I thought I would address some of the current misconceptions about lightning, especially given the clearer understanding high-speed video has provided. I was taught many of these ideas myself while growing up, and it was based on the best understanding of lightning at that time. However, our knowledge of lightning physics and behavior has evolved, so it is important that this revised knowledge is taught in our schools and shared with the general public via the many means available.
Here is a list of subjects that need to addressed.
Lightning always goes up.
I believe this arose from a description of lightning as originating in the cloud with an “invisible” stepped leader (not yet lightning) that propagates downward from a charge region and then connects with ground causing the bright return stroke that rapidly travels back up the leader channel (this was considered to be the lightning). Furthermore, some claim that only the return stroke produces the thunder from the intense brightness and temperature increase.
Lightning starts with the first ionizing “breakdown” of the air and is very simply the development of bipolar and bidirectional thermalized, conductive, bright plasma channels we know as leaders. One end of the leader has a surplus of electrons (the negative end) and the other end has a deficit (the positive end). Sometimes one end of the bidirectional leader connects with the ground. Leaders are a component of lightning as is a return stroke. No matter what polarity of the leader, the zone of accelerating electrons that results from a connection between the downward propagating leader and ground or a connection with an oppositely charged upward propagating connecting leader travels away from the connection point. If the connection point is the ground, it will always travel up away from the ground. If the connection involves the tips of two leaders there will be two zones of acceleration that both travel away from the connection point in opposite directions. For these cases, the connection point is usually within 200 m of the ground so the downward propagating zone reaches the ground quickly whereas the upward traveling zone continues upward into the cloud.
Since the return stroke is very bright and the downward leader was often described as “invisible,” we were taught that we can only see the upward propagating return stroke that always travels up from the ground connection. The truth is, we can see lightning leaders before they make connection with the ground. We see leaders illuminate the interior of clouds as well as propagate outside the cloud all the time even if they do not connect to ground, so they are NOT invisible. They are also always hot so they produce thunder whether or not they connect with ground. You can hear thunder from cloud flashes, but it is true that the thunder generated from a return stroke tends to be much louder due to the more intense thermalization and brightening that occurs during the return stroke.
Upward lightning initiates as an unidirectional upward propagating leader that develops from a tall object. It is the exception to the bipolar, bidirectional physical nature of lightning since it originates from the surface of the Earth which is essentially a huge conductor with, relatively speaking, an unlimited charge source.
Therefore, lightning can go up or down or both during a flash as leaders propagate in both directions and all leaders are visible and produce thunder.
Lightning initiates and propagates as a monodirectional leader that originates from an area of charge. The leader is comprised of charge from that charge region which flows into the leader, propagates to the ground and has that charge drained to the ground by the return stroke.
Thunderstorm charge resides on individual hydrometers (ice crystals, graupel, hail, snow, and rain) which are physically separated by the air between them. The regions of a thunderstorm that contain charged hydrometers collectively create an electric field between regions of opposite charged hydrometeors and the resulting electric field acts as the driving force for the ionization of the air which generates free electrons, and positive and negative ions. The leader is created from the bidirectional ionization or breakdown of the air and the electric field-induced movement of free electrons and ions within the resulting conductive plasma constitutes the charge movement or current during lightning. It is not a physical movement by the charged hydrometeors or the charge on the hydrometeors. The leaders that form can and do, however, travel into and through regions of charge driven by the electrical potential difference between the leader tips and region of charge ahead of the leader tip. And so, some hydrometeors and their associated charge can be incorporated into the volume of a leader. However, it is the air that serves as the source of charge that is moved during lightning and not the charge residing on the hydrometeors. At the termination of a lightning flash, the negative end of the leader leaves a net surplus of negative ions. This addition of negative ions into the positive charge region serves to aggregately reduce the overall strength of the electric field. Likewise, the positive leader leaves positive ions which reduces the electric field generated by the negative charge region.
Upon connection of a leader with the ground, which is at ground potential and therefore presents a large potential difference and low resistance path for enhanced current flow, a zone of intensely enhanced electron acceleration (the return stroke) traverses the leader channel causing increased thermalization and peak current flow as the leader potential attempts to equalize with the ground potential. It does not, however, “drain” the leader channel of charge that has moved down from the charge region. Once the return stroke traverses the leader network, it attains a potential close to ground potential and then the upper extent of the leader network will continue to grow if the potential difference between the now “ground connected” leader and cloud potential is large enough.
Rubber tires on a car or rubber boots that you wear will insulate you from the ground and therefore prevent you from being struck by lightning.
Lightning can travel many kilometers and will have no problem bridging the gap between your car’s rubber tires or your rubber boots even if they were perfect insulators. They in no way inhibit or protect you from lightning. What protects you in a car is the metal shell that serves as a quasi-Faraday cage which conducts the current on the onto surface of the metal around the occupant.
Any flash that emerges from the top of a thunderstorm and travels to ground away from the precipitation area is a positive ground flash.
We have already shown in the previous sections that this is not true. While it is true that positive ground flashes can occur from a storm’s upper vault and anvil region, most Bolts From the Blue (BFBs) that originate from the upper part of the main updraft region are negative ground flashes, where the negative end of the bidirectional leader propagates out from the upper positive charge region and then continues to ground. Negative BFBs are especially common when a storm grows in a high Convective Available Potential Energy (CAPE) environment that does not have much wind shear in the vertical wind profile (high-CAPE/low-shear).
Listening to music or talking on my mobile phone increases my chance of being struck by lightning.
Not true. Your body already has a level of conductivity that could result in your becoming part of a lightning channel if a leader travels downward toward you. Talking on a mobile phone, especially since these are not connected directly to ground, does not increase the likelihood that you will be struck nor does it increase the chance that lightning will initiate above you. Even tall conductive objects such as towers or tall buildings do not increase the chance that lightning will initiate in the cloud above the object. The initiation of lightning as a bidirectional leader within a storm is a random process based on electrification and development of charge regions within the storm. A tall object on the ground does not increase the chance that lightning will initiate in the cloud above the tall object, but it can increase the chance, due to the enhancement electric field locally near the object, that a downward propagating leader associated with the lightning may attach to the tall object.
The image below was taken while I was visiting The Great Wall in China and unfortunately displays a lack of understanding about lightning.
In the next section, I will specifically address lightning for those that chase storms and/or photograph lightning.
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