Simultaneous observations of storm-generated sprite and gravity wave over Bangladesh

We report simultaneous observations of sprite and gravity wave generated by a storm over Bangladesh. The origin of a concentric gravity wave can be traced to the storm region on 27 April 2014 over Bangladesh with a low cloud top surface temperature (175 K). After data analysis, the time period of the concentric gravity wave is found to be 8.8–8.9 min. The horizontal wavelength is found to be ~50 km for red emissions (~55 km for green emissions), and the horizontal phase velocity is 94.4 � 31.7 m s⁻¹ for red emissions (102.6 � 29.4 m s⁻¹ for green emissions). Using the dispersion relation of gravity wave, the elevation angle of wave propagation direction is found to be ~53.3�. The sprite associated with the gravity wave was also recorded at 1534 UT on 27 April 2014. The initiation time of storm-generated gravity wave is estimated to be 1454 UT at which lightning activity was relatively low using lightning data. At time 1534 UT of the recorded sprite, the lightning rate was close to its maximum value. The storm-generated gravity wave could be thought as a precursor phenomenon for lightning and sprites since one of the necessary conditions for gravity wave, lightning, and sprites is strong convection inside storms.