Lightning - Wikipedia. High- speed, slow- motion lightning video captured at 6,2. Lightning is a sudden electrostatic discharge that occurs during an electrical storm. This discharge occurs between electrically charged regions of a cloud (called intra- cloud lightning or IC), between that a cloud and another cloud (CC lightning), or between a cloud and the ground (CG lightning). The charged regions in the atmosphere temporarily equalize themselves through this discharge referred to as a strike if it hits an object on the ground, and a flash, if it occurs within a cloud.
Lightning causes light in the form of plasma, and sound in the form of thunder. Lightning may be seen and not heard when it occurs at a distance too great for the sound to carry as far as the light from the strike or flash. Contents. On Earth, the lightning frequency is approximately 4. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes. Because human beings are terrestrial and most of their possessions are on the Earth where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common types of lightning. Lightning's relative unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation. A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 kilometres (3. The actual discharge is the final stage of a very complex process. This occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, and it generally happens at the boundaries between them. Thunderstorm Days from 1961 to 2013 in South-West of Shandong Province Kun Dou Heze Meteorological Bureau of Shandong Province, Heze Shandong. Severe convective storms phenomena occurrence during the warm half of the year in Bulgaria (1961–2006) Petio Simeonov ANALYSIS OF THUNDERSTORMS ACTIVITY OVER PAKISTAN DURING (1961-2000). Thunderstorm is one of the major aviation hazards and every day. Amazon Try Prime Books. Thunderstorm Hardcover – 1961. Thunderstorm (1961) Country: Hong Kong Language: Mandarin Genre: Historical Drama Release Date: 05/31/1961 Director : Zhu Shi-Lin : Script : Zhu Shi-Lin : Cast. Thunderstorm New Mexico 1961. Published April 20, 2012 at 2440 . Contact; FAQs; Help; Submissions. ANSEL ADAMS (1902-1984) Thunderstorm, Great Plains, Cimarron, New Mexico, 1961 gelatin silver print, printed 1970-1975 signed in pencil (on the mount); title in ink. The flow of warm ocean currents past drier land masses, such as the Gulf Stream, partially explains the elevated frequency of lightning in the Southeast United States. Because the influence of small or absent land masses in the vast stretches of the world's oceans limits the differences between these variants in the atmosphere, lightning is notably less frequent there than over larger landforms. The North and South Poles are limited in their coverage of thunderstorms and therefore result in areas with the least amount of lightning. In general, cloud- to- ground (CG) lightning flashes account for only 2. Since the base of a thunderstorm is usually negatively charged, this is where most CG lightning originates. This region is typically at the elevation where freezing occurs within the cloud. Freezing, combined with collisions between ice and water, appears to be a critical part of the initial charge development and separation process. During wind- driven collisions, ice crystals tend to develop a positive charge, while a heavier, slushy mixture of ice and water (called graupel) develops a negative charge. Updrafts within a storm cloud separate the lighter ice crystals from the heavier graupel, causing the top region of the cloud to accumulate a positive space charge while the lower level accumulates a negative space charge. Because the concentrated charge within the cloud must exceed the insulating properties of air, and this increases proportionally to the distance between the cloud and the ground, the proportion of CG strikes (versus cloud- to- cloud (CC) or in- cloud (IC) discharges) becomes greater when the cloud is closer to the ground. In the tropics, where the freezing level is generally higher in the atmosphere, only 1. CG. At the latitude of Norway (around 6. On average, this region receives 1. The induced positive surface charge, when measured against a fixed point, will be small as the thundercloud approaches, increasing as the center of the storm arrives and dropping as the thundercloud passes. The referential value of the induced surface charge could be roughly represented as a bell curve. The oppositely charged regions create an electric field within the air between them. This electric field varies in relation to the strength of the surface charge on the base of the thundercloud . Although more common, intracloud (IC) and cloud to cloud (CC) flashes are very difficult to study given there are no . Also, given the very low probability lightning will strike the same point repeatedly and consistently, scientific inquiry is difficult at best even in the areas of high CG frequency. As such, knowing flash propagation is similar amongst all forms of lightning, the best means to describe the process is through an examination of the most studied form, cloud to ground. A lightning flash within the cloud, illuminates the entire blanket. Downward leaders. Edit. Leaders are electrically conductive channels of partially ionized gas that travel away from a region of dense charge. Negative leaders propagate away from densely charged regions of negative charge, and positive leaders propagate from positively charged regions. The positively and negatively charged leaders proceed in opposite directions, positive upwards within the cloud and negative towards the earth. Both ionic channels proceed, in their respective directions, in a number of successive spurts. The resulting jerky movement of these . The negative leaders continue to propagate and split as they head downward, often speeding up as they get closer to the Earth's surface. About 9. 0% of ionic channel lengths between . The electric current needed to establish the channel, measured in the tens or hundreds of amperes, is dwarfed by subsequent currents during the actual discharge. Initiation of the outward leaders is not well understood. The electric field strength within the thundercloud is not typically large enough to initiate this process by itself. One theory postulates that showers of relativistic electrons are created by cosmic rays and are then accelerated to higher velocities via a process called runaway breakdown. As these relativistic electrons collide and ionize neutral air molecules, they initiate leader formation. Another theory invokes locally enhanced electric fields being formed near elongated water droplets or ice crystals. The electric field is strongest on grounded objects whose tops are closest to the base of the thundercloud, such as trees and tall buildings. If the electric field is strong enough, a positively charged ionic channel, called a positive or upward streamer, can develop from these points. This was first theorized by Heinz Kasemir. Photographs have been taken on which unattached streamers are clearly visible. The unattached downward leaders are also visible in branched lightning, none of which are connected to the earth, although it may appear they are. This is the 'return stroke' and it is the most luminous and noticeable part of the lightning discharge. A large electric current flows along the plasma channel from the cloud to the ground, neutralising the positive ground charge as electrons flow away from the strike point to the surrounding area. This huge surge of current creates large radial voltage differences along the surface of the ground. Called step potentials, they are responsible for more injuries and deaths than the strike itself. In some cases, a positive ground to cloud (GC) lightning flash may originate from a positively charged region on the ground below a storm. These discharges normally originate from the tops of very tall structures, such as communications antennas. The rate at which the return stroke current travels has been found to be around 1. The core temperature of the plasma during the return stroke may exceed 5. K, causing it to brilliantly radiate with a blue- white color. Once the electric current stops flowing, the channel cools and dissipates over tens or hundreds of milliseconds, often disappearing as fragmented patches of glowing gas. The nearly instantaneous heating during the return stroke causes the air to expand explosively, producing a powerful shock wave which is heard as thunder. Re- strike. Edit. High- speed videos (examined frame- by- frame) show that most negative CG lightning flashes are made up of 3 or 4 individual strokes, though there may be as many as 3. Re- strikes often cause a noticeable . Each subsequent stroke usually re- uses the discharge channel taken by the previous one, but the channel may be offset from its previous position as wind displaces the hot channel. The transient nature of the current within a lightning flash results in several phenomena that need to be addressed in the effective protection of ground- based structures. Rapidly changing currents tend to travel on the surface of a conductor, in what is called the skin effect, unlike direct currents, which . Hence, conductors used in the protection of facilities tend to be multi- stranded, with small wires woven together. This increases the total bundle surface area in inverse proportion to the individual strand radius, for a fixed total cross- sectional area. The rapidly changing currents also create electromagnetic pulses (EMPs) that radiate outward from the ionic channel. This is a characteristic of all electrical discharges. The radiated pulses rapidly weaken as their distance from the origin increases. However, if they pass over conductive elements such as power lines, communication lines, or metallic pipes, they may induce a current which travels outward to its termination. Devices known as surge protectors (SPD) or transient voltage surge suppressors (TVSS) attached in parallel with these lines can detect the lightning flash's transient irregular current, and, through an alteration of its physical properties, route the spike to an attached earthing ground, thereby protecting the equipment from damage. There are three primary types of lightning, defined by what is at the .
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