Revising What We Were Taught In School About Lightning

I thought I would address some of the common 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 so I will be the first to admit that I too thought these to be true.  Hopefully, by addressing these, we can help improve public understanding and safety.

Lightning always goes up.

I believe this arose from the common description of lightning as originating in the cloud with an “invisible” stepped leader 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.  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 return stroke that is always traveling upward.  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.

The leaders, which are the essence of lightning, develop bidirectionally when they form in the cloud.  The exception is upward lightning which initiates as an unidirectional upward propagating leader that develops from a tall object.  Therefore, lightning can go up or down or both during a flash.

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.

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In the next section, I will specifically address lightning for those that chase storms and/or photograph lightning.