timers within the community), was also considered viable enough to preserve, with translation of the floating-point format from VAX D\_Float to the IEEE 754 representation. Thoth, the server housing these data, is populated with 200Gbyte drives for a total storage capacity of 3.4 TB. It is currently configured to have a total working capacity of 2.5TB, with 1.25 TB reserved for atmospheric electricity data. The URL of this database is http://globalcircuit.phys.uh.edu/. This server has been used to archive data in the above-mentioned formats. The data archived as of September 2004 are South Pole measurements taken from 1991-1993 and Vostok Station measurements taken 1998-2002. Given time and community cooperation, eventually all long term atmospheric electricity measurements that can be found and converted will be consolidated onto this website in these universal formats, ready for all researchers to utilize at a moments notice. The site is now ready to accept contributions and submissions of additional data.
http://globalcircuit.phys.uh.edu/
AE53A-02 13:52h
Balloon Study of the Global Circuit: Spatial Coherence and Correlation with Lightning Observations
The second campaign of the Polar Patrol Balloon (PPB) experiment (2nd-PPB) was carried out at Syowa Station in Antarctica during 2002-2003. This paper will present the global circuit results from the 2nd-PPB experiment. In that experiment, three balloons were launched for the purpose of upper atmosphere physics observation (3 balloons). Payloads of these 3 flights were identical with each other, and were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. Such a ``Balloon Cluster'' is suitable to observe temporal evolution and spatial distribution of phenomena in the ionospheric regions and boundaries that the balloons traversed during their circumpolar trajectory. More than 20 days of simultaneous fair weather 3-axis electric field and stratospheric conductivity data were obtained at geomagnetic latitudes ranging from sub-auroral to the polar cap. Balloon separation varied from $\sim$60 to $\sim$500 km. This paper will present the global circuit observations with emphasis on the times of apparent spatial variation in the vertical fair weather field. This paper will also present stratospheric conductivity observations with emphasis on the temporal and spatial variations that were observed. Finally, the inferred current density will be compared with data from the WWLL (TOGA) lightning monitor experiment.
http://ppb.nipr.ac.jp/
AE53A-03 14:04h
Differential charging of electrodes on moving balloon gondolas and DC electric field estimation by the Huygens Probe in Titan's atmosphere.
In January 2005 the HUYGENS probe will explore the atmosphere of Titan. In particular the on board HASI-PWA instrument is dedicated to the atmospheric electricity. The conductive probe body will move down under parachute from ~160 km to the ground with boom held electrodes to measure the ionic polar conductivities and DC electric field. From 1995 to now, several balloon tests with 1:1 probe mockups were performed in the terrestrial atmosphere that showed correct measurements for the ionic conductivities but non-expected behavior for the electric field measurement. Obviously differential charging between the conductive body and the electrodes occurred, with a maximum near the tropopause. The charging effects are clearly related to the probe velocity and to the ambient DC electric field. The pending question is to deduce precisely the DC field from the electric potential measurements. We present, compare and discuss the experimental results of these balloon experiments with regards to the current theoretical investigations and in view of the forthcoming entry of HUYGENS in the atmosphere of Titan.
AE53A-04 14:16h
FDTD Studies of Eigenfrequencies and Q-factors of the Earth-ionosphere Cavity
Resonance properties of the Earth-ionosphere cavity were predicted by W. O. Schumann in 1952 [Schumann, Z. Naturforsch., 7a, 149, 1952]. Since then observations of electromagnetic signals in the frequency range 1-500 Hz have become a powerful tool for variety of remote sensing applications [e.g., Williams, Science, 256, 1184, 1992; Cummer, IEEE Trans. Antennas Propagat., 48, 1420, 2000; Roldugin et al., JGR, 109, A01216, 2004], which in recent years included studies of thunderstorm related transient luminous events in the middle atmosphere and related lightning discharges [e.g., Sato and Fukunishi, GRL, 30, 1859, 2003; Su et al., Nature, 423, 974, 2003]. In this talk we will provide a comparison of a limited set of results from a simplified version of a 3-D FDTD model of the Earth-ionosphere cavity originally introduced in [Yang and Pasko, EOS Trans. AGU, 84, Fall Meet. Suppl., AE42A-0796, 2003] with a set of classical eigenfrequency (fn) and quality factor (Qn) solutions for laterally uniform spherically symmetric Earth-ionosphere cavity and with recent observations of Schumann resonances (SR) during solar proton events (SPEs) and X-ray bursts in order to demonstrate the potential and applicability of the FDTD technique for studies of realistic SR problems. The specific uniform cavities, which will be discussed in our talk, incorporate the following conductivity models: (1) a single-exponential profile with a perturbation [Sentman, JATP, 45, 55, 1983]; (2) a "knee" profile [e.g., Mushtak and Williams, JASTP, 64, 1989, 2002]; and (3) a two-exponential profile [Greifinger and Greifinger, Radio Sci., 13, 831, 1978; Sentman, JATP, 52, 35, 1990; JGR, 101, 9479, 1996; Mushtak and Williams, 2002]. The FDTD fn and Qn solutions for uniform cavity appear to be in excellent agreement (within several %) with well-known results documented in the literature [e.g., Sentman, 1983; Mushtak and Williams, 2002], including such particular details as a very flat frequency dependence of Q factor for the two-exponential conductivity model (see discussion in [Mushtak and Williams, 2002]). A potential of the FDTD model to treat 3-D systems will be demonstrated in our talk by introduction of non-uniformities in the model, which correspond to perturbations of the cavity associated with SPEs and X-ray bursts. The related analysis generally indicates the first mode SR frequency decrease during SPEs and increase during X-ray bursts by a fraction of a Hz, in agreement with physical arguments presented in [Sentman, 1983] and with recent time resolved observations reported by Roldugin et al. [JGR, 106, 18555, 2001; JGR, 108, 1103, 2003; 2004]. The validated FDTD model opens new perspectives for attacking problems in a realistic non-uniform cavity, including those related to diurnal, seasonal and inter-annual variations in SR parameters [e.g., Price and Melnikov, JASTP, 66, 1179, 2004].
AE53A-05 14:28h
The Use of the Waveguide Cutoff Region to Monitor Ionospheric Height Through the Day-Night Boundary
The use of electromagnetic waves to measure the height of the ionosphere is a well-known concept, as in any ionosonde. The waveguide cutoff phenomenon provides information about the height of a waveguide. This cutoff for the earth-ionosphere waveguide is illuminated by lightning sferics and can be used to monitor the change in ionosphere height through the day-night boundary. Using a wideband electric antenna in West Greenwich, Rhode Island with a flat frequency response across the ELF-to-VLF transition region, this study purports to do just that. Study has revealed that the observed ionospheric heights are found to be dependent on the three kinds of source-receiver paths: daytime, nighttime and mixed. Accurate locations for individual events are obtained from the National Lightning Detection Network (NLDN) to enable the analysis. Tweek sferics, which asymptote towards the transverse resonance frequency of the waveguide, predominate in the night path giving the most precise information about ionospheric heights. Weak dispersion and steep transitions in one-dimensional spectra provide information about daytime heights. Propagation over mixed paths reveals both daytime and nighttime signatures. Given that the effects of dispersion and waveguide attenuation at VLF are different for day and night, different approaches are used at different times. The two main approaches are outlined below: 1) During nighttime, tweek sferics are prevalent and the tranverse resonances of the Earth-ionosphere waveguide are weakly damped. In this case, frequency-time spectrograms are used to determine the cutoff frequency and asymptotically, the tranverse resonance frequencies. The effective ionospheric height is easily calculated from these results. 2) During daytime, VLF attenuation is enhanced and the quality factor of the transverse resonances much reduced. Consequently, we appeal to the extraction of the waveguide cutoff frequency from simple FFT's of individual sferics waveforms. This frequency is picked in the steep rise to VLF energy out of the broader frequency region with reduced waveguide energy.
AE53A-06 14:40h
Electromagnetic Pulses due to Meteor Trails Electromagnetic Pulses due to Meteor Trails
Entering the atmosphere meteoroids ablate their atoms and form columns of ionized particles. These columns or meteor trails act as pulses of electric current generating electromagnetic signals which can be observed on the ground. The objective of this paper is to develop a model of electromagnetic pulse caused by a meteor trail. The amplitude of such pulses is determined by the mass and velocity of the particle entering the ionosphere along with the ionospheric parameters such as the ambient electric field, plasma density, etc. Detected by a ground based magnetometers, those pulses can be used for the ionospheric and meteor diagnostics.
AE53A-07 14:52h
TARANIS : a Project of Microsatellite for the Study of Sprites and Associated Emissions
Taranis (Tool for the Analysis of RAdiations from lightNIngs and Sprites) is a CNES microsatellite project which will be in phase A in 2005. It proposes to measure sprites, halos, jets and elves and the associated terrestrial and X ray flashes, electromagnetic and electrostatic emissions, and energetic electrons at the nadir above thunderstorm. These complementary measurements will be carried on a local and global scale in order to understand the physical mechanisms responsible for the impulsive transfers of energy between the neutral atmosphere and plasmas of the ionosphere and magnetosphere. The purpose is to study the coupling between the low and middle atmosphere, the thermosphere, the ionosphere and the magnetosphere. The final goal is to establish the impact of these processes on the Earth's environment. The purpose of the presentation is to describe the project, its scientific objectives, the mission, the scientific payload. The sprite observation method at the nadir by spectral differentiation is already used by the experiment LSO (Lightning and Sprite Observations) on board of the International Space Station.
AE53A-08 15:04h
Observed Contemporaneous Electric-Field Pulses and X-ray Bursts in a Thunderstorm in Relation to Charge Distribution, Lightning Channels, and CG Flash Occurrence
We present data from contemporaneous observations of X-rays and electric-field changes made by means of balloon-borne instruments deployed in a thunderstorm on June 17, 2004 as part of the TELEX 2004 field program in central Oklahoma. The purpose of our observations was to provide data suitable for tests of hypotheses for runaway electron processes in thunderstorms. Our measurements show X-ray bursts in direct association with electric-field changes, suggesting the development of runaway discharges. However, the precise nature of the discharges is not entirely constrained by our data and is therefore subject to significant interpretation. The current high level of interest in the subject of runaway electron processes in thunderstorms prompts us to present the results with minimal interpretation. In this paper we proceed on the assumption that contemporaneous occurrence of X-rays and electric-field changes in thunderstorms is in fact a source of useful information about discharge processes. We present a brief review of the runaway breakdown theory and observations that motivated our investigation, and follow with an overview of the new results.
AE53A-09 15:16h
Gamma Ray Flashes Due to Plasma Processes in the Atmosphere: Role of Whistler Waves
In this paper a novel mechanism is identified for the generation of gamma ray flashes observed on Compton Gamma Ray Observatory satellite. In this model the relativistic electrons produced by a cosmic ray shower during a thunderstorm lead to a runaway discharge, which is maintained by the interaction with whistler waves and the relativistic electrons propagate up in ducts produced by the self-focusing of these waves. The focus of this paper is on the instability which develops in the lower stratosphere when a beam of hot magnetized electrons interacts with whistler waves. It was shown that the growth rate of such instability depends on the number density of hot electrons, and on their collision rate, and it peaks at about 25 km. The instability develops under the conditions for runaway breakdown similar to those leading to the generation of recently observed strong narrow bipolar radio pulses which indicates a possible correlation between these two phenomena. Such a correlation could be tested during a campaign involving high altitude air planes.
AE53A-10 15:28h
RHESSI Observations of Terrestrial Gamma-Ray Flashes
Terrestrial gamma-ray flashes (millisecond bursts of gamma-rays seen from space) have been observed by only one instrument until now, the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory. BATSE saw less than one event per month, but its 9-year lifetime was enough to establish a connection between these events and thunderstorms, suggesting a connection with other upper-atmosphere phenomena such as sprites and blue jets. Using data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite, we find that these events extend up to extremely high energies ($>$ 10 MeV) as predicted by theories of runaway breakdown -- BATSE was unable to establish this as its highest-energy channel included everything from 300 keV up. We also find an average of 12 events per month, despite having smaller collecting area than BATSE, indicating that the phenomenon is much more common than previously thought. RHESSI returns every photon with a 1-microsecond time tag, while BATSE had to trigger a special burst mode in order to get high-time-resolution data; this may account for RHESSI's ability to find more events. We will present individual and statistical properties of the RHESSI TGFs and report on efforts to correlate them with lightning storms, individual lightning strokes/sferics, and sprites/blue jets.