The blue luminous events (BLEs) recorded by ISUAL (Imager of Sprites and Upper Atmospheric Lightning) radiate unambiguous middle ultraviolet to blue emissions (230–450 nm) but contain dim red emissions (623–754 nm). The BLE appears to be dot‐like on one ISUAL image with an integration time of 29 ms. A few BLEs develop upward into blue jets/starters or type II gigantic jets (GJs). The associated sferics of the BLEs in the extremely low frequency to very low frequency band and in the low‐frequency band exhibit similar patterns to the narrow bipolar events (NBEs) identified in the very low frequency and low‐frequency band. The ISUAL BLEs are conjectured to be the accompanied light emissions of the NBEs. Both upward and downward propagating current obtained from the associated sferics of the BLEs have been found. The source heights of the six BLEs related to negative NBEs are estimated in the range of 16.2–17.8 km. These six events are suggested to occur between the upper positive charge layer and the negative screen charge layer on the top of the normally electrified thunderstorm. The six blue starters, one blue jet, and one type II GJ are inferred to be positive upward discharges from their associated sferics in the extremely low frequency to very low frequency band. Based on the simultaneous radio and optical observations, a NBE is conjectured to be the initiation discharge with rapidly flowing current within the thunderstorm, while a blue jet/starter or a type II GJ is suggested to be the ensuing discharge with slowly varying current propagating upward from the thunderstorm.

[1] Sprites were observed over thunderstorms in the southern China and in oceans around Taiwan. The observation sites were on the Ali Mountain of Taiwan's Central Ridge area with an altitude of 2413 m and in the campus of National Cheng Kung University with an altitude of 50 m. For the observed land sprites, 90% of them were either carrots or columniforms and 64% of the sprites occurred in groups. Among the observed oceanic sprites, 89% of them were carrots but only 22% of the sprites occurred in groups. We define a sprite active system as a thunderstorm that continuously produces at least one sprite in a 10-minute interval. The active sprites generating periods for the observed thunderstorms were typically shorter than 30 minutes. The sprite production rates for these Asian thunderstorms are estimated to be between I % 2 Â 10 À4 events/ km 2 /hr and I % 1 Â 10 À3 events/km 2 /hr.

Energetic positive and negative cloud‐to‐ground (CG) flashes are both capable of producing sprites. Negative CGs typically outnumber the positive ones by 10 to 1. However, >99.9 % of reported sprites were found to be initiated by positive CGs—thus the polarity paradox. Here, sprites recorded by the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) mission were analyzed along with extremely low‐frequency band magnetic field data to resolve this paradox. Approximately twenty‐five percent of the sprites are found to be associated with negative CG lightning. “Negative” sprites mainly congregate in the latitudinal regions below 20°, while positive sprites scatter up to 50°. The ISUAL negative sprites are evidently beyond the observable ranges of the ground sites reported in previous studies. Hence, the sprite polarity paradox is likely a selection effect of the middle‐ to high‐altitudinal observation sites. The charge moment changes and accompanying transient luminous events of sprites were also examined and found to be polarity dependent.

Based on synthetic flux spectra calculated from theoretical atmospheric models, a calibration of temperature and metallicity for the dwarfs observed in the Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor photometric system is presented in this paper. According to this calibration, stellar effective temperatures can be obtained from some temperature-sensitive color indices. The sample stars have colors and magnitudes in the ranges 0.1 < d − i < 0.9 and 14.0 < i < 20.5. The photometric metallicities for these sample stars can be derived by fitting SEDs. We determine the average stellar metallicity as a function of distance from the Galactic plane. The metallicity gradient is found to be d[Fe/H]/dz = −0.37 ± 0.1 dex/kpc for z < 4 kpc and d[Fe/H]/dz = −0.06 ± 0.09 dex/kpc between 5 and 15 kpc. These results can be explained in terms of different contributions in density distribution for Galactic models 'thin disk', 'thick disk' and 'halo' components. However, for the gradient in z > 5 kpc, it could not be interpreted according to the different contributions from the three components because of the large uncertainty. So it is possible that there is little or no gradient for z > 5 kpc. The overall distribution shows a metallicity gradient d[Fe/H]/dz = −0.17 ± 0.04 dex/kpc for z < 15 kpc.

The major types of transient luminous events (TLEs) are believed to be directly triggered by cloud-to-ground discharges. Intense lightning generally seems to have a higher production efficiency for TLEs, but this observation has not yet been statistically investigated. Two data sets, the upgraded World Wide Lightning Location Network (WWLLN) lightning stroke data and the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) TLE data, were used to investigate the energetics and the geographic distribution of TLE-producing lightning. The global median energy of the strokes that produced the TLEs is at least an order of magnitude higher than the global median stroke energy for WWLLN lightning in the same data window. Furthermore, the energy distributions of the elve-producing strokes exhibit no oceanic and land disparity. These results reveal that the elves are indeed triggered by energetic lightning and the production efficiency of elves with respect to the stroke energy of the causative lightning was insensitive to the underlying landform. Analysis of the spatial correlation between the ISUAL elves and the WWLLN lightning reveals that the geographic distribution of the ISUAL elves agreed well with that for the most energetic 10% of the WWLLN lightning strokes, better than for total lighting. We also found that elve occurrence rates in the apparently reduced detection regions behind the Earth's limb may have been greatly underestimated, partially due to the failure in providing triggers to initiate ISUAL recording or the severity of atmospheric attenuation to the elve emissions that may have caused them to be undetected.