AE22A-01 INVITED
Satellite Observations of Thunderstorm Induced Effects on Middle Atmospheric Chemistry
Sprites and other transient luminous events have been suggested to impact atmospheric chemistry, in particular through production of NOx. In order to find evidence of sprite induced chemical perturbations, we analysed MIPAS/ENVISAT measurements of night time middle atmospheric NO2 over regions of intense thunderstorm activity. MIPAS NO2 data were retrieved with the 2-dimensional GMTR algorithm thus enhancing the sensitivity to weak changes. Intense thunderstorms were localised through the WWLLN lightning detection network. The analysis showed a statistically significant enhancement of night time NO2 of about 10% at 52 km height in coincidence with intense thunderstorm activity (and thus high likelihood of sprite occurrence) over latitude bands 5° to 10° N and 15° to 20° N. The region 5° S to 5° N showed no significant change, while other regions had too few coincidences to be meaningful. An overall distribution of these perturbations showed the enhancement to weaken below 52 km height and increase around 60 km. The use of first order backward trajectories to account for advection by atmospheric winds led to consistent results. These results suggest that sprites can impact the chemistry of the middle atmosphere above active thunderstorms, consistently with recent sprite chemistry modelling if regional dilution and transport are accounted for.
AE22A-02 INVITED
Air Plasma Kinetics Under the Influence of Sprites
A full time-dependent kinetic study is presented for the main microscopic collisional and radiative processes underlying the optical flashes associated to an impulsive (t = 5 ms) discharge in the form of a single sprite streamer going through an air region of the mesosphere at three different altitudes (63 km, 68 km and 78 km). The kinetic formalism developed includes the coupling of the rate equations of each of the different species considered (electrons, ions, atoms and molecules) with the Boltzmann transport equation so that, in this way, all the kinetics is self-consistent, although, in the present approach, the electrodynamics (no Poisson equation is considered) is not coupled. The chemical model set up for air plasmas includes more than 75 species and almost 500 reactions. In addition, a complete set of reactions (more than 110) has been considered to take into account the possible impact of including H2O (humid chemistry) in the generated air plasmas. This study also considers the vibrational kinetics of N2 and CO2, and explicitly evaluates the optical emissions associated to a number of excited states of N2, O2, O in the visible, CO2 in the infrared (IR) and ultraviolet (UV) emissions of sprite streamers due to the N2 Lyman-Birge-Hopfield (LBH) and the NO-γ band systems. All the calculations are conducted for midnight conditions in mid- latitude regions (+ 38°), and 0° longitude, using as initial values for the neutral species those provided by the latest version of the Whole Atmosphere Community Climate Model (WACCM). According to our calculations, the impact of 4 ppm of H2O is only slightly visible in O3- at 68 km and 78 km while it strongly affects the behaviour of the anion CO4- at all the altitudes investigated. The local enhancement of NOX predicted by the present model varies with the altitude. At 68 km, the concentrations of NO and NO2 increase in about one order of magnitude while that of NO3 exhibits a remarkable growth of up to almost three orders of magnitude. The variation of the O3 density predicted by the model in the sprite streamer head is negligible in all the altitudes investigated. The analysis of the time dependence of the electron distribution function (EDF) in the sprite plasma during the pulse reveals that the EDF transient is quite fast, reaching its "steady" values during the pulse in less than 100 nanoseconds (much shorter than streamer head lifetimes). In addition, the calculated EDF during the pulse and in the afterglow is far from being Maxwellian, especially for energetic electrons (with ε > 30 eV). Finally, the evaluation of the mid-latitude nighttime electrical conductivity of air plasmas under the influence of a single sprite event reveals an increase of up to four orders of magnitude (at 68 km) above its measured background level of 10-11 mho/cm at an altitude of ~ 70 km. This sudden increase of the electrical conductivity lasts for 100 ms (at 68 km), being shorter (~ 1 ms) and longer (1 s) at 63 km and 78 km, respectively. The total power delivered by the streamer head of a single sprite event has been estimated to be approximately 1677 W (at 78 km), 230 kW (at 68 km) and 78 MW (at 63 km).
AE22A-03
Model of UV Flashes Due to Gigantic Blue Jets
The phenomenon termed Gigantic Blue Jet (GBJ) was discovered by Pasko et al. [1] when observing a thunderstorm over the Atlantic Ocean. A number of GBJ's was observed since from the ground and from space by the ISUAL optical detector flying on the board of the FORMOSA-2 satellite. Alike blue jets the GBJ's have a pencil-like shape however a trunk of GBJ is crowned with a few prongs which escape into the ionosphere. Current models suggest that a blue jet consists of the bi-leader, and is capped at the top side of the leader by its streamer zone [2]. The opposite polarity leaders grow in opposite directions and supply each other with the charge via the highly conductive channel. Evidently, if the bi-leader is initiated in the anvil, one of the leaders can extend beyond the cloud top. Furthermore, the UV instrument flying on board of microsatellite "Tatiana" detected a number of intense flashes with duration 1-64 ms originated in the equatorial region of the Earth [3]. The satellite was flying on the height 950 km along the circular orbit. The detector operates in the wavelength rage 300-400 nm. It should be emphasized that both GBJ and UV flashes were detected mainly over oceans and shores where the rate of lightning flashes is low. The detected UV flashes radiate about 0.1 MJ which in the range of the energy of gigantic blue jets. There are two scales of the flashes duration, 1-4 ms and 10-64 ms. The first one corresponds to the lifetime of individual long streamers (prongs), while the second corresponds to the lifetime of slow moving leader (or the streamer zone of a leader, since a number of individual streamers which form the streamer zone can radiate the UV emission). Therefore we suggest that the UV flashes detected by "Tatiana" were generated by GBJ. This paper presents a model of UV flashes due to an individual long streamer. Using earlier developed model of upward propagation of long streamer in the exponential atmosphere [2] the temporal evolution of the UV intensity generated by such streamer in the given spectral range 300-400 nm is described, and then check the model against the data obtained by "Tatiana". [1] V. Pasko et al., 2002 Nature, 416, 152 [2] Y. Raiser et al., 2007 J. Atm. Solar-Terr. Phys., 69, 925 [3] G. Garipov et al., 2005 JETP Lett., 82, 185.
AE22A-04
Numerical modeling of the formation of the screening charge near the thundercloud boundaries and its impact on the initiation and early stages of development of blue and gigantic jets
Both normal and anomalous polarity thunderstorms occasionally produce upward propagating discharges
called blue jets [Wescott et al., GRL, 22(10), 1995; Sentman and Wescott, Phys. Plasmas, 2(6),
1995; Boeck et al., JGR, 100, 1465, 1995] and gigantic jets [Pasko et al., Nature, 416, 152, 2002; Su et al., Nature, 423, 974, 2003; van der Velde et al., JGR, 112, D20104, 2007], depending on their
polarity, their initiation location in the thundercloud and their termination altitude [Krehbiel et al., Nature
Geoscience, 1(4), 233, 2008]. Such discharges are initiated by regular lightning leaders escaping the cloud
near the top [Petrov and Petrova, Tech. Phys., 44, 472, 1999]. The recent work by Krehbiel et al.,
2008] confirmed Petrov and Petrova's [1999] hypothesis and further demonstrated how charge
imbalances could be responsible for the initiation and early stages of development of both blue and gigantic
jets. Krehbiel et al. [2008] also identified three possible origins of these charge imbalances: occurrence
of a cloud-to-cloud discharge, of an unbalancing intracloud discharge, and dissipation of charge due to the
atmospheric conductivity. The first two hypotheses were supported by numerical simulations of the
thundercloud and new Lightning Mapping Array observations, respectively. The last was suggested as early
as the 1920's by C.T.R. Wilson [Phys. Trans. Roy. Soc. London A, 221, 73, 1921] and subsequently
investigating in a later publication [Wilson, Proc. R. Soc. London Ser. A, 236, 297, 1956].
In this work, we present a new two dimensional axisymmetric model of Maxwellian relaxation of the
atmosphere and demonstrate how realistic conductivity profiles combined with experimentally substantiated
thundercloud geometries lead to the formation of screening charges near the cloud boundaries, locally
reducing the net charge content or forming extra charge layers, ultimately resulting in the initiation of blue
and gigantic jets.
http://www.personal.psu.edu/jar471/files/
AE22A-05 INVITED
Global energy deposition and chemical effect by transient luminous events in the upper atmosphere
Based on the analysis of the data from the imager of sprites and upper atmospheric lightning (ISUAL) experiment on the FORMOSAT-2 satellite, it has been reported that elve is the most dominant type of transient luminous events (TLEs) and the global occurrence rates of sprites, halos and elves are ~1, ~1 and 35 events/min, respectively [Chen et al, 2008]. In this presentation, we will review some of the important findings in the ISUAL experiment, including the deduction of the reduced E-field in sprites, the comparison of the modeling results with the observed elves, and detailed analyses of gigantic jets. Also through computing the radiative emissions in ISUAL recorded TLE and their energy deposition in the upper atmosphere, we found that for sprites, halos and elves the energy deposition is 22, 14 and 19 MJ per event, respectively. After factoring in the global occurrence rates, the global energy deposition rates in the upper atmosphere are 22, 14 and 665 MJ /min from sprites, halos and elves. Also in-line with the works of Sentman et al. (2008) on the chemical processes in discharge phenomena, we will discuss the possible chemical effects of TLEs in the upper atmosphere. * Work performed at NCKU was supported in part by National Space Center and National Central University in Taiwan under grant numbers 97-NSPO(B)-ISUAL-FA09-01, NSC 96-2111-M-008-019, NSC 97-2111-M-006- 001-MY3.
AE22A-06
Comparison of acceleration, expansion and brightness of sprite streamers obtained from modeling and high-speed video observations
Filamentary streamer discharges are observed as basic components of sprite discharges in the Earth's upper atmosphere [e.g., Gerken and Inan, JASTP, 65, 567, 2003]. High speed video observations of sprites taken at frame rates >1000 fps provide detailed information on the temporal development of sprites and the characteristics of sprite streamers [e.g., Stanley et al., GRL, 26, 3201, 1999; Moudry et al., JASTP, 65, 509, 2003; McHarg et al., JGR, 107, 1364, 2002; Marshall and Inan, GRL, 32, L05804, 2005; Cummer et al., GRL, 33, L04104, 2006; McHarg et al., GRL, L06804, 2007; Stenbaek-Nielsen et al., GRL, L11105, 2007]. Sprites normally initiate in the form of downward propagating positive streamers. The propagation of streamers is accompanied with expansion and acceleration, and the emissions from sprite streamers are mostly confined to the streamer heads [McHarg et al., 2007; Stenbaek-Nielsen et al., 2007]. The analysis of the brightness of a sprite streamer head indicates that the brightness increases during the propagation of the streamer [Stenbaek-Nielsen et al., 2007]. The acceleration and expansion of sprite streamers have been noted in previous modeling work [Liu and Pasko, JGR, 109, A04301, 2004; GRL, 32, L05104, 2005]. In this talk, we compare modeling results on positive streamers with the observed sprite streamers reported by McHarg et al. [2007] and Stenbaek-Nielsen et al. [2007]. The acceleration computed from the modeling for applied electric fields close to the conventional breakdown threshold field is in a good agreement with the peak values observed experimentally. We investigate the effects of different spatial and temporal resolutions of an observational system on the visual appearances of the captured sprite streamers. It is found that the large variation in brightness of sprites estimated from several observational studies can be directly attributed to different temporal and spatial resolutions of used instruments. We further compare the time evolution of brightness for observed and modeled streamers. The results demonstrate that the brightness of a sprite streamer head increases exponentially with time and can span more than 4 orders of magnitude in a very short period of time of about 1 ms. In addition, the exponential growth rate of the brightness depends on the magnitude of the applied electric field. This result leads to formulation of a method for remote sensing of the lightning induced electric field in the mesospheric and lower ionospheric regions of the atmosphere, which drives the sprite phenomenon.
AE22A-07
Electromagnetic Signatures of a Negative Sprite and a Gigantic Jet Observed in the Southeastern U.S.
Triggered low light video observations have been made from a site near Duke University in North Carolina, USA beginning in early 2008. More than 60 lightning-driven high altitude transient luminous events (TLEs) have been captured in the first 6 months of operation, the overwhelming majority of which are sprites. These TLEs were produced by a wide variety storms that spanned winter to summer and include over-ocean and over-land systems. We were fortunate to capture, in different storms, images of two of the most uncommon forms of TLE: a negative polarity sprite and a gigantic jet. During both of these events, ground-based low frequency electromagnetic fields were recorded. We report the quantitative analysis of these signatures to measure the low altitude and high altitude electric charge motion that occurred either inside or in association with these TLEs. Our analysis will focus on the high altitude electric fields driving the negative sprite in comparison to observations of more common positive sprites, and on the association of charge motion in the gigantic jet with specific stages of its temporal development.
AE22A-08
Characterizing Lightning-Driven Negative Transient Luminous Events Over an Intense South American Storm
Over 440 transient luminous events (TLEs), were imaged over the Pampas of Argentina during a coordinated measurements campaign conducted from Santa Maria, Brazil during March 2006. All of these events were associated with a single, large Mesoscale Convective System that endured for several hours on the night of Feb 22-23, 2006. Detailed simultaneous measurements of the lightning location, TLE video imagery, and ELF/VLF data have revealed up to seven events closely linked with negative cloud to ground lightning. These are extremely rare events, and although theoretically predicted, our observations more than double the total number of negative events currently reported in the literature. This presentation will discuss the properties of these events, including their horizontal and vertical extents, and associated charge moments. We will also compare and contrast, when possible, their properties with similarly located positive TLEs with comparable charge moments.