. The most incredible images of thunder were created by scientists who shot rockets through thunderstorms at a US military base in Gainesville, Florida. These pictures show the energy of thunder that explodes from the sky in waves as lightning strikes. Southwest Research Institute (SwRI) presented the images during a meeting of American and Canadian geophysical societies. It took place in Montreal, May 3-7. Uncertainty about thunder and lightning Dr. Maher Al Dayeh from the SwRI Space Sciences and Engineering Division stated that while the general mechanics of thunder generation are well understood, the science behind it is still poorly understood. Although we have a good understanding of how thunder is generated, we don’t know what physical processes are involved in thunder. Below: Optical photos of two lightning-related events. (top), and corresponding acoustically recorded profiles. In the acoustic image, you can also see the tilt of lightning bolt shown in left photo. Image: swri.org “The distance to lightning determines how thunder is perceived by the listener. Thunder makes a loud, sharp sound from close by. It has a more pronounced, longer-lasting, rumbling sound from further away.” Though we think of lightning as a bright flashing bolt it is actually a complicated process that involves electrostatic charges in storm clouds. This causes step leaders, or paths of ionized water from clouds to form. These branches lead to main discharge channels. This channel opens up a pathway to nearly instantaneous returns, which create the lightning flash we see. Scientists can learn more about the history of thunder and the energy processes that lead to it by studying how the lightning channel’s acoustic power is radiated. Triggering lightning Dr. Dayeh stated: “Thunder, lightning, and other lightning phenomena are wild and surprising. Due to their unpredictable nature, they are best understood using “triggered events”. A trigger event is a way of artificially generating lightning. A small rocket is launched by the researchers to track a copper wire grounded into thunderclouds. Copper wire creates lightning paths by providing a conductor channel. Scientists can predict the path of the lightning bolt and set up their equipment to point at the exact spot where the bolts are likely to strike. This allows them the opportunity for a number of experiments. To capture the thunder’s acoustic signature, Dr. Dayeh conducted a proof of concept experiment with his colleagues. Photograph the sound of thunder. These experiments were performed at the International Center for Lightning Research and Testing, University of Florida in Gainesville. Florida has the most lightning strikes per year in the United States. To study the acoustic signature of thunder, Dr. Dayeh created a complex arrangement of microphones. 15 microphones were placed 1 meter apart and 92.5 metres away from rocket launch pads where lightning strikes. The team employed post-signal processing and directional amplifier of data signals from the microphones to capture the vertical profile of the bolt. Dr. Dayeh stated that the experiment was initially unsuccessful. These initial images were like modern art you can hang above your fireplace. The sound signature of lightning was not visible in the audio data. However scientists discovered that images were clearer at higher frequency ranges. This technique created a distinctive signature of thunder from the lightning bold. According to the authors, future experiments would allow scientists “to study independent the possible acoustic signatures current pulses and step leader branches as well as discharge channel zigzags.” Video: Triggering lightning using rockets
