A single lightning bolt is extremely powerful; measured in thousands and hundred thousands of amperes kiloamps or kA. I believe there are two reasons why all of my sources contained different information. First, all lightning bolts are different sizes and intensities due to different atmospheric conditions and other factors, therefore each bolt differs in its value of electric current. The currents are not the same for each bolt. Second, since a lightning strike is of such a short duration up to 18 strikes a second!
The actual discharge is the final stage of a very complex process. On Earth, the lightning frequency is approximately 40—50 times a second or nearly 1. Lightning primarily occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarising the atmosphere. Objects struck by lightning experience heat and magnetic forces of great magnitude.
The heat created by lightning currents travelling through a tree may vaporize its sap, causing a steam explosion that bursts the trunk. Even though roughly 90 percent of people struck by lightning survive, the injury may by severe. We show that when an aircraft triggers lightning, the electric currents will be much more severe in current magnitude, rate of rise of currents, and frequency spectrum than otherwise and are more severe than the parameters observed for the usual and well monitored and measured cloud to ground downward leader flashes.
The rate of rise of currents and the frequency spectrum of the ground to cloud lightning flash are also given here. The electric fields radiated by the lightning flashes that would appear in the ionosphere are presented for both the earth flash and the ground to cloud flash. The majority of the lightning flashes encountered at ground are the negative, downward flashes where the lightning leader stroke emanates from the thundercloud and makes contact with the ground.
Once the contact is made, the second, electrically severe return stroke—severe because it now has an ionized channel from the leader easing the flow of current—is generated at the earth end and travels along the leader channel towards the cloud [ 1 , 2 ]. These downward flash return stroke currents are measured at ground and used as standard current for testing both ground equipment and aircraft body. The other type of flash, less common, is the ground to cloud flash upward leader and downward return stroke which usually emanates from tall earthed structures, where the leader starts from the ground object and moves upward.
Once the leader makes contact with the cloud, another downward stroke is initiated at the cloud, and by the time it reaches ground its current magnitude as well as rate of rise of currents is attenuated by the resistive components of the now ionized channel. It has been shown that the return stroke is a transverse magnetic wave [ 3 ], and it is modelled well by a travelling wave on a distributed as opposed to lumped parameter transmission line with resistance, inductance, and capacitance elements [ 4 , 5 ].
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In the year , these were most prominently captured by video pictures of electrical activity above a thunder cloud [ 6 ]. Their diameters may range from a few tens to a few hundreds of meters. These ionospheric, luminous, transient electric discharge phenomena close to thunderstorm activity are caused by the microsecond, transient lightning return stroke radiated electric fields, as well as the slow charge transfer from cloud to ground [ 10 ].
On average a commercial aircraft is stuck by lightning once a year.
Lightning - Wikipedia
One of the earliest known lightning caused aircraft disasters was in the US on December 8, Lightning directly struck the Pan Am Flight aircraft causing a fuel tank explosion which killed 80 passengers including all cabin crew onboard [ 1 ]. This incident highlighted the importance of aircraft avoiding a thunderstorm environment and thus the need for early warning of an ESD environment. However, complete lightning avoidance still eludes both military and commercial aircraft, as seen for instance in Figure 1. In Figure 1 a , an aircraft that had just taken off suffers a direct lightning strike due to the aircraft itself initiating lightning activity as it flew in an electrically charged thunderstorm environment [ 1 ].
In Figure 1 b is shown a more recent direct strike to a commercial aircraft landing at Heathrow Airport in London. The fact that the shape of the lightning leader stroke and return stroke from aircraft to cloud is like an upright tree, whereas the lightning channel from aircraft to ground is like an inverted tree, indicates that the lightning current originated from the aircraft to cloud and from aircraft to ground.
Lightning Terms Glossary
This ground to cloud-like lightning flash from aircraft to cloud indicates that modelling and computing lightning currents of cloud to ground lightning are important to better understand the currents and the electromagnetically induced transients in the aircraft electrical power and navigational and communication electronics systems. This paper does just that.
In most cases of measured ground to cloud lightning flashes, it is thought that air breakdown initiation does not commence at stationary ground objects due to the fact that the ionized particles that gather around a ground structure in the presence of a thundercloud shield the structure from initiation of the leader stroke [ 11 ]. When it does occur, it is observed that leader initiation is due to strong radiated electric fields from lightning activity inside the cloud intracloud lightning.
This high electric field at the structure initiates the leader stroke of a ground to cloud lightning flash [ 12 ]. Similar high electric fields e. If the cloud of electric charges around ground structures is thought to prevent leader initiation from ground structures, it is not clear why the ionized particles that form the ionosphere do not prevent the highly luminous electric discharges e. However, it has been observed that when an external grounded or ungrounded electrode is suddenly introduced into the thundercloud-like environment, electric charges intensify around the conductor resulting in the production of leaders, as in the case of aircraft [ 12 ].
Thus from our present state of knowledge in relation to electric discharges and high current discharges from grounded objects e.
Although much of the past work has concentrated on cloud to ground flashes, in this paper we show that ground to cloud upward lightning flashes may produce larger electric fields to imitate high current electric discharges in the ionosphere. Further, we show that an aircraft attached to an upward going lightning flash may experience more severe electric current induced stress and interference. Lightning simulation using the distributed transmission line model for the return stroke and the computation of transient electric fields radiated by lightning have already been reported elsewhere [ 13 ].
The electric fields are computed using integral solutions to electromagnetic field radiation from a transient-current carrying conductor [ 14 , 15 ].