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Each of these leaders results in its own upward return stroke that reilluminates the channel. One or more subsequent downward leaders can retrace the channel. 14, 45 This return stroke rapidly heats the lightning channel, causing it to illuminate and quickly expand to create visible lightning and audible thunder. 45Īfter contact, a bright return stroke propagates upward from the ground, while electrons move downward toward the earth. The connection of the stepped leader with an upward leader determines the lightning-channel termination point on the ground. The upward leader rises from the ground and meets the descending stepped leader. Various objects on the ground (trees, chimneys, umbrellas, people, etc) can produce positively charged, upward leaders.
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The stepped leader creates a conducting path between the cloud source and the ground and distributes negative charge along this path.
#THUNDER IN THE VICINITY MEANING SERIES#
The resultant electrical potential gradients initiate the lightning flash that typically begins from a negatively charged region of the cloud as a stepped leader that moves in a series of steps toward the ground. This article focuses on cloud-to-ground lightning because that is the source of lightning casualties.Ī cloud-to-ground lightning flash is the product of the buildup of positively and negatively charged regions in the cloud. 45 The 2 primary types of lightning are cloud-to-ground and in cloud. The lightning channel is composed of ionized gas (plasma) that carries a peak temperature around 50 000☏ (27 760☌), about 5 times greater than the temperature of the surface of the sun. Lightning can be defined as a transient, high-current (typically tens of kiloamperes) electric discharge in the air with a length measured in kilometers. The evidence categories adhere to the American Family Physician's Strength of Recommendation Taxonomy (SORT) for grading evidence in the medical literature. The following recommendations are based on the most recent updates in lightning safety. The purpose of this position statement is to encourage proper lightning-safety policies and to educate athletic trainers and others involved with athletic or recreational activities about the hazards of lightning so they can be proactive in preventing lightning-related trauma. Each person should also ensure his or her own safety when a lightning hazard is present. 11 All individuals, particularly leaders in athletics and recreational activities, should appreciate the lightning hazard, learn the published lightning-safety guidelines, act prudently, and encourage safe behavior in others. 5, 17 Education regarding lightning danger and precautions to lessen the likelihood of being struck by lightning are critical to reducing casualties. On average, 25 million lightning flashes strike the ground each year in the United States. This map portrays the regions of highest cloud-to-ground lightning strikes (Florida and the Southeast) and the areas with the least frequent strikes (the West Coast and Western states).
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16 Worldwide, lightning causes an estimated 24 000 deaths and about 240 000 injuries annually. Other factors include the tendency for lightning in the western US to occur without concurrent heavy rain and for it to strike occasionally during snowstorms. Indeed, people living in areas with less thunderstorm activity, such as the Pacific Coast, need to be particularly attentive when lightning does occur because they may ordinarily be less aware of the potential threat. 15 However, no location in the United States is safe from lightning. The areas with the most lightning activity are Florida, the Gulf States, the Mississippi and Ohio River Valleys, the front range of the Southern Rocky Mountains, and parts of the Southwest ( Figure 1). 4, 12 – 14 Certain areas of the United States have greater thunderstorm activity than others coupled with larger populations, exposure to this threat is often greater. Lightning is a widespread danger to the physically active population, in part because of the prevalence of afternoon to early evening thunderstorms from late spring to early fall and a societal trend toward outdoor physical activities during those times. B Totals do not sum to 100 because of rounding.