AE13A-0298
Effects of weak electric fields on the chemistry in the trailing columns of sprite streamers
The chemical effects of undervoltage electric fields in the trailing columns of sprite streamers are investigated. The existence of such fields are suggested by observations of ELF radiation associated with optical emissions of bright sprites that has been interpreted as evidence for intense electrical currents flowing in the body of the sprite (Cummer et al., GRL, 25(8), 1281-1284, 1998). An earlier nonlinear coupled chemical kinetics modeling study involving 80+ species and 800+ reactions of the chemical response to the passage of a sprite streamer at 70 km altitude (Sentman et al., JGR, 113, D11112, 2008) is extended to include undervoltage fields in the trailing region behind the compact streamer head that would be responsible for driving such currents. Recent high speed imaging observations combined with chemical modeling results suggest the trailing field is less than ~0.5 Ek, where Ek=123 Td is the threshold electric field for ionization avalanche. Electron densities are slightly depressed on account of enhanced dissociative attachment in the undervoltage environment. The effects on the densities of O(3P) and the metastable species O(1D), and N2(A3Σu+) are enhancements by a modest factor of 2 or less. O2(a1Δg) shows slightly greater enhancements, by up to a factor of 3, and O- shows enhancements by up to a factor of 5.
AE13A-0299
Temporal-spatial modeling of non-linear electron density enhancement due to successive lightning strokes
We report results on the temporal-spatial modeling of non-linear electron density enhancement due to successive lightning strokes using World Wide Lightning Location Network (WWLLN) data to experimentally describe the rate of large lightning strokes. The WWLLN provides real-time lightning locations globally by measuring the very low frequency (VLF) radiation emanating from lightning discharges. These WWLLN stroke rates are used as input to an axi-symmetric FDTD model that describes the non-linear effect of lightning electromagnetic pulses (EMP) on the ionosphere. This non-linear effect results from accumulating electron density modifications due to the interaction of the EMP from multiple successive lightning strokes with the lower ionosphere. Further studies must be completed to narrow uncertainties in the model, but the qualitative ionospheric response to successive EMPs is presented in two-dimensional, axi-symmetric space. Results from this study show that the non-linear effect of lightning EMP due to successive lightning strokes must be taken into account and varies with altitude. The limiting maximum electron density is reached earlier in time for higher altitudes, and the most significant effect occurs at 88 km. The limiting maximum modeled electron density profile in the 83- to 91-km altitude range does not depend on the initial electron density.
AE13A-0300
Elves and Associated Ionospheric Density Perturbations due to Horizontal In-cloud Lightning EMP
Optical emissions in the lower ionosphere due to cloud-to-ground lightning EMP, known as elves, have been observed frequently in the past two decades from the ground and from space. Correlations between elves and ionospheric electron density perturbations known as "Early VLF" events show that elve-producing EMP may also cause significant electron density changes. Recently, in-cloud (IC) lightning discharges have been associated with sprites and with Early VLF events. It has also recently been shown that burst-like VLF activity is the signature of significant IC activity, and when associated with CG discharges, is likely the source of continuing current responsible for sprites. In this work, we investigate the potential for IC lightning EMP to cause measurable ionospheric density perturbations and optical emissions, using a new 3-dimensional time- domain model of the lightning EMP. We find that optical emissions in the ionosphere from IC pulses may be detectable with modern photometers. Furthermore, electron density changes are primarily negative due to dissociative attachment to molecular oxygen, resulting in a density "hole" that persists for 10-100 seconds. The magnitude of the optical emissions and the density changes on a per-unit-time basis are comparable to that of CG events; however, the shorter IC impulses (typically ~10 us compared to ~50-100 us for CG) yield proportionally smaller effects. We find that although larger amplitude IC pulses may cause ionization and thus increase the local electron density, the volumetric change in the electrons is still substantially negative in these cases. Furthermore, frequency-domain modeling of subionospheric VLF transmitter signals shows that perturbations caused by bursts of IC activity should be measurable as Early VLF events.
AE13A-0301
Correlated optical and radio signatures in sprite-producing lightning
We find a strong correlation between the optical and radio signatures of sprite-producing lightning, which suggests a possible new technique for the estimation of lightning current moment from measurement of optical emission intensity. During the period from 04 July 2004 to 23 June 2007, the ISUAL payload on FORMOSAT-2 satellite has observed 72 sprite events in the American and Caribbean region. In order to clarify the relationship between lightning processes and the generation of sprites, we analyze optical data observed with the ISUAL spectrophotometer and magnetic field data observed at Duke University (35.98 deg N, -79.10 deg E). In the present study, we select 5 sprite events in which the signal-to-noise ratios are sufficiently high both in the optical and electromagnetic data. By correcting instrumental functions and atmospheric transmittance using MODTRAN-4 code, the absolute luminosity of lightning 777.4 nm emissions is estimated. In all of 5 events, we find clear signatures of the return strokes, continuing currents, and M-component processes with luminosities of 100-800, 10-50, and 50-200 (MR), respectively. Concurrent waveforms of current moment change derived from magnetic field data also show corresponding signatures. It is found that the luminosity and current moment in lightning is strongly related with correlation coefficients of 0.774-0.968. To quantify a scaling factor between the luminosity and current moment, we find simple linear functions that best fit the observed data using the least square method. The estimated scaling factors are in the range of 0.66-0.85 (MR/kA-km) with an extraordinary value of 1.67 (MR/kA-km) in one event. We suggest that the lightning current moment, which is an essential parameter for the production of sprites, could be estimated from optical measurements by using a scaling factor of 1.06 (MR/kA-km) within an error of 30-50 %.
AE13A-0302
Sprite Spectra at 10,000 fps
Recent high-speed recordings of sprites have revealed that sprites start from a downward point-like streamer head followed by a columniform diffuse glow along the trail. Since these features are essentially optical point and line sources, it is possible to make spectroscopic measurement with slit-less spectrograph techniques commonly used in astronomy. The combination of our high-speed imager with slit-less spectrograph technique has provided higher spatial and temporal resolution than previous spectroscopic observations. We have recorded spectra of streamer head and of the associated diffuse glow separately at 10,000 frames- per-second. The observations were made from the Langmuir Laboratory, NM, in June 2007. The slitless spectrograph has a spectral resolution of about 3 nm within the 400-900 nm wavelength coverage. The spectra are primarily from molecular nitrogen 1PG band emissions as previously observed. Neither N2+ 1NG nor N2 2PG band emissions in the blue were detected presumably due to Rayleigh scattering along relatively long path in excess of 500 km. The diffuse glow spectra show temporal variation in the (4, 2) band mission. This may indicate that collisional processes play a role in exciting the N2 B 3Πg state in diffuse glow.
AE13A-0303
Meteorological aspects of elves and jets
Evidence for ocean-atmosphere-ionosphere coupling is revealed in recent studies of ISUAL transient luminous events (TLEs) [Chen et al., 2008]. The results suggest that the meteorological systems below the stratosphere, primarily driven by sea surface temperature and solar radiation, play essential roles in inducing TLEs between the cloud top and the lower ionosphere. Through analyzing the ISUAL-recorded TLEs since July 2004, we realize that different types of TLEs are likely associated with different meteorological systems. For example, the elves are mainly located above Intertropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ); elves also are strongly correlated with the atmospheric updraft and the precipitation. The fall/winter elves distribute along storm tracks poleward of 30 degrees north or south, implying their association with extratropical cyclones. Numerous blue jets and gigantic jets are recorded around tropical cyclones by ISUAL. Several recent examples indicate that blue jets and lightning often occur in rapid successions in the strong convective regions associated with the spiral rainbands of typhoons or hurricanes. Illustrative data and some of the probable mechanisms will be presented in the conference.
AE13A-0304
Streamer Splitting in Sprites
We report on observations of streamer tip splitting in sprites. High speed 10,000 frames per second with 50 micro second integration time observations of sprites were obtained on 23 June 2007 using a 300 mm lens on a Phantom 7 camera with a Video Scope HS 1845 HS image intensifier. Six sprites were observed showing clear streamer tip splitting. The locations of the parent lightning strikes were located using the National Lightning Detection Network, and the range to the 75 km altitude point above the parent lightning strike determined. The resulting resolution was approximately 30m per pixel. Streamer tip divisions were seen at altitudes from 60 to 76 km altitude, effectively across the entire vertical field of view. We observe streamers splitting into smaller and smaller streamer tips once the splitting starts. Typical distances between subsequent splitting of the same steamer tip are approximately 5 km, and the time needed to double the number of streamer tips due to splitting is approximately 100 to 200 micro seconds.
AE13A-0305
Transient Luminous Events and the 9 May 2007 Oklahoma Mesoscale Convective System
On 9 May 2007 an asymmetric mesoscale convective system (MCS) passed through the domain of the Oklahoma Lightning Mapping Array while producing 26 transient luminous events (TLEs) in a 2-hour period, which were observed at the Yucca Ridge Field Station in northeastern Colorado. During the observation period (03-05 UTC), the MCS consisted of a short NW-SE-oriented line with a stratiform region to its north. This stratiform region also contained intense embedded convection, and rotated cyclonically as a mesoscale convective vortex. The MCS was dominated by negative cloud-to-ground (CG) lightning, with 95% of the 3037 detected National Lightning Detection Network (NLDN) strokes being negative, and total flash rate sometimes exceeded 100 flashes per minute. Twenty-four of the 26 TLEs observed in this case coincided with parent positive CG strokes detected by the NLDN (the other two likely were associated with undetected positive CGs). Eighteen of these events had valid impulse charge moment change (iCMC) retrievals by the National Charge Moment Change Network. Thirteen of these had iCMC values in excess of 100 C km, roughly consistent with past studies that suggest iCMC values ~100 C km or greater are favorable for generating TLEs. Fifty-eight percent of the TLE- producing positive CG strokes also were detected by the World Wide Lightning Location Network, which suggests that this global network may have promising utility in TLE research studies. Both convective regions (southern convective line, and embedded convection in the stratiform region) produced TLE parent flashes, although most TLE producers initiated in the stratiform-embedded convection. TLE parent flashes initiated around 5.7 km MSL in the embedded convection, but slightly higher (7.5 km) in the southern convective line. Both sets of TLE parent flashes tended to propagate near 6 km MSL in the stratiform region while producing their TLEs. In general, TLE flash altitudes were lower (by ~2 km or more) and flash areas were smaller (by a factor of 2-3) than in the previously reported 20 June 2007 Oklahoma- Texas MCS. These differences were consistent with the observed differences in storm structures (radar, charge, etc.). The results suggest that, while a variety of flash scenarios can produce TLEs, some storm archetypes may be especially favorable for TLE production. In particular, a classic leading-line/trailing stratiform MCS, with advection of copious amounts of upper-level positive charge rearward from the convective line (e.g., 20 June 2007), may be a relatively good producer of TLEs compared to other MCS types.
AE13A-0306
Triangulated sprite initiation altitudes
In June/July 2008 high-speed sprite observations were made from the Langmuir Laboratory, NM, with concurrent video observations from two other sites in New Mexico, Portales and Las Vegas. The two outlying sites together with the observations at Langmuir provided data for locating the sprites geographically by triangulation, which, in turn, provide an altitude calibration of the high-speed images. High-speed observations (10,000 fps) from this and earlier campaigns have shown sprites to start with one or more downward propagating streamer heads. In the wake of the streamer head columnar luminosity forms creating the C-sprite signature easily recognizable in video recordings. In some sprite there are also upward propagating streamers. When they occur they occur later and their onset is from a lower altitude and from existing luminous sprite structure. The upward streamers form the diffuse higher altitude branches. In video recordings such sprites would be classified as carrot sprites. Preliminary analysis of the 2008 data show the altitude of the sprite onset, i.e. the altitude of the first detection of the initial downward streamer, vary from 66 km to 88 km. The higher onset altitudes appear to be associated primarily with C-sprite events.
AE13A-0307
Study of characteristics of the low frequency EM waves in the ionosphere by simultaneous measurements of satellite and ground-based experiment
Propagation characteristics of the low frequency electromagnetic waves in the ionosphere are experimentally derived using simultaneous measurement of electromagnetic waves from intensive lightning by satellite and ground-based observations. The lightning location and its electric characteristics are continuously monitored from ELF method whilst the low altitude satellite (DEMETER) successfully detects the electromagnetic waves over the same lightning source propagating through the ionosphere. Direct comparison of ELF weaves observed by satellite with ground experiments give the unique opportunity to derive the experimental ionospheric property such as an ionospheric transmission loss. The ionospheric transmission loss is obtained for different latitude and local times, and can be compared with the theoretical expectations.
AE13A-0308
Sprites over Africa During the AMMA with Multiple Electromagnetic Detections of Their Parent Lightning Flashes
The MIT C-band Doppler radar was operated for four months during the 2006 AMMA (African Monsoon Multidisciplinary Analysis) campaign in Niamey, Niger, and documented a large number of energetic positive ground flashes in the trailing stratiform regions of squall lines. Concurrently, a low-light video camera was operated in a vacant control tower at Niamey International Airport for the months of August and September. Large squall line MCSs were frequently present in eastern Niger and Nigeria for anticipated detection of sprites, but the heavy loading of the atmosphere by mineral aerosol and the prevalence of upper tropospheric cirrus cloud streaming westward from the same MCSs often thwarted sprite observations. Nevertheless, sprites were successfully imaged on two nights (August 30 and September 21, 2006), with 14 total events. These events are believed to be the first cases detected from the ground over Africa. The MCS storm sources, at distances of 300 km and 500 km from the observation site for the two nights, were confirmed with Meteosat satellite imagery. The network of VLF receivers in the World Wide Lightning Location Network (WWLLN) located four of these parent lightning flashes, in good agreement with the satellite imagery. The majority of parent lightning flashes were detected by independently operated, calibrated ELF receivers in Antarctica, Hungary, Israel, Japan and at two sites (North Carolina and Rhode Island) in the USA. Determinations of the vertical charge moment show excellent agreement among receiving sites, with values typically exceeding the threshold range for sprite occurrence (500 to 1000 C-km) in earlier studies. The availability of waveforms at multiple receivers for intense point sources such as these will enable further studies of the asymmetry of the Schumann cavity.
AE13A-0309
Ground-based observations of sprites and other Transient Luminous Events in Southern Brazil
Brazil is the second most active thunderstorm region of the globe. Within the last 6 years a total of 4 campaigns were performed in Brazil to observe sprites and other Transient Luminous Events (TLEs). The first three were large international collaborative efforts. In these campaigns all the instrumentation used to document the TLEs were temporarily imported for the duration of the campaign and belonged to our international collaborators. Last year we had our first local effort with INPE's equipment. It was a modest short duration campaign resulting in successful observations of 27 sprites above Uruguay. In this paper we will present the first results of this year's Brazilian TLE campaign. This time we attempt to perform simultaneous optical measurements of TLEs and high speed observations of the parent lighting discharges from two distinct ground optical sites.
AE13A-0310
Optical performance and trigger logic of the imager onboard SPRITE-SAT
Horizontal distribution of sprite columns, that provides a key to understand the sprite generation mechanism,
is difficult to observe on the ground. The nadir observation from space with satellite is an only method to
investigate it globally.
SPRITE-SAT is a small satellite to observe sprites and terrestrial gamma-ray flashes (TGFs), developed
mainly by Tohoku University. The onboard CMOS cameras named LSI-1 and -2 will image lightning and
sprites. LSI-1 with an optical band-pass filter for 744-840 nm captures mainly lightning flash, while LSI-2
detects 762 nm emission line mainly from sprites. The ratio of luminous intensity, obtained by LSI-1 and LSI-
2, enable us to identify the occurrence of sprites.
The focus of LSI is necessary to be adjusted with accuracy of +/- 70 micro meters. The method used in
focusing the REIMEI satellite optical system was applied to the assembling LSI. As a result, the diameters of
light spots were set to be smaller than the pixel size of the image sensor. We calibrated the sensitivity of LSI
and other cameras with an integrating sphere, and made sure that LSI can detect the luminosity higher than
~5 MR in 760-774 nm. On the other hand, LSI-2 can detect sprite luminosity, which is expected to be about
10-100 MR by nadir-looking observation based on the image data obtained from the International Space
Station.
We completed the total semantics of the trigger logic in the FPGA and CPU. The FPGA logic picks up the
transient luminosity. The CPU logic identifies sprites by calculating the ratio of the luminous intensity imaged
by LSI-1 and LSI-2. After the SPRITE-SAT is launched, the parameters of triggering logics will be adjusted
precisely based on the actual data obtained on the orbit. If they work properly, we could pick up only sprite
events, whose occurrence frequency is an order of 1 percent out of whole number of lightning discharge
events.
SPRITE-SAT is also equipped with two high-sensitivity CCD cameras developed by Tohoku University and
Watec Co. The all onboard cameras must be tolerant to the vibration, vacuum and thermal cycle
environment. We conducted the vibration test and thermal cycle test in vacuum condition, and made sure
that there is no problem in conducting the scientific observation in space. All onboard cameras are now
installed at the satellite, and the final environmental tests of the satellite are being performed in the
institutions of Japan Aerospace Exploration Agency (JAXA).
http://pat.geophys.tohoku.ac.jp/index_e.html
AE13A-0311
Imaging and Photometric Observations of TLEs by the JEM-GLIMS Mission
In order to study the generation mechanism of TLEs, global occurrence rates and distributions of lightning and TLEs, and the relationship between lightning, TLEs and TGFs, we will carry out the lightning and TLE observation at Exposure Facility of Japanese Experiment Module (JEM-EF) of International Space Station. In this mission named JEM-GLIMS (Global Lightning and sprIte MeasurementS on JEM-EF) two kinds of optical instruments and two sets of radio receivers will be integrated into the common port module and will be installed at JEM-EF. The optical instruments consist of two wide FOV CMOS cameras and six wide FOV photometers, and all these optical instruments look the nadir direction. CMOS cameras use the STAR-250 device as a detector, which has 512×512 pixels and 25×25 μm pixel size, and have 40° FOV. One CMOS camera with a wideband filter (730-830 nm) mainly measures lightning emission, while another camera with a narrowband filter (766±6 nm) mainly measures TLE emission. Five of six photometers have 40° FOV and use photomultiplier tube (PMT) as a photon detector. They equip band-pass filters (150-280 nm, 316±5 nm, 337±5 nm, 391±5 nm, and 762±5 nm) for the absolute intensity measurement of the TLE emission. One of six photometers equips a wide-band filter (600- 900 nm) to detect lightning occurring within 87° FOV. These output signals will be recorded with the sampling frequency of 20 kHz. These data will be analyzed to estimate the electron temperature and vibration temperature of N2. JEM-GIMS instruments will be launched in 2011, and we have started the development of the pre-flight model. We will report the development status of the JEM-GLISM mission and discuss the possibility of the cooperative observation with other missions such as TARANIS and ASIM.
AE13A-0312
TARANIS - a Microsatellite Project Dedicated to the Physics of TLEs and TGFs
TARANIS "Tool for the Analysis of RAdiations from lightNIngs and Sprites" is a CNES micro-satellite project dedicated to the study of impulsive transfers of energy between the Earth atmosphere and the space environment. Such impulsive transfers of energy, pointed out by the observation at ground and on satellite (FORMOSAT 2) of Transient Luminous Events (TLEs) and the detection on satellites (CGRO, RHESSI) of Terrestrial Gamma ray Flashes (TGFs), are likely to occur in other environments. The TARANIS mission and instrumentation is presented. The way the TARANIS programme (associated groundbased and balloon- based measurements included) may answer questions about the physics of TLEs and TGFs is examined. The questions include: the characterization of the region sources of TLEs and TGFs, the environmental conditions (lightning activities, variations in the thermal plasma, occurrence of Extensive Atmospheric Showers, etc.), the identification and characterization of Lightning induced Electron precipitations (LEPs) and Runaway electron Beams (RBs), the generation mechanisms, and the effects of TLEs, TGFs, and RBs on the atmosphere and the radiation belts. It is shown that TARANIS has a sufficiently complete package of instrumentation to answer specific questions raised by the observations and the existing models.
AE13A-0313
Remote Sensing of TLEs by Satellite ELF/VLF Wave Measurements
First recordings of satellite ELF/VLF waveform data associated with TLE observations are reported from the Summer 2005 campaign coordinated by Stanford University and LPCE. TLEs are optically observed from the US Langmuir Laboratory, while ELF/VLF waveform data are simultaneously recorded on-board the CNES microsatellite DEMETER and on the ground at Langmuir. Analyses of ELF/VLF measurements associated with two sprite events observed on July 28 2005 around 05:02:45 UT are presented. Conditions to trace back the wave emissions from the satellite to the entry point within the ionosphere are discussed. The main results concern: (i) the identification from a low Earth orbit satellite of the 0+ whistler signatures of the causative lightning, (ii) the identification of the propagation characteristics of proton whistlers triggered by the 0+ whistlers of the causative lightning, and the potential use of those characteristics to identify longitudinal or quasi-longitudinal 0+ whistlers, (iii) the difficulty to observe sprite-produced ELF bursts in the presence of proton-whistlers, (iv) an optimum transfer of energy from the atmosphere to the ionosphere for waves with wave normals anti-parallel to the Earth magnetic field direction at the altitude of the X= fpe2/f2 =1 plasma cut- off, with fpe the local plasma frequency.
AE13A-0314
Transient airglow enhancement by lightning observed by satellite
Transient airglow produced by lightning has been observed in many space missions. The ISUAL instrument on board the FORMOSAT 2 satellite has observed numerous cases of lightning events including sprite, ELVE, halo, and the enhancement in airglow layers for both OH and O2 airglow. The lightning events can produce excited states which react with background atmosphere to produce enhanced airglow. A mechanism involving O(1D) is discussed here.
AE13A-0315
E-CANES: A Research Network dedicated to Electromagnetic Coupling of the Atmosphere With Near-Earth Space
Transient luminous events in the stratosphere and mesosphere, the sprites, elves, blue jets and gigantic jets, are observed above intense thunderstorms in association with particularly intense lightning discharges. Their recent discovery (1989) offers an opportunity to study the fundamental process of the electric discharge under the different conditions of the troposphere (lightning), stratosphere (blue jets) and the mesosphere (sprites) and the coupling between these regions by electric and magnetic fields. It further facilitates studies of the more general questions of thunderstorm effects on the atmosphere and the role of thunderstorms in a changing climate. New space missions will be launched in the coming years to study the various effects of thunderstorms. They will focus on transient luminous events, the generation of relativistic electron beams in discharges, and the perturbation to the atmosphere, ionosphere and magnetosphere of lightning, transient luminous events, water vapour transport and gravity waves. The missions are the French micro-satellite TARANIS, the ESA ASIM payload on board the International Space Station and the Japanese Sprite Sat mission. These highly interdisciplinary missions will result in a wealth of new data, which require knowledge based capacity building to underpin the observations with improved statistical data analysis and theoretical modelling. We are therefore establishing a global framework for research on thunderstorm processes and their effect on the atmosphere, in particular (1) the fundamental process of the electric discharge as manifested in the stratosphere and mesosphere as sprites and jets, (2) the relationship between cosmic rays, lightning discharges, transient luminous events and terrestrial gamma ray flashes, and (3) the environmental impact of the above physical processes, and thunderstorms in general, on the atmosphere and near-Earth space. The first step has been the creation of the European research group (GDRE) dubbed E-CANES (Electromagnetic Coupling of the Atmosphere with the Near-Earth Space). It complements in a synergistic way the former EU Research Training Network 'Coupling of Atmospheric Layers', the existing COST action on 'The physics of lightning flash and its effects', the ASIM Topical Team, and other programs. The main objective of E-CANES is to initiate and promote coordination activities towards a global research community on the subject. The first actions include the establishment of an organization for coordinating ground, balloon and aircraft observation campaigns, the creation of a community-wide mailing list and website, and the promotion and coordination of joint activities with other structures to include new communities and to avoid the duplication of meetings and workshops.
AE13A-0316
TLEs, ITCZ, Storm Tracks and Their Correlation
Between July 2004 and February 2008, ISUAL has recorded 6747 elves, 718 sprites, 783 halos, 1081 blue jets, and 17 gigantic jets. We examine the correlation between the distribution of TLEs and the annual Inter- tropical Convergence Zone (ITCZ) distribution by analyzing the outgoing long-wave radiation (OLR) data from NOAA/ESRL Physical Sciences Division. The results indicate that there are two different TLE distribution patterns. For the low latitude region, the movement of TLEs occurrence follows the seasonal migration of the IITCZ. In northern hemisphere summer, the ITCZ is mainly located to the north of the equator and the distribution of TLEs follows. In southern hemisphere summer, part of ITCZ moves to south of the equator and so does the distribution of TLEs. In the middle and high latitude winter regions, the ISUAL recorded TLEs are defined as the winter TLEs, which are generally associated with cold fronts, air masses and mid-latitude cyclones. From the global distribution of winter TLEs, it is shown that they tend to congregate in some specific regions. Namely, in the northern winter , TLEs concentrate over the Japan Sea , north Pacific Ocean , northwest Atlantic Ocean and Mediterranean Sea ; while in the southern winter , TLEs distribute primarily over the south coast of Australia , south Pacific Ocean and east coast of south America. We find the distribution of winter TLEs is well collocated with the storm tracks. The correlation between the winter TLEs and storm tracks is thus analyzed.
AE13A-0317
Far-Ultraviolet Emission in ISUAL Recorded TLEs and Lightning Events
In analyzing events recorded by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL), we often found lightning events that appeared to have Lyman-Birge-Hopfield (LBH) emission (SP1; 150-280nm). Also for most of the seemingly LBH-emitting lightning events, the intensity of LBH emission is substantially lower than their elve-accompanying counterparts. If we further consider the ISUAL detection limit that imposed on by the background fluctuation, then the possibility for these so called pure lightning events to have dim accompanying elves cannot be ruled out. To provide a definitive answer on the lightning LBH emission problem, we will use the ISUAL SP1 as an indicator to study FUV-emitting events that occur in front of Earth limb. So far we have studied the relation between integrated photon flux in 630-750nm image and the corresponding time-integrated photon flux in SP1 for elves and found positive correlation. We are also comparing the peak current of the associated National Lightning Detection Network (NLDN) events and their correlation with ISUAL imager and SP recorded intensities. If the LBH emission in lightning were found to be from dim elves not lightning, then the result implies that the elve occurrence rate is higher than expected.
AE13A-0318
The Schumann Resonance: A Tool For Exploring The Atmospheric Environment And The Subsurface Of The Planets And Their Satellites
The propagation of Extremely Low Frequency (ELF) electromagnetic waves in the Earth surface-ionosphere cavity has been studied for more than fifty years to investigate a wide variety of atmospheric and ionospheric phenomena, namely ionospheric dynamics, thunderstorm, and lightning activity. The surface and the ionosphere acting as reflectors of ELF waves define a cavity where ELF can propagate. When the cavity is excited with broadband electromagnetic sources, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating waves; this phenomenon is known as Schumann resonance. A similar investigation can be performed for any other planet and satellite, provided this body is wrapped into an ionosphere and a low frequency electromagnetic source exists. There are, however, important differences between the Earth and other bodies, regarding the surface conductivity, the atmospheric electron density, the ionospheric cavity geometry, and the sources of electromagnetic energy. In this work we present a comparative planetology study of ELF wave propagation and atmospheric electricity of several environments, namely Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Titan. We revisit the available models for ELF propagation in several planetary cavities, recapitulate the similarities and differences among the planets, and compare simulations with in situ measurements whenever available. We review the propagation process of ELF electromagnetic waves in planetary cavities, with a particular emphasis on the application of the Schumann resonance observation to investigating the lower ionosphere of Venus and Mars, determining the water content of the gaseous envelope of Uranus and Neptune, and assessing the buried ocean of Titan predicted by theoretical models. The comparison of ELF wave propagation among rocky planets, gaseous giants, and icy satellites can be also used to improve the models of the Earth cavity. Instrumentation suitable to the measurement of ELF waves in planetary atmospheres, including ongoing and future missions such as Cassini-Huygens, ExoMars, Planet-C, and TSSM (Tandem), is briefly addressed.
AE13A-0319
Local Time Dependence of Whistler-Mode Waves Produced by Venus Lightning
Whistler-mode signals associated with atmospheric electrical discharges have been observed at Venus by the Venera landers, Pioneer Venus Orbiter and Venus Express. The Pioneer Venus electric field observations were at low latitudes and only available when the spacecraft was in darkness. The source region of these waves appeared to be in the region 19-23 LT, limited at earlier times by ionospheric propagation. Venus Express observations are obtained by a fluxgate magnetometer and available under all lighting conditions but observations are all at high latitudes. At this location lightning-generated whistler- mode waves are seen only from midnight through noon i.e. on the morning side of the planet. In this study we examine the second year of Venus Express measurements both to verify the statistics of year one and to determine the factors that control the local time occurrence of the signals.
AE13A-0320
Cloud Charging in the Atmosphere of Venus
The accumulation of charges on cloud particles in the atmosphere of Venus is investigated. Three cloud layers between 45 and 70 km exist in the atmosphere of Venus. The cloud particles are charged by the attachment of ions and electrons. Ion to particle and electron to particle attachment coefficients are calculated. The charge balance equations include ion-ion recombination, ion-electron recombination, electron attachment to neutrals, electron detachment from negative ions, and attachment of ions and electron to particles. It is found that the ion concentrations are reduced by a maximum of a factor of five by the attachment to the particles while the earlier studies showed a maximum reduction of about an order of magnitude due to the differences in the surface area of the particles used. A similar result is observed in the calculation of conductivity. Both monodisperse and polydisperse distribution of particles are considered. The conductivity was reduced by a factor of three when using the monodisperse distribution of particles, the maximum reduction observed was a factor of two when using the polydisperse distribution. This result implies that the monodisperse particle distribution overestimates the effect of particles on the atmospheric conductivity. The ratio of negative to positive charges is found to be very large in the middle and upper cloud layers.
AE13A-0321
Non-detection of Titan lightning radio emissions with RPWS after Cassini's nominal mission
We report on the non-detection of radio emissions associated with possible lightning flashes in Titan's atmosphere by the RPWS (Radio and Plasma Wave Science) instrument onboard Cassini. A valid proof for Titan lightning would be the detection of a number of bursty radio signals above Titan's ionospheric cutoff frequency, and they should be grouped near the closest approach of Cassini to Titan with an approximately quadratic fall-off of signal intensity with spacecraft distance. Such a clear signature has not been detected by the RPWS instrument during the nominal mission of Cassini with 44 close Titan flybys. We emphasize that the interpretation of any bursty signal as being due to a lightning discharge has to be done with the utmost caution. There are examples of spacecraft interferences, Jovian decametric arcs, Solar radio emissions, and enhanced background fluctuations causing bursty lightning-like signals during Cassini's Titan flybys. Similarly, the strong Saturn electrostatic discharges caused by a recent lightning storm located in Saturn's atmosphere were easily detected also at Titan's orbit.
AE13A-0322
Observation of Lightning on Jupiter by a Future Mission
Recent observational and theoretical studies suggest that thunderstorms, i.e., strong moist convective clouds in Jupiter's atmosphere are very important not only as an essential ingredient of meteorology of Jupiter but also as a potentially very useful "probe" of the water abundance of the deep atmosphere. Sugiyama et al. (2008) have been numerically investigating possible clouds structure of Jupiter by using moist convection model that can represent convective motion and associated cloud formation explicitly. One of the most important findings is the existence of quasi-periodic temporal variation of the convective clouds activity. The period of the "active/break" cycle is roughly proportional to the amount of condensable component in the sub-cloud layer. It should also be remarked that the clouds structure given by the numerical simulation is different from the classical three clouds layers structure that has been expected by the previous studies employing one-dimensional thermodynamic equilibrium model. The results suggest that all three components clouds are not always exist and the depth of clouds base varie over a wide range. Lightning activity represents the active moist convective area more directly than the optically observed clouds do. We are suggesting lightning observation in the JJSDT mission that is a future mission to Jupiter System. One of the promising direction of improvement is to enhance time resolution, i.e., high-speed imaging. All of past observations were conducted as long time exposure imaging, which could only estimate broad measure of total optical energy of lightning escaping from the clouds, which is not necessarily propotinal to the lightning energy due to the cloud depth effect for extinction; it could not give much information on the intensity of individual flashes nor the total activity of lightning. The another important direction is to observe lightening with two or more narrowband filters with different bandwidth; the ratio of observed intensities reflects the pressure broadening. This results in the estimate of the depth of flashes which is essential to calculate the actual energy dissipation by lightning discharge.
AE13A-0323
Distinguishing Solar Cycle Effects in Planetary Atmospheres
As solar radiation decreases with distance from the Sun, other sources of energy, such as ionization from galactic cosmic rays (GCR), assume a greater relative importance than at the terrestrial planets. Charged particle effects could therefore be more relevant to the formation of clouds and haze at the outer planets. The long-term solar modulation of Neptune's albedo is thought to be caused by either ion-induced nucleation of cloud-forming particles, or ultraviolet (UV) radiation effects on the colour of the clouds. On the basis of the 11 year solar cycle, the statistical evidence was slightly in favour of the UV mechanism, however distinguishing unambiguously between the two mechanisms will require more than the solar cycle variation alone. A 1.68 year quasi-periodicity, uniquely present at some times from heliospheric modulation of GCR, has previously been used to discriminate between solar UV and GCR effects in terrestrial data. The cosmic ray proton monitor data from both the Voyager spacecraft show this 1.68 year modulation during the 1980s when the spacecraft were close to the outer planets, indicating the possibility for applying a similar technique as far out as Neptune.
AE13A-0324
Status of development of lightning detector for PLANET-C mission
Magnetometer onboard Venus Express detected whistler mode waves whose source can be considered to be lightning discharge occurring well below the spacecraft orbit. However, there still remain some uncertainties to conclude finally such waves are originated by lightning discharge in the atmosphere. In order to identify the discharge phenomena in the atmosphere of Venus without any doubt, we plan to observe the lightning activity with high-speed optical detector onboard Planet-C, the Japanese Venus Climate Orbiter mission which will be launched in 2010 by JAXA. We are developing a new type of lightning detector, LAC (Lightning and Airglow Camera). Main difference from other equipments which have provided evidences of lightning existence in Venus is the high-speed sampling rate at 50kHz for each pixel, enabling us to distinguish the optical lightning flash from other pulsing noises. On the other hand, spatial resolution is not first priority as the first detector of Venus lightning. New type of APD (avalanche photo diode) array with a format of 8 x 8 is used and a narrow band interference filter at wavelength of 777.4 nm (OI) is selected for lightning measurement. The development is now at the stage for designing and manufacturing the flight model, based on the performance and environmental tolerance of the proto model. Especially, the algorithm for self- triggering is carefully improved in order to exclude false-trigger by other pulse-like noise.