The relationship between sprite luminous intensity and electrical property of parent lightning discharges using FORMOSAT-2/ISUAL data

Sprite, transient luminous phenomena induced by tropospheric lightning discharge in the mesosphere, has been extensively investigated for almost two decades. However, due to the atmospheric absorption and scattering, it is difficult to estimate its exact luminous intensity with ground base observation. Recently, FORMOSAT-2/ISUAL observed many sprite optical emissions without such atmospheric effects. The data enable us to discuss their luminosity and the parent lightning characteristics quantitatively. In this paper, we firstly report the relationships between them based on FORMOSAT-2/ISUAL and ELF network data. In order to estimate sprite luminosity, we use ISUAL/array photometer data. The array photometer consists of two photometers measuring two wavelength ranges, that is, 360-470 nm (blue) and 520-750 nm (red), with sixteen channels arrayed in vertical each. We can estimate the electron energy of sprite from the ratio between blue and red color intensities. Some channels with sprite are contaminated by scattering emission from cloud-to-ground and/or cloud-to-cloud lightning discharges. From contaminated data we subtract lightning emission using lightning channel data. Then, we can estimate corrected sprite luminosity integrated temporally and spatially. In addition, we estimate its parent lightning charge moment from ELF data. The result of comparison between luminosity of carrot type sprite and the charge moment shows that they have positive correlation, indicating that charge moment is one of the essential parameters that determine sprite luminosity. We also analyzed the ratio between blue and red emissions and found that there exists also positive correlation between the ratio and charge moment of parent lightning. This result seems consistent with quasi- electrostatic model assuming the electric field over thunderstorm is proportional to the lightning charge moment and that it determines sprite occurrence and its luminosity. Furthermore, we classified sprites into three types, that is, halo, carrot, and column, and discuss their relative luminous intensity and their relationship to the characteristics of parent lightning.