Corona discharges from a windmill and its lightning protection tower in winter thunderstorms

Abstract

This paper presents lightning mapping array (LMA) observations of corona discharges from a windmill and its lightning protection tower in winter thunderstorms in Japan. Corona discharges from the windmill, called windmill coronas, and those from the tower, called tower coronas, are distinctly different. Windmill coronas occur with periodic bursts, generally radiate larger power, and possibly develop to higher altitudes than tower coronas do. A strong negative electric field is necessary for the frequent production of tower coronas but is not apparently related with windmill coronas. These differences are due to the periodic rotation of the windmill and the moving blades which can escape space charges produced by corona discharges and sustain a large local electric field. The production period of windmill coronas is related with the rotation period of the windmill. Surprisingly, for one rotation of the windmill, only two out of the three blades produce detectable discharges and source powers of discharges from these two blades are different. The reason for this phenomenon is still unclear. For tower coronas, the source rate can get very high only when there is a strong negative electric field, and the source power can get very high only when the source rate is very low. The relationship between corona discharges and lightning flashes is investigated. There is no direct evidence that corona discharges can increase the chance of upward leader initiation, but nearby lightning flashes can increase the source rate of corona discharges right after the flashes. The peak of the source height distribution of corona discharges is about 100 m higher than the top of the windmill and the top of the tower. Possible reasons for this result are discussed.

Formation Features of Steps and Branches of an Upward Negative Leader

“…The frame where corona discharge first observed is numbered frame 1. Detailed description of corona discharges from this windmill can be found in Wu et al (). The average 2‐D propagation speed of the main leader and Branch 1 to Branch 4 were 5.7, 3.7, 4.2, 3.3, and 4.3 × 10 5 ms −1 , respectively.…”

Investigating the Origin of Continual Radio Frequency Impulses During Explosive Volcanic Eruptions

“…It is an open question as to which of these processes the LMA could have detected during the Sakurajima observations. The LMA has detected and located corona on towers and windmills during thunderstorms (Wu et al, ) and on airplanes passing through charged clouds (Hamlin, ). The source powers of CRF are in the range of the source powers of corona on towers and windmills (Wu et al, ).…”

“…The LMA has detected and located corona on towers and windmills during thunderstorms (Wu et al, ) and on airplanes passing through charged clouds (Hamlin, ). The source powers of CRF are in the range of the source powers of corona on towers and windmills (Wu et al, ). However, we do not know quantitatively the thresholds on the strength of corona or streamer discharges required for detection by the LMA.…”

Leader Polarity‐Reversal Feature and Charge Structure of Three Upward Bipolar Lightning Flashes

“…We have been conducting a comprehensive observation campaign of lightning striking on the windmill and its lightning protection tower at Uchinanda, Ishikawa prefecture, Japan, since 2005 (Lu et al, ; Wang et al, ; Wang & Takagi, ; Wu et al, ). The windmill and the tower, both being erected on a small hill about 40 m above the sea level with a distance of 45 m, are 100 and 105 m in height, respectively.…”

“…The windmill and the tower, both being erected on a small hill about 40 m above the sea level with a distance of 45 m, are 100 and 105 m in height, respectively. In order to further study the characteristics of upward lightning in Japanese winter thunderstorms, LMA with nine stations, forming an observation network of about 18 × 18 km 2 (Wu et al, ), was deployed for the first time near the coastal area of Japanese sea from 3 November 2014. The tower was around the center of the observation network, corresponding to (0,0) in Cartesian coordinate system.…”