We report the global transient luminous event (TLE) distributions and rates based on the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) experiment onboard the FORMOSAT-2 satellite. ISUAL observations cover 45°S to 25°N latitude during the northern summer and 25°S to 45°N latitude during the northern winter. From July 2004 to June 2007, ISUAL recorded 5,434 elves, 633 sprites, 657 halos, and 13 gigantic jets. Surprisingly, elve is the dominant type of TLEs, while sprites/halos are a distant second. Elve occurrence rate jumps as the sea surface temperature exceeds 26 degrees Celsius, manifesting an ocean-atmosphere-ionosphere coupling. In the ISUAL survey, elves concentrate over the Caribbean Sea, South China Sea, east Indian Ocean, central Pacific Ocean, west Atlantic Ocean, and southwest Pacific Ocean; while sprites congregate over central Africa, Japan Sea, and west Atlantic Ocean. The ISUAL experiment observed global rates of 3.23, 0.50, 0.39, and 0.01 events per minute for elves, sprites, halos, and gigantic jets, respectively. Taking the instrumental detection sensitivity and the restricted survey area into account, the corrected global occurrence rates for sprites and elves likely are a factor of two and an order of magnitude higher, respectively. ISUAL observations also indicate that the relative frequency of high peak current lightning (>80 kA) is 10 times higher over the oceans than over the land. On the basis of the corrected ISUAL elve global occurrence rate, the total electron content at the lower ionosphere above elve hot zones was computed to be elevated by more than 5%.
The structural and electrical properties of a metal-halide cubic perovskite, CH(3)NH(3)SnI(3), have been examined. The band structure, obtained using first-principles calculation, reveals a well-defined band gap at the Fermi level. However, the temperature dependence of the single-crystal electrical conductivity shows metallic behavior down to low temperatures. The temperature dependence of the thermoelectric power is also metallic over the whole temperature range, and the large positive value indicates that charge transport occurs with a low concentration of hole carriers. The metallic properties of this as-grown crystal are thus suggested to result from spontaneous hole-doping in the crystallization process, rather than the semi-metal electronic structure. The present study shows that artificial hole doping indeed enhances the conductivity.
Ferroelectrics are used in a wide range of applications including memory elements, capacitors, and sensors. Recently, molecular ferroelectric crystals have attracted interest as viable alternatives to conventional ceramic ferroelectrics, due to their solution processability and lack of toxicity. Here we show that a class of molecular compounds-known as plastic crystals-can exhibit ferroelectricity if the constituent molecules are judiciously chosen from polar ionic molecules. The intrinsic features of plastic crystals, for example the rotational motion of molecules and phase transitions with lattice symmetry changes, provide the crystals with unique ferroelectric properties relative to conventional molecular crystals. This allows flexible alteration of the polarization axis direction in a grown crystal by applying an electric field. Owing to the tunable nature of the crystal orientation, together with mechanical deformability, this type of molecular crystal represents an attractive functional material which could find use in a diverse range of applications. Table of contents summaryA major drawback of molecular ferroelectric crystals, low dimensionality, has now been overcome by ionic plastic crystals. Molecular rotation and phase transitions intrinsic to the crystals make the materials unique molecular ferroelectrics, where the polarization axis direction in a grown crystal can be flexibly altered by applying an electric field.
 In order to understand the response of the Jovian magnetosphere to solar wind dynamic pressure enhancements, we investigate magnetic field variations observed by the Galileo spacecraft. The lack of solar wind monitoring just upstream of the Jovian magnetosphere is overcome by simulating a one-dimensional magnetohydrodynamic (MHD) propagation of the solar wind from the Earth. We identify the events with an increase of the solar wind dynamic pressure >0.25 nPa at the Jovian orbit. Characteristic magnetic field variations are found in the Jovian magnetosphere for all of the nine events. The rectangular waveform due to the Jovian rotation disappears for eight of the nine events. Magnetic field disturbances in the frequency range from 0.3 to 10 mHz are enhanced simultaneously. The maximum amplitude of the disturbances is in proportional to the maximum amplitude of the solar wind dynamic pressure. We suggest that the current sheet is greatly deformed and reconnection bursts are induced under the compressed magnetosphere.
Observations of optical phenomena at high altitude above thunderstorms using a multichannel high‐speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40°40′N, 104°, 56′W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These new measurements indicate that diffuse optical flashes with a duration of < 1 ms and a horizontal scale of ∼100–300 km occur at 75–105 km altitude in the lower ionosphere just after the onset of cloud‐to‐ground lightning discharges, but preceding the onset of sprites. Here we designate these events as “elves” to distinguish them from “red sprites”. This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.
 The electromagnetic pulses (EMP) from tropospheric lightning produce transient luminous events (TLEs), known as elves, in the 80-90 km region above the lightning. The luminosity is evidence that the EMP carries sufficient electric field to excite optical emissions at these altitudes; however, it is still unknown whether the field is sufficient to ionize the atmosphere. The first multiwavelength, quantitative observatory on a free-flying satellite dedicated to observing TLEs, the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) instrument on FORMOSAT-2, formerly called ROCSAT-2, confirmed that a significant number of lightning events are accompanied by elves. The instrument consists of a low light level imager and a set of multichannel photometers. In a few cases where the lightning occurred beyond the solid Earth limb, pure spectral measurements of the elves were obtained. Here we analyze such an event and show that the elves contained significant 391.4 nm emission of the N 2 + ion. This is clear evidence that ionization takes place in elves. The ratio of cross sections for N 2 ionization and the production of the upper state of 391.4 nm emission is not a constant for low-energy electrons found in TLEs. We attempted to find this ratio by comparing our photometric measurements of the TLE produced emissions to theoretically derived emission intensities. The electron energy distribution and the ratios of the modeled N 2 Lyman-Birge-Hopfield (LBH) and the N 2 + first negative to the second positive were computed as a function of the reduced electric field. From these ratios it was possible to obtain the reduced electric field from the ratios. We estimated that the reduced electric field, which characterizes the local electron energy distribution, was >200 Td. We also made comparisons of the theoretically derived intensities to our measurements of the N 2 + first positive and Lyman-Birge-Hopfield (LBH) band emission in the elves. On the basis of the ratio between the N 2 + first negative emission and the time-integrated ionization production, we estimate that the elves produced an average electron density of 210 electrons cm À3 over a large (165 km diameter) circular region having an assumed 10 km altitude extent. These observations indicate that thunderstorms are a significant source of ionization in the low-to midlatitude nighttime D region.
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