Spatial and time distribution of lightning whistlers in the plasmasphere observed by VLF/WBA onboard AKEBONO

AKEBONO (EXOS-D) has been continuously operated for more than 25 years since 1989 to observe particles and plasma waves in the auroral region and the plasmasphere of the Earth. It covers altitude region from 300 km to about 10,000 km with an inclination of 75 degree. Analyses of large amounts of data obtained by AKEBONO enable us to study comprehensively how the magnetosphere varies temporally and spatially. The WBA (Wide Band Analyzer) is one of subsystems of the VLF instruments onboard AKEBONO. It measures 1 component of electric or magnetic analogue waveform in the frequency band of 50 Hz-15 kHz. Typical waves such as chorus, hiss and whistler were frequently observed by the WBA. Data obtained by the WBA for more than 25 years are originally recorded as analogue waveform format in the magnetic audio tapes. Data conversion from analogue to digital is now being carried out and the converted data are stored in our computer storage as digital WAVE format.