Observations of Red Sprites Above Hurricane Matthew. Issue 23 (12th December 2018) - Huang, Anjing
Abstract: More than three dozen red sprites were captured above Hurricane Matthew on the nights of 1 and 2 October 2016 as it passed to the north of Venezuela after undergoing rapid intensification. Analyses using broadband magnetic fields indicate that all of the sprites were produced by positive cloud‐to‐ground (CG) strokes located within the outer rainbands as defined by relatively cold cloud top brightness temperatures (≤194 K). Negative CG strokes with impulse charge transfers exceeding the threshold of sprite production also existed, but the timescale of the charge transfer was not sufficiently long to develop streamers. The reported observations are contrary to the finding of the Imager of Sprites/Upper Atmospheric Lightning showing that sprites are preferentially produced by negative strokes in the same geographic region. Further ground‐based observations are desired to obtain additional insights into the convective regimes associated with the dominance of negative sprites in many oceanic and coastal thunderstorms. Plain Language Summary: The contribution from citizen scientists has been greatly helpful for extending the scope of basic scientific research to the broad community. Thanks for the night sky photographer living in Puerto Rico, Frankie Lucena, more than three dozen red sprites were captured on both the long‐exposure DSLR camera and the low‐light‐level video camera, forming a very valuable data set to examine the sprite genesis above tropical cyclones. The comparison with coordinated broadband sferic measurements made at more than 2, 000‐km range near Duke University indicates that all of these sprites were produced by positive cloud‐to‐ground strokes located in the outer rainband region. None of these sprites were produced above the inner core region of the hurricane. The fact that all the sprites observed above Hurricane Matthew are positive events is contrary to the spaceborne observations of the Imager of Sprites/Upper Atmospheric Lightning (ISUAL) over the past 12 years (2004–2015) that almost all the sprites observed by ISUAL in the similar geographic region were of negative polarity. Therefore, it is worthwhile conducting the ground‐based observation of sprites in this region to document the thunderstorms responsible for the population of negative sprites over oceanic thunderstorms. Key Points: All the red sprites observed over Hurricane Matthew on two nights were produced by positive cloud‐to‐ground lightning strokes All the sprite‐parent CG strokes were located in the outer rainbands as defined by the relatively cold cloud top brightness temperature; none were in the inner core The observations are contrary to ISUAL observations showing the dominance of negative sprite‐producing CG strokes in the region of interest