Abstract 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.
Abstract One of the main challenges for the observation of a transient luminous event (TLE) is to observe TLEs in different emission bands. Here, we show TLEs recorded using the ISUAL 427.8 nm, 630 nm, N 2 1P (623–750 nm) and 762‐nm‐filtered imager, and we analyze the 630‐nm‐filtered, N 2 1P‐filtered, and 762‐nm‐filtered images of TLEs for estimating the N 2 (B 3 Π g ) Boltzmann vibrational temperature in comparison with the theoretical N 2 1P spectrum. For ISUAL recorded sprites, the average brightness of N 2 1P (I 1p ), 762 nm (I 762 ), and 630 nm (I 630 ) emission was 2.3, 0.6, and 0.02 MR. The N 2 (B 3 Π g ) vibrational temperatures ( T v ) was estimated to be 2800 K, 3200 K, and 4300 K for multiband emission ratios of I 630 /I 1p , I 630 /I 762 , and I 762 /I 1p . For observed elves, the average brightness I 1p , I 762 , and I 630 were 170, 50, and 3 kR. The estimated T v values were 3700 K, 3700 K, and 3800 K for ratios I 630 /I 1p , I 630 /I 762 , and I 762 /I 1p . For observed gigantic jets, the derived T v values were 3000–5000 K for a ratio I 762 /I 1p . Through N 2 (B 3 Π g ) T v analyses from emission ratios of ISUAL multiband observation, we derived the N 2 (B 3 Π g ) vibrational temperature that ranges between 3000 and 5000 K or higher in TLEs. Accuracy and variations of derived N 2 (B 3 Π g ) T v are also discussed while relative population of vibrational levels in the Boltzmann equilibrium are also compared with past spectra observation.
The atmosphere is a nonlinear fluid system with dissipation driven by external forcing.There exist multiple equilibria in it.As early as 1958,Yeh et al . pointed out thatthere exist two basic equilibria in the atmospheric circulation: winter circulation pattern andsummer circulation pattern.In the late 1970s,Charnery et al.studied the multipleequilibria of barotropic atmosphere and baroclinic atmosphere with simple models,andfounded the theory on the atmospheric multiple equilibria.
Abstract Coordinated TLE (transient luminous event) optical observations in Taiwan have been held since 2011, with an aim to achieve triangulation. Currently, there are four observation stations with baselines varying from 100 to 400 km between them. The system recorded eight gigantic jets (GJs) that were recorded by at least two stations on the night of 20 August 2014. The weather radar data indicate that these GJs occurred around the troposphere overshooting tops of a vigorous cumulonimbus cloud. A leader‐to‐streamer transition was discerned as the appearance of these GJs changed from jet‐like (leader) to fan‐like (streamer) at ~40 km altitude. Most of these GJs terminated at the lower ionosphere boundary (80–90 km), but one GJ topped with a 10 km thick diffuse region extended higher than 100 km. Moreover, three sets of the GJs occurred within 0.5–100 s in the same general region. The residual plasma patches from the preceding GJs appear to cause the subsequent GJs to contain more bead structures and to be brighter. Also, three streamer columns of a subsequent GJ that occurred more than 100 s after the preceding GJ were identified to have rebrightened at 55 to 70 km altitudes. The rebrightened streamers and the bead structure increments in the subsequent GJs suggest that there were GJ‐produced long‐lasting plasma patches in the mesosphere.
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